All-perovskite tandem 1 cm2 cells with improved interface quality

Synergistic Buried Interface Regulation of Tin-Lead Perovskite Solar Cells via Co-Self-Assembled Monolayers

Tin-lead (Sn-Pb) perovskite solar cells (PSCs) hold considerable potential for achieving efficiencies near the Shockley-Queisser (S-Q) limit. Notably, the inverted structure stands as the preferred fabrication method for the most efficient Sn-Pb PSCs. In this regard, it is imperative to implement a strategic customization of the hole selective layer to facilitate carrier extraction and refine the quality of perovskite films, which requires effective hole selectivity and favorable interactions with Sn-Pb perovskites. Herein, we propose the development of Co-Self-Assembled Monolayers (Co-SAM) by integrating both [2-(9H-carbazol-9-yl)ethyl]phosphonic acid (2PACz) and glycine at the buried contacts. The one-step deposition process employed in the fabrication of the Co-SAM ensures uniform coverage, resulting in a homogeneous surface potential. This is attributed to the molecular interactions occurring between 2PACz and glycine in the processing solution. Furthermore, the amine (-NH2) and ammonium (-NH3+) groups in glycine effectively passivate Sn4+ defects at the buried interface of Sn-Pb perovskite films, even under thermal stress. Consequently, the synergistic buried interface regulation of Co-SAM leads to a power conversion efficiency (PCE) of 23.46%, which outperforms devices modified with 2PACz or glycine alone. The Co-SAM-modified Sn-Pb PSC demonstrates enhanced thermal stability, maintaining 88% of its initial PCE under 65 °C thermal stress for 590 h.

Synchronized crystallization in tin-lead perovskite solar cells

Tin-lead halide perovskites with a bandgap near 1.2 electron-volt hold great promise for thin-film photovoltaics. However, the film quality of solution-processed Sn-Pb perovskites is compromised by the asynchronous crystallization behavior between Sn and Pb components, where the crystallization of Sn-based perovskites tends to occur faster than that of Pb. Here we show that the rapid crystallization of Sn is rooted in its stereochemically active lone pair, which impedes coordination between the metal ion and Lewis base ligands in the perovskite precursor. From this perspective, we introduce a noncovalent binding agent targeting the open metal site of coordinatively unsaturated Sn(II) solvates, thereby synchronizing crystallization kinetics and homogenizing Sn-Pb alloying. The resultant single-junction Sn-Pb perovskite solar cells achieve a certified power conversion efficiency of 24.13 per cent. The encapsulated device retains 90 per cent of the initial efficiency after 795 h of maximum power point operation under simulated one-sun illumination.

From Wide-Bandgap to Narrow-Bandgap Perovskite: Applications from Single-Junction to Tandem Optoelectronics

As perovskite solar device is burgeoning photoelectronic device, numerous studies to optimize perovskite solar device have been demonstrated. Amongst various advantages from perovskite light absorbing layer, attractive property of tunable bandgap allowed perovskite to be adopted in many different fields. Easily tunable bandgap property of perovskite opened the wide application and to get the most out of its potential, many researchers contributed as well. By precursor composition engineering, narrow bandgap with bandgap of less than 1.4 eV and wide bandgap with bandgap of more than 1.7 eV were achieved. Optimization of both narrow and wide bandgap perovskite solar cell could pave the way to all-perovskite tandem solar cell which is combination of top cell with wide bandgap and bottom cell with narrow bandgap. This review highlights numerous efforts to advance device performance of both narrow and wide bandgap perovskite solar cell and how they challenged the issues. And finally, efforts to operate and utilize all-tandem perovskite device in real world will be discussed.

Nuclei engineering for even halide distribution in stable perovskite/silicon tandem solar cells

Wide-bandgap (WBG) absorbers in tandem configurations suffer from poor crystallinity and weak texture, which leads to severe mixed halide-cation ion migration and phase segregation during practical operation. We control WBG film growth insensitive to compositions by nucleating the 3C phase before any formation of bromine-rich aggregates and 2H phases. The resultant WBG absorbers show improved crystallinity and strong texture with suppressed nonradiative recombination and enhanced resistance to various aging stresses. Perovskite/silicon tandem solar cells achieve power conversion efficiencies of 29.4% (28.8% assessed by a third party) in a 25-square centimeter active area and 32.5% in a 1-square centimeter active area. These solar cells retained 98.3 and 90% of the original efficiency after 1301 and 800 hours of operation at 25° and 50°C, respectively, at the maximum power point (AM 1.5G illumination, full spectrum, 1-sun) when encapsulated.

peri-Fused polyaromatic molecular contacts for perovskite solar cells

Molecule-based selective contacts have become a crucial component to ensure high-efficiency inverted perovskite solar cells1-5. These molecules always consist of a conjugated core with heteroatom substitution to render the desirable carrier-transport capability6-9. So far, the design of successful conjugation cores has been limited to two N-substituted π-conjugated structures, carbazole and triphenylamine, with molecular optimization evolving around their derivatives2,5,10-12. However, further improvement of the device longevity has been hampered by the concomitant limitations of the molecular stability induced by such heteroatom-substituted structures13,14. A more robust molecular contact without sacrificing the electronic properties is in urgent demand, but remains a challenge. Here we report a peri-fused polyaromatic core structure without heteroatom substitution that yields superior carrier transport and selectivity over conventional heteroatom-substituted core structures. This core structure produced a relatively chemically inert and structurally rigid molecular contact, which considerably improved the performance of perovskite solar cells in terms of both efficiency and durability. The champion device showed an efficiency up to 26.1% with greatly improved longevity under different accelerated-ageing tests.

Visualizing the Structure-Property Nexus of Wide-Bandgap Perovskite Solar Cells under Thermal Stress

Wide-bandgap perovskite solar cells (PSCs) toward tandem photovoltaic applications are confronted with the challenge of device thermal stability, which motivates to figure out a thorough cognition of wide-bandgap PSCs under thermal stress, using in situ atomic-resolved transmission electron microscopy (TEM) tools combing with photovoltaic performance characterizations of these devices. The in situ dynamic process of morphology-dependent defects formation at initial thermal stage and their proliferations in perovskites as the temperature increased are captured. Meanwhile, considerable iodine enables to diffuse into the hole-transport-layer along the damaged perovskite surface, which significantly degrade device performance and stability. With more intense thermal treatment, atomistic phase transition reveals the perovskite transform to PbI2 along the topo-coherent interface of PbI2/perovskite. In conjunction with density functional theory calculations, a mutual inducement mechanism of perovskite surface damage and iodide diffusion is proposed to account for the structure-property nexus of wide-bandgap PSCs under thermal stress. The entire interpretation also guided to develop a thermal-stable monolithic perovskite/silicon tandem solar cell.

Transparent Recombination Layers Design and Rational Characterizations for Efficient Two-Terminal Perovskite-Based Tandem Solar Cells

Two-terminal (2T) perovskite-based tandem solar cells (TSCs) arouse burgeoning interest in breaking the Shockley-Queisser (S-Q) limit of single-junction solar cells by combining two subcells with different bandgaps. However, the highest certified efficiency of 2T perovskite-based TSCs (33.9%) lags behind the theoretical limit (42-43%). A vital challenge limiting the development of 2T perovskite-based TSCs is the transparent recombination layers/interconnecting layers (RLs) design between two subcells. To improve the performance of 2T perovskite-based TSCs, RLs simultaneously fulfill the optical loss, contact resistance, carrier mobility, stress management, and conformal coverage requirements. In this review, the definition, functions, and requirements of RLs in 2T perovskite-based TSCs are presented. The insightful characterization methods applicable to RLs, which are inspiring for further research on the RLs both in 2T perovskite-based two-junction and multi-junction TSCs, are also highlighted. Finally, the key factors that currently limit the performance enhancement of RLs and the future directions that should be continuously focused on are summarized.

Recent Advances in Carbazole-Based Self-Assembled Monolayer for Solution-Processed Optoelectronic Devices

Self-assembled molecules (SAMs) have shown great potential in the application of optoelectronic devices due to their unique molecular properties. Recently, emerging phosphonic acid-based SAMs, 2-(9Hcarbazol-9-yl)ethyl]phosphonic acid (2PACz), have successfully applied in perovskite solar cells (PSCs), organic solar cells (OSCs) and perovskite light emitting diodes (PeLEDs). More importantly, impressive results based on 2PACz SAMs are reported recently in succession. Therefore, it is essential to provide an insightful summary to promote it further development. In this review, the molecule design strategies about 2PACz are first concluded. Subsequently, this work systematically reviews the recent advances of 2PACz and its derivatives for single junction PSCs, tandem PSCs, OSCs and PeLEDs. Finally, this work concludes and discusses future challenges for 2PACz and its derivatives to further develop in optoelectronic devices.

Advances in Mixed Tin-Lead Narrow-Bandgap Perovskites for Single-Junction and All-Perovskite Tandem Solar Cells

Organic-inorganic metal-halide perovskites have received great attention for photovoltaic (PV) applications owing to their superior optoelectronic properties and the unprecedented performance development. For single-junction PV devices, although lead (Pb)-based perovskite solar cells have achieved 26.1% efficiency, the mixed tin-lead (Sn-Pb) perovskites offer more ideal bandgap tuning capability to enable an even higher performance. The Sn-Pb perovskite (with a bandgap tuned to ≈1.2 eV) is also attractive as the bottom subcell for a tandem configuration to further surpass the Shockley-Queisser radiative limit for the single-junction devices. The performance of the all-perovskite tandem solar cells has gained rapid development and achieved a certified efficiency up to 29.1%. In this article, the properties and recent development of state-of-the-art mixed Sn-Pb perovskites and their application in single-junction and all-perovskite tandem solar cells are reviewed. Recent advances in various approaches covering additives, solvents, interfaces, and perovskite growth are highlighted. The authors also provide the perspective and outlook on the challenges and strategies for further development of mixed Sn-Pb perovskites in both efficiency and stability for PV applications.

Boosting All-Perovskite Tandem Solar Cells by Revitalizing the Buried Tin-Lead Perovskite Interface

Narrow-bandgap (NBG) mixed tin-lead (Sn-Pb) perovskite solar cells (PSCs) serve as crucial top subcells in all-perovskite tandem solar cells (TSCs). However, the prevalent use of poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT: PSS) hole transport layers (HTLs) in NBG PSCs compromises device efficiency and stability. To address this, the study proposes a revitalizing strategy for the buried interface of Sn-Pb perovskites by directly immersing acetylcholine chloride (ACh) into PEDOT: PSS. ACh acts as a proficient "diver," not only modulating the bottom PEDOT: PSS HTLs but also facilitating the reconstruction of the buried interface and significantly enhancing the quality of the top perovskite layers. This intervention with ACh prevents Sn2+ oxidation, mitigates buried defects, and encourages the growth of large, densely packed grains within Sn-Pb perovskites. Consequently, the optimized NBG PSCs exhibit significantly improved hole transport and reduced carrier recombination, achieving a steady-state efficiency of 22.98% with enhanced stability. Furthermore, these optimized NBG Sn-Pb cells enable highly efficient two-terminal and four-terminal all-perovskite TSCs, boasting steady-state efficiencies of 27.54% (certified at 26.41%) and 28.01%, respectively. This study emphasizes the importance of optimizing NBG PSCs through buried interface reconstruction, propelling the advancement of all-perovskite TSCs.

Large Orientation Angle Buried Substrate Enables Efficient Flexible Perovskite Solar Cells and Modules

Flexible perovskite solar cells (f-PSCs) have emerged as potential candidates for specific mechanical applications owing to their high foldability, efficiency, and portability. However, the power conversion efficiency (PCE) of f-PSC remains limited by the inferior contact between perovskite and flexible buried substrate. Here, an asymmetric π-extended self-assembled monolayer (SAM) (4-(9H-dibenzo[a,c]carbazol-9-yl)butyl)phosphonic acid (A-4PADCB) is reported as a buried substrate for efficient inverted f-PSCs. Employing this design strategy, A-4PADCB exhibits a significant orientation angle away from the surface normal, homogenizing the distribution of contact potentials. This enhancement improves the SAM/perovskite interface quality, controlling the growth of favorable perovskite films with low defect density and slight tensile stress. Integration of A-4PADCB into small-area f-PSCs and large-area flexible perovskite solar modules with an aperture area of 20.84 cm2 achieves impressive PCEs of up to 25.05% and 20.64% (certified 19.51%), respectively. Moreover, these optimized A-4PADCB-based f-PSCs possess enhanced light, thermal, and mechanical stability. This research paves a promising avenue toward the design of SAM-buried substrates with a large orientation angle, regulating perovskite growth, and promoting the commercialization of large-area flexible perovskite photovoltaics.

Fluorinated Naphthalene Diimides as Buried Electron Transport Materials Achieve Over 23% Efficient Perovskite Solar Cells

Naphthalene diimides (NDI) are widely serving as the skeleton to construct electron transport materials (ETMs) for optoelectronic devices. However, most of the reported NDI-based ETMs suffer from poor interfaces with the perovskite which deteriorates the carrier extraction and device stability. Here, a representative design concept for editing the peripheral groups of NDI molecules to achieve multifunctional properties is introduced. The resulting molecule 2,7-bis(2,2,3,3,4,4,4-heptafluorobutyl)benzo[lmn][3,8]phenanthroline-1,3,6,8(2H,7H)-tetraone (NDI-C4F) incorporated with hydrophobic fluorine units contributes to the prevention of excessive molecular aggregation, the improvement of surface wettability and the formation of strong chemical coordination with perovskite precursors. All these features favor retarding the perovskite crystallization and achieving superior buried interfaces, which subsequently promote charge collection and improve the structural compatibility between perovskite and ETMs. The corresponding PSCs based on low-temperature processed NDI-C4F yield a record efficiency of 23.21%, which is the highest reported value for organic ETMs in n-i-p PSCs. More encouragingly, the unencapsulated devices with NDI-C4F demonstrate extraordinary stability by retaining over 90% of their initial PCEs after 2600 h in air. This work provides an alternative molecular strategy to engineer the buried interfaces and can trigger further development of organic ETMs toward reliable PSCs.

Advancing Energy Sustainability Through Solar-to-Fuel Technologies: From Materials to Devices and Systems

To achieve carbon neutrality and sustainable development, innovative solar-to-fuel systems have been designed through the integration of solar energy harvesting and electrochemical devices. Over the last decade, there have been notable advancements in enhancing the efficiency and durability of these solar-to-fuel systems. Despite the advancements, there remains significant potential for further improvements in the performance of systems. Enhancements can be achieved by optimizing electrochemical catalysts, advancing the manufacturing technologies of photovoltaics and electrochemical cells, and refining the overall design of these systems. In the realm of catalyst optimization, the effectiveness of materials can be significantly improved through active site engineering and strategic use of functional groups. Similarly, the performance of electrochemical devices can be enhanced by incorporating specific additives into electrolytes and optimizing gas diffusion electrodes. Improvements in solar harvesting devices are achievable through efficient passivant and self-assembled monolayers, which enhance the overall quality and efficiency of these systems. Additionally, optimizing the energy conversion efficiency involves the strategic use of DC converters, photoelectrodes, and redox media. This review aims to provide a comprehensive overview of the advancements in solar-powered electrochemical energy conversion systems, laying a solid foundation for future research and development in the field of energy sustainability.

Oxygen-Mediated (0D) Cs4PbX6 Formation during Open-Air Thermal Processing Improves Inorganic Perovskite Solar Cell Performance

The desire to commercialize perovskite solar cells continues to mount, motivating the development of scalable production. Evaluations of the impact of open-air processing have revealed a variety of physical changes in the fabricated devices─with few changes having the capacity to be functionalized. Here, we highlight the beneficial role of ambient oxygen during the open-air thermal processing of metastable γ-CsPbI3-based perovskite thin films and devices. Physiochemical-sensitive probes elucidate oxygen intercalation and the formation of Pb-O bonds in the CsPbI3 crystal, entering via iodine vacancies at the surface, creating superoxide (O2-) through electron transfer reactions with molecular oxygen, which drives the formation of a zero-dimensional Cs4PbI6 capping layer during annealing (>330 °C). The chemical conversion permanently alters the film structure, helping to shield the subsurface perovskite from moisture and introduces lattice anchoring sites, stabilizing otherwise unstable γ-CsPbI3 films. This functional modification is demonstrated in γ-CsPbI2Br perovskite solar cells, boosting the operational stability and photoconversion efficiency of champion devices from 12.7 to 15.4% when annealed in dry air. Such findings prompt a reconsideration of glovebox-based perovskite solar cell research and establish a scenario where device fabrication can in fact greatly benefit from ambient oxygen.

All-perovskite tandem solar cells: from fundamentals to technological progress

Organic-inorganic perovskite materials have gradually progressed from single-junction solar cells to tandem (double) or even multi-junction (triple-junction) solar cells as all-perovskite tandem solar cells (APTSCs). Perovskites have numerous advantages: (1) tunable optical bandgaps, (2) low-cost, e.g. via solution-processing, inexpensive precursors, and compatibility with many thin-film processing technologies, (3) scalability and lightweight, and (4) eco-friendliness related to low CO2 emission. However, APTSCs face challenges regarding stability caused by Sn2+ oxidation in narrow bandgap perovskites, low performance due to V oc deficit in the wide bandgap range, non-standardisation of charge recombination layers, and challenging thin-film deposition as each layer must be nearly perfectly homogenous. Here, we discuss the fundamentals of APTSCs and technological progress in constructing each layer of the all-perovskite stacks. Furthermore, the theoretical power conversion efficiency (PCE) limitation of APTSCs is discussed using simulations.

Bisphosphonate-Anchored Self-Assembled Molecules with Larger Dipole Moments for Efficient Inverted Perovskite Solar Cells with Excellent Stability

In the fabrication of inverted perovskite solar cells (PSCs), the wettability, adsorbability, and compactness of self-assembled monolayers (SAMs) on conductive substrates have critical impacts on the quality of the perovskite films and the defects at the buried perovskite-substrate interface, which control the efficiency and stability of the devices. Herein, three bisphosphonate-anchored indolocarbazole (IDCz)-derived SAMs, IDCz-1, IDCz-2, and IDCz-3, are designed and synthesized by modulating the position of the two nitrogen atoms of the IDCz unit to improve the molecular dipole moments and strengthen the π-π interactions. Regulating the work functions (WF) of FTO electrodes through molecular dipole moments and energy levels, the perovskite band bends upwards with a small offset for ITO/IDCz-3/perovskite, thereby promoting hole extraction and blocking electrons. As a result, the inverted PSC employing IDCz-3 as hole-collecting layer exhibits a champion PCE of 25.15%, which is a record efficiency for the multipodal SAMs-based PSCs. Moreover, the unencapsulated device with IDCz-3 can be stored for at least 1800 h with little degradation in performance.

Ligand Homogenized Br-I Wide-Bandgap Perovskites for Efficient NiOx-Based Inverted Semitransparent and Tandem Solar Cells

Phase heterogeneity of bromine-iodine (Br-I) mixed wide-bandgap (WBG) perovskites has detrimental effects on solar cell performance and stability. Here, we report a heterointerface anchoring strategy to homogenize the Br-I distribution and mitigate the segregation of Br-rich WBG-perovskite phases. We find that methoxy-substituted phenyl ethylammonium (x-MeOPEA+) ligands not only contribute to the crystal growth with vertical orientation but also promote halide homogenization and defect passivation near the buried perovskite/hole transport layer (HTL) interface as well as reduce trap-mediated recombination. Based on improvements in WBG-perovskite homogeneity and heterointerface contacts, NiOx-based opaque WBG-perovskite solar cells (WBG-PSCs) achieved impressive open-circuit voltage (Voc) and fill factor (FF) values of 1.22 V and 83%, respectively. Moreover, semitransparent WBG-PSCs exhibit a PCE of 18.5% (15.4% for the IZO front side) and a high FF of 80.7% (79.4% for the IZO front side) for a designated illumination area (da) of 0.12 cm2. Such a strategy further enables 24.3%-efficient two-terminal perovskite/silicon (double-polished) tandem solar cells (da of 1.159 cm2) with a high Voc of over 1.90 V. The tandem devices also show high operational stability over 1000 h during T90 lifetime measurements.

Inhibiting perovskite decomposition by a creeper-inspired strategy enables efficient and stable perovskite solar cells

The commercialization of perovskite solar cells is badly limited by stability, an issue determined mainly by perovskite. Herein, inspired by a natural creeper that can cover the walls through suckers, we adopt polyhexamethyleneguanidine hydrochloride as a molecular creeper on perovskite to inhibit its decomposition starting from the annealing process. The molecule possesses a long-line molecular structure where the guanidinium groups can serve as suckers that strongly anchor cations through multiple hydrogen bonds. These features make the molecular creeper can cover perovskite grains and inhibit perovskite decomposition by suppressing cations' escape. The resulting planar perovskite solar cells achieve an efficiency of 25.42% (certificated 25.36%). Moreover, the perovskite film and device exhibit enhanced stability even under harsh damp-heat conditions. The devices can maintain >96% of their initial efficiency after 1300 hours of operation under 1-sun illumination and 1000 hours of storage under 85% RH, respectively.

Influence of Hole Transport Layers on Buried Interface in Wide-Bandgap Perovskite Phase Segregation

Light-induced phase segregation, particularly when incorporating bromine to widen the bandgap, presents significant challenges to the stability and commercialization of perovskite solar cells. This study explores the influence of hole transport layers, specifically poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine (PTAA) and [4-(3,6-dimethyl-9H-carbazol-9-yl)butyl]phosphonic acid (Me-4PACz), on the dynamics of phase segregation. Through detailed characterization of the buried interface, we demonstrate that Me-4PACz enhances perovskite photostability, surpassing the performance of PTAA. Nanoscale analyses using in situ Kelvin probe force microscopy and quantitative nanomechanical mapping techniques elucidate defect distribution at the buried interface during phase segregation, highlighting the critical role of substrate wettability in perovskite growth and interface integrity. The integration of these characterization techniques provides a thorough understanding of the impact of the buried bottom interface on perovskite growth and phase segregation.

Intermediate Phase Suppression with Long Chain Diammonium Alkane for High Performance Wide-Bandgap and Tandem Perovskite Solar Cells

Wide bandgap (WBG) perovskite can construct tandem cells with narrow bandgap solar cells by adjusting the band gap to overcome the Shockley-Queisser limitation of single junction perovskite solar cells (PSCs). However, WBG perovskites still suffer from severe nonradiative carrier recombination and large open-circuit voltage loss. Here, this work uses an in situ photoluminescence (PL) measurement to monitor the intermediate phase evolution and crystallization process via blade coating. This work reports a strategy to fabricate efficient and stable WBG perovskite solar cells through doping a long carbon chain molecule octane-1,8-diamine dihydroiodide (ODADI). It is found that ODADI doping not only suppresses intermediate phases but also promote the crystallization of perovskite and passivate defects in blade coated 1.67 eV WBG FA0.7Cs0.25MA0.05Pb(I0.8Br0.2)3 perovskite films. As a result, the champion single junction inverted PSCs deliver the efficiencies of 22.06% and 19.63% for the active area of 0.07 and 1.02 cm2, respectively, which are the highest power conversion efficiencies (PCEs) in WBG PSCs by blade coating. The unencapsulated device demonstrates excellent stability in air, which maintains its initial efficiency at the maximum power points under constant AM 1.5G illumination in open air for nearly 500 h. The resulting semitransparent WBG device delivers a high PCE of 20.06%, and the 4-terminal all-perovskite tandem device delivers a PCE of 28.35%.

Bandgap-universal passivation enables stable perovskite solar cells with low photovoltage loss

The efficiency and longevity of metal-halide perovskite solar cells are typically dictated by nonradiative defect-mediated charge recombination. In this work, we demonstrate a vapor-based amino-silane passivation that reduces photovoltage deficits to around 100 millivolts (>90% of the thermodynamic limit) in perovskite solar cells of bandgaps between 1.6 and 1.8 electron volts, which is crucial for tandem applications. A primary-, secondary-, or tertiary-amino-silane alone negatively or barely affected perovskite crystallinity and charge transport, but amino-silanes that incorporate primary and secondary amines yield up to a 60-fold increase in photoluminescence quantum yield and preserve long-range conduction. Amino-silane-treated devices retained 95% power conversion efficiency for more than 1500 hours under full-spectrum sunlight at 85°C and open-circuit conditions in ambient air with a relative humidity of 50 to 60%.

Sustainable thermal regulation improves stability and efficiency in all-perovskite tandem solar cells

Mixed Sn-Pb perovskites have emerged as promising photovoltaic materials for both single- and multi-junction solar cells. However, achieving their scale-up and practical application requires further enhancement in stability. We identify that their poor thermal conductivity results in insufficient thermal transfer, leading to heat accumulation within the absorber layer that accelerates thermal degradation. A thermal regulation strategy by incorporating carboranes into perovskites is developed; these are electron-delocalized carbon-boron molecules known for their efficient heat transfer capability. We specifically select ortho-carborane due to its low thermal hysteresis. We observe its existence through the perovskite layer showing a decreasing trend from the buried interface to the top surface, effectively transferring heat and lowering the surface temperature by around 5 °C under illumination. o-CB also facilitates hole extraction at the perovskite/PEDOT:PSS interface and reduces charge recombination. These enable mixed Sn-Pb cells to exhibit improved thermal stability, retaining 80% of their initial efficiencies after aging at 85 °C for 1080 hours. When integrated into monolithic all-perovskite tandems, we achieve efficiencies of over 27%. A tandem cell maintains 87% of its initial PCE after 704 h of continuous operation under illumination.

A regulation strategy of self-assembly molecules for achieving efficient inverted perovskite solar cells

Self-assembled monolayers (SAMs) have been successfully employed to enhance the efficiency of inverted perovskite solar cells (PSCs) and perovskite/silicon tandem solar cells due to their facile low-temperature processing and superior device performance. Nevertheless, depositing uniform and dense SAMs with high surface coverage on metal oxide substrates remains a critical challenge. In this work, we propose a holistic strategy to construct composite hole transport layers (HTLs) by co-adsorbing mixed SAMs (MeO-2PACz and 2PACz) onto the surface of the H2O2-modified NiOx layer. The results demonstrate that the conductivity of the NiOx bulk phase is enhanced due to the H2O2 modification, thereby facilitating carrier transport. Furthermore, the hydroxyl-rich NiOx surface promotes uniform and dense adsorption of mixed SAM molecules while enhancing their anchoring stability. In addition, the energy level alignment at the interface is improved due to the utilization of mixed SAMs in an optimized ratio. Furthermore, the perovskite film crystal growth is facilitated by the uniform and dense composite HTLs. As a result, the power conversion efficiency of PSCs based on composite HTLs is boosted from 22.26% to 23.16%, along with enhanced operational stability. This work highlights the importance of designing and constructing NiOx/SAM composite HTLs as an effective strategy for enhancing both the performance and stability of inverted PSCs.

Modulating Nucleation and Crystal Growth of Tin Perovskite Films for Efficient Solar Cells

The performance of tin halide perovskite solar cells (PSCs) has been severely limited by the rapid crystallization of tin perovskites, which usually leads to an undesirable film quality. In this work, we tackle this issue by regulating the nucleation and crystal growth of tin perovskite films using a small Lewis base additive, urea. The urea-SnI2 interaction facilitates the formation of larger and more uniform clusters, thus accelerating the nucleation process. Additionally, the crystal growth process is extended, resulting in a high-quality tin perovskite film with compact morphology, increased crystallinity, and reduced defects. Consequently, the efficiency of tin PSCs is significantly increased from 10.42% to 14.22%. This work highlights the importance of manipulating the nucleation and crystal growth of tin perovskites to realize efficient tin PSCs.

Hot-Carrier Cooling Regulation for Mixed Sn-Pb Perovskite Solar Cells

The rapid relaxation of hot carriers leads to energy loss in the form of heat and consequently restricts the theoretical efficiency of single-junction solar cells; However, this issue has not received much attention in tin-lead perovskites solar cells. Herein, tin(II) oxalate (SnC2O4) is introduced into tin-lead perovskite precursor solution to regulate hot-carrier cooling dynamics. The addition of SnC2O4 increases the length of carrier diffusion, extends the lifetime of carriers, and simultaneously slows down the cooling rate of carriers. Furthermore, SnC2O4 can bond with uncoordinated Sn2+ and Pb2+ ions to regulate the crystallization of perovskite and enable large grains. The strongly reducing properties of the C2O4 2- can inhibit the oxidation of Sn2+ to Sn4+ and minimize the formation of Sn vacancies in the resulting perovskite films. Additionally, as a substitute for tin(II) fluoride, the introduction of SnC2O4 avoids the carrier transport issues caused by the aggregation of F- ions at the interface. As a result, the SnC2O4-treated Sn-Pb cells show a champion efficiency of 23.36%, as well as 27.56% for the all-perovskite tandem solar cells. Moreover, the SnC2O4-treated devices show excellent long-term stability. This finding is expected to pave the way toward stable and highly efficient all-perovskite tandem solar cells.

Recent Progress in Dopant-Free and Green Solvent-Processable Organic Hole Transport Materials for Efficient and Stable Perovskite Solar Cells

Dopant-free hole transport layers (HTLs) are crucial in enhancing perovskite solar cells (pero-SCs). Nevertheless, conventional processing of these HTL materials involves using toxic solvents, which gives rise to substantial environmental concerns and renders them unsuitable for large-scale industrial production. Consequently, there is a pressing need to develop dopant-free HTL materials processed using green solvents to facilitate the production of high-performance pero-SCs. Recently, several strategies have been developed to simultaneously improve the solubility of these materials and regulate molecular stacking for high hole mobility. In this review, a comprehensive overview of the methodologies utilized in developing dopant-free HTL materials processed from green solvents is provided. First, the study provides a brief overview of fundamental information about green solvents and Hansen solubility parameters, which can serve as a guideline for the molecular design of optimal HTL materials. Second, the intrinsic relationships between molecular structure, solubility in green solvents, molecular stacking, and device performance are discussed. Finally, conclusions and perspectives are presented along with the rational design of highly efficient, stable, and green solvent-processable dopant-free HTL materials.

Anchoring Charge Selective Self-Assembled Monolayers for Tin-Lead Perovskite Solar Cells

Self-assembled monolayers (SAMs) have displayed great potential for improving efficiency and stability in p-i-n perovskite solar cells (PSCs). The anchoring of SAMs at the conductiv metal oxide substrates and their interaction with perovskite materials must be rationally tailored to ensure efficient charge carrier extraction and improved quality of the perovskite films. Herein, SAMs molecules with different anchoring groups and spacers to control the interaction with perovskite in the p-i-n mixed Sn-Pb PSCs are selected. It is found that the monolayer with the carboxylate group exhibits appropriate interaction and has a more favorable orientation and arrangement than that of the phosphate group. This results in reduced nonradiative recombination and enhanced crystallinity. In addition, the short chain length leads to an improved energy level alignment of SAMs with perovskite, improving hole extraction. As a result, the narrow bandgap (≈1.25 eV) Sn-Pb PSCs show efficiencies of up to 23.1% with an open-circuit voltage of up to 0.89 V. Unencapsulated devices retain 93% of their initial efficiency after storage in N2 atmosphere for over 2500 h. Overall, this work highlights the underexplored potential of SAMs for perovskite photovoltaics and provides essential findings on the influence of their structural modification.

Surface heterojunction based on n-type low-dimensional perovskite film for highly efficient perovskite tandem solar cells

Enhancing the quality of junctions is crucial for optimizing carrier extraction and suppressing recombination in semiconductor devices. In recent years, metal halide perovskite has emerged as the most promising next-generation material for optoelectronic devices. However, the construction of high-quality perovskite junctions, as well as characterization and understanding of their carrier polarity and density, remains a challenge. In this study, using combined electrical and spectroscopic characterization techniques, we investigate the doping characteristics of perovskite films by remote molecules, which is corroborated by our theoretical simulations indicating Schottky defects consisting of double ions as effective charge dopants. Through a post-treatment process involving a combination of biammonium and monoammonium molecules, we create a surface layer of n-type low-dimensional perovskite. This surface layer forms a heterojunction with the underlying 3D perovskite film, resulting in a favorable doping profile that enhances carrier extraction. The fabricated device exhibits an outstanding open-circuit voltage (VOC) up to 1.34 V and achieves a certified efficiency of 19.31% for single-junction wide-bandgap (1.77 eV) perovskite solar cells, together with significantly enhanced operational stability, thanks to the improved separation of carriers. Furthermore, we demonstrate the potential of this wide-bandgap device by achieving a certified efficiency of 27.04% and a VOC of 2.12 V in a perovskite/perovskite tandem solar cell configuration.

Self-Assembled Molecules with Asymmetric Backbone for Highly Stable Binary Organic Solar Cells with 19.7 % Efficiency

The hole-transporting material (HTM), poly (3,4-ethylene dioxythiophene) poly(styrene sulfonate) (PEDOT : PSS), is the most widely used material in the realization of high-efficiency organic solar cells (OSCs). However, the stability of PEDOT : PSS-based OSCs is quite poor, arising from its strong acidity and hygroscopicity. In addition, PEDOT : PSS has an absorption in the infrared region and high highest occupied molecular orbital (HOMO) energy level, thus limiting the enhancement of short-circuit current density (Jsc) and open-circuit voltage (Voc), respectively. Herein, two asymmetric self-assembled molecules (SAMs), namely BrCz and BrBACz, were designed and synthesized as HTM in binary OSCs based on the well-known system of PM6 : Y6, PM6 : eC9, PM6 : L8-BO, and D18 : eC9. Compared with BrCz, BrBACz shows larger dipole moment, deeper work function and lower surface energy. Moreover, BrBACz not only enhances photon harvesting in the active layer, but also minimizes voltage losses as well as improves interface charge extraction/ transport. Consequently, the PM6 : eC9-based binary OSC using BrBACz as HTM exhibits a champion efficiency of 19.70 % with a remarkable Jsc of 29.20 mA cm-2 and a Voc of 0.856 V, which is a record efficiency for binary OSCs so far. In addition, the unencapsulated device maintains 95.0 % of its original efficiency after 1,000 hours of storage at air ambient, indicating excellent long-term stability.

Anti-Solvent-Free Preparation for Efficient and Photostable Pure-Iodide Wide-Bandgap Perovskite Solar Cells

The perovskite/silicon tandem solar cell (TSC) has attracted tremendous attention due to its potential to breakthrough the theoretical efficiency set for single-junction solar cells. However, the perovskite solar cell (PSC) designed as its top component cell suffers from severe photo-induced halide segregation owing to its mixed-halide strategy for achieving desirable wide-bandgap (1.68 eV). Developing pure-iodide wide-bandgap perovskites is a promising route to fabricate photostable perovskite/silicon TSCs. Here, we report efficient and photostable pure-iodide wide-bandgap PSCs made from an anti-solvent-free (ASF) technique. The ASF process is achieved by mixing two precursor solutions, both of which are capable of depositing corresponding perovskite films without involving anti-solvent. The mixed solution finally forms Cs0.3DMA0.2MA0.5PbI3 perovskite film with a bandgap of 1.68 eV. Furthermore, methylammonium chloride additive is applied to enhance the crystallinity and reduce the trap density of perovskite films. As a result, the pure-iodide wide-bandgap PSC delivers efficiency as high as 21.30 % with excellent photostability, the highest for this type of solar cells. The ASF method significantly improves the device reproducibility as compared with devices made from other anti-solvent methods. Our findings provide a novel recipe to prepare efficient and photostable wide-bandgap PSCs.

Custom-tailored hole transport layer using oxalic acid for high-quality tin-lead perovskites and efficient all-perovskite tandems

All-perovskite tandem solar cells (TSCs) have exhibited higher efficiencies than single-junction perovskite solar cells (PSCs) but still suffer from the unsatisfactory performance of low-bandgap (LBG) tin-lead (Sn-Pb) subcells. The inherent properties of PEDOT:PSS are crucial to high-performance Sn-Pb perovskite films and devices; however, the underlying mechanism has not been fully explored and revealed. Here, we report a facile oxalic acid treatment of PEDOT:PSS (OA-PEDOT:PSS) to precisely regulate its work function and surface morphology. OA-PEDOT:PSS shows a larger work function and an ordered reorientation and fiber-shaped film morphology with efficient hole transport pathways, leading to the formation of more ideal hole-selective contact with Sn-Pb perovskite for suppressing interfacial nonradiative recombination losses. Moreover, OA-PEDOT:PSS induces (100) preferred orientation growth of perovskite for higher-quality Sn-Pb films. Last, the OA-PEDOT:PSS-tailored LBG PSC yields an impressive efficiency of up to 22.56% (certified 21.88%), enabling 27.81% efficient all-perovskite TSC with enhanced operational stability.

Enhancing Efficiency of Large-Area Wide-Bandgap Perovskite Solar Modules with Spontaneously Formed Self-Assembled Monolayer Interfaces

Wide-bandgap (WBG) perovskites play a crucial role in perovskite-based tandem cells. Despite recent advances using self-assembled monolayers (SAMs) to facilitate efficiency breakthroughs, achieving precise control over the deposition of such ultrathin layers remains a significant challenge for large-scale fabrication of WBG perovskite and, consequently, for the tandem modules. To address these challenges, we propose a facile method that integrates MeO-2PACz and Me-4PACz in optimal proportions (Mixed SAMs) into the perovskite precursor solution, enabling the simultaneous codeposition of WBG perovskite and SAMs. This technique promotes the spontaneous formation of charge-selective contacts while reducing defect densities by coordinating phosphonic acid groups with the unbonded Pb2+ ions at the bottom interface. The resulting WBG perovskite solar cells (PSCs) demonstrated a power conversion efficiency of 19.31% for small-area devices (0.0585 cm2) and 17.63% for large-area modules (19.34 cm2), highlighting the potential of this codeposition strategy for fabricating high-performance, large-area WBG PSCs with enhanced reproducibility. These findings offer valuable insights for advancing WBG PSCs and the scalable fabrication of modules.

Narrow Bandgap Metal Halide Perovskites for All-Perovskite Tandem Photovoltaics

All-perovskite tandem solar cells are attracting considerable interest in photovoltaics research, owing to their potential to surpass the theoretical efficiency limit of single-junction cells, in a cost-effective sustainable manner. Thanks to the bandgap-bowing effect, mixed tin-lead (Sn-Pb) perovskites possess a close to ideal narrow bandgap for constructing tandem cells, matched with wide-bandgap neat lead-based counterparts. The performance of all-perovskite tandems, however, has yet to reach its efficiency potential. One of the main obstacles that need to be overcome is the─oftentimes─low quality of the mixed Sn-Pb perovskite films, largely caused by the facile oxidation of Sn(II) to Sn(IV), as well as the difficult-to-control film crystallization dynamics. Additional detrimental imperfections are introduced in the perovskite thin film, particularly at its vulnerable surfaces, including the top and bottom interfaces as well as the grain boundaries. Due to these issues, the resultant device performance is distinctly far lower than their theoretically achievable maximum efficiency. Robust modifications and improvements to the surfaces of mixed Sn-Pb perovskite films are therefore critical for the advancement of the field. This Review describes the origins of imperfections in thin films and covers efforts made so far toward reaching a better understanding of mixed Sn-Pb perovskites, in particular with respect to surface modifications that improved the efficiency and stability of the narrow bandgap solar cells. In addition, we also outline the important issues of integrating the narrow bandgap subcells for achieving reliable and efficient all-perovskite double- and multi-junction tandems. Future work should focus on the characterization and visualization of the specific surface defects, as well as tracking their evolution under different external stimuli, guiding in turn the processing for efficient and stable single-junction and tandem solar cell devices.

Multifunctional Trifluoroborate Additive for Simultaneous Carrier Dynamics Governance and Defects Passivation to Boost Efficiency and Stability of Inverted Perovskite Solar Cells

The main obstacles to promoting the commercialization of perovskite solar cells (PSCs) include their record power conversion efficiency (PCE), which still remains below the Shockley-Queisser limit, and poor long-term stability, attributable to crystallographic defects in perovskite films and open-circuit voltage (Voc) loss in devices. In this study, potassium (4-tert-butoxycarbonylpiperazin-1-yl) methyl trifluoroborate (PTFBK) was employed as a multifunctional additive to target and modulate bulk perovskite defects and carrier dynamics of PSCs. Apart from simultaneously passivating anionic and cationic defects, PTFBK could also optimize the energy-level alignment of devices and weaken the interaction between carriers and longitudinal optical phonons, resulting in a carrier lifetime of greater than 3 μs. Furthermore, it inhibited non-radiative recombination and improved the crystallization capacity in the target perovskite film. Hence, the target rigid and flexible p-i-n PSCs yielded champion PCEs of 24.99 % and 23.48 %, respectively. More importantly, due to hydrogen bonding between formamidinium and fluorine, the target devices exhibited remarkable thermal, humidity, and operational tracking at maximum power point stabilities. The reduced Young's modulus and residual stress in the perovskite layer also provided excellent bending stability for flexible target devices.

Highly Efficient Monolithic Perovskite/Perovskite/Silicon Triple-Junction Solar Cells

Wide-bandgap metal halide perovskites have demonstrated promise in multijunction photovoltaic (PV) cells. However, photoinduced phase segregation and the resultant low open-circuit voltage (Voc) have greatly limited the PV performance of perovskite-based multijunction devices. Here, a alloying strategy is reported to achieve uniform distribution of triple cations and halides in wide-bandgap perovskites by doping Rb+ and Cl- with small ionic radii, which effectively suppresses halide phase segregation while promoting the homogenization of surface potential. Based on this strategy, a Voc of 1.33 V is obtained from single-junction perovskite solar cells, and a VOC approaching 3.0 V and a power conversion efficiency of 25.0% (obtained from reverse scan direction, certified efficiency: 24.19%) on an 1.04 cm2 photoactive area can be achieved in a perovskite/perovskite/c-Si triple-junction tandem cell, where the certification efficiency is by far the greatest performance of perovskite-based triple-junction tandem solar cells. This work overcomes the performance deadlock of perovskite-based triple-junction tandem cells by setting a materials-by-design paradigm.

Optimizing Crystallization in Wide-Bandgap Mixed Halide Perovskites for High-Efficiency Solar Cells

Wide-bandgap (WBG) perovskites have attracted considerable attention due to their adjustable bandgap properties, making them ideal candidates for top subcells in tandem solar cells (TSCs). However, WBG perovskites often face challenges such as inhomogeneous crystallization and severe nonradiative recombination loss, leading to high open-circuit voltage (VOC) deficits and poor stability. To address these issues, a multifunctional phenylethylammonium acetate (PEAAc) additive that enhances uniform halide phase distribution and reduces defect density in perovskite films by regulating the mixed-halide crystallization rate, is introduced. This approach successfully develops efficient WBG perovskite solar cells (PSCs) with reduced VOC loss and enhanced stability. By applying this universal strategy to the FAMACsPb(I1- xBrx)3 system with a range of bandgaps of 1.73, 1.79, 1.85, and 1.92 eV, power conversion efficiencies (PCE) of 21.3%, 19.5%, 18.1%, and 16.2%, respectively, are attained. These results represent some of the highest PCEs reported for the corresponding bandgaps. Furthermore, integrating WBG perovskite with organic photovoltaics, an impressive PCE of over 24% for two-terminal perovskite/organic TSCs, with a record VOC of ≈ 2.2 V is achieved. This work establishes a foundation for addressing phase separation and inhomogeneous crystallization in Br-rich perovskite components, paving the way for the development of high-performance WBG PSCs and TSCs.

Current State and Future Perspectives of Printable Organic and Perovskite Solar Cells

Photovoltaic technology presents a sustainable solution to address the escalating global energy consumption and a reliable strategy for achieving net-zero carbon emissions by 2050. Emerging photovoltaic technologies, especially the printable organic and perovskite solar cells, have attracted extensive attention due to their rapidly transcending power conversion efficiencies and facile processability, providing great potential to revolutionize the global photovoltaic market. To accelerate these technologies to translate from the laboratory scale to the industrial level, it is critical to develop well-defined and scalable protocols to deposit high-quality thin films of photoactive and charge-transporting materials. Herein, the current state of printable organic and perovskite solar cells is summarized and the view regarding the challenges and prospects toward their commercialization is shared. Different printing techniques are first introduced to provide a correlation between material properties and printing mechanisms, and the optimization of ink formulation and film-formation during large-area deposition of different functional layers in devices are then discussed. Engineering perspectives are also discussed to analyze the criteria for module design. Finally, perspectives are provided regarding the future development of these solar cells toward practical commercialization. It is believed that this perspective will provide insight into the development of printable solar cells and other electronic devices.

Co-Self-Assembled Monolayers Modified NiOx for Stable Inverted Perovskite Solar Cells

[4-(3,6-dimethyl-9H-carbazol-9yl)butyl]phosphonic acid (Me-4PACz) self-assembled molecules (SAM) are an effective method to solve the problem of the buried interface of NiOx in inverted perovskite solar cells (PSCs). However, the Me-4PACz end group (carbazole core) cannot forcefully passivate defects at the bottom of the perovskite film. Here, a Co-SAM strategy is employed to modify the buried interface of PSCs. Me-4PACz is doped with phosphorylcholine chloride (PC) to form a Co-SAM to improve the monolayer coverage and reduce leakage current. The phosphate group and chloride ions (Cl-) in PC can inhibit NiOx surface defects. Meantime, the quaternary ammonium ions and Cl- in PC can fill organic cations and halogen vacancies in the perovskite film to enable defects passivation. Moreover, Co-SAM can promote the growth of perovskite crystals, collaboratively solve the problem of buried defects, suppress nonradiative recombination, accelerate carrier transmission, and relieve the residual stress of the perovskite film. Consequently, the Co-SAM modified devices show power conversion efficiencies as high as 25.09% as well as excellent device stability with 93% initial efficiency after 1000 h of operation under one-sun illumination. This work demonstrates the novel approach for enhancing the performance and stability of PSCs by modifying Co-SAM on NiOx.

Mixed tin-lead perovskites with balanced crystallization and oxidation barrier for all-perovskite tandem solar cells

Mixed tin-lead perovskite solar cells have driven a lot of passion for research because of their vital role in all-perovskite tandem solar cells, which hold the potential for achieving higher efficiencies compared to single-junction counterparts. However, the pronounced disparity in crystallization processes between tin-based perovskites and lead-based perovskites, coupled with the easy Sn2+ oxidation, has long been a dominant factor contributing to high defect densities. In this study, we propose a multidimensional strategy to achieve efficient tin-lead perovskite solar cells by employing a functional N-(carboxypheny)guanidine hydrochloride molecule. The tailored N-(carboxypheny)guanidine hydrochloride molecule plays a pivotal role in manipulating the crystallization and grain growth of tin-lead perovskites, while also serving as a preservative to effectively inhibit Sn2+ oxidation, owing to the strong binding between N-(carboxypheny)guanidine hydrochloride and tin (II) iodide and the elevated energy barriers for oxidation. Consequently, single-junction tin-lead cells exhibit a stabilized power conversion efficiency of 23.11% and can maintain 97.45% of their initial value even after 3500 h of shelf storage in an inert atmosphere without encapsulation. We further integrate tin-lead perovskites into two-terminal monolithic all-perovskite tandem cells, delivering a certified efficiency of 27.35%.

Stability of organic solar cells: toward commercial applications

Organic solar cells (OSCs) have attracted a great deal of attention in the field of clean solar energy due to their advantages of transparency, flexibility, low cost and light weight. Introducing them to the market enables seamless integration into buildings and windows, while also supporting wearable, portable electronics and internet-of-things (IoT) devices. With the development of photovoltaic materials and the optimization of fabrication technology, the power conversion efficiencies (PCEs) of OSCs have rapidly improved and now exceed 20%. However, there is a significant lack of focus on material stability and device lifetime, causing a severe hindrance to commercial applications. In this review, we carefully review important strategies employed to improve the stability of OSCs over the past three years from the perspectives of material design and device engineering. Furthermore, we analyze and discuss the current important progress in terms of air, light, thermal and mechanical stability. Finally, we propose the future research directions to overcome the challenges in achieving highly stable OSCs. We expect that this review will contribute to solving the stability problem of OSCs, eventually paving the way for commercial applications in the near future.

Efficient all-small-molecule organic solar cells processed with non-halogen solvent

All-small-molecule organic solar cells with good batch-to-batch reproducibility combined with non-halogen solvent processing show great potential for commercialization. However, non-halogen solvent processing of all-small-molecule organic solar cells are rarely reported and its power conversion efficiencies are very difficult to improve. Herein, we designed and synthesized a small molecule donor BM-ClEH that can take advantage of strong aggregation property induced by intramolecular chlorine-sulfur non-covalent interaction to improve molecular pre-aggregation in tetrahydrofuran and corresponding micromorphology after film formation. Tetrahydrofuran-fabricated all-small-molecule organic solar cells based on BM-ClEH:BO-4Cl achieved high power conversion efficiencies of 15.0% in binary device and 16.1% in ternary device under thermal annealing treatment. In contrast, weakly aggregated BM-HEH without chlorine-sulfur non-covalent bond is almost inefficient under same processing conditions due to poor pre-aggregation induced disordered π-π stacking, indistinct phase separation and exciton dissociation. This work promotes the development of non-halogen solvent processing of all-small-molecule organic solar cells and provides further guidance.

Perovskite Single Crystals with Self-Cleaning Surface for Efficient Photovoltaics

Metal halide perovskite single crystals are promising for diverse optoelectronic applications. As a universal issue of solution-grown perovskite single crystals, surface contamination causes adverse effect on material properties and device performance. Herein, learning from the self-cleaning effect of lotus leaf, we address the surface contamination issue by introducing an amphiphilic long-chain organic amine into the perovskite crystal growth solution. Self-assembly of CTAC provides a hydrophobic crystal surface, inducing spontaneous removal of residual growth solution, which results in clean surface and better optoelectronic properties of perovskite single crystals. An impressive efficiency of 23.4 % is obtained, setting a new record for FAx MA1-x PbI3 single-crystal perovskite solar cells (PSCs). Moreover, our strategy also applies to perovskite single crystals with different morphology and composition, which may contribute to improvement of other single-crystal perovskite optoelectronic devices.

Homogeneous crystallization and buried interface passivation for perovskite tandem solar modules

Scalable fabrication of all-perovskite tandem solar cells is challenging because the narrow-bandgap subcells made of mixed lead-tin (Pb-Sn) perovskite films suffer from nonuniform crystallization and inferior buried perovskite interfaces. We used a dopant from Good's list of biochemical buffers, aminoacetamide hydrochloride, to homogenize perovskite crystallization and used it to extend the processing window for blade-coating Pb-Sn perovskite films and to selectively passivate defects at the buried perovskite interface. The resulting all-perovskite tandem solar module exhibited a certified power conversion efficiency of 24.5% with an aperture area of 20.25 square centimeters.

Tandem modules get better

An all-perovskite tandem solar module breaks 24% efficiency.

Strain Engineering and Halogen Compensation of Buried Interface in Polycrystalline Halide Perovskites

Inverted perovskite solar cells based on weakly polarized hole-transporting layers suffer from the problem of polarity mismatch with the perovskite precursor solution, resulting in a nonideal wetting surface. In addition to the bottom-up growth of the polycrystalline halide perovskite, this will inevitably worse the effects of residual strain and heterogeneity at the buried interface on the interfacial carrier transport and localized compositional deficiency. Here, we propose a multifunctional hybrid pre-embedding strategy to improve substrate wettability and address unfavorable strain and heterogeneities. By exposing the buried interface, it was found that the residual strain of the perovskite films was markedly reduced because of the presence of organic polyelectrolyte and imidazolium salt, which not only realized the halogen compensation and the coordination of Pb2+ but also the buried interface morphology and defect recombination that were well regulated. Benefitting from the above advantages, the power conversion efficiency of the targeted inverted devices with a bandgap of 1.62 eV was 21.93% and outstanding intrinsic stability. In addition, this coembedding strategy can be extended to devices with a bandgap of 1.55 eV, and the champion device achieved a power conversion efficiency of 23.74%. In addition, the optimized perovskite solar cells retained 91% of their initial efficiency (960 h) when exposed to an ambient relative humidity of 20%, with a T80 of 680 h under heating aging at 65 °C, exhibiting elevated durability.

Identification the Role of Grain Boundaries in Polycrystalline Photovoltaics via Advanced Atomic Force Microscope

Atomicforce microscopy (AFM)-based scanning probing techniques, including Kelvinprobe force microscopy (KPFM) and conductive atomic force microscopy (C-AFM), have been widely applied to investigate thelocal electromagnetic, physical, or molecular characteristics of functional materials on a microscopic scale. The microscopic inhomogeneities of the electronic properties of polycrystalline photovoltaic materials can be examined by these advanced AFM techniques, which bridge the local properties of materials to overall device performance and guide the optimization of the photovoltaic devices. In this review, the critical roles of local optoelectronic heterogeneities, especially at grain interiors (GIs) and grain boundaries (GBs) of polycrystalline photovoltaic materials, including versatile polycrystalline silicon, inorganic compound materials, and emerging halide perovskites, studied by KPFM and C-AFM, are systematically identified. How the band alignment and electrical properties of GIs and GBs affect the carrier transport behavior are discussed from the respective of photovoltaic research. Further exploiting the potential of such AFM-based techniques upon a summary of their up-to-date applications in polycrystalline photovoltaic materials is beneficial to acomprehensive understanding of the design and manipulation principles of thenovel solar cells and facilitating the development of the next-generation photovoltaics and optoelectronics.

Minimizing Interfacial Recombination in 1.8 eV Triple-Halide Perovskites for 27.5% Efficient All-Perovskite Tandems

All-perovskite tandem solar cells show great potential to enable the highest performance at reasonable costs for a viable market entry in the near future. In particular, wide-bandgap (WBG) perovskites with higher open-circuit voltage (VOC ) are essential to further improve the tandem solar cells' performance. Here, a new 1.8 eV bandgap triple-halide perovskite composition in conjunction with a piperazinium iodide (PI) surface treatment is developed. With structural analysis, it is found that the PI modifies the surface through a reduction of excess lead iodide in the perovskite and additionally penetrates the bulk. Constant light-induced magneto-transport measurements are applied to separately resolve charge carrier properties of electrons and holes. These measurements reveal a reduced deep trap state density, and improved steady-state carrier lifetime (factor 2.6) and diffusion lengths (factor 1.6). As a result, WBG PSCs achieve 1.36 V VOC , reaching 90% of the radiative limit. Combined with a 1.26 eV narrow bandgap (NBG) perovskite with a rubidium iodide additive, this enables a tandem cell with a certified scan efficiency of 27.5%.

High-Stable Lead-Free Solar Cells Achieved by Surface Reconstruction of Quasi-2D Tin-Based Perovskites

Tin halide perovskites are an appealing alternative to lead perovskites. However, owing to the lower redox potential of Sn(II)/Sn(IV), particularly under the presence of oxygen and water, the accumulation of Sn(IV) at the surface layer will negatively impact the device's performance and stability. To this end, this work has introduced a novel multifunctional molecule, 1,4-phenyldimethylammonium dibromide diamine (phDMADBr), to form a protective layer on the surface of Sn-based perovskite films. Strong interactions between phDMADBr and the perovskite surface improve electron transfer, passivating uncoordinated Sn(II), and fortify against water and oxygen. In situ grazing incidence wide-angle X-ray scattering (GIWAXS) analysis confirms the enhanced thermal stability of the quasi-2D phase, and hence the overall enhanced stability of the perovskite. Long-term stability in devices is achieved, retaining over 90% of the original efficiency for more than 200 hours in a 10% RH moisture N2 environment. These findings propose a new approach to enhance the operational stability of Sn-based perovskite devices, offering a strategy in advancing lead-free optoelectronic applications.