Transporting holes stably under iodide invasion in efficient perovskite solar cells

A Pyrrole Modified 3,4-Propylenedioxythiophene Conjugated Polymer as Hole Transport Layer for Efficient and Stable Perovskite Solar Cells

Despite the outstanding electric properties and cost-effectiveness of poly(3,4-ethylenedioxythiophene) (PEDOT) and its derivatives, their performance as hole transport layer (HTL) materials in conventional perovskite solar cells (PSCs) has lagged behind that of widely used spirobifluorene-based molecules or poly(triaryl amine). This gap is mainly from their poor solubility and energy alignment mismatch. In this work, the design and synthesis of a pyrrole-modified HTL (PPr) based on 3,4-propylenedioxythiophene (ProDOT) are presented for efficient and stable PSCs. As a result of the superior defects passivation ability, excellent contact with perovskite, enhanced hole extraction, and high hydrophobicity, the unencapsulated PPr-based PSCs showed the peak PCE of 21.49% and outstanding moisture stability (over 4000 h). This work highlights the potential application of ProDOT-based materials as HTL for PSCs and underscores the importance of the rational design of PEDOT and its derivatives.

Gradient Hole Injection Inducing Efficient Exciton Recombination in Blue (475 nm) Perovskite QLEDs

Perovskite quantum dots (QDs) are emerging as excellent light sources for light-emitting diodes (LEDs). However, the performance of blue perovskite QD-based LEDs (QLEDs) still lags behind that of red and green counterparts, which is hindered by blue perovskite QDs with broad bandgaps that tend to increase nonradiative recombination. Here, we designed a gradient energy for hole injection utilizing multiple hole injection layers (HTLs) combined with carbazole-based small-molecule modification to reduce the hole injection barrier between HTLs and QD layers and improve the hole injection efficiency, realizing efficient exciton recombination in blue perovskite QLEDs. Moreover, the QD film on the designed HTLs demonstrates a lower surface roughness and improved photoluminescence properties. The optimized blue CsPbCl3-xBrx QLEDs exhibit an impressive external quantum efficiency of 20.7% with an electroluminescence peak at 475 nm and a turn-on voltage of 2.6 V, representing the state-of-the-art for blue perovskite LEDs emitting in the range of 460-480 nm.

Dynamic Evolution of Antisite Defect and Coupling Anionic Redox in High-Voltage Ultrahigh-Ni Cathode

High-voltage ultrahigh-Ni cathodes (LiNixCoyMn1-x-yO2, x≥0.9) can significantly enhance the energy density and cost-effectiveness of Li-ion batteries beyond current levels. However, severe Li-Ni antisite defects and their undetermined dynamic evolutions during high-voltage cycling limit the further development of these ultrahigh-Ni cathodes. In this study, we quantify the dynamic evolutions of the Li-Ni antisite defect using operando neutron diffraction and reveal its coupling relationship with anionic redox, another critical challenge restricting ultrahigh-Ni cathodes. We detect a clear Ni migration coupled with an unstable oxygen lattice, which accompanies the oxidation of oxygen anions at high voltages. Based on these findings, we propose that minimized Li-Ni antisite defects and controlled Ni migrations are essential for achieving stable high-voltage cycling structures in ultrahigh-Ni cathodes. This is further demonstrated by the optimized ultrahigh-Ni cathode, where reduced dynamic evolutions of the Li-Ni antisite defect effectively inhibit the anionic redox, enhancing the 4.5 V cycling stability.

Long-term stability in perovskite solar cells through atomic layer deposition of tin oxide

Robust contact schemes that boost stability and simplify the production process are needed for perovskite solar cells (PSCs). We codeposited perovskite and hole-selective contact while protecting the perovskite to enable deposition of SnOx/Ag without the use of a fullerene. The SnOx, prepared through atomic layer deposition, serves as a durable inorganic electron transport layer. Tailoring the oxygen vacancy defects in the SnOx layer led to power conversion efficiencies (PCEs) of >25%. Our devices exhibit superior stability over conventional p-i-n PSCs, successfully meeting several benchmark stability tests. They retained >95% PCE after 2000 hours of continuous operation at their maximum power point under simulated AM1.5 illumination at 65°C. Additionally, they boast a certified T97 lifetime exceeding 1000 hours.

High Efficiency n-Type Doping of Organic Semiconductors by Cation Exchange

Achieving efficient doping in n-type conjugated polymers is crucial for their application in electronic devices. In this study, an n-type doping method is developed based on cation exchange that maintains a high doping level while ensuring a high degree of structural order, leading to significantly improved electrical conductivity. By investigating various dopants and ionic liquids, it is discovered that the choice of dopant influences doping efficiency, while the selection of ionic liquid affects cation exchange efficiency. Through careful selection of suitable dopants and ionic liquids, High doping levels are achieved remarkably in a short period, resulting in the highest conductivity (nearly 1 × 10- 2 S cm-¹) compared to other doping methods for poly{[N,N'-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5'-(2,2'-bithiophene)} (N2200). The findings highlight the robustness and efficiency of cation exchange doping as an effective approach for achieving high-quality n-type doping in conjugated polymers, thereby opening new avenues for the development of advanced polymer-based electronic devices.

Enhanced charge carrier transport and defects mitigation of passivation layer for efficient perovskite solar cells

Surface passivation has been developed as an effective strategy to reduce trap-state density and suppress non-radiation recombination process in perovskite solar cells. However, passivation agents usually own poor conductivity and hold negative impact on the charge carrier transport in device. Here, we report a binary and synergistical post-treatment method by blending 4-tert-butyl-benzylammonium iodide with phenylpropylammonium iodide and spin-coating on perovskite surface to form passivation layer. The binary and synergistical post-treated films show enhanced crystallinity and improved molecular packing as well as better energy band alignment, benefiting for the hole extraction and transfer. Moreover, the surface defects are further passivated compared with unary passivation. Based on the strategy, a record-certified quasi-steady power conversion efficiency of 26.0% perovskite solar cells is achieved. The devices could maintain 81% of initial efficiency after 450 h maximum power point tracking.

Highly Efficient and Stable Perovskite Solar Modules Based on FcPF6 Engineered Spiro-OMeTAD Hole Transporting Layer

Li-TFSI doped spiro-OMeTAD is widely recognized as a beneficial hole transport layer (HTL) in perovskite solar cells (PSCs), contributing to high device efficiencies. However, the uncontrolled migration of lithium ions (Li+) during device operation has impeded its broad adoption in scalable and stable photovoltaic modules. Herein, an additive strategy is proposed by employing ferrocenium hexafluorophosphate (FcPF6) as a relay medium to enhance the hole extraction capability of the spiro-OMeTAD via the instant oxidation function. Besides, the novel Fc-Li interaction effectively restricts the movement of Li+. Simultaneously, the dissociative hexafluorophosphate group is cleverly exploited to regulate the unstable iodide species on the perovskite surface, further inhibiting the formation of migration channels and stabilizing the interfaces. This modification leads to power conversion efficiencies (PCEs) reaching 22.13% and 20.27% in 36 cm2 (active area of 18 cm2) and 100 cm2 (active area of 56 cm2) perovskite solar modules (PSMs), respectively, with exceptional operational stability obtained for over 1000 h under the ISOS-L-1 procedure. The novel FcPF6-based engineering approach is pivotal for advancing the industrialization of PSCs, particularly those relying on high-performance spiro-OMeTAD- based HTLs.

Robust chelated lead octahedron surface for efficient and stable perovskite solar cells

PbI6 octahedron as a fundamental framework endows the perovskite with excellent photoelectric properties, but also the defective and flimsy surface. Here, we report that the treatment of perovskite surface by bidentate ligands molecules N, N'-Dimethyl-1,2-ethanediamine can in-situ form a lead iodide chelates layer with excellently robust chelated lead octahedron, leading to effectively stabilize and passivate the underlying perovskite. The strong chelation with the lead enables the surface to largely inhibit the defects generation, iodide ion migration and skeleton collapse under external stimuli. It also prolongs the carrier lifetime and adjusts the surface energy-level of perovskite. The resultant perovskite solar cells deliver a power conversion efficiency of 25.7% (certified 25.04%) and retain >90% of their initial value after almost 1000 hours aging at maximum power point under simulated AM1.5 illumination.

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.

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.

Stabilizing Lead Halide Perovskites via an Organometallic Chemical Bridge for Efficient and Stable Photovoltaics

Defects around the surface and grain boundaries of perovskite films normally cause severe nonradiative recombination and imbalanced charge carrier transport, further limiting both the efficiency and stability of perovskite solar cells (PSCs). To tackle this critical issue, we propose a chemical bridge strategy to reconstruct the interface using organometallic molecules. The commercially available molecule bis(diphenylphosphino)ferrocene (FcP2), with a unique bridge molecular structure, anchors and chelates Pb atoms by forming strong Pb-P bonds and further passivates both surfaces and grain boundaries. Detailed characterization revealed that bridge molecule FcP2 reconstruction can effectively suppress nonradiative recombination, and the electron delocalization properties of the ferrocene core can further achieve more balanced interfacial carrier transport. The resultant N-i-P PSC device outputs close to 25% efficiency together with one of the best reported operational stabilities, maintaining over 95% of the initial efficiency after 1000 h of continuous operation at the maximum power point under 1-sun illumination.

Efficient and stabilized molecular doping of hole-transporting materials driven by a cyclic-anion strategy for perovskite solar cells

Bis(trifluoromethane)sulfonimide lithium salt (Li-TFSI) is commonly used as an effective dopant to improve the performance of the hole-transporting material (HTM) in n-i-p perovskite solar cells (PSCs). However, the ultra-hygroscopic and migratory nature of Li-TFSI leads to inferior stability of PSCs. Here, we report on a strategy to regulate the anion unit in Li-TFSI from linear to cyclic, constructing a new dopant, lithium 1,1,2,2,3,3-hexafluoropropane-1,3-disulfonimide (Li-CYCLIC), for the state-of-the-art poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA). Mechanistic and experimental results reveal that the cyclic anion CYCLIC- exhibits stronger interaction with Li+ and PTAA˙+ compared with the linear anion TFSI-, thus significantly restraining the moisture absorption and migration of Li+ and improving the thermodynamic stability of PTAA˙+CYCLIC-. With this molecular engineering, the resulting PSCs based on Li-CYCLIC obtained an improved efficiency, along with remarkably enhanced stability, retaining 96% of the initial efficiency after over 1150 hours under continuous 1 sun illumination in an N2 atmosphere, yielding an extrapolated T 80 of over 12 000 hours. In a broader context, the proposed strategy of linear-to-cyclic doping provides substantial guidance for the subsequent advancement in the development of effective dopants for photoelectric devices.

Dynamic Reversible Oxidation-Reduction of Iodide Ions for Operationally Stable Perovskite Solar Cells under ISOS-L-3 Protocol

Despite rapid advancements in the photovoltaic efficiencies of perovskite solar cells (PSCs), their operational stability remains a significant challenge for commercialization. This instability mainly arises from light-induced halide ion migration and subsequent oxidation into iodine (I2). The situation is exacerbated when considering the heat effects at elevated temperatures, leading to the volatilization of I2 and resulting in irreversible device degradation. Mercaptoethylammonium iodide (ESAI) is thus incorporated into perovskite as an additive to inhibit the oxidation of iodide anion (I-) and  the light-induced degradation pathway of FAPbI3→FAI+PbI2. Additionally, the formation of a thiol-disulfide/I--I2 redox pair within the perovskite film provides a dynamic mechanism for the continuous reduction of I2 under light and thermal stresses, facilitating the healing of iodine-induced degradations. This approach significantly enhances the operational stability of PSCs. Under the ISOS-L-3 testing protocol (maximum power point (MPP) tracking in an environment with relative humidity of ≈50% at ≈65 °C), the treated PSCs maintain 97% of their original power conversion efficieney (PCE) after 300 h of aging. In contrast, control devices exhibit almost complete degradation, primarily due to rapid thermal-induced I2 volatilization. These results demonstrate a promising strategy to overcome critical stability challenges in PSCs, particularly in scenarios involving thermal effects.

Cascade Reaction in Organic Hole Transport Layer Enables Efficient Perovskite Solar Cells

The doped organic hole transport layer (HTL) is crucial for achieving high-efficiency perovskite solar cells (PSCs). However, the traditional doping strategy undergoes a time-consuming and environment-dependent oxidation process, which hinders the technology upgrades and commercialization of PSCs. Here, we reported a new strategy by introducing a cascade reaction in traditional doped Spiro-OMeTAD, which can simultaneously achieve rapid oxidation and overcome the erosion of perovskite by 4-tert-butylpyridine (tBP) in organic HTL. The ideal dopant iodobenzene diacetate was utilized as the initiator that can react with Spiro to generate Spiro⋅+ radicals quickly and efficiently without the participation of ambient air, with the byproduct of iodobenzene (DB). Then, the DB can coordinate with tBP through a halogen bond to form a tBP-DB complex, minimizing the sustained erosion from tBP to perovskite. Based on the above cascade reaction, the resulting Spiro-based PSCs have a champion PCE of 25.76 % (certificated of 25.38 %). This new oxidation process of HTL is less environment-dependent and produces PSCs with higher reproducibility. Moreover, the PTAA-based PSCs obtain a PCE of 23.76 %, demonstrating the excellent applicability of this doping strategy on organic HTL.

Aza[5]helicene-Derived Semiconducting Polymers for Improved Performance in Perovskite Solar Cells: Exploring Energetic and Morphological Influences

The strategic design of solution-processable semiconducting polymers possessing both matched energy levels and elevated glass transition temperatures is of urgent importance in the progression of thermally robust n-i-p perovskite solar cells with efficiencies exceeding 25 %. In this work, we employed direct arylation polymerization to achieve the high-yield synthesis of three aza[5]helicene-derived copolymers with distinct HOMO energy levels and exceptional glass transition temperatures. Upon integration of these semiconducting polymers into formamidinium lead triiodide-based perovskite solar cells, marked disparities in photovoltaic parameters manifest, primarily stemming from variations in the electrical conductivity and film morphology of the hole transport layers. The p-A5HP-E-POZOD-E copolymer, featuring a main chain comprising alternating repeats of aza[5]helicene, ethylenedioxythiophene, phenoxazine, and ethylenedioxythiophene, attains an initial average efficiency of 25.5 %, markedly surpassing reference materials such as spiro-OMeTAD (23.0 %), PTAA (17.0 %), and P3HT (11.6 %). Notably, p-A5HP-E-POZOD-E exhibits a high cohesive energy density, resulting in enhanced Young's modulus and diminished external species diffusion coefficients, thereby conferring perovskite solar cells with exceptional 85 °C tolerance and operational stability.

Diffusion-Optimized Long Lifespan 4.6 V LiCoO2: Homogenizing Cycled Bulk-To-Surface Li Concentration with Reduced Structure Stress

Increasing the charging cut-off voltage (e.g., 4.6 V) to extract more Li ions are pushing the LiCoO2 (LCO) cathode to achieve a higher energy density. However, an inhomogeneous cycled bulk-to-surface Li distribution, which is closely associated with the enhanced extracted Li ions, is usually ignored, and severely restricts the design of long lifespan high voltage LCO. Here, a strategy by constructing an artificial solid-solid Li diffusion environment on LCO's surface is proposed to achieve a homogeneous bulk-to-surface Li distribution upon cycling. The diffusion optimized LCO not only shows a highly reversible capacity of 212 mA h g-1 but also an ultrahigh capacity retention of 80% over 600 cycles at 4.6 V. Combined in situ X-ray diffraction measurements and stress-evolution simulation analysis, it is revealed that the superior 4.6 V long-cycled stability is ascribed to a reduced structure stress leaded by the homogeneous bulk-to-surface Li diffusion. This work broadens approaches for the design of highly stable layered oxide cathodes with low ion-storage structure stress.

Polymer-acid-metal quasi-ohmic contact for stable perovskite solar cells beyond a 20,000-hour extrapolated lifetime

The development of a robust quasi-ohmic contact with minimal resistance, good stability and cost-effectiveness is crucial for perovskite solar cells. We introduce a generic approach featuring a Lewis-acid layer sandwiched between dopant-free semicrystalline polymer and metal electrode in perovskite solar cells, resulting in an ideal quasi-ohmic contact even at elevated temperature up to 85 °C. The solubility of Lewis acid in alcohol facilitates nondestructive solution processing on top of polymer, which boosts hole injection from polymer into metal by two orders of magnitude. By integrating the polymer-acid-metal structure into solar cells, devices exhibit remarkable resilience, retaining 96% ± 3%, 96% ± 2% and 75% ± 7% of their initial efficiencies after continuous operation in nitrogen at 35 °C for 2212 h, 55 °C for 1650 h and 85 °C for 937 h, respectively. Leveraging the Arrhenius relation, we project an impressive T80 lifetime of 26,126 h at 30 °C.

Moisture-Resilient Perovskite Solar Cells for Enhanced Stability

With the rapid rise in device performance of perovskite solar cells (PSCs), overcoming instabilities under outdoor operating conditions has become the most crucial obstacle toward their commercialization. Among stressors such as light, heat, voltage bias, and moisture, the latter is arguably the most critical, as it can decompose metal-halide perovskite (MHP) photoactive absorbers instantly through its hygroscopic components (organic cations and metal halides). In addition, most charge transport layers (CTLs) commonly employed in PSCs also degrade in the presence of water. Furthermore, photovoltaic module fabrication encompasses several steps, such as laser processing, subcell interconnection, and encapsulation, during which the device layers are exposed to the ambient atmosphere. Therefore, as a first step toward long-term stable perovskite photovoltaics, it is vital to engineer device materials toward maximizing moisture resilience, which can be accomplished by passivating the bulk of the MHP film, introducing passivation interlayers at the top contact, exploiting hydrophobic CTLs, and encapsulating finished devices with hydrophobic barrier layers, without jeopardizing device performance. Here, existing strategies for enhancing the performance stability of PSCs are reviewed and pathways toward moisture-resilient commercial perovskite devices are formulated.

Multifunctional Surface Treatment against Imperfections and Halide Segregation in Wide-Band Gap Perovskite Solar Cells

Mixed-halide wide-band gap perovskites (WBPs) still suffer from losses due to imperfections within the absorber and the segregation of halide ions under external stimuli. Herein, we design a multifunctional passivator (MFP) by mixing bromide salt, formamidinium bromide (FABr) with a p-type self-assembled monolayer (SAM) to target the nonradiative recombination pathways. Photoluminescence measurement shows considerable suppression of nonradiative recombination rates after treatment with FABr. However, WBPs still remained susceptible to halide segregation for which the addition of 25% p-type SAM was effective to decelerate segregation. It is observed that FABr can act as a passivating agent of the donor impurities, shifting the Fermi-level (Ef) toward the mid-band gap, while p-type SAM could cause an overweight of Ef toward the valence band. Favorable band bending at the interface could prevent the funneling of carriers toward I-rich clusters. Instead, charge carriers funnel toward an integrated SAM, preventing the accumulation of polaron-induced strain on the lattice. Consequently, n-i-p structured devices with an optimal MFP treatment show an average open-circuit voltage (VOC) increase of about 20 mV and fill factor (FF) increase by 4% compared with the control samples. The unencapsulated devices retained 95% of their initial performance when stored at room temperature under 40% relative humidity for 2800 h.

Poly(3-hexylthiophene)/perovskite Heterointerface by Spinodal Decomposition Enabling Efficient and Stable Perovskite Solar Cells

The best research-cell efficiency of perovskite solar cells (PSCs) is comparable with that of mature silicon solar cells (SSCs); However, the industrial development of PSCs lags far behind SSCs. PSC is a multiphase and multicomponent system, whose consequent interfacial energy loss and carrier loss seriously affect the performance and stability of devices. Here, by using spinodal decomposition, a spontaneous solid phase segregation process, in situ introduces a poly(3-hexylthiophene)/perovskite (P3HT/PVK) heterointerface with interpenetrating structure in PSCs. The P3HT/PVK heterointerface tunes the energy alignment, thereby reducing the energy loss at the interface; The P3HT/PVK interpenetrating structure bridges a transport channel, thus decreasing the carrier loss at the interface. The simultaneous mitigation of energy and carrier losses by P3HT/PVK heterointerface enables n-i-p geometry device a power conversion efficiency of 24.53% (certified 23.94%) and excellent stability. These findings demonstrate an ingenious strategy to optimize the performance of PSCs by heterointerface via Spinodal decomposition.

Long-chain organic molecules enable mixed dimensional perovskite photovoltaics: a brief view

The remarkable optoelectronic properties of organometal halide perovskite solar cells have captivated significant attention in the energy sector. Nevertheless, the instability of 3D perovskites, despite their extensive study and attainment of high-power conversion efficiency, remains a substantial obstacle in advancing PSCs for practical applications and eventual commercialization. To tackle this issue, researchers have devised mixed-dimensional perovskite structures combining 1D and 3D components. This innovative approach entails incorporating stable 1D perovskites into 3D perovskite matrices, yielding a significant improvement in long-term stability against various challenges, including moisture, continuous illumination, and thermal stress. Notably, the incorporation of 1D perovskite yields a multitude of advantages. Firstly, it efficiently passivates defects, thereby improving the overall device quality. Secondly, it retards ion migration, a pivotal factor in degradation, thus further bolstering stability. Lastly, the inclusion of 1D perovskite facilitates charge transport, ultimately resulting in an elevated device efficiency. In this succinct review, we thoroughly encapsulate the recent progress in PSCs utilizing 1D/3D mixed-dimensional architectures. These advancements encompass both stacked bilayer configurations of 1D/3D structures and mixed monolayer structures of 1D/3D. Additionally, we tackle critical challenges that must be surmounted and offer insights into the prospects for further advancements in this domain.

Multifunctional sulfonium-based treatment for perovskite solar cells with less than 1% efficiency loss over 4,500-h operational stability tests

The stabilization of grain boundaries and surfaces of the perovskite layer is critical to extend the durability of perovskite solar cells. Here we introduced a sulfonium-based molecule, dimethylphenethylsulfonium iodide (DMPESI), for the post-deposition treatment of formamidinium lead iodide perovskite films. The treated films show improved stability upon light soaking and remains in the black α phase after two years ageing under ambient condition without encapsulation. The DMPESI-treated perovskite solar cells show less than 1% performance loss after more than 4,500 h at maximum power point tracking, yielding a theoretical T80 of over nine years under continuous 1-sun illumination. The solar cells also display less than 5% power conversion efficiency drops under various ageing conditions, including 100 thermal cycles between 25 °C and 85 °C and an 1,050-h damp heat test.

Fully Aromatic Self-Assembled Hole-Selective Layer toward Efficient Inverted Wide-Bandgap Perovskite Solar Cells with Ultraviolet Resistance

Ultraviolet-induced degradation has emerged as a critical stability concern impeding the widespread adoption of perovskite solar cells (PSCs), particularly in the context of phase-unstable wide-band gap perovskite films. This study introduces a novel approach by employing a fully aromatic carbazole-based self-assembled monolayer, denoted as (4-(3,6-dimethoxy-9H-carbazol-9-yl)phenyl)phosphonic acid (MeO-PhPACz), as a hole-selective layer (HSL) in inverted wide-band gap PSCs. Incorporating a conjugated linker plays a pivotal role in promoting the formation of a dense and highly ordered HSL on substrates, facilitating subsequent perovskite interfacial interactions, and fostering the growth of uniform perovskite films. The high-quality film could effectively suppress interfacial non-radiative recombination, improving hole extraction/transport efficiency. Through these advancements, the optimized wide-band gap PSCs, featuring a band gap of 1.68 eV, attain an impressive power conversion efficiency (PCE) of 21.10 %. Remarkably, MeO-PhPACz demonstrates inherent UV resistance and heightened UV absorption capabilities, substantially improving UV resistance for the targeted PSCs. This characteristic holds significance for the feasibility of large-scale outdoor applications.

Enhanced Quasi-Fermi Level Splitting of Perovskite Solar Cells by Universal Dual-Functional Polymer

Perovskite solar cells (PSCs) have attracted extensive attention due to their higher power conversion efficiency (PCE) and simple fabrication process. However, the open-circuit voltage (VOC ) loss remains a significant impediment to enhance device performance. Here, a facile strategy to boost the VOC to 95.5% of the Shockley-Queisser (S-Q) limit through the introduction of a universal multifunctional polymer additive is demonstrated. This additive effectively passivates the cation and anion defects simultaneously, thereby leading to the transformation from the strong n-type to weak n-type of perovskite films. Benefitting from the energy level alignment and the suppression of bulk non-radiative recombination, the quasi-Fermi level splitting (QFLS) is enhanced.  Consequently, the champion devices with 1.59 eV-based perovskite reach the highest VOC value of 1.24 V and a PCE of 23.86%. Furthermore, this strategy boosts the VOC by at least 0.07 V across five different perovskite systems, a PCE of 25.04% is achieved for 1.57 eV-based PSCs, and the corresponding module (14 cm2 ) also obtained a high PCE of 21.95%. This work provides an effective and universal strategy to promote the VOC approach to the detailed balance theoretical limit.

Iodonium Initiators: Paving the Air-free Oxidation of Spiro-OMeTAD for Efficient and Stable Perovskite Solar Cells

To date, perovskite solar cells (pero-SCs) with doped 2,2',7,7'-tetrakis(N,N-di-p-methoxyphenylamine)-9,9'-spirobifluorene (Spiro-OMeTAD) hole transporting layers (HTLs) have shown the highest recorded power conversion efficiencies (PCEs). However, their commercialization is still impeded by poor device stability owing to the hygroscopic lithium bis(trifluoromethanesulfonyl)imide and volatile 4-tert-butylpyridine dopants as well as time-consuming oxidation in air. In this study, we explored a series of single-component iodonium initiators with strong oxidability and different electron delocalization properties to precisely manipulate the oxidation states of Spiro-OMeTAD without air assistance, and the oxidation mechanism was clearly understood. Iodine (III) in the diphenyliodonium cation (IP+ ) can accept a single electron from Spiro-OMeTAD and forms Spiro-OMeTAD⋅+ owing to its strong oxidability. Moreover, because of the coordination of the strongly delocalized TFSI- with Spiro-OMeTAD⋅+ in a stable radical complex, the resulting hole mobility was 30 times higher than that of pristine Spiro-OMeTAD. In addition, the IP-TFSI initiator facilitated the growth of a homogeneous and pinhole-free Spiro-OMeTAD film. The pero-SCs based on this oxidizing HTL showed excellent efficiencies of 25.16 % (certified: 24.85 % for 0.062-cm2 ) and 20.71 % for a 15.03-cm2 module as well as remarkable overall stability.

A Homopolymer of Xanthenoxanthene-Based Polycyclic Heteroaromatic for Efficient and Stable Perovskite Solar Cells

Highly efficient perovskite solar cells typically rely on spiro-OMeTAD as a hole transporter, achieving a 25.7 % efficiency record. However, these cells are susceptible to harsh 85 °C conditions. Here, we present a peri-xanthenoxanthene-based semiconducting homopolymer (p-TNI2) with matched energy levels and a high molecular weight, synthesized nearly quantitatively through facile oxidative polymerization. Compared to established materials, p-TNI2 excels in hole mobility, morphology, modulus, and waterproofing. Implementing p-TNI2 as the hole transport layer results in n-i-p perovskite solar cells with an initial average efficiency of 24.6 %, rivaling 24.4 % for the spiro-OMeTAD control cells under identical conditions. Furthermore, the p-TNI2-based cells exhibit enhanced thermostability at 85 °C and operational robustness.

Potential window alignment regulating ion transfer in faradaic junctions for efficient photoelectrocatalysis

In the past decades, a band alignment theory has become a basis for designing different high-performance semiconductor devices, such as photocatalysis, photoelectrocatalysis, photoelectrostorage and third-generation photovoltaics. Recently, a faradaic junction model (coupled electron and ion transfer) has been proposed to explain charge transfer phenomena in these semiconductor heterojunctions. However, the classic band alignment theory cannot explain coupled electron and ion transfer processes because it only regulates electron transfer. Therefore, it is very significant to explore a suitable design concept for regulating coupled electron and ion transfer in order to improve the performance of semiconductor heterojunctions. Herein, we propose a potential window alignment theory for regulating ion transfer and remarkably improving the photoelectrocatalytic performance of a MoS2/Cd-Cu2ZnSnS4 heterojunction photocathode. Moreover, we find that a faradaic potential window, rather than the band position of the intermediate layer, is a criterion for identifying interface charge transfer direction. This finding can offer different perspectives for designing high-performance semiconductor heterojunctions with suitable potential windows for solar energy conversion and storage.

Redox: Organic Robust Radicals and Their Polymers for Energy Conversion/Storage Devices

Persistent radicals can hold their unpaired electrons even under conditions where they accumulate, leading to the unique characteristics of radical ensembles with open-shell structures and their molecular properties, such as magneticity, radical trapping, catalysis, charge storage, and electrical conductivity. The molecules also display fast, reversible redox reactions, which have attracted particular attention for energy conversion and storage devices. This paper reviews the electrochemical aspects of persistent radicals and the corresponding macromolecules, radical polymers. Radical structures and their redox reactions are introduced, focusing on redox potentials, bistability, and kinetic constants for electrode reactions and electron self-exchange reactions. Unique charge transport and storage properties are also observed with the accumulated form of redox sites in radical polymers. The radical molecules have potential electrochemical applications, including in rechargeable batteries, redox flow cells, photovoltaics, diodes, and transistors, and in catalysts, which are reviewed in the last part of this paper.

Highly Stable and Efficient Formamidinium-Based 2D Ruddlesden-Popper Perovskite Solar Cells via Lattice Manipulation

Formamidinium (FA)-based 2D perovskites have emerged as highly promising candidates in solar cells. However, the insertion of 2D spacer cations into the perovskite lattice concomitantly introduces microstrain and unfavorable orientations that hinder efficiency and stability. In this study, by finely tuning the FA-based 2D perovskite lattice through spacer cation engineering, a stable lattice structure with balanced distortion, microstrain relaxation, and reduced carrier-lattice interactions is achieved. These advancements effectively stabilize the inherently soft lattice against light and thermal-aging stress. To reduce the photocurrent loss induced by undesired crystal texture, a polarity-matched molecular-type selenourea (SENA) additive is further employed to modulate the crystallization kinetics. The introduction of the SENA significantly inhibits the disordered crystallization induced by spacer cations and drives the templated growth of the quantum well structure with a vertical orientation. This controlled crystallization process effectively reduces crystal defects and enhances charge separation. Ultimately, the optimized FA-based perovskite photovoltaic devices achieve a remarkable power conversion efficiency (PCE) of 20.03% (certified steady-state efficiency of 19.30%), setting a new record for low-n 2D perovskite solar cells. Furthermore, the devices exhibit less than 1% efficiency degradation after operating at maximum power point for 1000 h and maintain excellent stability after thermal aging and cycles of cold-warm shock, respectively.

Doping of molecular semiconductors through proton-coupled electron transfer

The chemical doping of molecular semiconductors is based on electron-transfer reactions between the semiconductor and dopant molecules; here, the redox potential of the dopant is key to control the Fermi level of the semiconductor1,2. The tunability and reproducibility of chemical doping are limited by the availability of dopant materials and the effects of impurities such as water. Here we focused on proton-coupled electron-transfer (PCET) reactions, which are widely used in biochemical processes3,4; their redox potentials depend on an easily handled parameter, that is, proton activity. We immersed p-type organic semiconductor thin films in aqueous solutions with PCET-based redox pairs and hydrophobic molecular ions. Synergistic reactions of PCET and ion intercalation resulted in efficient chemical doping of crystalline organic semiconductor thin films under ambient conditions. In accordance with the Nernst equation, the Fermi levels of the semiconductors were controlled reproducibly with a high degree of precision-a thermal energy of about 25 millielectronvolts at room temperature and over a few hundred millielectronvolts around the band edge. A reference-electrode-free, resistive pH sensor based on this method is also proposed. A connection between semiconductor doping and proton activity, a widely used parameter in chemical and biochemical processes, may help create a platform for ambient semiconductor processes and biomolecular electronics.

Screen-Printing Technology for Scale Manufacturing of Perovskite Solar Cells

As a key contender in the field of photovoltaics, third-generation thin-film perovskite solar cells (PSCs) have gained significant research and investment interest due to their superior power conversion efficiency (PCE) and great potential for large-scale production. For commercialization consideration, low-cost and scalable fabrication is of primary importance for PSCs, and the development of the applicable film-forming techniques that meet the above requirements plays a key role. Currently, large-area perovskite films are mainly produced by printing techniques, such as slot-die coating, inkjet printing, blade coating, and screen-printing. Among these techniques, screen printing offers a high degree of functional layer compatibility, pattern design flexibility, and large-scale ability, showing great promise. In this work, the advanced progress on applying screen-printing technology in fabricating PSCs from technique fundamentals to practical applications is presented. The fundamentals of screen-printing technique are introduced and the state-of-the-art studies on screen-printing different functional layers in PSCs and the control strategies to realize fully screen-printed PSCs are summarized. Moreover, the current challenges and opportunities faced by screen-printed perovskite devices are discussed. This work highlights the critical significance of high throughput screen-printing technology in accelerating the commercialization course of PSCs products.

Porphyrin Supramolecule as Surface Carrier Modulator Imparts Hole Transporter with Enhanced Mobility for Perovskite Photovoltaics

Modulating the surface charge transport behavior of hole transport materials (HTMs) would be as an potential approach to improve their hole mobility, while yet realized for fabricating efficient photovoltaic devices. Here, an oxygen bridged dimer-based monoamine FeIII porphyrin supramolecule is prepared and doped in HTM film. Theoretical analyses reveal that the polaron distributed on dimer can be coupled with the parallel arranged polarons on adjacent dimers. This polaron coupling at the interface of supramolecule and HTM can resonates with hole flux to increase hole transport efficiency. Mobility tests reveal that the hole mobility of doped HTM film is improved by 8-fold. Doped perovskite device exhibits an increased efficiency from 19.8 % to 23.2 %, and greatly improved stability. This work provides a new strategy to improve the mobility of HTMs by surface carrier modulation, therefore fabricating efficient photovoltaic devices.

Gelation of Hole Transport Layer to Improve the Stability of Perovskite Solar Cells

To achieve high power conversion efficiency (PCE) and long-term stability of perovskite solar cells (PSCs), a hole transport layer (HTL) with persistently high conductivity, good moisture/oxygen barrier ability, and adequate passivation capability is important. To achieve enough conductivity and effective hole extraction, spiro-OMeTAD, one of the most frequently used HTL in optoelectronic devices, often needs chemical doping with a lithium compound (LiTFSI). However, the lithium salt dopant induces crystallization and has a negative impact on the performance and lifetime of the device due to its hygroscopic nature. Here, we provide an easy method for creating a gel by mixing a natural small molecule additive (thioctic acid, TA) with spiro-OMeTAD. We discover that gelation effectively improves the compactness of resultant HTL and prevents moisture and oxygen infiltration. Moreover, the gelation of HTL improves not only the conductivity of spiro-OMeTAD, but also the operational robustness of the devices in the atmospheric environment. In addition, TA passivates the perovskite defects and facilitates the charge transfer from the perovskite layer to HTL. As a consequence, the optimized PSCs based on the gelated HTL exhibit an improved PCE (22.52%) with excellent device stability.

Lead-chelating hole-transport layers for efficient and stable perovskite minimodules

The defective bottom interfaces of perovskites and hole-transport layers (HTLs) limit the performance of p-i-n structure perovskite solar cells. We report that the addition of lead chelation molecules into HTLs can strongly interact with lead(II) ion (Pb²⁺), resulting in a reduced amorphous region in perovskites near HTLs and a passivated perovskite bottom surface. The minimodule with an aperture area of 26.9 square centimeters has a power conversion efficiency (PCE) of 21.8% (stabilized at 21.1%) that is certified by the National Renewable Energy Laboratory (NREL), which corresponds to a minimal small-cell efficiency of 24.6% (stabilized 24.1%) throughout the module area. Small-area cells and large-area minimodules with lead chelation molecules in HTLs had a light soaking stability of 3010 and 2130 hours, respectively, at an efficiency loss of 10% from the initial value under 1-sun illumination and open-circuit voltage conditions.

Unveiling and Modulating the Interfacial Reaction at the Metal-Hole Conductor Heterojunction toward Reliable Perovskite Solar Cells

Interfaces between functional layers in perovskite solar cells (PSCs) are of paramount importance in determining their efficiency and stability, but the interaction and stability of metal-hole conductor (HC) interfaces have received less attention. Here, we discover an intriguing transient behavior in devices which induces a profound efficiency fluctuation from 9 to 20% during the initial performance testing. Air exposure (e.g., oxygen and moisture) can significantly accelerate this nonequilibrium process and simultaneously enhance the device maximal efficiency. Structural analysis reveals that the chemical reaction between Ag and HC occurred during the metal deposition by thermal evaporation, leading to the formation of an insulating barrier layer at their interfaces, which results in a high charge-transport barrier and poor device performance. Accordingly, we propose a metal diffusion-associated barrier evolution mechanism to understand the metal/HC interfaces. To mitigate these detrimental effects, we strategically develop an interlayer strategy by introducing an ultrathin layer of molybdenum oxide (MoO₃) between Ag and HC, which is found to effectively suppress the interfacial reaction, yielding highly reliable PSCs with instant high efficiency. This work provides new insights into understanding the metal-organic interfaces, and the developed interlayer strategy can be generally applicable to engineer other interfaces in realizing efficient and stable contacts.

Inhibited Crack Development by Compressive Strain in Perovskite Solar Cells with Improved Mechanical Stability

Metal halide perovskites are promising as next-generation photovoltaic materials, but stability issues are still a huge obstacle to their commercialization. Here, the formation and evolution of cracks in perovskite films during thermal cycling, which affect their mechanical stability, are investigated. Compressive strain is employed to suppress cracks and delamination by in situ formed polymers with low elastic modulus during crystal growth. The resultant devices pass the thermal-cycling qualification (IEC61215:2016), retaining 95% of the initial power conversion efficiency (PCE) and compressive strain after 230 cycles. Meanwhile, the p-i-n devices deliver PCEs of 23.91% (0.0805 cm² ) and 23.27% (1 cm² ). The findings shed light on strain engineering with respect to their evolution, which enables mechanically stable perovskite solar cells.

Recent Advances in Wide-Bandgap Organic-Inorganic Halide Perovskite Solar Cells and Tandem Application

Perovskite-based tandem solar cells have attracted increasing interest because of its great potential to surpass the Shockley-Queisser limit set for single-junction solar cells. In the tandem architectures, the wide-bandgap (WBG) perovskites act as the front absorber to offer higher open-circuit voltage (VOC) for reduced thermalization losses. Taking advantage of tunable bandgap of the perovskite materials, the WBG perovskites can be easily obtained by substituting halide iodine with bromine, and substituting organic ions FA and MA with Cs. To date, the most concerned issues for the WBG perovskite solar cells (PSCs) are huge VOC deficit and severe photo-induced phase separation. Reducing VOC loss and improving photostability of the WBG PSCs are crucial for further efficiency breakthrough. Recently, scientists have made great efforts to overcome these key issues with tremendous progresses. In this review, we first summarize the recent progress of WBG perovskites from the aspects of compositions, additives, charge transport layers, interfaces and preparation methods. The key factors affecting efficiency and stability are then carefully discussed, which would provide decent guidance to develop highly efficient and stable WBG PSCs for tandem application.

Fluorine-Containing Passivation Layer via Surface Chelation for Inorganic Perovskite Solar Cells

Minimizing surface defect is vital to further improve power conversion efficiency (PCE) and stability of inorganic perovskite solar cells (PSCs). Herein, we designed a passivator trifluoroacetamidine (TFA) to suppress CsPbI_3-x Br_x film defects. The amidine group of TFA can strongly chelate onto the perovskite surface to suppress the iodide vacancy, strengthened by additional hydrogen bonds. Moreover, three fluorine atoms allow strong intermolecular connection via intermolecular hydrogen bonds, thus constructing a robust shield against moisture. The TFA-treated PSCs exhibit remarkably suppressed recombination, yielding the record PCEs of 21.35 % and 17.21 % for 0.09 cm² and 1.0 cm² device areas, both of which are the highest for all-inorganic PSCs so far. The device also achieves a PCE of 39.78 % under indoor illumination, the highest for all-inorganic indoor photovoltaic devices. Furthermore, TFA greatly improves device ambient stability by preserving 93 % of the initial PCE after 960 h.

Radical polymeric p-doping and grain modulation for stable, efficient perovskite solar modules

High-quality perovskite light harvesters and robust organic hole extraction layers are essential for achieving high-performing perovskite solar cells (PSCs). We introduce a phosphonic acid-functionalized fullerene derivative in mixed-cation perovskites as a grain boundary modulator to consolidate the crystal structure, which enhances the tolerance of the film against illumination, heat, and moisture. We also developed a redox-active radical polymer, poly(oxoammonium salt), that can effectively p-dope the hole-transporting material by hole injection and that also mitigates lithium ion diffusion. Power conversion efficiencies of 23.5% for 1-square-centimeter mixed-cation-anion PSCs and 21.4% for 17.1-square-centimeter minimodules were achieved. The PSCs retained 95.5% of their initial efficiencies after 3265 hours at maximum power point tracking under continuous 1-sun illumination at 70° ± 5°C.

Inhibiting Li+ migration by thenoyltrifluoroacetone toward efficient and stable perovskite solar cells

Thenoyltrifluoroacetone (TTA) modifies the perovskite/spiro-OMeTAD interface to inhibit Li+ migration from the hole transport layer to the perovskite layer and improves the performance of perovskite solar cells.

24.20%-Efficiency MA-Free Perovskite Solar Cells Enabled by Siloxane Derivative Interface Engineering

Suppressing defects at the interface between the TiO₂ electron transport layer (ETL) and perovskite film is critical for high efficiency and stable perovskite solar cells (PSCs). Herein, a siloxane derivative diethylphosphatoethylsilicic acid (PSiOH) is developed to modify the interface of TiO₂ ETL/FA_0.83 Cs_0.17 PbI₃ perovskite. Comprehensive characteristics reveal that silicon hydroxyl (SiOH) in PSiOH can reduce surface defects, improve the electrical properties and optimize the energy band structure of TiO₂ by forming a SiOTi bond, while the phosphate bond (PO) in PSiOH can passivate Pb-related defects on the perovskite bottom surface. Consequently, PSiOH-modified PSCs yield a remarkable power conversation efficiency of 24.20% and improved air, thermal, or illumination stabilities. This study provides insight into passivation defects at the buried interface for efficient and stable PSCs.