Halogen-halogen bonds enable improved long-term operational stability of mixed-halide perovskite photovoltaics

Multi-Noncentrosymmetric Polar Order in 2D Hybrid Lead Chloride with Broadband Emission and High-Temperature Second-Harmonic Generation Switching

Two-dimensional lead halide perovskites represent a fascinating class of hybrid semiconductors for solar cell, light-emitting, nonlinear optical (NLO), and ferroelectric applications. A notable subset within this category is luminescent ferroelectrics, which have garnered considerable attention for their potential in integrated photoelectronic devices. In this study, we employed an organic amine halogenation strategy (also referred to as halogen engineering), which is renowned for its efficacy in inducing polar order through crystal engineering. Consequently, we synthesized a layered Ruddlesden-Popper (RP) lead chloride comprising 3-chloropropylammonium cations (CPA+), with the chemical formula CPA2PbCl4. This compound features as many as four temperature-dependent crystal phases, with phase transitions observed at T1 = 353.1 K (343.9 K), T2 = 211.7 K (208.6 K), and T3 = 182.0 K (178.2 K) in the heating (cooling) cycles. Employing a multitechnique approach─including thermal analysis, X-ray diffraction, dielectric and pyroelectric current measurements, Raman spectroscopy, and second-harmonic generation (SHG) studies─we determined the mechanisms of the structural phase transitions. Our findings demonstrate polar order of phase II (space group Cmc21), phase III (space group Pna21), and phase IV (space group Pca21), while also confirming the centrosymmetric nature of phase I (space group Cmce). X-ray diffraction data revealed that the I to II PT is of a ferroelectric nature, devoid of ferroelastic strain, a conclusion further supported by pyroelectric measurements. CPA2PbCl4 features negative linear thermal expansion and broadband emission, which transitions to white light above 180 K. Remarkably, CPA2PbCl4 also demonstrates high-temperature SHG on-off switching with a high contrast ratio of 300:1 along with good switching stability, as evidenced by SHG cycling studies at heating/cooling rates ranging from 5 to 50 K/min. This SHG study also sets new standards for the field of SHG switching by providing a method to quantify the thermal responsiveness of SHG-switchable materials using the treq (time requirement) parameter. Overall, our findings show that the halogenation strategy has led to the discovery of a rare example of an RP perovskite exhibiting coexistence of white-light emission, SHG on-off thermal bistability, ferroelectricity, and negative linear thermal expansion.

Inhibiting Ion Migration and Stabilizing Crystal-Phase in Halide Perovskite via Directly Incorporated Fluoride Anion

Fluoride anion (F-) with extremely high electronegativity has been under intensive investigation in perovskite solar cells due to its remarkable defect suppression and great improvement of device performance. Nevertheless, these researches only focus on the surface, grain boundaries, or interface modification, the direct insertion of F- into the crystal lattice of regular lead halide perovskite films is still unrevealed. Herein, F- was successfully incorporated into the perovskite lattice by overcoming the insolubility of PbF2 via the introduced pyridinium halide as a novel volatile solubilizing ligand. The strong electronegativity of F- can strongly increase the binding energy of all the ions in CsPbI2Br and inhibit their defect formations. A trace amount of F- incorporation not only enhanced the optoelectronic properties but also effectively mitigated the ion migration and phase separation simultaneously. The photovoltaic performance and operational stability of perovskite solar cells were significantly improved with a champion efficiency of 17.78 % (38.01 %) under AM 1.5G (1000 lux indoor light). Moreover, F- can also be directly inserted into the hybrid perovskite lattice and greatly stabilized crystal-phase, enabling efficient fully MA-free FAPbI3 devices with 25.10 % efficiency. Our strategy sheds light on F-containing perovskites and provides a promising way to tackle ion migration and stabilize the crystal phase in halide perovskites.

Bulk Photovoltaic Effect Induced by Non-Covalent Interactions in Bilayered Hybrid Perovskite for Efficient Passive X-Ray Detection

Hydrogen bonding as a multifunctional tool has always influenced the structure of hybrid perovskites. Compared with the research on hydrogen bonding, the study of halogen-halogen interactions on the structure and properties of hybrid perovskites is still in its early stages. Herein, a polar bilayered hybrid perovskite (IEA)2FAPb2I7 (IEA+ is 2-iodoethyl-1-ammonium, FA is formamidinium) with iodine-substituted spacer is successfully constructed by changing the configuration of interlayer cations and regulating non-covalent interactions at the organic-inorganic interface, which shows a shorter interlayer spacing and higher density (ρ = 3.862 g cm-3). The generation of structure polarity in (IEA)2FAPb2I7 is caused by the synergistic effect of hydrogen bonding and halogen-halogen interactions. Especially, as the length of the carbon chain in organic cations decreases, the I---I interaction in the system gradually strengthens, which may be the main reason for the symmetry-breaking. Polarity-induced bulk photovoltaics (Voc = 1.0 V) and higher density endow the device based on (I-EA)2FAPb2I7 exhibit a high sensitivity of 175.6 µC Gy-1 cm-2 and an ultralow detection limit of 60.4 nGy s-1 at 0 V bias under X-ray irradiation. The results present a facile approach for designing polar multifunctional hybrid perovskites, also providing useful assistance for future research on halogen-halogen interactions.

Suppressed Ion Migration by Heterojunction Layer for Stable Wide-Bandgap Perovskite and Tandem Photovoltaics

Wide-bandgap (WBG) perovskite has demonstrated great potential in perovskite-based tandem solar cells. The power conversion efficiency (PCE) of such devices has surpassed 34%, signifying a new era for renewable energy development. However, the ion migration reduces the stability and hinders the commercialization, which is yet to be resolved despite many attempts. A big step forward has now been achieved by the simulation method. The detailed thermodynamics and kinetics of the migration process have been revealed for the first time. The stability has been enhanced by more than 100% via the heterojunction layer on top of the WBG perovskite film, which provided extra bonding for kinetic protection. Hopefully, these discoveries will open a new gate for WBG perovskite research and accelerate the application of perovskite-based tandem solar cells.

Improved Hole-Selective Contact Enables Highly Efficient and Stable FAPbBr3 Perovskite Solar Cells and Semitransparent Modules

Self-assembled monolayers (SAMs) as the hole-selective contact have achieved remarkable success in iodine-based perovskite solar cells (PSCs), while their impact on bromine-based PSCs is limited due to the poor perovskite crystallization behavior and mismatched energy level alignment. Here, a highly efficient SAM of (2-(3,6-diiodo-9H-carbazol-9-yl)ethyl)phosphonic acid (I-2PACz) is employed to address these challenges in FAPbBr3-based PSCs. The incorporation of I atoms into I-2PACz not only releases tensile stress within FAPbBr3 perovskite, promoting oriented crystallization and minimizing defects through halogen-halogen bond, but also optimizes the energy levels alignment at hole-selective interface for enhanced hole extraction. Ultimately, a power conversion efficiency (PCE) of 11.14% is achieved, which stands among the highest reported value for FAPbBr3 PSCs. Furthermore, the semitransparent devices/modules exhibit impressive PCEs of 8.19% and 6.23% with average visible transmittance of 41.98% and 38.99%. Remarkably, after operating at maximum power point for 1000 h, the encapsulated device maintains 93% of its initial PCE. These results demonstrate an effective strategy for achieving high-performance bromine-based PSCs toward further applications.

Alkyl Chains Tune Molecular Orientations to Enable Dual Passivation in Inverted Perovskite Solar Cells

Nonradiative recombination losses occurring at the interface pose a significant obstacle to achieve high-efficiency perovskite solar cells (PSCs), particularly in inverted PSCs. Passivating surface defects using molecules with different functional groups represents one of the key strategies for enhancing PSCs efficiency. However, a lack of insight into the passivation orientation of molecules on the surface is a challenge for rational molecular design. In this study, aminothiol hydrochlorides with different alkyl chains but identical electron-donating (-SH) and electron-withdrawing (-NH3 +) groups were employed to investigate the interplay between molecular structure, orientation, and interaction on perovskite surface. The 2-Aminoethane-1-thiol hydrochloride with shorter alkyl chains exhibited a preference of parallel orientations, which facilitating stronger interactions with the surface defects through strong coordination and hydrogen bonding. The resultant perovskite films following defect passivation demonstrate reduced ion migration, inhibition of nonradiative recombination, and more n-type characteristics for efficient electron transfer. Consequently, an impressive power conversion efficiency of 25 % was achieved, maintaining 95 % of its initial efficiency after 500 hours of continuous maximum power point tracking.

Dimensional Regulation in Metal-Free Perovskites by Compositional Engineering to Achieve Record Low X-Ray Detection Limits

Utilizing the manipulation of perovskite dimensions has been proven as an effective approach in regulating perovskite properties. Nevertheless, achieving precise control over the dimensions of perovskites within the same system poses a significant challenge. In this study, we introduce a sophisticated method to attain precise dimensional control in metal-free perovskites (MFPs), specifically through the process of octahedron tailoring by compositional engineering. Accordingly, we successfully instigated a transition from HPIP-NH4I3 ⋅ H2O (3D), HPIP2-NH4I5 (2D) and HPIP3-NH4I7 (1D) structures. Notably, HPIP2-NH4I5 is the first 2D MFP. As anticipated, these perovskites exhibited completely distinct fluorescence and X-ray detection capabilities due to their differing dimensions. Remarkably, the 2D HPIP2-NH4I5 device effectively hindered ion migration perpendicular to the 2D layers, achieving the lowest detection limit of 12.2 nGyair s-1 among metal-free single crystals-based detectors. This study expands the dimensionality control strategies for MFPs and introduces, for the first time, the potential of 2D MFPs as high-performance X-ray detectors, thereby enriching the diversity of the MFPs family.

Kornblum Oxidation Reaction-Induced Collective Transformation of Lead Polyhalides for Stable Perovskite Photovoltaics

The iodide vacancy defects generated during the perovskite crystallization process are a common issue that limits the efficiency and stability of perovskite solar cells (PSCs). Although excessive ionic iodides have been used to compensate for these vacancies, they are not effective in reducing defects through modulating the perovskite crystallization. Moreover, these iodide ions present in the perovskite films can act as interstitial defects, which are detrimental to the stability of the perovskite. Here, an effective approach to suppress the formation of vacancy defects by manipulating the coordination chemistry of lead polyhalides during perovskite crystallization is demonstrated. To achieve this suppression, an α-iodo ketone is introduced to undergo a process of Kornblum oxidation reaction that releases halide ions. This process induces a rapid collective transformation of lead polyhalides during the nucleation process and significantly reduces iodide vacancy defects. As a result, the ion mobility is decreased by one order of magnitude in perovskite film and the PSC achieves significantly improved thermal stability, maintaining 82% of its initial power conversion efficiency at 85 °C for 2800 h. These findings highlight the potential of halide ions released by the Kornblum oxidation reaction, which can be widely used for achieving high-performance perovskite optoelectronics.

In Situ Synthesized Low-Dimensional Perovskite for >25% Efficiency Stable MA-Free Perovskite Solar Cells

Developing an additive to effectively regulate the perovskite crystallization kinetics for the optimized optoelectronic properties of perovskite film plays a vital role in obtaining high efficiency and stable perovskite solar cells (PSCs). Herein, a new additive is designed and directly synthesized in perovskite precursor solution by utilizing an addition reaction between but-3-yn-1-amine hydrochloride (BAH) and formamidinium iodide. It is found that its product may control the intermediate precursor phase for regulating perovskite nucleation, leading to advantageous 2D perovskite to induce growth of perovskite along the preferred [001] orientation with not only released lattice strain but also strong interaction with perovskite to passivate its surface defects. By taking advantage of the above synergistic effects, the optimized PSC delivers an efficiency of 25.19% and a high open-circuit voltage (VOC) of 1.22 V. Additionally, the devices demonstrate good stability, remaining over 90% of their initial efficiencies under ambient atmosphere conditions for 60 days, high temperature of 85 °C for 200 h, or maximum power point tracking for 500 h.

Epitaxial Growth of α-FAPbI3 at a Well-Matched Heterointerface for Efficient Perovskite Solar Cells and Solar Modules

Although the FAPbI3 perovskite system exhibits an impressive optoelectronic characteristic and thermal stability because of its energetically unstable black phase at room temperature, it is considerably challenging to attain a controllable and oriented nucleation of α-FAPbI3 . To overcome this challenge, a 2D perovskite with a released inorganic octahedral distortion designed by weakening the hydrogen interactions between the organic interlayer and [PbI6 ]4- octahedron is presented in this study. A highly matched heterointerface can be formed between the (002) facet of the 2D structure and the (100) crystal plane of the cubic α-FAPbI3 , thereby lowering the crystallization energy and inducing a heterogeneous nucleation of α-FAPbI3 . This "epitaxial growth" mechanism results form the highly preferred crystallographic orientation of the (100) facets, improved crystal quality and film uniformity, substantially increased charge transporting characteristics, and suppressed nonradiative recombination losses. An impressive power conversion efficiency (PCE) of 25.4% (certified 25.2%) is achieved using target PSCs, which demonstrates outstanding ambient and operational stability. The feasibility of this strategy is proved for the scalable deposition of homogeneous and high-quality perovskite thin films by demonstrating the remarkably increased PCE of the large-area perovskite solar module, from 18.2% to 20.1%.

Structural Modification Strategies, Interfacial Charge-Carrier Dynamics, and Solar Energy Conversion Applications of Organic-Inorganic Halide Perovskite Photocatalysts

Over the past few decades, organic-inorganic halide perovskites (OIHPs) as novel photocatalyst materials have attracted intensive attention for an impressive variety of photocatalytic applications due to their excellent photophysical (chemical) properties. Regarding practical application and future commercialization, the air-water stability and photocatalytic performance of OIHPs need to be further improved. Accordingly, studying modification strategies and interfacial interaction mechanisms is crucial. In this review, the current progress in the development and photocatalytic fundamentals of OIHPs is summarized. Furthermore, the structural modification strategies of OIHPs, including dimensionality control, heterojunction design, encapsulation techniques, and so on for the enhancement of charge-carrier transfer and the enlargement of long-term stability, are elucidated. Subsequently, the interfacial mechanisms and charge-carrier dynamics of OIHPs during the photocatalytic process are systematically specified and classified via diverse photophysical and electrochemical characterization methods, such as time-resolved photoluminescence measurements, ultrafast transient absorption spectroscopy, electrochemical impedance spectroscopy measurements, transient photocurrent densities, and so forth. Eventually, various photocatalytic applications of OIHPs, including hydrogen evolution, CO2 reduction, pollutant degradation, and photocatalytic conversion of organic matter.

Eliminating Halogen Vacancies Enables Efficient MACL-Assisted Formamidine Perovskite Solar Cells

Methylammonium chloride (MACl) additive is almost irreplaceable in high-performance formamidine perovskite photovoltaics. Nevertheless, Some of the problems that can arise from adding MACl are rarely mentioned. Herein, it is proposed for the first time that the addition of MACl would cause the non-stoichiometric ratio in the perovskite film, resulting in the halogen vacancy. It is demonstrated that the non-synchronous volatilization of methylamine cations and chloride ions leads to the formation of halogen vacancy defects. To solve this problem, the NH4 HCOO is introduced into the perovskite precursor solution to passivate the halogen vacancy. The HCOO- ions have a strong force with lead ions and can fill the halogen vacancy defects. Consequently, the champion devices' power conversion efficiency (PCE) can be improved from 21.23% to 23.72% with negligible hysteresis. And the unencapsulated device can still retain >90% of the initial PCE even operating in N2 atmosphere for over 1200 h. This work illustrates another halogen defect source in the MACl-assisted formamidine perovskite photovoltaics and provides a new route to obtain high-performance perovskite solar cells.

Inhibition of Ion Migration for Highly Efficient and Stable Perovskite Solar Cells

In recent years, organic-inorganic halide perovskites are now emerging as the most attractive alternatives for next-generation photovoltaic devices, due to their excellent optoelectronic characteristics and low manufacturing cost. However, the resultant perovskite solar cells (PVSCs) are intrinsically unstable owing to ion migration, which severely impedes performance enhancement, even with device encapsulation. There is no doubt that the investigation of ion migration and the summarization of recent advances in inhibition strategies are necessary to develop "state-of-the-art" PVSCs with high intrinsic stability for accelerated commercialization. This review systematically elaborates on the generation and fundamental mechanisms of ion migration in PVSCs, the impact of ion migration on hysteresis, phase segregation, and operational stability, and the characterizations for ion migration in PVSCs. Then, many related works on the strategies for inhibiting ion migration toward highly efficient and stable PVSCs are summarized. Finally, the perspectives on the current obstacles and prospective strategies for inhibition of ion migration in PVSCs to boost operational stability and meet all of the requirements for commercialization success are summarized.

Unraveling Size-Dependent Ion-Migration for Stable Mixed-Halide Perovskite Light-Emitting Diodes

Mixed-halide perovskites show tunable emission wavelength across the visible-light range, with optimum control of the light color. However, color stability remains limited due to the notorious halide segregation under illumination or an electric field. Here, a versatile path toward high-quality mixed-halide perovskites with high emission properties and resistance to halide segregation is presented. Through systematic in and ex situ characterizations, key features for this advancement are proposed: a slowed and controllable crystallization process can promote achievement of halide homogeneity, which in turn ensures thermodynamic stability; meanwhile, downsizing perovskite nanoparticle to nanometer-scale dimensions can enhance their resistance to external stimuli, strengthening the phase stability. Leveraging this strategy, devices are developed based on CsPbCl1.5 Br1.5 perovskite that achieves a champion external quantum efficiency (EQE) of 9.8% at 464 nm, making it one of the most efficient deep-blue mixed-halide perovskite light-emitting diodes (PeLEDs) to date. Particularly, the device demonstrates excellent spectral stability, maintaining a constant emission profile and position for over 60 min of continuous operation. The versatility of this approach with CsPbBr1.5 I1.5 PeLEDs is further showcased, achieving an impressive EQE of 12.7% at 576 nm.

Homomeric chains of intermolecular bonds scaffold octahedral germanium perovskites

Perovskites with low ionic radii metal centres (for example, Ge perovskites) experience both geometrical constraints and a gain in electronic energy through distortion; for these reasons, synthetic attempts do not lead to octahedral [GeI6] perovskites, but rather, these crystallize into polar non-perovskite structures1-6. Here, inspired by the principles of supramolecular synthons7,8, we report the assembly of an organic scaffold within perovskite structures with the goal of influencing the geometric arrangement and electronic configuration of the crystal, resulting in the suppression of the lone pair expression of Ge and templating the symmetric octahedra. We find that, to produce extended homomeric non-covalent bonding, the organic motif needs to possess self-complementary properties implemented using distinct donor and acceptor sites. Compared with the non-perovskite structure, the resulting [GeI6]4- octahedra exhibit a direct bandgap with significant redshift (more than 0.5 eV, measured experimentally), 10 times lower octahedral distortion (inferred from measured single-crystal X-ray diffraction data) and 10 times higher electron and hole mobility (estimated by density functional theory). We show that the principle of this design is not limited to two-dimensional Ge perovskites; we implement it in the case of copper perovskite (also a low-radius metal centre), and we extend it to quasi-two-dimensional systems. We report photodiodes with Ge perovskites that outperform their non-octahedral and lead analogues. The construction of secondary sublattices that interlock with an inorganic framework within a crystal offers a new synthetic tool for templating hybrid lattices with controlled distortion and orbital arrangement, overcoming limitations in conventional perovskites.

Mixed-Halide Perovskites with Halogen Bond Induced Interlayer Locking Structure for Stable Pure-Red PeLEDs

Mixed-halide perovskites enable precise spectral tuning across the entire spectral range through composition engineering. However, mixed halide perovskites are susceptible to ion migration under continuous illumination or electric field, which significantly impedes the actual application of perovskite light-emitting diodes (PeLEDs). Here, we demonstrate a novel approach to introduce strong and homogeneous halogen bonds within the quasi-two-dimensional perovskite lattices by means of an interlayer locking structure, which effectively suppresses ion migration by increasing the corresponding activation energy. Various characterizations confirmed that intralattice halogen bonds enhance the stability of quasi-2D mixed-halide perovskite films. Here, we report that the PeLEDs exhibit an impressive 18.3% EQE with pure red emission with CIE color coordinate of (0.67, 0.33) matching Rec. 2100 standards and demonstrate an operational half-life of ∼540 min at an initial luminance of 100 cd m^-2, representing one of the most stable mixed-halide pure red PeLEDs reported to date.

Two-Dimensional Metal Halides for X-Ray Detection Applications

Metal halide perovskites have recently emerged as promising candidates for the next generation of X-ray detectors due to their excellent optoelectronic properties. Especially, two-dimensional (2D) perovskites afford many distinct properties, including remarkable structural diversity, high generation energy, and balanced large exciton binding energy. With the advantages of 2D materials and perovskites, it successfully reduces the decomposition and phase transition of perovskite and effectively suppresses ion migration. Meanwhile, the existence of a high hydrophobic spacer can block water molecules, thus making 2D perovskite obtain excellent stability. All of these advantages have attracted much attention in the field of X-ray detection. This review introduces the classification of 2D halide perovskites, summarizes the synthesis technology and performance characteristics of 2D perovskite X-ray direct detector, and briefly discusses the application of 2D perovskite in scintillators. Finally, this review also emphasizes the key challenges faced by 2D perovskite X-ray detectors in practical application and presents our views on its future development.

Hole-Transport Management Enables 23%-Efficient and Stable Inverted Perovskite Solar Cells with 84% Fill Factor

NiOx-based inverted perovskite solar cells (PSCs) have presented great potential toward low-cost, highly efficient and stable next-generation photovoltaics. However, the presence of energy-level mismatch and contact-interface defects between hole-selective contacts (HSCs) and perovskite-active layer (PAL) still limits device efficiency improvement. Here, we report a graded configuration based on both interface-cascaded structures and p-type molecule-doped composites with two-/three-dimensional formamidinium-based triple-halide perovskites. We find that the interface defects-induced non-radiative recombination presented at HSCs/PAL interfaces is remarkably suppressed because of efficient hole extraction and transport. Moreover, a strong chemical interaction, halogen bonding and coordination bonding are found in the molecule-doped perovskite composites, which significantly suppress the formation of halide vacancy and parasitic metallic lead. As a result, NiOx-based inverted PSCs present a power-conversion-efficiency over 23% with a high fill factor of 0.84 and open-circuit voltage of 1.162 V, which are comparable to the best reported around 1.56-electron volt bandgap perovskites. Furthermore, devices with encapsulation present high operational stability over 1,200 h during T90 lifetime measurement (the time as a function of PCE decreases to 90% of its initial value) under 1-sun illumination in ambient-air conditions.

Halogen microregulation in metal-organic frameworks for enhanced adsorption performance of ReO4-/TcO4. JOURNAL OF HAZARDOUS MATERIALS 2023;446:130744. [PMID: 36630874 DOI: 10.1016/j.jhazmat.2023.130744]

Effective and selective removal of ⁹⁹TcO₄^-, one of the most nuisance radionuclides in nuclear waste, is highly desirable but remains a significant challenge. Herein, two isostructural MOFs, NCU-3-X (X = Cl, Br) were constructed by ZnX₂ coordinated to nitrogen-containing neutral ligand tri(4-(1H-imidazole-1-l) phenyl) amine for efficient adsorption ReO₄^-/TcO₄^-. Owning to the twofold interpenetrating structure, both of them exhibit strong alkaline resistance. Consequently, NCU-3-Br exhibited superior adsorption performances with a maximum capacity as high as 483 mg/g, which is 2.23 times larger than that of NCU-3-Cl. The primary reasons accounting for the enhanced adsorption performances of NCU-3-Br are that compared to chlorine atoms, the smaller electronegativity of bromine atoms as halogen bonds donor can facilitate the formation of σ-holes, enhance positively charged skeleton, and reduce the adsorption energy associated with ReO₄^-/TcO₄^-. In addition, the one-dimensional hydrophobic channels in the NCU-3-Br framework enable NCU-3-Br to have highly selective toward ReO₄^-, which has a low relative charge density against interfering ions. The SRS simulation removal experiment further confirmed the excellent adsorption capacity of NCU-3-Br to ReO₄^-/TcO₄^-. This work illustrated that the halogenated new strategy incorporated different halogen atoms into MOF skeletons can dramatically modulate the adsorption performances for ReO₄^-/TcO₄^-.

Ligand-Assisted Coupling Manipulation for Efficient and Stable FAPbI3 Colloidal Quantum Dot Solar Cells

For emerging perovskite quantum dots (QDs), understanding the surface features and their impact on the materials and devices is becoming increasingly urgent. In this family, hybrid FAPbI₃ QDs (FA: formamidium) exhibit higher ambient stability, near-infrared absorption and sufficient carrier lifetime. However, hybrid QDs suffer from difficulty in modulating surface ligand, which is essential for constructing conductive QD arrays for photovoltaics. Herein, assisted by an ionic liquid formamidine thiocyanate, we report a facile surface reconfiguration methodology to modulate surface and manipulate electronic coupling of FAPbI₃ QDs, which is exploited to enhance charge transport for fabricating high-quality QD arrays and photovoltaic devices. Finally, a record-high efficiency approaching 15 % is achieved for FAPbI₃ QD solar cells, and they retain over 80 % of the initial efficiency after aging in ambient environment (20-30 % humidity, 25 °C) for over 600 h.

Suppressing Phase Segregation in Wide Bandgap Perovskites for Monolithic Perovskite/Organic Tandem Solar Cells with Reduced Voltage Loss

Wide bandgap (WBG) perovskites through tuning iodine/bromine ratios are capable of merging with narrow bandgap organic bulk heterojunctions to construct tandem solar cells to overcome the Shockley-Queisser limitation. However, WBG perovskites readily suffer from light-induced halide ion migration, leading to detrimental phase segregation and hence severe open-circuit voltage (V_OC ) loss. Here, to solve this issue, lead thiocyanate (Pb(SCN)₂ ) and 2-thiopheneethylammonium chloride (TEACl) are synergistically employed to passivate and stabilize WBG perovskites with 1.79 eV bandgap. It is demonstrated that the synergetic employment of Pb(SCN)₂ and TEACl suppresses light-induced phase segregation, passivates WBG perovskite defects, and reduces non-radiative recombination, hence alleviating V_OC loss. As a result, optimized WBG perovskite solar cells (PSCs) are obtained with an impressive V_OC of 1.26 V and power conversion efficiency (PCE) over 17.0%. Furthermore, the interconnection layer is optimized to minimize the V_OC loss and construct two-terminal perovskite/organic tandem solar cells with a narrow bandgap organic blend bulk heterojunction of PM6:Y6 and achieve a champion PCE of 22.29% with a high V_OC of 2.072 V. In addition, these tandem solar cells maintain 81% of their initial efficiency after 1000 h continuous tracking at the maximum power point (MPP) under 100 mW cm^-2 white light illumination.

An alkali-resistant metal-organic framework as halogen bond donor for efficient and selective removing of ReO4-/TcO4. ENVIRONMENTAL SCIENCE AND POLLUTION RESEARCH INTERNATIONAL 2022;29:86815-86824. [PMID: 35794336 DOI: 10.1007/s11356-022-21870-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

⁹⁹Tc is one of the most problematic nuclear fuel products due to its long half-life and high environmental mobility. Direct removal of TcO₄^- from the highly alkaline solution of nuclear fuel is a serious and challenging environmental issue. In this work, the first efficient synthetic approach introducing halogens into a two-dimensional metal-organic framework, named Mn-MOF, is established using MnCl₂·4H₂O coordinating with neutral nitrogen-donor ligand, showing ultrahigh stability in alkaline aqueous even under 1 M NaOH. The luxuriant Mn-Cl bonds and ordered hydrophobic pore channels enable the Mn-MOF to have an efficient adsorption capacity for ReO₄^- with a large capacity (403 mg g^-1), which is higher than most MOF adsorbents. More importantly, the Mn-MOF shows an excellent selectivity toward ReO₄^- in high-density competitive anions, such as NO₃^- and SO₄^2-. Moreover, the outstanding performance of Mn-MOF in removing ReO₄^- endowed it successfully separated ReO₄^- from the simulated Savannah River Site (SRS) high-level waste (HLW) stream with high removal of 66.84% at the phase ratio of 10. The adsorption mechanism is further demonstrated by FT-IR, XPS analysis, and DFT calculation, showing that the ReO₄^- can selectively interact with Mn-Cl bonds and imidazole groups, forming unique halogen bonds Cl-O-Re, and a series of hydrogen bonds, respectively. This work suggests a new approach to the removal of TcO₄^- from nuclear fuel.

Improved p-i-n MAPbI3 perovskite solar cells via the interface defect density suppression by PEABr passivation

Organic-inorganic hybrid perovskite solar cells (PSCs) are promising candidates for next-generation photovoltaics due to their excellent optoelectronic properties and process compatibility. In this report, numerical simulations show the effect of perovskite surface defect density on the inverted MAPbI₃ perovskite device. The Phenethylammonium bromide (PEABr) is introduced to passivate the MAPbI₃ layer surface of the perovskite solar cell devices, PEA⁺ diffuses into the grain boundaries of the 3D perovskite to form 2D/3D hybrid structure during the thermal annealing process, thus improve the surface morphology and decrease the interface defects between MAPbI₃ layer and PCBM layer. The power conversion efficiency (PCE) of the PSCs increased from 17.95% to 19.24% after PEABr treatment. In addition, the 2D/3D hybrid structure can also hinder the intrusion of water and oxygen, the stability of perovskite devices has been greatly improved.

Improved Perovskite Structural Stability by Halogen Bond from Excessive Lead Iodide via Numerical Simulation

The short lifetime of perovskite solar cell devices limits the application of the technique, which is yet to be resolved, despite many attempts. An important step is made here by the numerical modelling method, which reveals the decomposition kinetics under the protection of halogen bonds from excess PbI2. Irregular diffusion behaviour of water molecules is observed when excessive PbI2 is introduced, possibly due to the passivation and hindrance from the halogen bond, resulting in a lifetime enhancement of at least five times. The detailed kinetics are also obtained by analyzing the decomposition rate curve, offering a possible path towards high-stability PCE perovskite solar devices, by increasing the PbI2 concentration to above the threshold, which opens an unprecedented route in perovskite solar cell research, and is, hopefully, of intrinsic interest to the broad materials research community as well.

Suppressing Residual Lead Iodide and Defects in Sequential-Deposited Perovskite Solar Cell via Bidentate Potassium Dichloroacetate Ligand

In sequential-deposited polycrystalline perovskite solar cells, the unreacted lead iodide due to incomplete conversion of lead iodide to perovskite phase, can contribute to ionic defects, such as residual lead ions (Pb²⁺ ). At present, passivation of interfacial and grain boundary defects has become an effective strategy to suppress charge recombination. Here, we introduced potassium acetate (KAc) and potassium dichloroacetate (KAcCl₂ ) as additives in the sequential deposition of polycrystalline perovskite thin films and found that acetate ions (Ac^- ) can effectively reduce the residual lead iodide. Compared with acetate (Ac), dichloroacetate (AcCl₂ ) can form Pb-Cl and Pb-O bonding as "dual anchoring" bonds with residual Pb²⁺ , resulting in strong binding force and effective passivation of residual Pb²⁺ defects. Furthermore, K⁺ can enlarge grain size and restrain ion migration at the grain boundaries. Consequently, perovskite solar cells with KAcCl₂ additive show power conversion efficiencies (PCE) from 19.67 % to 22.12 %, with the open-circuit voltage increasing from 1.06 V to 1.14 V. The unencapsulated device can maintain 82 % of the initial PCE under a humidity of 30±5 % for 1200 h. This work provides a new approach for the regulation of ionic defects and grain boundaries at the same time to develop high-performance planar perovskite solar cells.

Multifunctional Heterocyclic-Based Spacer Cation for Efficient and Stable 2D/3D Perovskite Solar Cells

Two-dimensional/three-dimensional (2D/3D) Ruddlesden-Popper perovskite materials have shown the enormous potential to achieve both efficient and stable photovoltaic devices for commercial applications. Unfortunately, the single function of spacer cations limits their further improvements in efficiency to reach values as high as those of 3D perovskites. Herein, we developed a new-type multifunctional heterocyclic-based spacer cation of 2-(methylthio)-4,5-dihydro-1H-imidazole (MTIm⁺) to achieve a synchronous improvement of efficiency and stability for 2D/3D perovskite solar cells (PSCs). Owing to the presence of special chemical groups (imidazole and methylthio), strong interactions have been found between MTIm⁺ and the 3D perovskite component, leading to an excellent passivation effect. More important, at the initial stage of crystallization, uniform nucleation distribution would be generated around the spacer cation, which is helpful for improved crystallinity and reduced growth defects. The smaller layer space compared to that of cations based on aromatic hydrocarbons caused effective carrier transfer between inorganic layers in 2D/3D perovskites. As a result, the 2D/3D (n = 30) PSCs based on MTIm exhibit a champion PCE up to 21.25% with a high V_oc of 1.14 V. Besides, the 2D/3D perovskite devices have realized dramatically enhanced humidity and thermal stability, maintaining 94% of the starting PCE enduring aging at about 50% RH for 2880 h and at 85 °C for 360 h, respectively. We believe that it would provide a significant strategy to further promote the photovoltaic performances and the long-term stability of 2D/3D perovskite devices toward future practical applications.

Halogen Bonding in Perovskite Solar Cells: A New Tool for Improving Solar Energy Conversion

Hybrid organic–inorganic halide perovskites (HOIHPs) have recently emerged as a flourishing area of research. Their easy and low‐cost production and their unique optoelectronic properties make them promising materials for many applications. In particular, HOIHPs hold great potential for next‐generation solar cells. However, their practical implementation is still hindered by their poor stability in air and moisture, which is responsible for their short lifetime. Optimizing the chemical composition of materials and exploiting non‐covalent interactions for interfacial and defects engineering, as well as defect passivation, are efficient routes towards enhancing the overall efficiency and stability of perovskite solar cells (PSCs). Due to the rich halogen chemistry of HOIHPs, exploiting halogen bonding, in particular, may pave the way towards the development of highly stable PSCs. Improved crystallization and stability, reduction of the surface trap states, and the possibility of forming ordered structures have already been preliminarily demonstrated.