Chen Weijie

A new PBTI2(30HD)‐FT terpolymer acceptor enables all‐polymer solar cells (all‐PSCs) with an ultrabroad donor:acceptor (D:A) ratio tolerance from 1:30 to 10:1 and better stability than other types of organic solar cells. PBTI2(30HD)‐FT can lead to well‐maintained interpenetrating network even at very low loading in blend films, yielding decent photovoltaic performance.

Achieving a broad donor:acceptor (D:A) composition tolerance in efficient organic solar cells (OSCs) is important for printing large‐area solar cell modules. Herein, all‐polymer solar cells (all‐PSCs) based on new terpolymer acceptors and a well‐known polymer donor PTB7‐Th are fabricated to explore the effect of D:A ratio on morphology and photovoltaic performances. The all‐PSCs show a promising power conversion efficiency (PCE) of 7.23% with an optimum D:A ratio of 1:2 and retain over 40% of its optimal PCE with ultrabroad D:A composition tolerance from 1:30 to 10:1. In addition, the all‐PSCs can maintain 90% of its original PCE after 400 h of storage despite such broad range of D:A ratio, which is much better than those of other types of OSCs and even better than the benchmark all‐polymer system with N2200 as the acceptor under the same condition. The results show the superiority of the all‐PSCs in terms of D:A ratio tolerance and performance stability, which should be conducive to practical applications of all‐PSCs.

A novel perovskite‐compatible carbon electrode based on low polar alkane solvent decreases the defect at CsPbI₂Br/carbon interface and hinders moisture in the atmosphere. The champion device obtains a power conversion efficiency (PCE) of 13.16% and provides outstanding stability with a PCE maintaining 93% of the initial value after 1000 h under a humidity of 30–40% without additional encapsulation.

Carbon electrodes are a promising alternative to metal electrodes in the access of high‐stable and low‐cost perovskite solar cells (PSCs). However, polar components (including cyclohexanone, terpineol, etc.) in commercial carbon pastes for carbon electrodes usually corrode perovskite materials, thereby deteriorating the photovoltaic performance of the resulting solar cells. Therefore, the development of perovskite‐compatible carbon pastes and carbon electrodes is of great significance in obtaining high‐performance carbon‐based PSCs. Herein, carbon pastes based on low polar alkane solvents are developed for perovskite‐compatible carbon electrode (PCCE) in the construction of carbon‐based CsPbI₂Br PSCs. The optimized cells based on PCCE offer a champion efficiency of 13.16% (J _SC = 14.33 mA cm⁻², V _OC = 1.22 V, and fill factor (FF) = 0.75), which is remarkably higher than that of commercial carbon paste‐derived counterparts (11.51%). Even without encapsulation, CsPbI₂Br PSCs based on PCCE maintain over 93% of their initial efficiency in an air atmosphere with a humidity of 30–40% for over 1000 h.

A bipolar organic material 1,4‐bis(perfluorophenyl)‐2,5‐di(pyridin‐4‐yl)‐1,4‐dihydropyrrolo [3,2‐b] pyrrole (PFPPY) is utilized to passivate perovskite surface and boundary defects via solvent engineering approach, generating an impressive power conversion efficiency (PCE) of 19.62% and greatly enhanced stability.

At the device operating conditions, defects such as interstitials, vacancies, and impurities at the grain boundary and surface of photoactive layer have great impact on the power conversion efficiency (PCE) and device stability. To better passivate the surface and boundary defects, and further enhance the PCE and device stability, herein, a bipolar organic material termed 1,4‐bis(perfluorophenyl)‐2,5‐di(pyridin‐4‐yl)‐1,4‐dihydropyrrolo [3,2‐b] pyrrole (PFPPY) is introduced as modifier in antisolvent. The effects of PFPPY on perovskite film quality, photovoltaic performance, and charge transfer properties are systematically investigated. Under the optimized conditions, the PFPPY‐treated device shows an impressive PCE of 19.62%, which is 12% higher than the reference device (17.59%), and greatly enhanced stability, maintaining 95% of its initial efficiency under room temperature (RT) and relative humidity (RH) 30% condition for 650 h without encapsulation.

A modified monomolecular layer strategy (m‐MLS) enables high‐quality perovskite films formation on the hydrophobic polymer hole transporting layer (HTL), and minimizes the ohmic loss induced by the HTL. The perovskite solar cells (PSCs) based on m‐MLS‐modified HTL (F‐PSCs) give a superior reproducibility and a champion efficiency of 19.7% with a fill factor of over 80%.

The hole transport materials that interact with the indium tin oxide (ITO) surface can be processed into monomolecular layers (MLs), which often exhibit different surface and electronic properties than their thin‐film counterparts. Herein, it is found that poly[bis(4‐phenyl)(2,4,6‐trimethylphenyl)amine] (PTAA) films (R‐PTAA) can be easily processed into ML (M‐PTAA) due to the van der Waals interaction between ITO and PTAA. However, compared with R‐PTAA, the work function (WF) and conductivity of M‐PTAA are simultaneously reduced by the charge transfer at the ITO/PTAA interface. To address this issue, a modified monomolecular layer strategy (m‐MLS) is developed, where a small amount of 2,3,5,6‐tetrafluoro‐7,7,8,8‐tetracyanoquinodimethane (F4TCNQ) is introduced to enhance the interaction force between ITO and PTAA. PTAA treated by m‐MLS (F‐PTAA) has a hydrophilic physical surface, closely matching electronic energy level with the perovskite layer and smaller bulk resistance. As a result, the efficiency and reproducibility of perovskite solar cells (PSCs) are substantially improved. PSCs based on F‐PTAA demonstrated the highest power conversion efficiency (PCE) of 19.7% with a fill factor of over 80%. This study inspires the development of novel interface modification materials, and provides a simple and convenient direction for the fabrication of high‐performance and reproducible inverted PSCs with high fill factors.

The commercially available pyridinedicarboxylic acid (PDA) molecule with one pyridine and two carboxylic acid groups is used as a passivating agent to cure the defects at both the surfaces and grain boundaries of MAPbI₃ perovskites. A champion power conversion efficiency (PCE) approaching 19% with optimized long‐term stability and thermal stability is achieved in PDA‐passivated perovskite solar cells (PSCs).

Electronic defects and grain boundaries of perovskite films will significantly deteriorate both the efficiency and the stability of perovskite solar cells (PSCs), and various methods aimed to reduce these defects are proposed. Herein, an organic solid molecule of pyridinedicarboxylic acid (PDA) with one pyridine and two carboxylic acid groups is used as a passivating agent to cure the defects by regulating the perovskite microstructures in a multiple manner. The defects located at both the surfaces and grain boundaries of polycrystalline MAPbI₃ perovskites are simultaneously passivated through the multiple coordination effects between the used functional groups and uncoordinated Pb²⁺, regardless of the substitution sites of the carboxylic acid and pyridine. Impressively, the PDA‐passivated inverted PSCs achieve remarkably enhanced power conversion efficiencies (PCEs) from 16.43% to nearly 19% and maintain over 90% of its original PCE after 1300 h under an inert environment. These findings indicate that the commercially available PDA molecule emerges as an efficient passivating agent of perovskite defects capable of stimulating the combined effects of the multiple functional groups, which is highly promising for the practical applications of PSCs with both high efficiency and good stability.

Herein, a bulk heterojunction structure hybridizing SnS QDs and CsPbBr₃ is designed as an absorber layer for solar cells. The prominent SnS QD–CsPbBr₃ structure improves the crystallinity of perovskite, enhances the charge transfer efficiency, and reduces the trap state density of the CsPbBr₃ film, thereby further boosting the photoelectric performance of perovskite solar cells.

Inorganic cesium lead halide perovskite solar cells (PSCs) have attracted great attention due to their remarkable thermal and moisture stability. However, the low photoelectric conversion efficiency (PCE) of inorganic PSCs due to the high trap state density, high carrier recombination rate, and poor carrier transport kinetics impedes their industrial applications. Herein, a remarkable bulk heterojunction structure coupling SnS quantum dots (QDs) with CsPbBr₃ is prepared for the first time via a facile spin‐coating process using a SnS‐QD‐dispersed toluene solution as an antisolvent. The introduction of SnS QDs provides extra crystallization sites and promotes the crystallization of perovskites along (100) and (200) faces. Meanwhile, the bulk heterojunction structure with matched energy structure can effectively reduce the trap state density of the perovskite film and improves the dynamic performance of carriers, suppressing the charge recombination rate and effectively boosting the PCE of solar cells. As a result, the optimal bulk heterojunction solar cell achieves a PCE of 8.01%, about 52% higher than that of the pristine solar cell. This work provides a low‐cost and facile strategy for preparing high‐performance bulk heterojunction PSCs and an effective method to boost the PCE by nontoxic QDs.

Pinhole‐free perovskite films with large grains are fabricated in ambient air by a spinning–bathing–spinning method. The effects of moisture on the formation of I‐dominant grain and Cl‐enriched boundaries and surfaces in the perovskite films are revealed, which enable the air‐processed perovskite solar cells with a high efficiency of more than 20%.

Metallic halide perovskite films are usually fabricated in inert environment due to their high sensitivity to moisture and oxygen. However, the fabrication process in the strictly controlled environment is not economical for mass production. Therefore, the fabrication of high‐quality perovskite films in ambient air is more practical for optoelectronic devices. Herein, a spinning–bathing–spinning (SBS) method is demonstrated to deposit pinhole‐free perovskite films with large grains in ambient air for solar cells. The effect of moisture on the rapid crystallization and grain coarsening can be suppressed using this SBS method. Furthermore, the moisture is found to encourage the halogen separation in the perovskite films when using PbI₂–PbCl₂ as the lead halide precursor, resulting in the formation of I‐dominant perovskite grains and Cl‐enriched boundaries and surface in the films. The Cl‐enriched grain boundaries and film surface, which mainly originate from the confined methylammonium chloride (MACl), can passivate defects and prevent further damage from moisture and oxygen. This spontaneous inner‐to‐outside passivation enables the air‐processed perovskite solar cells with the high power conversion efficiencies of more than 20% and improved stability.

A novel ternary active layer for polymer solar cells, PTQ10:4TIC‐4F:PC₆₁BM, is processed in semi‐industrial conditions. The devices show a promising performance–cost–photostability compromise. It is shown that PC₆₁BM is critical to balance the holes and electrons mobilities to increase significantly the fill factor due to an optimized bulk heterojunction morphology.

Bulk heterojunction polymer solar cells based on a novel combination of materials are fabricated using industry‐compliant conditions for large area manufacturing. The relatively low‐cost polymer PTQ10 is paired with the nonfullerene acceptor 4TIC‐4F. Devices are processed using a nonhalogenated solvent to comply with industrial usage in absence of any thermal treatment to minimize the energy footprint of the fabrication. No solvent additive is used. Adding the well‐known and low‐cost fullerene derivative PC₆₁BM acceptor to this binary blend to form a ternary blend, the power conversion efficiency (PCE) is improved from 8.4% to 9.9% due to increased fill factor (FF) and open‐circuit voltage (V _OC) while simultaneously improving the stability. The introduction of PC₆₁BM is able to balance the hole–electron mobility in the ternary blends, which is favourable for high FF. This charge transport behavior is correlated with the bulk heterojunction (BHJ) morphology deduced from grazing‐incidence wide‐angle X‐ray scattering (GIWAXS), atomic force microscopy (AFM), and surface energy analysis. In addition, the industrial figure of merit (i‐FOM) of this ternary blend is found to increase drastically upon addition of PC₆₁BM due to an increased performance–stability–cost balance.

Ternary organic solar cells (TOSCs) are developed through synergizing small‐molecule donor BPR‐SCl into PM6:Y6 host binary blend, which effectively addresses the trade‐off between photovoltage and photocurrent of regular bulk heterojunction OSCs. An optimal power conversion efficiency of 16.74% is obtained for TOSCs, accounting for 10% and 70% improvements over those of pristine PM6:Y6 and BPR‐SCl:Y6 binary devices, respectively.

Despite the impressive progress that has been achieved for organic solar cells (OSCs) in recent years, challenges remain for OSCs due to the presence of the trade‐off between photovoltage and photocurrent that sets limitation on the performance enhancement of regular bulk heterojunction (BHJ) blends. Herein, a new small‐molecule (SM) donor, BPR‐SCl, with the deep‐lying highest occupied molecular orbital and strong crystallinity has been developed, which, as the third component, is synergized with PM6:Y6 host blend. The introduction of BPR‐SCl enhances molecular packing, exciton dissociation, as well as charge mobilities of ternary blends, yielding simultaneous enhancement of open‐circuit voltage, short‐circuit current density, and fill factor of ternary OSCs (TOSCs). As a result, an optimal power conversion efficiency (PCE) of 16.74% is obtained for TOSCs with 25 wt% BPR‐SCl, accounting for 10% and 70% improvements over those of pristine PM6:Y6 and BPR‐SCl:Y6 binary devices, respectively. Overall, herein, it is demonstrated that the design of SM donor as the third component is effective in achieving high‐performance TOSCs.

The combination of two well‐defined conjugated small‐molecule (SM) donors FG3 and FG4 and Y6 as well‐known nonfullerene SM acceptors provides the fabrication of efficient ternary OSCs. This contribution shows an excellent power conversion efficiency (PCE) of 14.31% with a high fill factor (FF) and J _sc, in contrast with the binary counter parts.

An efficient organic solar cell (OSC) based on a ternary active layer consisting of two conjugated small‐molecule (SM) donors (FG3 and FG4) and a well‐known nonfullerene SM acceptor (Y6) is fabricated using a nonhalogenated solvent. An overall power conversion efficiency (PCE) of 14.31% is achieved, higher than that for the binary counterparts, i.e., 10.75% and 11.07% for FG3:Y6 and FG4:Y6, respectively. The short‐circuit current density (J _SC) of the ternary active layer organ is related to the broader absorption spectra when compared with the binary active layers. The open‐circuit voltage (V _OC) of the ternary active layer‐based OSCs falls between those of the OSCs based on FG3:Y6 and FG4:Y6, a situation that is consistent with the lowest unoccupied molecular orbital (LUMO) level of both SM donors (FG3 and FG4), and forms the alloy between the two donors. The overlap of the absorption spectra of FG4 with the photoluminescence of FG3 confirms the energy transfer from FG3 to FG4 and this leads to improvement in J _SC. The balanced charge transport, reduced charge recombination, and the fast charge extraction in the ternary active layer leads to the higher fill factor (FF) value. A combination of all of these effects affords a high PCE value.

All‐inorganic hole‐transport layer (HTL)‐free CsPbBr₃‐based perovskite solar cells doped with Eu²⁺ are studied. The decrement in trap‐state density and suppression of nonradiative recombination after doping is achieved with a higher power conversion efficiency (PCE) of 7.28% and V _OC of 1.45 V.

All‐inorganic perovskite of CsPbBr₃ thin‐films solar cells has attracted increasing interest in recent years due to its potential long‐term stability over the generally used hybrid perovskites. Herein, all‐inorganic CsPbBr₃ perovskites are doped with Eu²⁺ to enhance the efficiency of perovskite solar cells (PVSCs). The perovskite films exhibit a better crystallinity with smooth morphology after the introduction of rare‐earth elements. Hence, the hole‐transport layer‐free device with presence of Eu²⁺ and low‐cost carbon electrode achieves both enhanced efficiency and stability. In particular, the power conversion efficiency (PCE) enhances from 5.66% to 7.28% with high V _OC of 1.45 V by optimizing the doping concentration of Eu²⁺. In addition, the storage stability measurements reveal excellent performances of PCE without encapsulation in air with relative humidity of 70–80%. These results can pave changes in future inorganic PVSCs.

High‐performance thick‐film OSCs are essential for well matching the roll‐to‐roll (R2R) technology to realize its large‐area potential application. The critical factors and smart strategies on performance improvement of thick‐film OSCs are well summarized to inspire more fantastic ideas on achieving efficient thick‐film OSCs. Meanwhile, the challenges on achieving efficient thick‐film OSCs are outlined.

To date, the power conversion efficiency (PCE) of lab‐scale organic solar cells (OSCs) has exceeded 17%, which heralds the bright future for commercial applications of OSCs. High‐performance OSCs with thick active layers are essential for large‐scale production. First, the relatively thick active layers should be more compatible with the roll‐to‐roll (R2R) large‐area processing, which is conducive to forming uniform and defect‐free active layers in the process of high‐speed, mass production. Second, the thick active layers can absorb more incident light in their spectral range, which helps thick‐film OSCs to obtain relatively high short‐circuit current density (J _SC). So far, relatively little attention has been paid to thick‐film OSCs, and the PCE of thick‐film OSCs lags far behind its thin‐film analogues. Herein, the recent development of thick‐film OSCs is highlighted and the critical limit factors on the PCE of thick‐film OSCs are pointed out. Some strategies are highlighted to improve the efficiency of thick‐film OSCs. This review study will be helpful to the researchers engaging in the development of efficient thick‐film OSCs.

The latest research advancements of all‐inorganic perovskite solar cells (PSCs) are summarized systematically and discussed deeply from the perspective of phase stability, effective inorganic charge transport materials, device structures, and interfacial engineering.

The large‐scale commercial application of organic–inorganic hybrid perovskite solar cells (PSCs) based on organic hole transport material (HTM) is still hindered by poor long‐term operational stability, although a certified record power conversion efficiency (PCE) as high as 25.2% can be achieved. In the recent several years, all‐inorganic PSCs have received tremendous attention due to their superb thermal and moisture stability and considerable progresses have been witnessed. Herein, the recent advancements of all‐inorganic PSCs are reviewed comprehensively. First, the recent progresses of the strategies for stabilizing the black phase of inorganic perovskites through either increasing tolerance factor or enhancing the energy barrier of phase transition from black to yellow phase are summarized and discussed. Second, the deposition and growth techniques of inorganic perovskite films are discussed. Third, the effective inorganic HTMs in normal all‐inorganic PSCs are described. Fourth, HTM‐free normal all‐inorganic PSCs are discussed. Afterward, the effective inorganic electron transport materials in inverted all‐inorganic PSCs are discussed. Subsequently, the advancements of interface engineering for increasing the PCE and stability of all‐inorganic PSCs are reviewed. Finally, a brief summary and outlook are presented to push up the PCE of all‐inorganic PSCs to over 20% in the near future.

The spontaneous black‐to‐yellow phase transition of cesium lead halides (CsPbX₃) after long‐time storage hinders their development in solar cells despite ever‐growing efficiencies. This review focuses on the current advances from recognizing phase transition behaviors to addressing phase instability issue of CsPbX₃ and provides potential avenues for further enhancing stability of CsPbX₃ based on current understandings.

Cesium lead halide (CsPbX₃) perovskite solar cells have gained considerable attention for their rapid evolution to over 19% power conversion efficiency. Despite high chemical stability, the spontaneous phase transition from desired black phase to nonperovskite yellow phase after long‐time storage or under attack of extrinsic factors significantly hinders their development and application. This review summarizes the current advances in recognizing phase transition behaviors of cesium lead halides, especially cesium lead tri‐iodide, and addressing phase instability issues. Advancing strategies that are used for phase stabilization, including compositional engineering, grain size reduction, modification of surface termination, and strain engineering, are highlighted as well as their present limitations. Also, existing scientific debates on phase transition and stability, origin of these arguments, and possible solutions are presented and discussed. Finally, some potential avenues for further enhancing stability of cesium lead halides are proposed based on current understandings.

Herein, all‐vacuum‐processed perovskite solar cells are reported in an inverted device architecture using copper (II) phthalocyanine (CuPC) as the hole transporting layer (HTL), and power conversion efficiencies (PCEs) of 20.3% and 18.68% on rigid and flexible substrates are achieved, respectively.

The fabrication of efficient perovskite solar cells (PSCs) using all‐vacuum processing is still challenging due to the limitations in the vacuum deposition of the hole transporting layer (HTL). Herein, inverted PSCs using copper (II) phthalocyanine (CuPC) as an ideal alternative HTL for vacuum processing are fabricated. After proper optimization, a PSC with a power conversion efficiency (PCE) of 20.3% is achieved, which is much better than the PCEs (16.8%) of devices with solution‐based CuPC. As it takes a long time to dissolve CuPC in the solution‐based device, the evaporation approach has better advantage in terms of fast processing. In addition, the device with the evaporated CuPC HTL indicates an excellent operational stability, showing only 9% PCE loss under continuous illumination after 100 h, better than its counterpart device. Interestingly, the device shows negligible hysteresis. As all fabrication processes are conducted at low temperatures, flexible PSCs are also fabricated on ITO/PET substrates and a PCE of 18.68% is obtained. After 200 bending cycles, the flexible device retains 87.5% of its initial PCE value, indicating its great flexibility. Herein, the role of a suitable HTL for the fabrication of all‐vacuum‐processing PSCs with great efficiency and stability is highlighted.

Bearing high hole mobility and appropriate energy levels, an organic small molecule 2,7‐bis(4‐octylphenyl)naphtho[2,1‐b:6,5‐b 0] difuran (C₈‐DPNDF) is introduced as a dopant‐free hole transporting material in inverted perovskite solar cells. The device with C₈‐DPNDF as HTM shows a decent power conversion efficiency of 17.5% and can keep 92% of its initial value after 30 days in ambient air.

Hole transport material (HTM) is a significant constituent in perovskite solar cells (PSCs). However, HTM generally is not utilized in its pristine form but with dopants (such as lithium salt, tert‐butyl pyridine, F₄‐TCNQ), which accelerates device degradation and leads to poor stability. Therefore, dopant‐free HTM is highly desirable to fabricate stable devices. Herein, a fused furan organic small molecule (C₈‐DPNDF) is introduced as a dopant‐free HTM in inverted PSCs. As a potential HTM candidate, C₈‐DPNDF shows excellent properties, such as high hole mobility, matched energy level with perovskite, and resistance to perovskite precursor solution. As a result, the device based on C₈‐DPNDF as HTM shows a power conversion efficiency (PCE) of 17.5%, compared with 17.1% of the control device based on classic poly(bis(4‐phenyl)(2,4,6‐trimethylphenyl)amine) (PTAA) as the HTM. In addition, the unencapsulated device based on C₈‐DPNDF as HTM keeps 92% of its initial PCE after 30 days of storage in ambient air with a relative humidity of ≈40%. This finding is expected to pave the way toward stable and highly efficient inverted PSCs based on dopant‐free HTMs.

Current density–voltage (J–V) hysteresis in perovskite solar cells (PSCs) is a major challenge in this field. Herein, the possible origins and factors of J–V hysteresis behavior in PSCs are focused and the strategies to suppress the hysteresis are summarized. Finally, insights on the future development of the J–V hysteresis in PSCs are also provided.

The power conversion efficiency (PCE) of perovskite solar cells (PSCs) has exceeded 25%, showing great potential in the photovoltaic field. However, PSCs often show anomalous current density–voltage (J–V) hysteresis behavior in the forward and reverse scanning directions, which makes it impossible to accurately evaluate the performance of PSCs. Therefore, it is necessary to clearly understand the mechanism of hysteresis and suppress the hysteresis. Herein, the J–V hysteresis behavior in PSCs and strategies to suppress hysteresis is focused: first, the various factors that affect J–V hysteresis in PSCs are summarized. And the mechanism behind the various possible origins of hysteresis and the challenges encountered are explored. Then, the strategies to suppress or eliminate the hysteresis are summarized, including optimizing the perovskite light‐absorbing layer, improving the performance of the carrier transport layer and interface engineering. Finally, insights on the future development of the hysteresis are also provided.

Perovskite solar cells with the 2D passivation layer display excellent photovoltaic performance and superior stability via introducing hydrophobic alkyl molecules with polyfunctional groups.

The charges stuck in trap sites hinder charge transport and lead to V _oc below the radiative limit, which seriously restrict the performance and stability of organic–inorganic halide perovskite solar cells (PSCs). Chemical passivation is an effective method to reduce defects and suppress nonradiative recombination. Herein, a new passivation molecule l‐cysteine methyl ester hydrochloride (CME) with thiol and ester groups is designed to modify the interface between the perovskite layer and hole transport layer (HTL). It reveals that thiol possesses outstanding moisture resistance and ester suppresses nonradiative recombination by coordinating with undercoordinated Pb²⁺. Furthermore, the 2D modified layer at the grain boundaries and surface passivates surface defects and promotes hole extraction. As a result, the CME device achieves the highest PCE of 20.33% with an enhanced open‐circuit voltage (V _oc) of 1.11 V. Due to the barrier of highly hydrophobic 2D perovskites, the modified devices show excellent stability while exposed to humidity and high‐temperature environment. A facile and effective strategy to design organic molecular structures with polyfunctional groups to passivate trap‐assisted nonradiative recombination at the surface and grain boundaries is provided.

State‐of‐the‐art perovskite and organic solar cells use inorganic hole transport materials (HTMs) due to their superior electronic properties. These HTMs are, however, expensive and prone to degradation. A range of robust inorganic HTMs are emerging, that provide a trade‐off between efficiency, stability, and cost, and are critically reviewed herein.

Interfaces in perovskite and organic solar cells play a central role in advancing efficiency and prolong device durability. They improve charge transport/transfer from the absorber layer to the collecting electrodes, while also blocking the opposite charge carriers, minimize voltage losses by suppressing charge recombination. and may act as buffer/protective layers and nanomorphology regulators for the absorber layer. One such interface is formed by the hole transport layer (HTL) and the organic/perovskite absorber. These HTLs typically consist of organic semiconductors, which, although are solution processable at low temperatures and allow perfect energy‐level alignment with the absorber layer and therefore efficient charge collection, are prone to degradation in ambient conditions and under continuous light exposure. In a quest for robust alternatives, inorganic materials such as metal oxides, graphene oxide, bronzes, copper thiocyanate, and transition metal dichalcogenides are actively investigated. However, their hole extraction capability is inferior compared with organic semiconductors as they possess specific energetics leading to significant charge extraction barriers and moderate charge collection. To achieve further advancements in their hole transporting capabilities, strongly interconnecting knowledge of their synthesis, electronic properties, and device performance metrics is required.

This article introduces sodium benzenesulfonate (SBS) to modify the poly (3,4‐ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) layer to improve hole extraction capacity and work function for better energy‐level alignment. As a result, the power conversion efficiency of inverted perovskite solar cells (PSCs) achieves 19.41% and maintains ≈95% after 20 days, with a V _oc up to 1.08 V.

The p‐type conducting polymer poly (3,4‐ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) is widely utilized as the hole transport layer (HTL) for solution‐processed planar perovskite solar cells (PSCs) with a p‐i‐n structure. However, the inverted PSCs based on PEDOT:PSS HTL suffer from deficient open‐circuit voltage (V _OC) and poor stability issues, because of the high electron affinity and acid nature of PEDOT:PSS. Herein, sodium benzenesulfonate (C₆H₅SO₃Na) (SBS) is applied to modify the PEDOT:PSS (SBS–PEDOT:PSS) layer to form a smoother surface and better energy‐level alignment with the perovskite layer. In addition, the SBS–PEDOT:PSS layer with improved hole extraction capacity and suppressed charge recombination, significantly increases the grain size and crystallinity of the MA_0.8FA_0.2PbI_3‐x Cl _x perovskite film. Consequently, the power conversion efficiency (PCE) and V _OC of the inverted PSCs are improved from 18.07% and 1.04 V to 19.41% and 1.08 V, respectively, after SBS modification. Moreover, the efficiency of the unencapsulated PSCs based on SBS–PEDOT:PSS remains above 90% after storing in ambient condition for 20 days. This research provides an accessible route to surmount the intrinsic imperfection of PEDOT:PSS and ameliorate the performance of PSCs.

A significant increase in photovoltaic performance is observed by connecting two dye molecules to be double branch (DB) dyes with acetylenic bond(s) as the isolation groups. Nearly 3‐fold power conversion efficiency is achieved for the DB dye FSDD‐2 with a diyne as the isolation group compared with the single branch dye FSSD‐EH.

Double branch (DB) dyes could reduce intermolecular interactions and realize good photovoltaic performances. Herein, symmetric DB dyes (FSDD‐1 and FSDD‐2) featuring with one and two acetylenic bonds as the isolation groups are reported. The corresponding single branch (SB) dye FSSD‐EH is synthesized for comparison. For the adsorption spectra, bathochromic shifts and higher ε are observed for DB dyes FSDD‐1 and FSDD‐2 compared with SB dye FSSD‐EH, which suggests better light‐harvesting capabilities for the DB dyes. Dye‐sensitized solar cells (DSSCs) sensitized by DB dyes FSDD‐1 and FSDD‐2 exhibit significant increases for the J _sc and V _oc compared with SB dye FSSD‐EH, so much better η are achieved by the DB dyes (5.34, 7.14, and 2.46% for FSDD‐1, FSDD‐2, and FSSD‐EH, respectively). FSDD‐2 with a diyne unit exhibits higher η compared with FSDD‐1 with an yne unit as the isolation groups. The research shows that a much better photovoltaic performance of DSSCs can be achieved after connecting two dye molecules to be a DB dye by adopting acetylenic bonds as the isolation group. A longer distance between the two branches realized by a diyne unit is beneficial and effective to achieve better photovoltaic performance.

Vacuum‐based perovskite solar cells are developed on random pyramidal microtextured glass. This improves light management and resembles the typical topography of silicon solar cells for monolithic tandem integration. Optimized precursor rate ratios enable high charge carrier lifetimes and proper film morphology on texture. This results in >15% efficiency and the first reported perovskite solar cell on microscopically textured glass by evaporation.

Solar cells based on metal halide perovskites have attracted tremendous attention due to the rapid increase in performance of single junctions and tandem solar cells. Recently, highest perovskite/silicon tandem efficiencies are realized with front‐side polished silicon wafers or adapted microstructure of textured silicon solar cells. One way to integrate perovskite top cells on typical micrometer‐sized pyramidal structures, is conformal vacuum‐based perovskite deposition. Herein, fully vacuum‐based perovskite solar cells are developed on top of random pyramidal microtextured glass substrates with a pyramid size up to 9 μm. This method allows improvement of the light management of the textured perovskite solar cell and resembles the typical pyramid topography of silicon solar cells as a step toward monolithic tandem integration. Moreover, to improve the quality of the perovskite on the textured substrates, three different methylammonium lead iodide (MAPbI₃) films are tested by adjusting the rate ratio of the precursors. Optimized ratios for textured substrates with higher PbI₂ rates enable a transient photoluminescence decay time above 0.75 μs approaching that of planar substrates at around 1.2 μs. Finally, a efficiency over 15% is achieved, which is, to the best of our knowledge, the first reported device on microscopically textured glass by co‐evaporated ion.

Defect passivation is an effective strategy to adjust the energy band structure, reduce the density of defect states, and suppress the nonradiative recombination of carriers. Herein, the recent progress in the passivation strategy for perovskite films is summarized and the development direction of passivation strategies to further improve the performance of perovskite solar cells (PSCs) is proposed.

Organic–inorganic halide perovskite photovoltaic devices have advanced rapidly in recent years, and the photoelectric conversion efficiency of perovskite solar cells (PSCs) has exceeded 25%. However, the defects from the crystallization process become nonradiation recombination centers and hinder the performance and the stability of PSCs. Defect passivation by tuning grain size and grain boundary (GB) is an effective strategy to reduce the defects on GBs and film surface. Herein, recent progress in the passivation strategy for perovskite films is summarized, including nonstoichiometric passivation, iodide vacancies filling, dimensional engineering, passivation with crosslink, physical passivation, and other passivation methods. These passivation strategies play an important role in improving the quality of perovskite films, adjusting the energy band structure, reducing the density of defect states, and suppressing the nonradiative recombination of carriers. Finally, this review puts forward the development direction of passivation strategies to further improve the performance of PSCs.

Layer‐by‐layer solution‐processed organic solar cells optimize the donor layer and acceptor layer separately to make the two components ideally distribute in the vertical direction, which facilitates charge transport and collection. This bilayer structure has less dependence on donor/acceptor ratio, solvent concentration, and so on. It is easy to prepare high‐performance devices with good stability and a high repetition rate.

Organic solar cells (OSCs) have attracted wide attention due to their economy, environmental protection, and potential for large‐scale commercial production. The layer‐by‐layer (LbL) solution processing method, where donor solution and acceptor solution are coated sequentially, is a simple and effective way to fabricate OSCs, achieving a high power conversion efficiency (PCE) of up to 17%. Compared with bulk‐heterojunction (BHJ) OSCs, LbL solution‐processed OSCs separately adjust different layers, making the components distribute ideally in the vertical direction that is beneficial for exciton dissociation, charge transport, and charge collection. Moreover, the LbL approach has better potential in the preparation of large‐area devices, which is a key link in the commercialization of OSCs. Herein, the basic principles and the latest research progress of LbL solution‐processed OSCs are summarized, and the existing challenges and prospects of the LbL solution processing method in industrial production are discussed.

Photo‐oxidation of the dangling hydroxyl group on ZnO surface under visible light illumination leads to the formation of hydroxyl radicals, which decompose the acceptor molecule IT‐4F and consequently decrease PM6:IT‐4F solar cell performance.

Power conversion efficiencies (PCEs) of polymer solar cells (PSCs) have exceeded 18% in the last few years. Stability has therefore become the next most important issue before commercialization. Herein, the degradation behaviors of the inverted PM6:IT‐4F (PBDB‐T‐2F:3,9‐bis(2‐methylene‐((3‐(1,1‐dicyanomethylene)‐6,7‐difluoro)‐indanone))‐5,5,11,11‐tetrakis(4‐hexylphenyl)‐dithieno[2,3‐d:2′,3′‐d′]‐s‐indaceno[1,2‐b:5,6‐b′]dithiophene) solar cells with different ZnO layers are systematically investigated. The PCE decay rates of the cells and the photobleaching process of the IT‐4F containing organic films on ZnO surface are directly correlated with the light‐absorption ability of the ZnO layer in the visible light range, indicating that photochemical decomposition of IT‐4F is initiated by the light absorption of ZnO layer. By analyzing the products of the aged ZnO/IT‐4F films with matrix‐assisted laser desorption ionization time‐of‐flight mass spectrometry (MALDI‐TOF‐MS), it is confirmed that photochemical reactions at the IT‐4F/ZnO interface include de‐electron‐withdrawing units and dealkylation on the side‐phenyl ring. Hydroxyl radicals generated by the photo‐oxidation of dangling hydroxide by ZnO are confirmed by electron spin resonance (ESR) spectroscopy measurements, which is attributed as the main reason causing the decomposition of IT‐4F. Surface treatment of ZnO with hydroxide and/or hydroxyl radical scavenger is found to be able to improve the stability of the PSCs, which further supports the proposed degradation mechanism.

An ultrafast and scalable laser process is developed to anneal TiO₂ films for perovskite solar cells. This laser process allows processing stacked layers of substrates simultaneously with a uniform annealing area up to 15.2 cm² and achieves a production rate of over 43 cm² min⁻¹, which potentially opens a new route for scalable annealing of thin films.

A conventional annealing method to fabricate metal oxide films used for perovskite solar cells (PSCs) is a time‐consuming batch process. Herein, a near‐IR fiber laser process with a unique design of power ramping program and beam configuration is developed to achieve ultrafast and scalable processing of TiO₂ films for PSCs. Highly crystalline anatase TiO₂ films can be synthesized in only 18.5 s by the laser process with a peak annealing temperature up to 800–850 °C, compared with that of the furnace‐annealing at 500 °C for 30 min and an overall processing time of 3 h. Then, a unique capability of using this laser process is presented to anneal stacked layers of substrates coated with the TiO₂ films simultaneously, with a uniform annealing area up to 15.2 cm², thereby potentially achieving an in‐line production rate of over 43 cm² min⁻¹ (1 cm² in ≈1.4 s). Planar PSCs fabricated under a high relative humidity of 60–70% based on the TiO₂ films annealed under optimal laser conditions show enhanced photovoltaic performance than the furnace‐annealed samples. This laser process potentially opens a new avenue for scalable annealing and rapid production of thin films.

This study provides a new molecular design strategy for inverted nonfullerene organic solar cell (NFOSC) devices with low synthetic complexity. To our knowledge, the P(F‐BiT)‐COOBOCl(out)‐based device reached the best performance among reported NFOSCs processed in an eco‐friendly solvent under ambient air conditions.

Realizing the commercial applications of nonfullerene organic solar cells (NFOSCs) require a balanced of power conversion efficiency (PCE), production cost, and stability. However, because most high‐performance NFOSC devices contain air‐sensitive donor polymers that have low solubility in eco‐friendly solvents, their fabrication requires halogenated solvents and an inert atmosphere. Herein, an air‐processed inverted NFOSC device is developed using a relatively cost‐effective chlorine‐ and carboxylate‐functionalized bithiophene‐based donor polymer, P(F‐BiT)‐COOBOCl(out). When blended with 3,9‐bis(2‐methylene‐((3‐(1,1‐dicyanomethylene)‐6,7‐difluoro)‐indanone))‐5,5,11,11‐tetrakis(4‐hexylphenyl)‐dithieno[2,3‐d:2′,3′‐d′]‐s‐indaceno[1,2‐b:5,6‐b′]dithiophene (IT‐4F), the resultant device yields a high PCE of 11.91%, with good shelf‐life stability and photostability under ambient conditions without encapsulation, and less performance degradation than most reported NFOSCs. Importantly, when the polymer blend is processed in air with an eco‐friendly solvent, 1,2,4‐trimethylbenzene, the resultant device exhibits a reasonably high PCE of 10.60% (certified PCE: 10.467%) without encapsulation, which is the highest value reported to date for NFOSCs fabricated under such conditions. The potential of this high‐performance and eco‐friendly processable polymer is further demonstrated in the excellent PCE of 14.22% of a device with a P(F‐BiT)‐COOBOCl(out):Y6‐BO‐4Cl blend prepared in o‐xylene solvent. This study provides perspectives and opportunities for designing and developing efficient photoactive materials as a new strategy for the commercialization of NFOSCs.

Herein, a small amount of the ionic liquid methylammonium difluoroacetate is introduced to anchor the organic cations via hydrogen bonding and to enhance the Pb–O interaction in perovskite precursors for efficient and stable solar cells.

The instability of organic cations in lead halide perovskite materials is a major obstacle for the commercial breakthrough of perovskite photovoltaics due to desorption of organic cations during the thermal annealing and device operation. Herein, a novel strategy is reported to improve the performance and stability of organic halide perovskite solar cells containing organic cations by adding a small amount of the ionic liquid methylammonium difluoroacetate (MA⁺DFA⁻). Nuclear magnetic resonance and Fourier‐transform infrared spectroscopy measurements show that MA⁺DFA⁻ can anchor the organic cations via hydrogen bonding and enhance the Pb–O interaction in perovskite precursors, leading to the retardation of the perovskite crystallization and improved stability of the perovskite precursor solution. Dynamic light scattering and scanning electron microscopy verify the defect‐passivation effect of MA⁺DFA⁻ on the perovskite precursors and films. The passivated perovskite film shows superior photo carrier dynamics as investigated by time‐resolved photoluminescence and transient absorption spectra. Moreover, the hydrogen bonding of the perovskite with MA⁺DFA⁻ imparts excellent ambient and thermal stability to the film as revealed by X‐ray diffraction measurements. As a result, devices with a high efficiency of 21.46% and excellent stability over 180 days in nitrogen atmosphere at room temperature are achieved with the ionic liquid.

A series of phenylhydroxylammonium halide salts is adopted to passivate the surface of the mixed perovskite film, resulting in enormously enhanced photoluminescence (PL) intensity and prolonged carrier lifetime. As a result, the best perovskite solar cell treated with phenylbutylammonium bromide realizes a power conversion efficiency (PCE) of 22.67% with a V _oc of 1.216 V, corresponding to a small V _oc deficit of ≈344 mV.

Abstract

Suppressing non‐radiative recombination via passivating surface defects of perovskite films has demonstrated an excellent strategy for high‐performance perovskite solar cells (PSCs). However, it is still hard to realize both high open‐circuit voltage (V _oc) of >1.2 V and high power conversion efficiency (PCE) of >22%, because the optimized bandgap of perovskite films is less than 1.60 eV for efficient light harvesting and V _oc deficit is generally unavoidable due to carriers recombination. Here, the surface of the perovskite film is treated with a series of phenylhydroxylammonium halide salts and it is found that all of them can remarkably prolong the carrier lifetime owing to their excellent capability of surface defects passivation. The best PSC with phenylbutylammonium bromide treatment realizes a PCE of 22.67% with a V _oc of 1.216 V, corresponding to a small V _oc deficit of ≈344 mV.

A generally applicable sequential deposition (SD) strategy is developed to construct high‐performance organic solar cells (OSCs) without involving complicated procedures for morphological control. The SD‐processed OSCs via simple adjustment of the acceptor layer to impact the blend phase can afford higher efficiencies than their conventional OSC counterparts, providing an avenue toward promoting better photovoltaic performance and reducing production requirements.

Abstract

Bulk‐heterojunction (BHJ) organic solar cells (OSCs) are prepared by a common one‐step solution casting of donor‐acceptor blends often encounter dynamic morphological evolution which is hard to control to achieve optimal performance. To overcome this hurdle, a generally applicable, sequential processing approach has been developed to construct high‐performance OSCs without involving tedious processes. The morphology of photoactive layers comprising a polymer donor (PM6) and a nonfullerene acceptor (denoted as Y6‐BO) can be precisely manipulated by tuning Y6‐BO layer with a small amount of 1‐chloronaphthalene additive to induce the structural order of Y6‐BO molecules to impact the blend phase. The results of a comparative investigation elucidate that such two‐step procedure can afford more favorable BHJ microstructure than that achievable with the single blend‐casting route. This translates into improved carrier generation and transport, and suppressed charge recombination. Consequently, the devices based on sequential deposition (SD) deliver a remarkable efficiency up to 17.2% (the highest for SD OSCs to date), outperforming that from the conventional BHJ devices (16.4%). The general applicability of this approach has also been tested on several other nonfullerene acceptors which show similar improvements. These results highlight that SD is a promising processing alternative to promote better photovoltaic performance and reduce production requirements.