Chen Weijie

Poly(3‐hexylthiophene‐2,5‐diyl) (P3HT) is doped with 0.025 mol% molecular organic Lewis acid bis(pentafluorophenyl)zinc, which exhibits higher hole mobility and well‐matched energy. An enhanced highest power conversion efficiency of 17.49% is achieved for a perovskite solar cell based on doped P3HT without destroying its stability.

The molecular organic Lewis acid bis(pentafluorophenyl)zinc [Zn(C₆F₅)₂] is reported as an efficient p‐type dopant for poly(3‐hexylthiophene‐2,5‐diyl) (P3HT), to be used as hole‐transporting material (HTM) in perovskite solar cells (PSCs) for the first time. To date, the most efficient PSCs use lithium bis(trifluoromethane)sulfonimide lithium salt (LiTFSI) and 4‐tert‐butylpyridine (tBP) as standard additives for HTMs. However, such dopants can induce deleterious effects on device stability. Herein, the effect of the concentration of Zn(C₆F₅)₂ in P3HT HTM on the performance of PSCs is investigated. The P3HT‐based PSCs using a low concentration of the dopant (0.025 mol%) in the HTM layer exhibit the best performance and the highest power conversion efficiency (PCE) of 17.49%, which is almost 3.5% higher than the achieved PCE for pristine P3HT‐based PSCs. The origin of the improved performance for PSCs is further investigated, by studying the conductivity and hole mobility of the thin films based on pristine and doped P3HT. Adding a small amount of Zn(C₆F₅)₂ to P3HT increases its thin‐film hole mobility and its hole extraction ability.

High‐quality Cu₂O thin films are synthesized by a facile solution method and the Cu₂O/Si heterojunction solar cells are fabricated, showing an outstanding photovoltaic performance. Significantly, the photovoltaic conversion efficiency of Cu₂O/Si solar cells can be greatly improved to a record value of 9.54% by sequential interfacial engineering.

Cuprous oxide (Cu₂O) is a nontoxic and earth‐abundant semiconductor material, which is a promising candidate for low‐cost photovoltaic applications. Although Cu₂O‐based solar cells have been studied for a few decades, they still suffer from disappointing photovoltaic performance due to its high trap‐state density and inferior carrier collection efficiency. Herein, a facile solution method is demonstrated to synthesize high‐quality Cu₂O films with low defects as hole transport layers (HTLs) and the Cu₂O/Si heterojunction solar cells are fabricated. Moreover, a variety of interfacial engineering and light management strategies are adopted to push the efficiency limit of Cu₂O/Si solar cells, including a Ag transparent conductive layer, HNO₃ passivation, Mg electrode back contact, and MoO _x antireflection layer, which enable the boosting of carrier separation and reduce the loss of incident solar light, yielding a record high power conversion efficiency of 9.54%. This work may pave the way for economical and environment‐friendly use of Cu₂O/Si heterojunction solar cells in daily life.

Herein, a facile method is provided to fabricate the CsPbIBr₂ inorganic perovskite solar cells under low temperatures. The ZnO electron transport layer modification and band‐alignment engineering contribute to the outstanding power conversion efficiency of 10.16%, representing the highest efficiency for CsPbIBr₂ when the fabrication temperature is lower than 160 °C.

Recently, the thermally stable and facilely fabricated inorganic CsPbIBr₂ perovskite solar cells (PSCs) have attracted tremendous attention where the electron transport layer (ETL) is vital. However, the typical sintering temperature for the widely used electron transport material, that is, TiO₂, is more than 400 °C, elevating the cost and hindering the application. Due to high electron mobility and low fabrication temperature, ZnO becomes a desirable alternative for TiO₂, as the ETL in CsPbIBr₂ PSCs, albeit with low open‐circuit voltage (V _oc). Herein, this work introduces a trace of NH₄Cl to the sol–gel‐derived ZnO precursor to decrease the work function of the ZnO film, tune the surface morphology of the perovskite film, and thus suppress the density of trap states in the CsPbIBr₂ films. Consequently, full‐coverage and pure‐phase CsPbIBr₂ films consisting of micron‐size and high‐crystallinity grains are obtained. More importantly, for the optimal NH₄Cl‐modified ZnO, a shining improvement in V _oc from 1.08 to 1.27 V boosts the champion CsPbIBr₂ PSCs to obtain a power conversion efficiency of 10.16%, which is the highest value reported among pure‐CsPbIBr₂ PSCs under a low fabrication temperature of 160 °C. In addition, the NH₄Cl‐modified ZnO ETL reduces the severe hysteresis and increases the device stability significantly.

This review presents the present status and the future perspectives of Sn‐based perovskite solar cells. The strategies to find the breakthrough of highly efficient and robust Sn‐perovskite solar cells are discussed by focusing on current fabrication processes and defect physics scenario including compositional and dimensional engineering.

Sn‐based halide perovskites have attracted much interest due to their highly valuable electrical and optical properties. The promising optical and electrical properties of Sn‐based perovskites have enticed a lot of research to focus on developing the strategies and explore the in‐depth material characteristics. Sn‐halide perovskites exhibit apparent merits and demerits. The ideal electrical and optical properties are even better than that of Pb‐analogs, namely close‐to‐optimal bandgap, strong optical absorption, and good carrier mobilities. However, the present achievement of Sn‐halide perovskite solar cells is not satisfactory, which is commonly attributed to relatively low defect tolerance, fast crystallization, and oxidative instability. The efficiency of Sn‐based perovskites is far ahead, with a 9% power conversion efficiency (PCE), than the other (Ge, Bi, Sb, Cu, etc.) Pb‐free options but simultaneously lagging far behind Pb‐based analogs that have a 25.2% PCE. This review is aimed at presenting milestone works and revealing the pros and cons of Sn‐halide perovskites. In addition, the defect physics of Sn‐based perovskites is described. The improvement of open‐circuit voltage is a critical issue for Sn‐halide perovskites to compete with Pb‐based perovskites. The understanding of defect physics plays an instrumental role in designing strategies for efficient and robust Sn‐halide perovskite solar cells.

Organic solar cells are a promising low‐carbon technology for electricity generation. Recently, such cells have reached the milestone of 17% power conversion efficiency. Herein, the key players behind this recent surge in efficiency are discussed. Novel organic photovoltaic materials and device architectures are critically reviewed. Non‐fullerene donors and acceptors dramatically increase device efficiency.

Organic solar cells (OSCs) are one of the most promising low‐carbon technologies for the generation of electricity. It is blessed with a relatively lower installation time and cost, light weight, semitransparent nature, and suitability for roll‐to‐roll printing process. In the past, critics of OSCs were concerned about its limited efficiency compared with other contemporary photovoltaic (PV) technologies. However, in the past few years, researchers in this field have made sufficient progress in terms of high performance, and OSC efficiency has witnessed significant growth. Today, a large number of OSCs are demonstrating >10% efficiency, recently reaching the milestone of 17%. The boost in efficiency is crucial for the successful commercialization of OSC. Herein, the recent advancements in OSC are highlighted to analyze the key players working behind the surge in its efficiency. The contributions of novel organic photovoltaics materials and their morphology as well as novel device architectures are discussed. Finally, the major challenges facing the upscaling and commercialization of OSCs are addressed.

An effective method is proposed for excellent power conversion efficiency (PCE) with high V _oc in polymer solar cells (PSCs) by introducing a weak electron‐deficient thiophene‐based IC terminal group into thieno[3,2‐b]thiophene central core‐based small molecule acceptors. An excellent PCE of 13.11% with V _oc of 0.88 V is obtained, which is the highest reported for A–D–A‐type nonfullerene acceptors containing the central thieno[3,2‐b]thiophene unit with sp³ hybridized carbon‐bridged cyclopentadiene fragments in binary PSCs.

A pair of pure regioisomeric acceptor–donor–acceptor (A–D–A) typed nonfullerene small molecule acceptors (NF‐SMAs) (4TTIC and 4TTIC‐Cl), containing a central thieno[3,2‐b]thiophene‐sp³ hybridized “carbon‐bridge”‐based fused ring core unit and thiophene‐based IC or chlorinated thiophene‐based IC are synthesized for polymer solar cells (PSCs). Compared with 4TTIC, 4TTIC‐Cl not only achieves a red‐shifted absorption spectra and lower energy levels but also enhancement of molecular packing and crystallinity. The 4TTIC‐Cl‐based blend films display higher and more balanced charge carrier mobilities, more favorable morphology, and more efficient exciton dissociation in comparison with the 4TTIC‐based blend film. The optimized devices based on PBDB‐ST:4TTIC‐Cl deliver an impressively high power conversion efficiency (PCE) of 13.11% and fill factor of 74%, much higher than that of the PBDB‐ST:4TTIC‐based devices. Moreover, a small energy loss of ≈0.54 eV and a decent V _oc of 0.88 V are simultaneously achieved for PBDB‐ST:4TTIC‐Cl‐based devices. Noticeably, the PCE of 13.11% is the highest reported value for NF‐SMAs containing the central thieno[3,2‐b]thiophene unit with sp³ hybridized carbon‐bridged cyclopentadiene fragments in binary PSCs. This study proves that introduction of less electron‐deficient thiophene‐based IC terminal group into thieno[3,2‐b]thiophene central core‐based SMAs is a very effective method for making high V _oc and excellent PCE simultaneously.

Propyl ammonium (C3A) is introduced into phenethylammonium (PEA)‐based 2D perovskites with <n> = 3. It is found that tuning the CH···π interaction between organic cations can remove undesirable n = 1 phase, lower the density of trap states, and achieve larger crystalline grains to improve the perovskite solar cell efficiency to ≈10%. C3A with other aromatic cations shows similar improvement.

Phenethylammonium (PEA)‐based 2D perovskite is an interesting example of 2D perovskites, serving as the gateway for further introduction of functional conjugated organic cations into 2D perovskites for a variety of applications, for example, photovoltaics. However, the efficiency of photovoltaic devices based on PEA 2D perovskites only achieved ≈7% for <n> = 3, which was significantly lower than that achieved for other cation‐based 2D perovskites. Here, by introducing propyl ammonium (C3A) into the PEA‐based 2D perovskites, the device efficiency is improved to ≈10% for 1:1 C3A:PEA‐based 2D perovskites (<n> = 3). Further investigation reveals that tuning the CH···π interaction (between C3A and PEA or between two PEA molecules) can have multiple beneficial impacts on such modified 2D perovskites, including a) removal of undesirable n = 1 phase, b) lowering the density of trap states, and c) achieving larger crystalline grains. Additionally, after substitution with 50% C3A, other aromatic ammonium cation‐based 2D perovskites (<n> = 3) also show similar efficiency enhancement in their photovoltaic devices, thus exhibiting the general applicability of this method. The results of this study highlight that the strategic tuning of non‐covalent interactions (such as CH···π interaction) is a viable and important method to further develop 2D perovskites for photovoltaics.

A hybrid electron transport layer (ETL) of SnO₂ and carbon nanotubes (CNTs) is designed by simple thermal decomposition of a mixed solution of SnCl₄·5H₂O and pretreated CNTs. Based on the hybrid ETL, a high efficiency of 20.33% is achieved in the hysteresis‐free perovskite solar cell, which shows 13.58% enhancement compared with the conventional device (power conversion efficiency = 17.90%).

Tin oxide (SnO₂) has recently received increasing attention as an electron transport layer (ETL) in planar perovskite solar cells (PSCs) and is considered a possible alternative to titanium oxide (TiO₂). However, planar devices based on pure solution‐processed SnO₂ ETL still have hysteresis, which greatly limits the application of SnO₂ in high‐efficiency solar cells. Herein, to address this issue, a hybrid ETL of SnO₂ and carbon nanotubes (CNTs) is fabricated by a simple thermal decomposing of a mixed solution of SnCl₄·5H₂O and pretreated CNTs (termed SnO₂–CNT). The addition of CNTs can significantly improve the conductivity of SnO₂ films and reduce the trap‐state density of SnO₂ films, which benefit carrier transfer from the perovskite layer to the cathode. As a result, a high efficiency of 20.33% is achieved in the hysteresis‐free PSCs based on SnO₂–CNT ETL, which shows 13.58% enhancement compared with the conventional device (power conversion efficiency = 17.90%).

A method of combined electron transporting bilayer is reported to reduce energy loss and inhibit defects in the perovskite solar cells (PSCs) by combining the commercially accessible SnO₂ and home‐made TiO₂ nanoparticles. Consequently, the PSCs devices acquire a high efficiency of 20.50%, which is superior to that based on SnO₂ layers with a efficiency of 18.09%.

Herein, commercially accessible SnO₂ and home‐made TiO₂ nanoparticles as a combined electron transporting bilayer (ETBL) are applied to achieve highly efficient planar perovskite solar cells (PSCs). With the formed cascade‐aligned energy levels from the proper stacking of SnO₂ and TiO₂ layers and the excellent defect‐passivation ability of TiO₂, SnO₂/TiO₂ ETBLs effectively reduce energy loss and inhibit defects formation both at the electron transporting layers (ETL)/perovskite interfaces and within the bulk of perovskite layer as revealed by a comprehensive analysis of photoelectric characteristic analysis, including ultraviolet photoelectron spectroscopy, photoluminescence, and electrochemical impedance spectroscopy. Consequently, the PSC devices acquired a power conversion efficiency (PCE) of 20.50% with a V _oc of 1.10 V, a J _sc of 24.2 mA cm⁻² and an fill factor of 77%, which are superior to the values of the control device based on single SnO₂ layer with a PCE of 18.09% (a 13.3% boosting on PCE). Moreover, there was no degradation after 49 days, indicating the great stability after adding TiO₂ layer. Herein, it is demonstrated that the cascaded alignment of energy levels between the electrode and perovskite layer by ETBLs could be an effective approach to improve the photovoltaic performance of the PSCs with excellent long‐term stability.

Herein, the major optical losses of monolithic perovskite/silicon tandem solar cells (TSCs) are summarized, analyzing material selection and device design to date. Relevant strategies and challenges in monolithic perovskite/silicon TSCs are highlighted, comprising bandgap engineering of perovskites and light trapping methods, providing guidance for further improvement of tandem devices.

Perovskite/silicon tandem solar cells (TSCs), especially two‐terminal, with a record efficiency of 28% already realized, present great potential as low‐cost and efficient substitutes for dominant silicon photovoltaics. Achieving efficiencies exceeding 30% is quite realistic, as indicated by extensive optical simulations. Super light management in monolithic perovskite/silicon TSCs is one of the prerequisites to make this a reality. In this Review, various forms of optical losses, such as reflection loss, parasitic absorption, and current mismatch, are analyzed systematically to provide a better understanding of the performance of perovskite/silicon TSCs. Particularly, a simple refractive index matching rule derived from the Fresnel equation is proposed as a basis for material selection and device design. Meanwhile, an overview of the current strategies and challenges in monolithic perovskite/silicon TSCs is provided, comprising bandgap engineering of perovskites and light trapping methods, aiming to provide guidance for further improvement of tandem devices.

Two novel nonfullerene acceptors (NFAs) 4TFIC‐4F and 4TCIC‐4F are designed based on fluorene and carbazole. Compared with 4TFIC‐4F, 4TCIC‐4F exhibits higher lowest unoccupied molecular orbital (LUMO) level and narrower optical bandgap. Therefore, polymer solar cells based on PBDB‐T‐2Cl:4TCIC‐4F achieve a high‐power conversion efficiency of 13.02%, which is the highest value for the carbazole‐containing NFAs‐based devices.

It is important to tune the energy levels of nonfullerene acceptors (NFAs) to achieve more balanced open‐circuit voltage (V _oc) and short‐circuit current density (J _sc) to improve the device performance. Herein, two novel NFAs are designed via fusing fluorene or carbazole with two thieno[3,2‐b]thiophene and end capped with INIC‐2F, namely, 4TFIC‐4F and 4TCIC‐4F, respectively. The impact of the fluorene and carbazole unit on the PSC performance is systematically studied. Compared with 4TFIC‐4F, 4TCIC‐4F exhibits a higher lowest unoccupied molecular orbital (LUMO) energy level of −3.95 eV and a narrower optical bandgap of 1.51 eV owing to the stronger electron‐donating capacity of fused‐carbazole ring core. Consequently, the 4TCIC‐4F device achieves a high power conversion efficiencies (PCE) of 13.02% with a higher V _oc of 0.94 V and a larger J _sc of 18.98 mA cm⁻², whereas the 4TFIC‐4F device shows a PCE of 11.24%. The PCE of 13.02% is the highest value so far reported with the carbazole‐containing NFAs‐based PSCs. More importantly, the 4TCIC‐4F device shows good film thickness insensitive and long‐term thermal stability. The investigation demonstrates that the fused‐carbazole ring is a superior option to fused‐fluorene ring as electron‐donating core for designing high‐performance NFAs by improving V _oc and J _sc simultaneously.

Via an energy‐transfer mechanism, ternary organic solar cells based on a wide‐bandgap donor (PBDB‐T‐2Cl), a middle‐bandgap acceptor (ITC‐2Cl), and an ultranarrow‐bandgap acceptor (IOIC‐2Cl) achieve a champion power conversion efficiency of 14.75% with a low energy loss of 0.48 eV, outcompeting PBDB‐T‐2Cl: ITC‐2Cl (13.66%) and PBDB‐T‐2Cl: IOIC‐2Cl (11.60%) binary devices.

An effective way to improve the power conversion efficiency of organic solar cells (OSCs) is to use the ternary architecture consisting of a donor, an acceptor, and a third component. Identifying the proper third component for successful ternary OSCs, however, is not an easy task. Herein, it is demonstrated that a middle‐bandgap acceptor, ITC‐2Cl, functions as a successful third component for several wide‐bandgap donor: ultranarrow bandgap acceptor binary systems (PBDB‐T‐2F: F8IC, PBDB‐T‐2F: IOIC‐2Cl, and PBDB‐T‐2Cl: IOIC‐2Cl). Photovoltaic parameters, including V _OC, J _SC, fill factor (FF), and power conversion efficiency (PCE), are effectively improved by incorporating ITC‐2Cl, which lies in the complementary absorption of ITC‐2Cl and host binary system, high‐lying LUMO level of ITC‐2Cl, and the inhibition of bimolecular recombination. The ternary device based on PBDB‐T‐2Cl: ITC‐2Cl: IOIC‐2Cl achieves a champion PCE of 14.75% (certified as 13.78%) with a very low energy loss of 0.48 eV. These results provide critical insight into the ternary strategy and encourage re‐evaluation and restudy of the photoactive materials previously reported with moderate performance.

Hole‐transport material based on dibenzo[b,d]thiophene (DBTMT) is synthesized with low costs. A champion power conversion efficiency of the optimized p–i–n planar perovskite solar cells based on dopant‐free DBTMT reaches 21.12% with a high fill factor of 83.25%, due to good hole‐transport properties and the passivation effect of DBTMT.

N ²,N ²,N ⁸,N ⁸‐tetrakis(4‐(methylthio)phenyl)dibenzo[b,d]thiophene‐2,8‐diamine (DBTMT) is synthesized from three commercial monomers for application as a promising dopant‐free hole‐transport material (HTM) in perovskite solar cells (pero‐SCs). The intrinsic properties (optical properties and electronic energy levels) of DBTMT are investigated, proving that DBTMT is a suitable HTM for the planar p–i–n pero‐SCs. The champion power conversion efficiency (PCE) of the optimized pero‐SCs (with structure as ITO/pristine DBTMT/MAPbI₃/C₆₀/BCP/Ag) reaches 21.12% with a fill factor (FF) of 83.25%, which is among the highest PCEs and FFs reported for planar p–i–n pero‐SCs based on dopant‐free HTMs. The Fourier‐transform infrared spectroscopy, X‐ray diffraction, and X‐ray photoelectron spectroscopy spectra of MAPbI₃ and DBTMT–MAPbI₃ films demonstrate that there is an interaction between DBTMT and MAPbI₃ at the interface through the sulfur atoms in DBTMT to passivate the defects, which is corresponding to the higher FF and PCE of the corresponding device.

Stability and toxicity are bottlenecks for halide perovskite solar cells despite their remarkable efficiency. Double halide perovskites with heterovalent metal cations pave a way for lead‐free‐based devices for enhanced stability. This Review summarizes the theoretical and experimental progress of lead‐free double perovskite. The issues, challenges, applications, and future prospects are integrated to provide a full picture.

Perovskite solar cells (PSCs) have achieved a high power conversion efficiency (PCE) with a credible certified value over 25%. More efforts have been devoted to the development of stable and ecofriendly perovskite materials. Lead‐free double perovskites (LFDPs) are a noteworthy choice as a photoactive layer because of their favorable photovoltaic (PV) properties, intrinsic chemical stability, and environmental friendliness. This Review presents various LFDP materials whose structural stability and optoelectronic properties are predicted by theoretical calculations. The synthesis and experimental properties of LFDPs and their applications in PSCs and optoelectronics in pursuing high performance, low toxicity, and functional stability are also reviewed. Perovskites active layers are critical for PSCs, and their appropriate properties are responsible for achieving a high PCE. On the other side, the stability of PSCs under working conditions is a critical requirement for their practical applications. Defect‐ordered perovskites are also presented to provide another outlook on lead‐free perovskite‐based PVs. The introduction and interest toward LFDP in PSCs can represent a viable solution to the toxicity issue, stimulate further research, and bring a real impact to future PV technologies.

A two‐step annealing method is developed for studying the water effect on different kinds of perovskites. It is demonstrated that 60 °C is favorable to the formation of hydrate phase which leads to a reconstruction process in the second annealing stage. The corresponding water effects highly depend on the cations of the perovskite itself.

Water effect on perovskite solar cells has received growing interest in recent years. A widely accepted view is that moderate water content induces the formation of hydrate phase which enhances the recrystallization of the perovskite. However, the underlying factors which influence the formation of hydrate phase are yet to be investigated. Herein, by controlling the annealing temperature, it is demonstrated that 60 °C is the most suitable temperature for the formation of hydrated perovskite. After further annealing at 120 °C, the resulting perovskite film reveals enhanced crystallinity with a more uniform morphology, contributing to device efficiency above 20%. In addition, the water effect on different types of perovskites is studied and it is concluded that the formation of hydrated perovskite is mainly determined by the cations of the perovskite itself. The findings in this work elucidate the conditions for the formation of hydrated perovskite, contributing to the fabrication of highly efficient perovskite solar cells.

Herein, three polyfluorene copolymers (TFB, PFB, and PFO) are investigated as hole‐transport materials (HTMs) for the construction of inverted perovskite solar cells. The photovoltaic performance of the device is found to be closely correlated with the electronic properties of HTMs. The TFB‐based device exhibits the highest efficiency of 18.48% due to its high mobility and favored energy‐level alignment.

Inverted perovskite solar cells (PSCs) that can be entirely processed at low temperatures have attracted growing attention due to their cost‐effective production. Hole‐transport materials (HTMs) play an essential role in achieving efficient inverted PSCs, as they determine the effectiveness of charge extraction and recombination at interfaces. Herein, three polyfluorene copolymers (TFB, PFB, and PFO) are investigated as HTMs for construction of inverted PSCs. It is found that the photovoltaic performance of the solar cells is closely correlated with the electronic properties of the HTMs. Due to its high mobility along with the favored energy‐level alignment with perovskite, TFB shows superior charge extraction and suppressed interfacial recombination than PFB‐ and PFO‐based devices, which delivers a high efficiency of 18.48% with an open‐circuit voltage (V _OC) of up to 1.1 V. In contrast, the presence of a large energy barrier in the PFO‐based devices results in substantial losses in both V _OC and photocurrent. These results demonstrate that TFB can serve as a superior HTM for inverted PSCs. Moreover, it is anticipated that the performance of the three HTMs identified here might guide the molecular design of novel HTMs for the manufacture of highly efficient inverted PSCs.

Herein, it is demonstrated that solution‐processed dopant‐free spiro molecules can serve as superior hole‐transport materials (HTMs) to fabricate efficient inverted (p‐i‐n) perovskite solar cells. An entirely solution process is achieved by rational choice of orthogonal solvent, which allows to deposit uniform and pinhole‐free perovskite films without compromising the hole‐extraction capability of the spiro interlayers.

Spiro‐linked compounds have been used as benchmark hole‐transport materials (HTMs) for the construction of efficient normal architecture (n‐i‐p) perovskite solar cells (PSCs). However, the heavy reliance on the use of dopants not only complicates the device fabrication but imposes long‐term stability concern of the devices. Herein, it is reported that solution‐processed dopant‐free spiro molecules can serve as superior HTMs to fabricate efficient inverted (p‐i‐n) PSCs. Rational choice of orthogonal solvent allows us to solution deposit uniform and pinhole‐free perovskite films without compromising the hole‐extraction capability of the spiro‐based interface layers. To illustrate the generality of the strategy, three spiro‐linked molecules are investigated side by side as HTMs in one‐step solution‐processed CH₃NH₃PbI₃ PSCs. Due to the favored energy‐level alignment and high hole mobility, solar cells based on the HTM of spiro‐TTB yield a high efficiency of 18.38% with open‐circuit voltages (V _OC) up to 1.09 V. These results suggest that small molecular HTMs commonly developed for normal structure devices can be of great potential to fabricate cost‐effective and highly efficient inverted PSCs.

Herein, the dipolar polarization in a quasi‐2D organic–inorganic hybrid‐perovskite nanorod network–based solar cell using impedance spectroscopy is studied. Electric field and photoinduced dipole–dipole interaction plays an important role for the solar cell working at steady states.

Layered quasi‐2D organic–inorganic hybrid perovskites (OIHPs) prevent oxygen and moisture permeation, for long‐lifetime photovoltaic performance. Unfortunately, the electrical and photoinduced surface and dipolar polarizations caused due to the presence of the organic cation spacer in the structure remain unclear. Herein, a high‐performance planar quasi‐2D OIHP solar cell comprising (PEA)₂(MA)₃Pb₄I₁₃ (n = 4) is designed. It displays a large area coverage and an interconnected nanorod network, which contributes to efficient light absorption and charge carrier transport. The surface and dipolar polarizations exhibit remarkable light intensity and electric field–dependent characteristics at short‐circuit‐current (J _sc) and steady‐state (i.e., V _oc) conditions. More importantly, Voc exhibits a nonlinear behavior at steady states. Such a unique feature is in accordance with the dipolar polarization measured at the same condition. The phenomenon can be explained by the significant dipole–dipole interaction at lower electric field strengths. At higher field strengths, the screen of the dipoles due to charge accumulation at the surface of the organic cation spacer leads to slower increment of Voc. Thus, carefully designing the quasi‐2D perovskite nanostructure, together with the dielectric property of the organic cation spacer, may play an exceptionally important role for future high‐performance quasi‐2D perovskite solar cells.

Solution‐processed α‐In₂Se₃ is first used as the hole transport layer in polymer solar cells (PSCs) due to its significant photoelectric properties. A high power conversion efficiency of 9.58% is achieved in α‐In₂Se₃‐based devices, which is comparable with that of poly(3,4‐ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS)‐based devices. Furthermore, the α‐In₂Se₃ film possesses excellent thermal stability and enhances the long‐term stability of PSCs.

Herein, a 2D α‐In₂Se₃ nanosheet, a binary III–VI group compound semiconductor, is fabricated by liquid‐phase exfoliation method, and the photoelectric properties of α‐In₂Se₃ material are investigated in depth. It is found that α‐In₂Se₃ film exhibits significant conductivity, outstanding optical transmission, and a suitable work function. Combined with its smooth surface and preferable hydrophobicity, α‐In₂Se₃ film can efficiently facilitate hole transporting in the polymer solar cells (PSCs). Due to the aforesaid advantages, a 2D α‐In₂Se₃ nanosheet is used as a hole transport layer (HTL) in conventional PSCs for the first time, and a relatively high power conversion efficiency (PCE) of 9.58% is achieved with the structure of ITO/α‐In₂Se₃/PBDB‐T:ITIC/Ca/Al, which is comparable with poly(3,4‐ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS)‐based devices (9.50%). Interestingly, it is demonstrated that the α‐In₂Se₃ film possesses excellent thermal stability in the range from room temperature to 280 °C, and a PCE of 9.35% is achieved without annealing treatment of α‐In₂Se₃ film, which exhibits a great potential of α‐In₂Se₃ for an annealing‐free approach. Furthermore, the incorporation of α‐In₂Se₃ HTL also remarkably enhances the long‐term stability of PSCs compared with PEDOT:PSS‐based devices. So, the results show that 2D α‐In₂Se₃ is a promising candidate to be an efficient and stable hole‐extraction layer.

Niobium oxides are successfully prepared via a urea‐metal chloride route. Remarkably, the monoclinic NbO₂ counter electrode exhibits superior electrocatalytic activity and yields a high power conversion efficiency of 6.06% in dye‐sensitized solar cells, close to that of Pt counter electrodes (6.46%). The catalytic mechanism of the Nb‐based counter electrode is clarified in terms of its electronic structure and I adsorption using first‐principle calculations.

Two types of nanosized niobium oxides and their composites, pseudohexagonal Nb₂O₅ (TT‐Nb₂O₅), monoclinic NbO₂ (M‐NbO₂), and the coexistence of TT‐Nb₂O₅ and M‐NbO₂ (TT‐Nb₂O₅/M‐NbO₂), are successfully synthesized through the urea‐metal chloride route, and they exhibit excellent catalytic activity and photovoltaic performance in dye‐sensitized solar cells (DSSCs). First‐principles density function theory (DFT) calculations show that their catalytic activity is significantly influenced by their intrinsic electronic structures and properties. The lone‐pair 4d¹ electrons of Nb⁴⁺ in M‐NbO₂ enhance the Nb–I interaction and promote electron transfer from the M‐NbO₂ counter electrode (CE) to I, thus resulting in superior catalytic properties in M‐NbO₂‐based DSSCs. In addition, the adsorption energy of I on the M‐NbO₂ surface is in the optimal energy range of 0.3—1.2 eV, and the Fermi level of M‐NbO₂ is 0.6 eV, which is higher than the I₃ ⁻ reduction reaction potential, and I₃ ⁻ can be spontaneously reduced to 3I⁻. Herein, a general strategy for understanding the electronic structures and catalytic activities of transition metal compounds as CE catalysts for DSSCs is provided.

Solution‐processed MoO₃ (SM), synthesized by a simple low‐temperature process, is utilized as an efficient and stable anode interfacial layer for organic solar cells (OSCs). The ultrasmooth SM film, without pinholes, exhibits excellent photovoltaic performance and device stability in OSCs, maintaining ≈92% of its initial solar cell efficiency over 2500 h storage in inert conditions.

The interfacial layer (IL) in organic solar cells (OSCs) can be an important boosting factor for improving device efficiency and stability. Herein, a facile and cost‐effective approach to form a uniform molybdenum oxide (MoO₃) film with desirable stability is provided, based on solution processing at low temperatures by simplified precursor solution synthesis. The solution‐processed MoO₃ (SM) film, with oxygen vacancies induced by the hydroxyl group, functions as an efficient anode IL in conventional OSCs. The hole‐transporting performance of SM is well demonstrated in nonfullerene‐based OSCs exhibiting over 10% of power conversion efficiency. The enhanced device performance of SM‐based OSCs over that of poly(3,4‐ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) is investigated by analyzing the morphology, electronic state, and electrical conductivity of such a hole‐transporting layer, as well as the charge dynamics in the completed devices. Furthermore, the high stability of the SM films in OSCs is examined under various environmental conditions, including long‐term and thermal stability. In particular, fullerene‐based OSCs with SM maintain over 90% of their initial cell performance over 2500 h under inert conditions. It is shown that solution‐processed metal oxides can be viable ILs with high functionality and versatility, overcoming the drawbacks of conventionally adopted conducting polymer interlayers.

Quantum dots are regarded as neutralized charged intermedia to transfer ligands for interfacial modification, which can significantly adjust surface electric properties to reduce V _OC loss and improve device performance. A stable V _OC enhancement with excellent reproducibility is fulfilled by simple solution‐processed QDs modification, achieving 20.6% power conversion efficiency (PCE) and enhanced stability.

The tremendous passion for inverted planar heterojunction perovskite solar cells (PSCs) is originated from their great tendency in the roll‐to‐roll process‐compatible fabrication and huge potential for integration into tandem solar cells. But the device efficiency is still lower than regular structured PSCs. Engineering of the cathode interface to efficiently control and reduce V _OC loss lights a lamp for increasing electrochemical properties and boosting overall performance. Herein, a simple interfacial modification strategy is developed by introducing a hybrid ligand interfacial layer to reduce V _OC loss in PSCs with inverted planar structure. Heavily washed QDs are used as neutral charged intermedia to enable alloying reaction to transfer ligands without damage to perovskite (PVK). A band bending is immediately generated on the top surface of PVK film after QDs modification, which is directly confirmed by ultraviolet photoelectron spectroscopy (UPS) and Kelvin probe force microscopy (KPFM). This contributes to ≈50 mV reduced V _OC loss, leading to a V _OC of 1.15 V and a power conversion efficiency (PCE) of 20.6% in inverted PSCs. Meanwhile, enhanced stability is achieved for these devices after QDs modification, in which PCE is maintained at >90% of initial value after 1000 h storage.

Reduced energetic disorder and activation energy are realized in organic solar cells composed of PCE10:F8IC:Eh‐IDTBR. The additional Eh‐IDTBR increases the crystalline phases of the acceptor in the ternary mixture, conducing to narrower distributed density of states, and a lower zero‐field activation energy of 55 meV in the ternary device than those of the reference.

Solution‐processed ternary organic solar cells (OSCs) contain a third component in the active layer in addition to the donor/acceptor materials. Two main avenues are considered to fabricate ternary OSCs: 1) to improve the short‐circuit current density by the selected third component that broadens and/or enhances the absorption of the host films and 2) to increase the fill factor by adding materials with diverse crystallinity to tune the film morphology. However, little work is reported for the improvement of open‐circuit voltage (V _OC), energetic disorder, charge transfer state energy (E _CT), and activation energy in ternary OSCs. Herein, ternary OSCs with active layer composed of PCE10:F8IC:Eh‐IDTBR as the model to examine these parameters in addition to the morphology are used. In the ternary device, the additional Eh‐IDTBR improves the crystallinity of the acceptor phase in the ternary mixture; the V _OC is 58 mV higher than that of the reference caused by the reduced energetic disorder; due to the good miscibility of Eh‐IDTBR with both PCE10 and F8IC, only 50 meV in E _CT is observed; and the zero‐field activation energy is lower than that for the reference. The findings provide an alternative way to understand the complex ternary OSC structural–electrical properties’ correlations.

Using diluted poly(3,4‐ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) as the hole transport layer (HTL), Sn–Pb‐based low‐E _g perovskite solar cells (PSCs) with a maximum power conversion efficiency (PCE) of up to 19.58% and J _sc of 29.81 mA cm⁻² are achieved. Then, an all‐perovskite four‐terminal tandem cell with a PCE of 23.26% is demonstrated with this low‐E _g PSC as the bottom cell. This easy and effective approach also reduces the cost of devices.

Recently, Sn–Pb low‐bandgap (E _g) perovskite solar cells (PSCs) have attracted enormous interest as an ideal bottom cell for all‐perovskite tandem solar cells. However, due to the lack of high‐performance Sn–Pb low‐E _g PSCs, the development of all‐perovskite tandem solar cells is severely constrained. Herein, the performance of Sn–Pb low‐E _g (1.2 eV) PSC is improved significantly using diluted poly(3,4‐ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) as a hole transport layer with a maximum power conversion efficiency (PCE) up to 19.58% and short‐circuit current density of 29.81 mA cm⁻². The four‐terminal (4‐T) all‐perovskite tandem solar cell is constructed using an optical splitting system with this high‐efficient low‐E _g PSC as the bottom cell and a wide‐E _g (1.6 eV) PSC as the top cell. The best all‐perovskite 4‐T tandem solar cell shows a PCE of 23.26%.

The in situ reduction of parasitic Sn⁴⁺ to Sn²⁺ by metallic tin powder effectively reduces Sn⁴⁺ content and thereby decreases the trap density of the perovskite films, giving rise to a remarkably long charge carrier lifetime and favorable energy‐level alignment at the interfaces. Consequently, a high power conversion efficiency of 20.7% is achieved for low‐bandgap Pb–Sn‐alloyed perovskite solar cells.

Although the theoretical power conversion efficiency (PCE) of low‐bandgap Pb–Sn‐alloyed perovskite solar cells (PSCs) is higher than that of its conventional pure Pb counterpart, its device performance currently has been severely restricted by the large open‐circuit voltage (V _oc) loss. Herein, it is discovered that the Sn⁴⁺‐induced trap states of the perovskite film can be effectively suppressed by introducing excess Sn powder into the precursor solution (FASnI₃) to reduce the Sn⁴⁺ content. As a result, the average charge carrier lifetime of the perovskite film increases remarkably from 115 to 701 ns due to the suppressed nonradiative recombination, and the energy levels have up‐shifted by about 0.27 eV, rendering a more favorable energy‐level alignment at the interface. Ultimately, the champion PSCs using a low‐bandgap (FASnI₃)_0.6(MAPbI₃)_0.4 perovskite film with Sn⁴⁺ reduction show a high V _oc of 0.843 V corresponding to a V _oc loss as low as 0.397 eV and a high fill factor of 80.34%, leading to an impressive PCE of 20.7%, which is one of the few instances of a PCE over 20% for low‐bandgap mixed Pb–Sn PSCs to date.

The studies from the steady‐state and time‐dependent measurements indicate that the extended absorption range, short charge carrier extraction time, and high charge carrier mobility by the non‐fullerene electron acceptors in the photoactive layer are responsible for enhanced photocurrent in ternary organic solar cells.

Ternary organic solar cells, a single active layer comprising three different components, are demonstrated to be one of the most efficient ways to approach high‐performance organic solar cells. But nevertheless, most of the ternary organic solar cells are characterized by steady‐state measurements, which are helpful but inadequate to fully understand the underlying charge carrier behavior at a short time scale. Herein, a comparison of the steady‐state and time‐dependent measurements is used to investigate the functionality of non‐fullerene electron acceptors in ternary organic solar cells. The steady‐state measurements indicate that non‐fullerene electron acceptors enlarge the absorption range of the photoactive layer, suppress charge carrier recombination, reduce charge carrier transfer resistance, and thereby increase photocurrent in ternary organic solar cells. The time‐dependent measurements demonstrate that a short charge carrier extraction time and a high charge carrier mobility are responsible for enhanced photocurrent in ternary organic solar cells. A comprehensive method understanding the underlying of enhanced efficiency of ternary organic solar cells is provided herein.

Herein, the electronic and optical properties of the Janus Ga₂SeTe monolayer are calculated via first principles. The multilayer Janus Ga₂SeTe solar cells give rise to a photocurrent exceeding that of thin‐film silicon devices at a phonon energy below 2.5 eV, indicating that Janus Ga₂SeTe is a potential material that can be used in photovoltaic devices.

The electronic and optical properties of Janus Ga₂SeTe monolayer are calculated using first‐principles calculations and it is found that it has potential in solar cells. It is found that ultrathin cross‐plane pn‐junctions are obtained by stacking Ga₂SeTe structures. The graphene‐Ga₂SeTe‐graphene sandwich‐structured solar cells are configured to explore the device performance of Ga₂SeTe solar cells. The photocurrent and the power conversion efficiency of the Janus Ga₂SeTe solar cells are evaluated. The results show that multilayer Janus Ga₂SeTe solar cells give rise to a photocurrent exceeding that of thin‐film silicon devices, indicating that Ga₂SeTe is a potential material that could be used in photovoltaics devices.

The strong anisotropy of Sb₂S₃ is a challenge for efficient doping. A facile coevaporation strategy is implemented to deposit copper‐doped Sb₂S₃ thin films. Such a strategy could help rotate the Sb₂S₃ chains to vertical orientations, improve the carrier transport mobility, and reduce the back‐contact barrier so as to improve the full‐inorganic device power conversion efficiency from 4.2% to 4.61%.

Sb₂S₃ being a light‐absorbing material is used for photovoltaic (PV) application due to its superior stability and progressive power conversion efficiency (PCE) benefiting from its low cost, less toxic, earth‐abundant, and facile nature. Due to the difficulty in efficient doping for such 1D structure, the performance of as‐fabricated thin‐film solar cells is limited by high resistivity and hole extraction barrier. Herein, a coevaporation scheme is introduced for copper‐doped Sb₂S₃ by rapid thermal evaporation (RTE). The Cu‐doped Sb₂S₃ thin film discloses the enhanced crystallinity with a grain diameter greater than 1 µm and conductivity along with improved carrier concentration. At the same time, the deep valance band obtains a minor upshift, favoring the hole extraction at back contact. Consequently, all the PV parameters are enhanced leading to the PCE boosting from 4.18% to 4.61%. Herein, a facile doping technique is demonstrated to improve its performance without any modification of the present RTE method.

Using the oxygen‐containing functional group (—COOH and/or —C—OH)‐decorated multiwalled carbon nanotubes as the electrode, the power conversion efficiency of perovskite solar cells shows an improvement after long‐term storage. The reason is confirmed to be the self‐reconstruction ability of perovskite material and the interface reconstruction for its morphology and charge transfer resistance showing significant improvement.

Perovskite solar cells (PSCs) have attracted a lot of interest because of their high efficiency and low cost. However, in commercial applications, standard PSCs suffer from low stability of the cell components, including the hole transportation material (HTM). Owing to their characteristics of high chemical stability, hydrophobicity, and high conductivity, carbon nanotubes (CNTs) can be an alternative electrode to use to form HTM‐free PSCs. Enhancing the interaction with perovskite is vital not only for photovoltaic performance but also for the stability of CNT‐based PSCs. Herein, oxygen‐containing functional groups are introduced into CNTs via acid treatment to enhance the chemical interactions with perovskite. The self‐recrystallization ability of the perovskite material is discovered; its morphology shows significant improvement after long‐term storage. Results show that acid oxidization of CNTs enable the self‐recrystallization characteristics of MAPbI₃‐induced interfacial improvement, such that even with a dispersed initial photovoltaic performance, through storage in an ambient medium with relative humidity of 20–50%, the PSCs possess better interface contact, which results in lower charge transfer resistance, higher photovoltaic performance, and stability. As a result, PSCs with an initial power conversion efficiency range of 3.21–7.89% finally converge to within the range of 9.54–12.14% after long‐term storage.

Perovskite solar cells fabricated on aluminum‐doped zinc oxide (AZO)/quartz substrates are shown with a record efficiency of 15%, and their radiation hardness to 150 keV protons is presented. The cells show robust stability up to 10¹³ protons cm⁻², with degradation at 10¹⁴ and 10¹⁵ protons ccm⁻². Transient photovoltage measurements show an increase in minority carrier density and lifetime from 10¹² protons cm⁻².

Perovskite solar cells (PSCs) have gained increasing interest for space applications. However, before they can be deployed into space, their resistance to ionizing radiations, such as high‐energy protons, must be demonstrated. Herein, the effect of 150 keV protons on the performance of PSCs based on aluminum‐doped zinc oxide (AZO) transparent conducting oxide (TCO) is investigated. A record power conversion efficiency of 15% and 13.6% is obtained for cells based on AZO under AM1.5G and AM0 illumination, respectively. It is demonstrated that PSCs can withstand proton irradiation up to 10¹³ protons cm⁻² without significant loss in efficiency. From 10¹⁴ protons cm⁻², a decrease in short‐circuit current of PSCs is observed, which is consistent with interfacial degradation due to deterioration of the Spiro‐OMeTAD holes transport layer during proton irradiation. The structural and optical properties of perovskite remain intact up to high fluence levels. Although shallow trap states are induced by proton irradiation in perovskite bulk at low fluence levels, charges are released efficiently and are not detrimental to the cell's performance. This work highlights the potential of PSCs based on AZO TCO to be used for space applications and gives a deeper understanding of interfacial degradation due to proton irradiation.