Chen Weijie

Publication date: 17 February 2021

Source: Joule, Volume 5, Issue 2

Author(s): Shaobing Xiong, Zhangyu Hou, Shijie Zou, Xiaoshuang Lu, Jianming Yang, Tianyu Hao, Zihao Zhou, Jianhua Xu, Yihan Zeng, Wei Xiao, Wei Dong, Danqin Li, Xiang Wang, Zhigao Hu, Lin Sun, Yuning Wu, Xianjie Liu, Liming Ding, Zhenrong Sun, Mats Fahlman

Publication date: April 2021

Source: Nano Energy, Volume 82

Author(s): Sisi Wang, Zhipeng Zhang, Zikang Tang, Chenliang Su, Wei Huang, Ying Li, Guichuan Xing

Publication date: April 2021

Source: Nano Energy, Volume 82

Author(s): Yufei Gao, Wenbo Ning, Xiaoliang Zhang, Yizhi Liu, Yanguang Zhou, Dawei Tang

Publication date: April 2021

Source: Nano Energy, Volume 82

Author(s): Junsheng Luo, Fangyan Lin, Jianxing Xia, Hua Yang, Ruilin Zhang, Haseeb Ashraf Malik, Hongyu Shu, Zhongquan Wan, Keli Han, Ruilin Wang, Xiaojun Yao, Chunyang Jia

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.

Fe(III) ion grafted metal–organic complexes (Fe(III)⊂MOCs) are introduced as p‐type dopants into hole transport layers (HTLs), contributing to outstanding n–i–p perovskite solar cells (PSCs) with improved power conversion efficiency (PCE, 20.46%), reduced J–V hysteresis, and enhanced air stability, which is significantly superior to the reference devices.

Realizing the rapid/controllable oxidation of 2,2′,7,7′‐tetrakis(N,N‐di‐p‐methoxyphenylamine)‐9,9′‐spirobifluorene (Spiro‐OMeTAD) under an inert atmosphere, reducing the J–V hysteresis and enhancing the air stability of devices is extremely significant to fabricate high‐performance perovskite solar cells (PSCs). Herein, the Fe(III) ion grafted metal–organic complexes (Fe(III) ⊂ MOCs) are assembled and used as the p‐type dopants of hole transport layers (HTLs) to prepare efficient and stable PSCs. Consequently, the optimal Fe(III) ⊂ In‐2‐bpydc‐doped device presents a significantly enhanced power conversion efficiency (PCE) of 20.46%, benefitting from the improved hole extraction and weakened carrier recombination at the interface between HTLs and perovskite films. More importantly, the modified device possesses a reduced J–V hysteresis index (HI) of 0.094, and can maintain nearly 90% of its initial PCE value after being exposed to the air at ≈25 °C and relative humidity (RH) of ≈35% for 4 weeks, which is attributed to the restrained detrimental penetration behavior by the MOC carrier part of dopants. This work is of important guiding significance for the application of MOC materials in photovoltaic fields.

A series of anchorable perylene diimide derivatives are explored to construct efficient and chemically inert electron transport layers (ETLs) for n–i–p‐structured perovskite solar cells. The ETLs effective electron extraction, high solvent resistance, improved perovskite crystallization, and suppressed interfacial perovskite decomposition, achieving ≈19% devices efficiency with high reproducibility and excellent stability.

Oxide semiconductors like TiO₂ and SnO₂ are exclusively used to construct electron transport layer (ETL) in n–i–p‐structured perovskite solar cells (PSCs). Despite high electron mobility and suitable energy levels, their complicated surface chemistry is detrimental to the interfacial stability as well as fabrication reproducibility. Alternatively, organic n‐type semiconductors address these issues due to their defined molecular structures. Herein, the novel use of anchorable perylene diimides (PDI) and naphthalene diimide (NDI) as chemically inert ETLs is proposed to improve the stability and reproducibility of n–i–p‐structured PSCs. Compared with NDI, the PDI analogues show more suitable lowest unoccupied molecular orbital (LUMO) energy levels (−4.1 vs. −3.8 eV) for matching the conduction band edge of metal halide perovskites, thus favoring the interfacial electron collection. The anchoring chains decorated on PDI entity are found to affect not only the solution processability of ETLs, but also the crystal quality of perovskites. More importantly, the interfacial perovskite decomposition is suppressed in such organic ETLs‐based PSCs. These merits of the anchorable PDI‐based ETLs enable ≈19% efficiency devices with excellent reproducibility and long‐term stability, which outperform traditional TiO₂‐based n–i–p PSCs.

A facile yet effective thioamides passivation strategy is proposed to suppress defects at the surface and grain boundary of CsSnI₃ perovskite, which reduces the deep level trap density from undercoordinated Sn²⁺ and Sn²⁺ oxidation. The surface passivated CsSnI₃ perovskite solar cell (PSC) delivers a efficiency of 8.20% which is the highest among all lead‐free all‐inorganic PSCs.

Abstract

Despite remarkable progress in hybrid perovskite solar cells (PSCs), the concern of toxic lead ions remains a major hurdle in the path towards PSC's commercialization; tin (Sn)‐based PSCs outperform the reported Pb‐free perovskites in terms of photovoltaic performance. However, it is of a particularly great challenge to develop effective passivation strategies to suppress Sn(II) induced defect densities and oxidation for attaining high‐performance all‐inorganic CsSnI₃ PSCs. Herein, a facile yet effective thioamides passivation strategy to modulate defect state density at surfaces and grain boundaries in CsSnI₃ perovskites is reported. The thiosemicarbazide (TSC) with SCN functional groups can make strong coordination interaction with charge defects, leading to enhanced electron cloud density around defects and increased vacancy formation energies. Importantly, the surface passivation can reduce the deep level trap state defect density originated from undercoordinated Sn²⁺ ion and Sn²⁺ oxidation, significantly restraining nonradiative recombination and elongating the carrier lifetime of TSC treated CsSnI₃ PSCs. The surface passivated all‐inorganic CsSnI₃ PSCs based on an inverted configuration delivers a champion power conversion efficiency (PCE) of 8.20%, with a prolonged lifetime over 90% of initial PCE, after 500 h of continuous illumination. The present strategy sheds light on surface defect passivation for achieving highly efficient all‐inorganic lead‐free Sn‐based PSCs.

Publication date: 17 February 2021

Source: Joule, Volume 5, Issue 2

Author(s): Xiaoyan Du, Larry Lüer, Thomas Heumueller, Jerrit Wagner, Christian Berger, Tobias Osterrieder, Jonas Wortmann, Stefan Langner, Uyxing Vongsaysy, Melanie Bertrand, Ning Li, Tobias Stubhan, Jens Hauch, Christoph J. Brabec

The adaptation of the two‐step deposition method is demonstrated, which enables the direct probe into the growth dynamics of perovskites using in situ diagnostics. A detailed view of the effects of solvent, lead halide film solvation, and Br incorporation and alloying on the transformation behavior is presented.

Inorganic−organic hybrid perovskites MAPb(I _x Br_1−x )₃ (0 < x < 1) hold promise for efficient multi‐junction or tandem solar cells due to tunable bandgap and improved long‐term stability. However, the phase transformation from Pb(I _x Br_1−x )₂ precursors to perovskites is not fully understood which hinders further improvement of optoelectronic properties and device performance. Here, adaptation of the two‐step deposition method, which enables the direct probe into the growth dynamics of perovskites using in situ diagnostics, and a detailed view of the effects of solvent, lead halide film solvation, and Br incorporation and alloying on the transformation behavior is presented. The in situ measurements indicate a strong tendency of lead halide solvation prior to crystallization during solution‐casting Pb(I _x Br_1−x )₂ precursor from a dimethyl sulfoxide (DMSO) solvent. Highly‐efficient intramolecular exchange is observed between DMSO molecules and organic cations, leading to room‐temperature conversion of perovskite and high‐quality films with tunable bandgap and superior optoelectronic properties in contrast to that obtained from crystalline Pb(I _x Br_1−x )₂. The improved properties translate to easily tunable and a relatively higher power conversion efficiency of 16.42% based on the mixed‐halide perovskite MAPb(I_0.9Br_0.1)₃. These findings highlight the benefits that solvation of the precursor phases, together with bromide incorporation, can have on the microstructure, morphology, and optoelectronic properties of these films.

A low‐temperature solution‐processed, annealing‐free, amorphous metal oxyhydroxide cathode interlayer is used to facilitate charge extraction and suppress interfacial charge recombination in inverted perovskite photovoltaics, delivering a power conversion efficiency of 21.3%.

The state‐of‐the‐art high‐performance perovskite solar cells (PSCs) with inverted p‐i‐n device structure normally use crystalline metal oxide materials or organic small molecules as the cathode interlayer between the fullerene layer and metal electrode. However, these interlayers are made by either high‐temperature or complicated vacuum‐assisted fabrication process, and in many cases, they are not efficient and effective enough to simultaneously extract the electrons and suppress the interfacial charge recombination. Herein, for the first time, a facile low‐temperature solution‐processed strategy is demonstrated to fabricate an amorphous metal oxyhydroxide (a‐MOH) thin film, which is used as a robust cathode interlayer in inverted PSCs. The a‐MOH interlayer not only facilitates electron extraction and collection via “energy‐favorable” electron tunneling, but also suppresses the interfacial charge recombination via effective hole blocking and electron backflow inhibition. As a result, the PSCs based on a‐MOH interlayer achieve a stabilized power conversion efficiency (PCE) of 21.1% and retain 93% of initial PCE after continuous one‐sun illumination for 500 hours.

Dimethylammonium (DMA) is incorporated in controlled, incremental amounts into the A‐site of CsPbI₃ perovskite materials. Confirming that the stabilization afforded from the DMA iodide precursors in CsPbI₃ perovskites comes from an alloy of the A‐site with an organic cation. The limit to DMA incorporation is ≈25%, making a Cs_0.75DMA_0.25PbI₃ material that is more stable than neat CsPbI₃.

All‐inorganic perovskite materials are attractive alternatives to organic–inorganic perovskites because of their potential for higher thermal stability. Although CsPbI₃ is compositionally stable under elevated temperatures, the cubic perovskite α‐phase is thermodynamically stable only at >330 °C and the low‐temperature perovskite γ‐phase is metastable and highly susceptible to non‐perovskite δ‐phase conversion in moisture. Many methods have been reported which show that the incorporation of acid (aqueous HI) or “HPbI₃”—recently shown to be dimethylammonium lead iodide (DMAPbI₃) —lowers the annealing temperature required to produce the black, perovskite phase of CsPbI₃. Herein, the optical and crystallographic data presented show that dimethylammonium (DMA) can successfully incorporate as an A‐site cation to replace Cs in the CsPbI₃ perovskite material. This describes the stabilization and lower phase transition temperature reported in the literature when HI or HPbI₃ is used as precursors for CsPbI₃. The Cs–DMA alloy only forms a pure‐phase material up to ≈25% DMA; at higher concentrations, the CsPbI₃ and DMAPbI₃ begin to phase segregate. These alloyed materials are more stable to moisture than neat CsPbI₃, but do not represent a fully inorganic perovskite material.

Thermal cross‐linking of new enamine‐based hole‐transporting materials is shown to provide an advantage in p–i–n perovskite solar cells. Due to the improved resistance to organic solvents, the cross‐linked films manage to withstand solution processing of the perovskite absorber layer. This leads to an improved open‐circuit voltage and over 18% efficiency for the devices with the V1187 material.

The development of the simple synthesis schemes of organic semiconductors can have an important contribution to the advancement of related technologies. In particular, one of the fields where the high price of the hole‐transporting materials may become an obstacle toward successful commercialization is perovskite solar cells. Herein, enamine‐based materials that are capable of undergoing cross‐linking due to the presence of two vinyl groups are synthesized. It is shown that new compounds can be thermally polymerized, making the films resistant to organic solvents. This can allow the use of a wet‐coating process for the deposition of the perovskite absorber film, without the need for orthogonal solvents. Cross‐linked films are used in perovskite solar cells, and, upon optimization of the film thickness, the highest power conversion efficiency of 18.1% is demonstrated.

Comprehensive experimental and theoretical evidence is presented to elucidate the charge carrier recombination in mesoscopic perovskite solar cells (PSC). The spatially decoupled electron and hole migration inside the nanoporous charge extraction scaffold is examined by a 2D electrical model that explains the remarkably high photovoltages achieved in hole extraction layer‐free, carbon–graphite‐based PSCs.

A physical model to explain the 2D charge recombination in mesoscopic graphite‐based perovskite solar cells (PSCs) having a highly selective front electrode and a nonselective back electrode is presented. Steady‐state photovoltage and photoluminescence (PL) as well as transient PL are studied for a wide range of device configurations, providing insights in the interface recombination at the front and back contact, namely, the mesoporous titania (m‐TiO₂) and the graphite layer. Combining experimental evidence with the first 2D simulation of a perovskite solar cell, it is found that the characteristic thick absorber layer of mesoscopic graphite‐based PSC is a necessity to enhance the photovoltage. This is because the interface recombination at the back contact is a diffusion‐limited process. The electrode spacing should, however, not be enhanced by increasing the perovskite/m‐TiO₂ thickness as this increases surface recombination losses at this interface. The study determines design rules for the optimal geometry of the mesoporous layers and helps to identify the limiting recombination pathways for an improvement of future device architectures.

A series of novel n‐doped conjugated polyelectrolytes are designed and synthesized via highly efficient aldol condensation polymerization. The designed conjugated polyelectrolytes possess an electron‐deficient and rigid conjugated backbone, resulting in easy charge delocalization, enhanced n‐doping behaviors, and high conductivity. These conjugated polyelectrolytes can be used as electron transport materials to enable high‐performance nonfullerene polymer solar cells.

Doping provides an efficient strategy to control the electronic properties of organic semiconductors. However, compared with the widely reported p‐type doping protocols, n‐type doping of organic semiconductors still remains a challenge. Herein, a series of novel n‐doped conjugated polyelectrolytes (CPEs) with high doping levels and conductivity are designed. These CPEs are synthesized via a facile, metal‐free, and high‐yield aldol condensation protocol from bis‐isatin and bis‐oxindole monomers. The designed CPEs possess a n‐type electron‐deficient and rigid conjugated backbone, resulting in easy charge delocalization, enhanced n‐doping behaviors, and high conductivity. The evolution on the counterions of these CPEs further alters their n‐doping behaviors, charge transporting properties, and work function tunability, etc. By using these CPEs as electron transport materials (ETMs) for nonfullerene polymer solar cells (NF–PSCs), high power conversion efficiencies (PCEs) over 16% can be achieved when PM6:Y6 is used as the active component. Moreover, these CPEs can enable efficient NF–PSCs even if their thicknesses are up to 60 nm, indicating the potential of these CPEs as thickness‐insensitive ETMs for the fabrication of large‐area NF–PSCs.

Quasi‐Fermi level splitting (QFLS), which sets the maximum value of the open‐circuit voltage (V _OC) of a photovoltaic device, in state‐of‐the‐art organic solar cells is evaluated using spectroscopic and semiconductor device physics approaches.

The power conversion efficiency (PCE) of state‐of‐the‐art organic solar cells is still limited by significant open‐circuit voltage (V _OC) losses, partly due to the excitonic nature of organic materials and partly due to ill‐designed architectures. Thus, quantifying different contributions of the V _OC losses is of importance to enable further improvements in the performance of organic solar cells. Herein, the spectroscopic and semiconductor device physics approaches are combined to identify and quantify losses from surface recombination and bulk recombination. Several state‐of‐the‐art systems that demonstrate different V _OC losses in their performance are presented. By evaluating the quasi‐Fermi level splitting (QFLS) and the V _OC as a function of the excitation fluence in nonfullerene‐based PM6:Y6, PM6:Y11, and fullerene‐based PPDT2FBT:PCBM devices with different architectures, the voltage losses due to different recombination processes occurring in the active layers, the transport layers, and at the interfaces are assessed. It is found that surface recombination at interfaces in the studied solar cells is negligible, and thus, suppressing the non‐radiative recombination in the active layers is the key factor to enhance the PCE of these devices. This study provides a universal tool to explain and further improve the performance of recently demonstrated high‐open‐circuit‐voltage organic solar cells.

A small molecule of 18C6 is introduced into the perovskite precursor for elongating the antisolvent dripping window from 2 to 20 s, achieving a high‐quality and reproducible perovskite film.

Although perovskite solar cells (PSCs) have exhibited a high‐power conversion efficiency, the reproducibility of high‐quality perovskite films is still a big challenge for large‐scale flexible devices. One reason is the super narrow antisolvent dripping window, the other one is the difficulty in controlling the secondary phases. Herein, 18C6 is introduced into the perovskite precursor to achieve a high‐quality and reproducible large‐scale (7 × 7 cm²) flexible perovskite film by enlarging the antisolvent dripping window from 2 to 20 s, with an average efficiency of 13.33% (best 15.80%). Moreover, from the in situ grazing‐incidence wide‐angle X‐ray scattering result, the 2H phase perovskite is highly suppressed with the additive of 18C6. The generality of the approach is also demonstrated in other antisolvents such as ethyl acetate. This finding provides an innovative solution to the realization of repeatable, large‐scale solution fabrication of PSCs.

The “double dipole step” model is used to explain the physicochemical property of the indium tin oxide (ITO)/polyvinylpyrrolidone (PVP) interface that the W _F reduction is caused by the directional intrinsic molecular dipole moments and the image dipole moments. Moreover, high‐performance inverted organic solar cells (OSCs) are achieved by introducing a self‐assembled ultrathin PVP layer using a simple immersion method.

Polyvinylpyrrolidone (PVP) has been successfully used as the cathode interfacial layer (CIL) in organic solar cells (OSCs) for work function (W _F) modification. However, detailed insight into the effect of a PVP interlayer on the physicochemical properties of the indium tin oxide (ITO) electrode in inverted OSCs (I‐OSCs) is still largely absent. Herein, the ITO/PVP interface is investigated by photoelectron spectroscopy and the mechanisms for the energy level alignment of PVP on different substrates in general are unraveled. The results indicate that the dipole formation that reduces the W _F is driven by not only the directional intrinsic molecular dipole moments associated with the γ‐lactam of PVP, but also an additional dipole step with the same direction created by the image charges in the contacting (semi‐)conductor layer. In addition, high‐performance inverted OSCs (I‐OSCs) are achieved by introducing a self‐assembled ultrathin PVP layer using a simple immersion method. This work provides enhanced understanding of the PVP‐based CIL and demonstrates its great potential in I‐OSC fabrication, which can pave the way to simplified manufacturing of low‐cost and large‐area devices in organic electronic technologies.

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 facile and efficient strategy of gradient doping is adopted for optimizing inverted CsPbI₂Br‐based perovskite solar cells (PeSCs) using a bicationic iodine salt, namely BFBAI₂, as the dopant. The doped PeSCs exhibit significantly improved photovoltaic performance and stability, which is attributed to efficient defect passivation and enhanced electric field upon the gradient doped BFBAI₂.

Cesium‐based all‐inorganic perovskites (PVKs) are prized for their high thermal stability and wide bandgap suitable for the top layer of tandem solar cells. To further boost the photovoltaic performance of inorganic PVK solar cells (PeSCs), a variety of strategies aiming to either passivate defects or enhance the electric field are developed. Nevertheless, a double‐aim strategy is less explored. Herein, a facile strategy of gradient doping is adopted for optimizing the inverted CsPbI₂Br PeSCs. Particularly, a bicationic iodine salt, namely 2,2′‐bis(trifluoromethyl)‐[1,1′‐biphenyl]‐4,4′‐diamine iodine (BFBAI₂), is used to realize gradient doping in PVK and ZnO layers, respectively. As a result, the inverted PeSCs with the doped PVK/ZnO bilayer deliver improves power conversion efficiency (PCE) up to 14.38% along with enhanced device stability under ambient or thermal aging conditions, greatly surpassing the pristine devices. The improvements are attributed principally to the low‐defect PVK layer as well as enhanced electric field across the inverted PeSCs upon gradient doping. This work thus demonstrates an efficient bifunctional strategy toward highly efficient and stable CsPbI₂Br PeSCs with inverted configuration.

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.

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.

Herein, the chemistry of tin perovskite compounds for the fabrication of high‐efficiency nontoxic solar cells is described. The reaction mechanisms among the compounds and additives present in the Sn perovskite films are discussed to correlate with the device performance.

Lead (Pb)‐based perovskite solar cells (Pb‐PSCs) have been recorded with a fascinating power conversion efficiency (PCE) of 25.5%. However, the presence of toxic Pb in the perovskite absorber material hinders the commercial aspects of Pb‐PSCs as a promising and efficient new generation of solar cells. Fortunately, theoretical calculations have predicted that tin (Sn)‐based perovskite solar cells (Sn‐PSCs) could have superior performance comparable to the Pb‐PSCs. Recently, many approaches have been reported for developing efficient Sn‐PSCs but yet they have shown the best PCE of 13.24%. This low PCE compared to Pb‐PSCs might be because Sn‐PSCs have been approached in the same way as Pb‐PSCs. However, from a chemistry viewpoint, the understanding of Sn‐PSCs might be very different from that of Pb‐based ones. Herein, the fundamental knowledge of the chemistry and coordination chemistry of Sn^II compounds and their structural properties is described. Then, an insight is provided into understanding the recent trends of Sn perovskite formation using various Lewis base additives in the precursor solution and incorporation as a cation in the perovskite lattice. Finally, the influence of utilizing Lewis base additives on the device dynamics is discussed.

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.

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.

The rise and commercialization of perovskite solar cells (PSCs) is hindered by the toxicity of lead present in the perovskites employed as the solar light absorber. To counter this problem, Pb can be fully (lead‐free) or partially (lead‐less) replaced by diverse elements. The former compounds suffer from poor efficiency and poor stability while the later appear more promising. This review offers a survey of the methods reported in the literature to reduce Pb content in PSCs to fabricate “lead‐less” (also called “lead‐deficient”) PSCs. We develop, first, the comparison of Sn and Pb elements and the partial replacement of Pb by Sn. Then, its substitution by either Ge, Sr or other alkaline‐earth‐metals, transition metals and elements from columns 12, 13 and 15 of the periodic table are detailed. The new families of perovskites based on the insertion of organic cations to replace lead and halogen units, namely the “lead‐deficient” and “hollow” halide perovskites are then presented and discussed. Finally, atypical ways to reduce the toxicity of PSCs are presented: perovskite layer thickness reduction via optimization of photon collection, integration of photonic structures and employment of recycled lead. The present achievements and the outlook of those strategies are presented and discussed.

This article is protected by copyright. All rights reserved.