Chen Weijie

Polycrystalline FAPbI₃ and monocrystalline MAPbBr₃ are synthesized from low‐grade purity commercial products (FAI, PbI₂, MABr, and PbBr₂). The crystal powder‐derived precursor (CP) and commercial products‐derived typical precursor (TP) are used to fabricate planar inverted (FAPbI₃)_0.85(MAPbBr₃)_0.15 perovskite solar cells. CP devices yield a champion power conversion efficiency of 20.5%, which is higher than TP of 16.7%.

Solution‐processed perovskite precursors, especially for MAPbBr₃‐assisted FAPbI₃ crystallization, has been noted to achieve high power conversion efficiency (PCE) for perovskite solar cells (PSCs). However, this low‐temperature processed (FAPbI₃) _x (MAPbBr₃)_1−x typical precursor derived from commercial products (FAI, PbI₂, MABr, and PbBr₂) suffers from environmental sensitivity, poor film crystallinity and less than ideal device reproducibility. Herein, (FAPbI₃) _x (MAPbBr₃)_1–x (0.80 ≤ x  ≤ 0.90)‐based planar inverted PSCs are fabricated, employing grinded monocrystalline MAPbBr₃ and powdered polycrystalline FAPbI₃ as precursors. The champion device with optimal molar ratio x  = 0.85 comprising highly crystalline larger‐grained perovskite film with enhanced carrier transport kinetics and reduced trap‐state density exhibits boosted efficiency reaching 20.50%, which shows a 22.90% improvement over typical precursors with a PCE of 16.68%. In addition, the crystal powder precursor yields obvious film stability under ambient conditions (23 °C, 65–85% humidity) for 150 days and improved device storage stability in the glove box within two months. This protocol using stock crystal powders for perovskite precursor formulation provides a relatively facile and reproducible device fabrication route for the commercialization of PSCs.

A power conversion efficiency of 16.88% (certified as 16.4%) is achieved based on PM6:Y6 by morphology optimization, which is the most efficient for organic solar cells. Through the study of single structure and film morphology, a well‐ordered 2D crystal is found, which helps to enhance ultrafast hole and electron transfer, thus improving performance.

Abstract

Single‐layered organic solar cells (OSCs) using nonfullerene acceptors have reached 16% efficiency. Such a breakthrough has inspired new sparks for the development of the next generation of OSC materials. In addition to the optimization of electronic structure, it is important to investigate the essential solid‐state structure that guides the high efficiency of bulk heterojunction blends, which provides insight in understanding how to pair an efficient donor–acceptor mixture and refine film morphology. In this study, a thorough analysis is executed to reveal morphology details, and the results demonstrate that Y6 can form a unique 2D packing with a polymer‐like conjugated backbone oriented normal to the substrate, controlled by the processing solvent and thermal annealing conditions. Such morphology provides improved carrier transport and ultrafast hole and electron transfer, leading to improved device performance, and the best optimized device shows a power conversion efficiency of 16.88% (16.4% certified). This work reveals the importance of film morphology and the mechanism by which it affects device performance. A full set of analytical methods and processing conditions are executed to achieve high efficiency solar cells from materials design to device optimization, which will be useful in future OSC technology development.

A series of feasible approaches to stabilizing the black phases (α, β, γ) are summarized, including 1) partial substitution with small monovalent ions, 2) partial substitution of Pb²⁺ (B‐site cation) with different metal ions, 3) the construction of 2D/3D mixture, and 4) smaller X‐site ions incorporation. Moreover, the origin of phase segregation is discussed.

Abstract

Organic–inorganic hybrid perovskite solar cells (PSCs) have demonstrated high efficiency and improved stability, which shows promising potential for commercialization. However, among all challenges, the material and device instability of the methylammonium lead iodide (MAPbI₃) absorber are regarded as serious obstacles to the future development of devices for long‐term operation. Compared with conventional MAPbI₃, formamidinium lead iodide (FAPbI₃) and cesium lead iodide (CsPbI₃) have attracted more attention due to their superior thermal stability. Due to their undesirable tolerant factor, however, these materials suffer from poor phase stability, which is worthy of careful investigation. This perspective highlights the recent progress on the phase stabilization of FAPbI₃ and inorganic CsPbI₃ materials with emphasis on the fundamental understanding of the origin of phase instability. In addition, strategies to fabricate corresponding devices toward high‐efficiency and long‐lifetime are discussed. This review sheds light onto the design and synthesis of FAPbI₃ and inorganic CsPbI₃ perovskite materials. In the end, the potential of FAPbI₃ and inorganic CsPbI₃ perovskite materials as stable absorbers is discussed, which promotes the development of corresponding solar cells and other optoelectronic devices for practical applications.

A fused‐ring electron acceptor (F10IC2) with solubilizing alkoxy side chains is designed and synthesized, and as‐cast blade‐coated organic solar cells based on PTB7‐Th: F10IC2 blended films are fabricated from chlorobenzene or chlorine‐free o‐xylene as solvents in air without any post‐treatment deliver a PCE of 12.5% and 11.4%, respectively.

The rapid development of organic solar cells (OSCs) based on nonfullerene acceptors has achieved significant breakthroughs in the power conversion efficiency (PCE) of spin‐coated devices. However, the spin‐coating method in a protective atmosphere seems unsuitable for the practical printing of high‐performance solar panels. In addition, the use of highly toxic solvents is also a stumbling block to the commercial application of OSCs. Thus, photoactive materials for scalable coating and ecofriendly manufacturing approaches are necessary to be developed for OSCs. Herein, a fused‐ring electron acceptor named F10IC2 bearing a decacycle core and solubilizing alkoxyl side chains is synthesized and applied in as‐cast blade‐coated OSCs by blending with polymer donor PTB7‐Th. As‐cast OSCs based on PTB7‐Th: F10IC2 blended films fabricated from chlorobenzene or chlorine‐free o‐xylene solvents in air without any posttreatment deliver a PCE of 12.5% and 11.4%, respectively, which are among the highest values reported for as‐cast blade‐coated OSCs. Herein, a strategy of alkoxyl solubilizing to design high‐performance material systems for ecofriendly scalable OSCs is provided, which is suitable for future industrial production.

Low‐temperature‐processed Zr/F co‐doped SnO₂ is an excellent successor of electron transport layers (ETLs) for high‐efficiency planar perovskite solar cells. Benefiting from an accurate energy level match and enhanced ETL conductivity, the photoelectric conversion efficiency, and hysteresis effect are obviously improved.

The energy band position and conductivity of electron transport layers (ETLs) are essential factors that restrict the efficiency of planar perovskite solar cells (p‐PSCs). Tin oxide (SnO₂) has become a primary material in ETLs due to its mild synthesis condition, but its low conduction band position and limited intrinsic carriers are disadvantageous in electron transport. To solve these problems, this work exquisitely designs a Zr/F co‐doped SnO₂ ETL. The doping of Zr can raise the conduction band of SnO₂, which reduces the energy barrier in electron extraction and inhibits the interface recombination between the ETL and perovskite. The open‐circuit voltage (V _OC) of p‐PSCs consequently increases. F⁻ doping belongs to n‐type doping. Thus, it equips SnO₂ with a large number of free electrons and improves the conductivity of the ETL and short‐circuit current (J _SC). The device based on Zr/F co‐doped ETL achieves a high efficiency of 19.19% and exhibits a reduced hysteresis effect, which is more satisfactory than that of a pristine device (17.35%). Overall, this research successfully adjusts the energy band match and boosts the conductivity of ETL via Zr/F co‐doping. The results provide an effective strategy for fabricating high‐efficiency p‐PSCs.

Ligands around inorganic perovskite nanocrystals (PNCs) play a critical role in improving the PNCs‐based solar cell performance. Herein, a facile hexane/ethyl acetate solvent treatment method to manage the ligand amount around PNCs is reported. Finally, a power conversion efficiency of 12.2%, which is the highest performance reported for mixed‐halide CsPbX₃ NCs solar cells, is achieved.

CsPbX₃ (X = Cl, Br, I) inorganic perovskite nanocrystals (PNCs) not only maintain the excellent optical and electronic properties of bulk material but also possess the features of nano‐materials, such as tunable bandgap and easily processable colloidal ink, and enable them to be suitable for incorporation into various electronic devices and compatible with printing techniques. In contrast to the traditional II‐VI and III‐V semiconductor nanocrystals, the unique defect‐tolerance effect makes the CsPbX₃ PNCs promising materials for optoelectronic applications. The ligands around the PNCs play a critical role in the optoelectronic devices performance. Herein, through a facile hexane/ethyl acetate (MeOAc) solvent treatment method to control the ligand amount around CsPbBrI₂ PNCs, the impact of ligand amount on the performance of solar cell is systematically demonstrated and the ligand amount is quantified precisely via the nuclear magnetic resonance internal standard method. Through controlling the ligand amount, the film quality, charge transfer, and transport properties are largely improved. In addition, a simple annealing process is applied to improve the interface properties by partial crystal fusion. As a consequence, the photovoltaic power conversion efficiency of 12.2% is achieved, which is the highest performance reported for mixed‐halide CsPbX₃ PNCs solar cells.

Tin fluoride and methylammonium iodide are employed as precursors for the fabrication of methylammonium tin iodide (MASnI₃) film via an ion exchange/insertion reactions approach, and a highly uniform, pinhole‐free perovskite film is obtained with a high concentration of SnF₂ and a low content of Sn⁴⁺. The corresponding solar cell exhibits the highest power conversion efficiency of 7.78% with high reproducibility and stability.

Abstract

The low toxicity, narrow bandgaps, and high charge‐carrier mobilities make tin perovskites the most promising light absorbers for low‐cost perovskite solar cells (PSCs). However, the development of the Sn‐based PSCs is seriously hampered by the critical issues of poor stability and low power conversion efficiency (PCE) due to the facile oxidation of Sn²⁺ to Sn⁴⁺ and poor film formability of the perovskite films. Herein, a synthetic strategy is developed for the fabrication of methylammonium tin iodide (MASnI₃) film via ion exchange/insertion reactions between solid‐state SnF₂ and gaseous methylammonium iodide. In this way, the nucleation and crystallization of MASnI₃ can be well controlled, and a highly uniform pinhole‐free MASnI₃ perovskite film is obtained. More importantly, the detrimental oxidation can be effectively suppressed in the resulting MASnI₃ film due to the presence of a large amount of remaining SnF₂. This high‐quality perovskite film enables the realization of a PCE of 7.78%, which is among the highest values reported for the MASnI₃‐based solar cells. Moreover, the MASnI₃ solar cells exhibit high reproducibility and good stability. This method provides new opportunities for the fabrication of low‐cost and lead‐free tin‐based halide perovskite solar cells.

A strategy is demonstrated for efficacious regulation of perovskite crystallinity using glycolic acid (GA) against nonvolatile thioglycolic acid (TGA) following dimethyl sulfoxide sublimation, resulting in enhanced device performance. A champion power conversion efficiency as high as 21.32% is achieved for the GA‐based device, which is almost 13% or 20% higher than those of the control device or TGA‐based device.

Abstract

A strategy for efficaciously regulating perovskite crystallinity is proposed by using a volatile solid glycolic acid (HOCH₂COOH, GA) in an FA_0.85MA_0.15PbI₃ (FA: HC(NH₂)₂; MA: CH₃NH₃) perovskite precursor solution that is different from the common additive approach. Accompanied with the first dimethyl sulfoxide sublimation process, the subsequent sublimation of GA before 150 °C in the FA_0.85MA_0.15PbI₃ perovskite film can artfully regulate the perovskite crystallinity without any residual after annealing. The improved film formation upon GA modification induced by the strong interaction between GA and Pb²⁺ delivers a champion power conversion efficiency (PCE) as high as 21.32%. In order to investigate the role of volatility in perovskite solar cells (PSCs), nonvolatile thioglycolic acid (HSCH₂COOH, TGA) with a similar structure to GA is utilized as an additive reference. Large perovskite grains are obtained by TGA modification but with obvious pinholes, which directly leads to an increased defect density accompanied by a decline in PCE. Encouragingly, the champion PCE achieved for GA‐based PSC device (21.32%) is almost 13% or 20% higher than those of the control device or TGA‐based device. In addition, GA‐modified PSCs exhibit the best stability in light‐, thermal‐, and humidity‐based tests due to the improved film formation.

Tin fluoride and methylammonium iodide are employed as precursors for the fabrication of methylammonium tin iodide (MASnI₃) film via an ion exchange/insertion reactions approach, and a highly uniform, pinhole‐free perovskite film is obtained with a high concentration of SnF₂ and a low content of Sn⁴⁺. The corresponding solar cell exhibits the highest power conversion efficiency of 7.78% with high reproducibility and stability.

Abstract

The low toxicity, narrow bandgaps, and high charge‐carrier mobilities make tin perovskites the most promising light absorbers for low‐cost perovskite solar cells (PSCs). However, the development of the Sn‐based PSCs is seriously hampered by the critical issues of poor stability and low power conversion efficiency (PCE) due to the facile oxidation of Sn²⁺ to Sn⁴⁺ and poor film formability of the perovskite films. Herein, a synthetic strategy is developed for the fabrication of methylammonium tin iodide (MASnI₃) film via ion exchange/insertion reactions between solid‐state SnF₂ and gaseous methylammonium iodide. In this way, the nucleation and crystallization of MASnI₃ can be well controlled, and a highly uniform pinhole‐free MASnI₃ perovskite film is obtained. More importantly, the detrimental oxidation can be effectively suppressed in the resulting MASnI₃ film due to the presence of a large amount of remaining SnF₂. This high‐quality perovskite film enables the realization of a PCE of 7.78%, which is among the highest values reported for the MASnI₃‐based solar cells. Moreover, the MASnI₃ solar cells exhibit high reproducibility and good stability. This method provides new opportunities for the fabrication of low‐cost and lead‐free tin‐based halide perovskite solar cells.

This work mainly focuses on materials composition and working mechanism of the hydroiodic acid (HI) hydrolysis‐derived intermediate compound DMAI/DMAPbI _x . Importantly, the main component of the CsPbI₃ film prepared by such precursor is proved to be still inorganic. Finally, the optimized CsPbI₃ film–based device shows significantly enhanced stability in ambient environment with a high power conversion efficiency of 17.32%.

Abstract

Introducing hydroiodic acid (HI) as a hydrolysis‐derived precursor of the intermediate compounds has become an increasingly important issue for fabricating high quality and stable CsPbI₃ perovskite solar cells (PSCs). However, the materials composition of the intermediate compounds and their effects on the device performance remain unclear. Here, a series of high‐quality intermediate compounds are prepared and it is shown that they consist of DMAI/DMAPbI _x . Further characterization of the products show that the main component of this system is still CsPbI₃. Most of the dimethylammonium (DMA⁺) organic component is lost during annealing. Only an ultrasmall amount of DMA⁺ is doped into the CsPbI₃ and its structure is stabilized. Meanwhile, excessive DMA⁺ forms Lewis acid–base adducts and interactions with Pb²⁺ on the CsPbI₃ surface. This process passivates the CsPbI₃ film and decreases the recombination rate. Finally, CsPbI₃ film is fabricated with high crystalline, uniform morphology, and excellent stability. Its corresponding PSC exhibits stable property and improved power conversion efficiency (PCE) up to 17.3%.

A universal and stable photovoltaic cell based on Cs_0.05MA_0.95PbBr _x I_{3− x} perovskite and Nb:TiO₂ electron transport layer is reported to harvest artificial light by a synergetic manipulating strategy. Morphology, composition, and energy band engineering produce a remarkable power conversion efficiency of 36.3%. Diverse practical applications are successfully demonstrated by the online driving of a sodium‐ion battery and electronic devices.

Abstract

As the fastest developing photovoltaic device, perovskite solar cells have achieved an extraordinary power conversion efficiency (PCE) of 25.3% under AM 1.5 illumination. However, few studies have been devoted to perovskite solar cells harvesting artificial light, owing to the great challenge in the simultaneous manipulation of bandgap‐adjustable perovskite materials, corresponding matched energy band structure of carrier transport materials, and interfacial defects. Herein, through systematic morphology, composition, and energy band engineering, high‐quality Cs_0.05MA_0.95PbBr _x I_{3− x} perovskite as the light absorber and Nb _y Ti_{1− y} O₂ (Nb:TiO₂) as the electron transport material with an ideal energy band alignment are obtained simultaneously. The theoretical‐limit‐approaching record PCEs of 36.3% (average: 34.0 ± 1.2%) under light‐emitting diode (LED, warm white) and 33.2% under fluorescent lamp (cold white) are achieved simultaneously, as well as a PCE of 19.5% (average: 18.9 ± 0.3%) under solar illumination. An integrated energy conversion and storage system based on an artificial light response solar cell and sodium‐ion battery is established for diverse practical applications, including a portable calculator, quartz clock, and even environmental monitoring equipment. Over a week of stable operation shows its great practical potential and provides a new avenue to promote the commercialization of perovskite photovoltaic devices via integration with ingenious electronic devices.

Self‐crystallized multifunctional 2D perovskite (M2P) is formed on top of a 3D perovskite light absorber. The M2P layer performs as a hole‐transfer facilitator and a surface‐trap passivator in perovskite solar cells (PSCs). PSCs using the developed 3D/2D perovskites achieve a power conversion efficiency of 20.79% with highly improved long‐term stability compared to devices without M2P.

Abstract

Recently, perovskite solar cells (PSC) with high power‐conversion efficiency (PCE) and long‐term stability have been achieved by employing 2D perovskite layers on 3D perovskite light absorbers. However, in‐depth studies on the material and the interface between the two perovskite layers are still required to understand the role of the 2D perovskite in PSCs. Self‐crystallization of 2D perovskite is successfully induced by deposition of benzyl ammonium iodide (BnAI) on top of a 3D perovskite light absorber. The self‐crystallized 2D perovskite can perform a multifunctional role in facilitating hole transfer, owing to its random crystalline orientation and passivating traps in the 3D perovskite. The use of the multifunctional 2D perovskite (M2P) leads to improvement in PCE and long‐term stability of PSCs both with and without organic hole transporting material (HTM), 2,2′,7,7′‐tetrakis‐(N,N‐di‐p‐methoxyphenyl‐amine)‐9,9′‐spirobifluorene (spiro‐OMeTAD) compared to the devices without the M2P.

Two hepta‐ring and octa‐ring asymmetric small molecular acceptors IDTP‐4F and IDTTP‐4F are synthesized. S‐shape IDTP‐4F‐based polymer solar cells perform better than their counterparts based on C‐shape IDTTP‐4F, regardless of the polymer donors. The champion efficiency afforded by PM7: IDTP‐4F is as high as 15.2%.

Abstract

The prosperous period of polymer solar cells (PSCs) has witnessed great progress in molecule design methods to promote power conversion efficiency (PCE). Designing asymmetric structures has been proved effective in tuning energy level and morphology, which has drawn strong attention from the PSC community. Two hepta‐ring and octa‐ring asymmetric small molecular acceptors (SMAs) (IDTP‐4F and IDTTP‐4F) with S‐shape and C‐shape confirmations are developed to study the relationship between conformation shapes and PSC efficiencies. The similarity of absorption and energy levels between two SMAs makes the conformation a single variable. Additionally, three wide‐bandgap polymer donors (PM6, S1, and PM7) are chosen to prove the universality of the relationship between conformation and photovoltaic performance. Consequently, the champion PCE afforded by PM7: IDTP‐4F is as high as 15.2% while that of PM7: IDTTP‐4F is 13.8%. Moreover, the S‐shape IDTP‐4F performs obviously better than their IDTTP‐4F counterparts in PSCs regardless of the polymer donors, which confirms that S‐shape conformation performs better than the C‐shape one. This work provides an insight into how conformations of asymmetric SMAs affect PCEs, specific functions of utilizing different polymer donors to finely tune the active‐layer morphology and another possibility to reach an excellent PCE over 15%.

Light transmission is largely decoupled from harvesting by optically tailoring an organic cell architecture with 50% average visible transmission. In an outdoor measurement of vertically positioned devices, a 9.80% sunlight energy conversion into electricity during 1 day is demonstrated.

Abstract

For many years, it has been recognized that potential organic photovoltaic cells must be integrated into elements requiring high transparency. In most of such elements, sunlight is likely to be incident at large angles. Here it is demonstrated that light transmission can be largely decoupled from harvesting by optically tailoring an infrared shifted nonfullerene acceptor based organic cell architecture. A 9.67% power conversion efficiency at 50° incidence is achieved together with an average visual transmission above 50% at normal incidence. The deconstruction of a 1D nanophotonic structure is implemented to conclude that just two λ/4 thick layers are essential to reach, for a wide incidence angle range, a higher than 50% efficiency increase relative to the standard configuration reference. In an outdoor measurement of vertically positioned 50% visible transparent cells, it is demonstrated that 9.80% of sunlight energy can be converted into electricity during the course of 1 day.

A method is introduced to experimentally measure the efficiency potential of any neat perovskite film on glass with/without attached transport layers using intensity‐dependent photoluminescence measurements. This approach allows decoupling efficiency losses due to insufficient charge transport, bulk, interface, and surface recombination. These findings also shine light on the ideality factor in perovskite solar cells and thereby fill factor limitations.

Abstract

Perovskite photovoltaic (PV) cells have demonstrated power conversion efficiencies (PCE) that are close to those of monocrystalline silicon cells; however, in contrast to silicon PV, perovskites are not limited by Auger recombination under 1‐sun illumination. Nevertheless, compared to GaAs and monocrystalline silicon PV, perovskite cells have significantly lower fill factors due to a combination of resistive and non‐radiative recombination losses. This necessitates a deeper understanding of the underlying loss mechanisms and in particular the ideality factor of the cell. By measuring the intensity dependence of the external open‐circuit voltage and the internal quasi‐Fermi level splitting (QFLS), the transport resistance‐free efficiency of the complete cell as well as the efficiency potential of any neat perovskite film with or without attached transport layers are quantified. Moreover, intensity‐dependent QFLS measurements on different perovskite compositions allows for disentangling of the impact of the interfaces and the perovskite surface on the non‐radiative fill factor and open‐circuit voltage loss. It is found that potassium‐passivated triple cation perovskite films stand out by their exceptionally high implied PCEs > 28%, which could be achieved with ideal transport layers. Finally, strategies are presented to reduce both the ideality factor and transport losses to push the efficiency to the thermodynamic limit.

A 2D/3D layered heterostructure with 2D perovskites self‐assembled atop 3D MAPbI₃ via a one‐step printing process is reported. The 2D perovskite capping layer significantly suppresses nonradiative recombination of the devices, leading to a remarkably high open‐circuit voltage of 1.2 V. Moreover, notable enhancement in light, thermal, and moisture stability is obtained as a result of the protective barrier of 2D perovskites.

Abstract

As perovskite solar cells (PSCs) are highly efficient, demonstration of high‐performance printed devices becomes important. 2D/3D heterostructures have recently emerged as an attractive way to relieving the film inhomogeneity and instability in perovskite devices. In this work, a 2D/3D ensemble with 2D perovskites self‐assembled atop 3D methylammonium lead triiodide (MAPbI₃) via a one‐step printing process is shown. A clean and flat interface is observed in the 2D/3D bilayer heterostructure for the first time. The 2D perovskite capping layer significantly suppresses nonradiative charge recombination, resulting in a marked increase in open‐circuit voltage (V _OC) of the devices by up to 100 mV. An ultrahigh V _OC of 1.20 V is achieved for MAPbI₃ PSCs, corresponding to 91% of the Shockley–Queisser limit. Moreover, notable enhancement in light, thermal, and moisture stability is obtained as a result of the protective barrier of the 2D perovskites. These results suggest a viable approach for scalable fabrication of highly efficient perovskite solar cells with enhanced environmental stability.