Chen Weijie

The different aggregation forms of hole‐transporting materials (HTMs) affect intermolecular charge transfer and hole transporting in achieving highly efficient dopant‐free perovskite solar cells. The combination of twisted periphery groups with planar core units shows an efficient approach to regulate the state of molecular aggregation after a systematical investigation of 6,12‐dihydroindeno[1,2‐b]fluorine (IDF)‐HTMs with the same IDF core and the different periphery groups.

Abstract

Although several hole‐transporting materials (HTMs) have been designed to obtain perovskite solar cells (PSCs) devices with high performance, the dopant‐free HTMs for efficient and stable PSCs remain rare. Herein, a rigid planar 6,12‐dihydroindeno[1,2‐b]fluorine (IDF) core with different numbers of bulky periphery groups to construct dopant‐free HTMs of IDF‐SFXPh, IDF‐DiDPA, and IDF‐TeDPA is modified. Thanks to the contributions of the planar IDF core and the twisted SFX periphery groups, the dopant‐free IDF‐SFXPh‐based PSCs device achieves a device performance of 17.6%, comparable to the doped 2,2′,7,7′‐tetrakis(N,N‐di‐p‐methoxyphenylamine)‐9,9′‐spirobifluorene (spiro‐OMeTAD)‐based device (17.6%), with much enhanced device stability under glovebox and ambient conditions.

Three colors: A rational synthesis of CsPbX₃ (X=Cl, Br, and I) nanocrystals gives all three perovskites with near unity photoluminescence quantum yield. Careful analysis of the reaction chemistry and the parameters allows a generic reaction to be developed.

Abstract

In a generic synthesis approach, all three CsPbX₃ (X=Cl, Br and I) perovskite nanocrystals having near unity quantum yields is reported. This has been achieved by injecting the desired amount of preformed alkylammonium halide salts which acted as a dual source providing halide ions and the capping agent to an equimolar amount of non‐halide Pb and Cs precursors in a reaction flask at an optimized reaction temperature. The composition sensitivity of Pb to Cs ratio, high temperature reaction, and injection of ammonium halide remained the key parameters for obtaining the high quantum yields. Details of the reaction process, use of different reagents and setting up the reaction parameters are reported.

Perovskite solar cells (PSCs) have emerged as a promising candidate for photovoltaic applications. This review summarizes the recent progress and discusses the obstacles for PSCs toward industrial production, including upscaling of high‐quality perovskites for efficient PSC modules, stability issue of PSCs, Pb substitution, and greener manufacturing process, which can promote the development of PSCs toward commercialization.

Abstract

In the last few years, organometal halide perovskites (OHPs) have emerged as a promising candidate for photovoltaic (PV) applications. A certified efficiency as high as 23.7% has been achieved, which is comparable with most of the well‐established PV technologies. Their good solubility due to the ionic nature enables versatile low‐temperature solution processes, including blade coating, slot‐die coating, etc., most of which are scalable and compatible with roll‐to‐roll large‐scale manufacturing processes. The low cost, high efficiency, and facile processable features make perovskite solar cells (PSCs) a very competitive PV technology. Despite the great progress, long‐term durability concerns, toxicity issues of both materials and manufacturing process, and lack of robust high‐throughput production technology for fabricating efficient large‐area modules are major obstacles toward commercialization. In this review, the recent progress of commercially available process of PSCs is surveyed, the underlying determinants for upscaling high‐quality PSCs from hydrodynamic characteristics and crystallization thermodynamic mechanism are identified, the influence of external stress factors on stability of PSCs and intrinsic instability mechanism in OHPs themselves is revealed, and the environmental impact and sustainable development of PSC technology are analyzed. Strategies and opportunities for large‐scale production of PSCs are suggested to promote the development of PSCs toward commercialization.

High‐throughput density functional theory (DFT) methods are used to screen 1845 halide perovskite materials in search of nontoxic, stable, optimal bandgap materials with high photovoltaic efficiencies for use in single junction, quantum dot, and tandem Si‐perovskite solar cells. A total of 15 promising halide perovskite materials, including (CH₃NH₃)_0.75Cs_0.25SnI₃, ((NH₂)₂CH)Ag_0.5Sb_0.5Br₃, CsMn_0.875Fe_0.125I₃, ((CH₃)₂NH₂)Ag_0.5Bi_0.5I₃, and ((NH₂)₂CH)_0.5Rb_0.5SnI₃, are found.

Abstract

Two critical limitations of organic–inorganic lead halide perovskite materials for solar cells are their poor stability in humid environments and inclusion of toxic lead. In this study, high‐throughput density functional theory (DFT) methods are used to computationally model and screen 1845 halide perovskites in search of new materials without these limitations that are promising for solar cell applications. This study focuses on finding materials that are comprised of nontoxic elements, stable in a humid operating environment, and have an optimal bandgap for one of single junction, tandem Si‐perovskite, or quantum dot–based solar cells. Single junction materials are also screened on predicted single junction photovoltaic (PV) efficiencies exceeding 22.7%, which is the current highest reported PV efficiency for halide perovskites. Generally, these methods qualitatively reproduce the properties of known promising nontoxic halide perovskites that are either experimentally evaluated or predicted from theory. From a set of 1845 materials, 15 materials pass all screening criteria for single junction cell applications, 13 of which are not previously investigated, such as (CH₃NH₃)_0.75Cs_0.25SnI₃, ((NH₂)₂CH)Ag_0.5Sb_0.5Br₃, CsMn_0.875Fe_0.125I₃, ((CH₃)₂NH₂)Ag_0.5Bi_0.5I₃, and ((NH₂)₂CH)_0.5Rb_0.5SnI₃. These materials, together with others predicted in this study, may be promising candidate materials for stable, highly efficient, and nontoxic perovskite‐based solar cells.

Controlling the retarding reaction process enhances perovskite crystal growth, resulting in >20% efficiency. The dual retarding process enables large perovskite thin film grain size, which facilitates enhanced photovoltaic performance.

Abstract

Mixed‐cation perovskite solar cells (PSCs) have become of enormous interest because of their excellent efficiency, which is now crossing 23.7%. Their broader absorption, relatively high stability with low fabrication cost compared to conventional single phase ABX₃ perovskites (where A: organic cation; B: divalent metal ion; and X: halide anion) are key properties of mixed‐halide mixed‐cation perovskites. However, the controlling reaction rate and formation of extremely dense, textured, smooth, and large grains of perovskite layer is a crucial task in order to achieve highly efficient PSCs. Herein, a new simple dual‐retarded reaction processing (DRP) method is developed to synthesize a high‐quality mixed‐cation (FAPbI₃)_0.85(MAPbBr₃)_0.15 (where MAPbBr₃ stands for methylammonium lead bromide and FAPbI₃ stands for formamidinium lead iodide) perovskite thin film via intermediate phase and incorporation of nitrogen‐doped reduced graphene oxide (N‐rGO). The reaction rate is retarded via two steps: first the formation of intermediate phase and second the interaction of the nitrogen groups on N‐rGO with hydrogen atoms from formamidinium cations. This DRP process allows for the fabrication of PSCs with maximum conversion efficiency higher than 20.3%.

Ring fusion and backbone fluorination yield a novel ladder‐type building block f‐FBTI2, a desirable “stronger acceptor” for enabling n‐type electron‐acceptor polymers. The resulting polymer semiconductor f‐FBTI2‐T shows an excellent power conversion efficiency of 8.1% with a very small energy loss of 0.53 eV in all‐polymer solar cell devices.

Abstract

A novel imide‐functionalized arene, di(fluorothienyl)thienothiophene diimide (f‐FBTI2), featuring a fused backbone functionalized with electron‐withdrawing F atoms, is designed, and the synthetic challenges associated with highly electron‐deficient fluorinated imide are overcome. The incorporation of f‐FBTI2 into polymer affords a high‐performance n‐type semiconductor f‐FBTI2‐T, which shows a reduced bandgap and lower‐lying lowest unoccupied molecular orbital (LUMO) energy level than the polymer analog without F or with F‐functionalization on the donor moiety. These optoelectronic properties reflect the distinctive advantages of fluorination of electron‐deficient acceptors, yielding “stronger acceptors,” which are desirable for n‐type polymers. When used as a polymer acceptor in all‐polymer solar cells, an excellent power conversion efficiency of 8.1% is achieved without any solvent additive or thermal treatment, which is the highest value reported for all‐polymer solar cells except well‐studied naphthalene diimide and perylene diimide‐based n‐type polymers. In addition, the solar cells show an energy loss of 0.53 eV, the smallest value reported to date for all‐polymer solar cells with efficiency > 8%. These results demonstrate that fluorination of imide‐functionalized arenes offers an effective approach for developing new electron‐deficient building blocks with improved optoelectronic properties, and the emergence of f‐FBTI2 will change the scenario in terms of developing n‐type polymers for high‐performance all‐polymer solar cells.

An n‐doping of SnO₂ is successfully realized through the use of the triphenylphosphine‐oxide molecule, where electrons are revealed to be transferred from the R₃P⁺O⁻ σ‐bond to the peripheral tin atoms and delocalized. That novel effect enlarges the built‐in‐field from 0.01 to 0.07 eV and reduces the energy‐barrier from 0.55 to 0.39 eV at the SnO₂–perovskite interface enabling a device conversion‐efficiency from 19.01% to 20.69%.

Abstract

Molecular doping of inorganic semiconductors is a rising topic in the field of organic/inorganic hybrid electronics. However, it is difficult to find dopant molecules which simultaneously exhibit strong reducibility and stability in ambient atmosphere, which are needed for n‐type doping of oxide semiconductors. Herein, successful n‐type doping of SnO₂ is demonstrated by a simple, air‐robust, and cost‐effective triphenylphosphine oxide molecule. Strikingly, it is discovered that electrons are transferred from the R3P⁺O⁻σ‐bond to the peripheral tin atoms other than the directly interacted ones at the surface. That means those electrons are delocalized. The course is verified by multi‐photophysical characterizations. This doping effect accounts for the enhancement of conductivity and the decline of work function of SnO₂, which enlarges the built‐in field from 0.01 to 0.07 eV and decreases the energy barrier from 0.55 to 0.39 eV at the SnO₂/perovskite interface enabling an increase in the conversion efficiency of perovskite solar cells from 19.01% to 20.69%.

A novel approach to stabilize α‐CsPbI₃ perovskite through strain engineering, whereby CsPbI₃ perovskite is confined by a vertically aligned nanoporous template, is developed. By imposing a strain on the perovskite lattice, the ultrastable black α‐CsPbI₃ with its desirable optoelectrical properties is obtained. The density functional theory calculations on the formation energy confirm that the strain‐mediated phase stabilization is thermodynamically allowed.

Abstract

All‐inorganic cesium lead triiodide (CsPbI₃) perovskite is considered a promising solution‐processable semiconductor for highly stable optoelectronic and photovoltaic applications. However, despite its excellent optoelectronic properties, the phase instability of CsPbI₃ poses a critical hurdle for practical application. In this study, a novel stain‐mediated phase stabilization strategy is demonstrated to significantly enhance the phase stability of cubic α‐phase CsPbI₃. Careful control of the degree of spatial confinement induced by anodized aluminum oxide (AAO) templates with varying pore sizes leads to effective manipulation of the phase stability of α‐CsPbI₃. The Williamson–Hall method in conjunction with density functional theory calculations clearly confirms that the strain imposed on the perovskite lattice when confined in vertically aligned nanopores can alter the formation energy of the system, stabilizing α‐CsPbI₃ at room temperature. Finally, the CsPbI₃ grown inside nanoporous AAO templates exhibits exceptional phase stability over three months under ambient conditions, in which the resulting light‐emitting diode reveals a natural red color emission with very narrow bandwidth (full width at half maximum of 33 nm) at 702 nm. The universally applicable template‐based stabilization strategy can give in‐depth insights on the strain‐mediated phase transition mechanism in all‐inorganic perovskites.

A linear hole‐transporting material (HTM) based on 9,9‐dihexyl‐9H‐fluorene and N,N‐di‐p‐methylthiophenylamine (denoted as FMT) is synthesized. The p‐i‐n perovskite solar cells (pp‐PSCs) with the indium‐doped tin oxide (ITO)/FMT/CH₃NH₃PbI₃ (MAPbI₃)/PCBM/Al structure shows a high power conversion efficiency (PCE) of 19.06%. Hence, FMT is one of the simplest HTMs applied in pp‐PSCs, which shows a PCE of over 19% without dopants.

Abstract

For commercial applications, it is a challenge to find suitable and low‐cost hole‐transporting material (HTM) in perovskite solar cells (PSCs), where high efficiency spiro‐OMeTAD and PTAA are expensive. A HTM based on 9,9‐dihexyl‐9H‐fluorene and N,N‐di‐p‐methylthiophenylamine (denoted as FMT) is designed and synthesized. High‐yield FMT with a linear structure is synthesized in two steps. The dopant‐free FMT‐based planar p‐i‐n perovskite solar cells (pp‐PSCs) exhibit a high power conversion efficiency (PCE) of 19.06%, which is among the highest PCEs reported for the pp‐PSCs based on organic HTM. For comparison, a PEDOT:PSS HTM‐based pp‐PSC is fabricated under the same conditions, and its PCE is found to be 13.9%.

Publication date: June 2019

Source: Nano Energy, Volume 60

Author(s): Long Zhou, Xing Guo, Zhenhua Lin, Jing Ma, Jie Su, Zhaosheng Hu, Chunfu Zhang, Shengzhong (Frank) Liu, Jingjing Chang, Yue Hao

Graphical abstract

Low temperature processed high performance all-inorganic perovskite solar cells with MoO₃ as interfacial layer have been achieved with PCE exceeding 14% via sequential graded thermal annealing process. Moreover, the unencapsulated device exhibited enhanced operational stability under continuously simulated sunlight illumination, thermal stability and outstanding air stability after 60 days of storage under N₂ condition.

High‐quality, pinhole‐free CH₃NH₃SnI₃ films are achieved from pristine NH₂NH₃SnI₃ perovskite, and the oxidation of Sn²⁺ to Sn⁴⁺ can be efficiently suppressed owing to the reduction agent hydrazine generated inside the films in the conversion. With the CH₃NH₃SnI₃ film as light absorber, mesoporous MASnI₃ perovskite solar cells were fabricated with a maximum PCE of 7.13 %.

Abstract

Tin‐based halide perovskite materials have been successfully employed in lead‐free perovskite solar cells, but the overall power conversion efficiencies (PCEs) have been limited by the high carrier concentration from the facile oxidation of Sn²⁺ to Sn⁴⁺. Now a chemical route is developed for fabrication of high‐quality methylammonium tin iodide perovskite (MASnI₃) films: hydrazinium tin iodide (HASnI₃) perovskite film is first solution‐deposited using presursors hydrazinium iodide (HAI) and tin iodide (SnI₂), and then transformed into MASnI₃ via a cation displacement approach. With the two‐step process, a dense and uniform MASnI₃ film is obtained with large grain sizes and high crystallization. Detrimental oxidation is suppressed by the hydrazine released from the film during the transformation. With the MASnI₃ as light harvester, mesoporous perovskite solar cells were prepared, and a maximum power conversion efficiency (PCE) of 7.13 % is delivered with good reproducibility.

In this work, organic ternary solar cells based on a model system comprising the polymers PDCBT and PTB7‐Th and PC₇₀BM are presented as electron accepting units. The photophysics of this blend is governed by a fast energy transfer process from PDCBT to PTB7‐Th allowed by a favorable molecular affinity between PDCBT and PTB7‐Th.

Abstract

Ternary blends with broad spectral absorption have the potential to increase charge generation in organic solar cells but feature additional complexity due to limited intermixing and electronic mismatch. Here, a model system comprising the polymers poly[5,5‐bis(2‐butyloctyl)‐(2,2‐bithiophene)‐4,4‐dicarboxylate‐alt‐5,5‐2,2‐bithiophene] (PDCBT) and PTB7‐Th and PC₇₀BM as an electron accepting unit is presented. The power conversion efficiency (PCE) of the ternary system clearly surpasses the performance of either of the binary systems. The photophysics is governed by a fast energy transfer process from PDCBT to PTB7‐Th, followed by electron transfer at the PTB7‐Th:fullerene interface. The morphological motif in the ternary blend is characterized by polymer fibers. Based on a combination of photophysical analysis, GIWAXS measurements and calculation of the intermolecular parameter, the latter indicating a very favorable molecular affinity between PDCBT and PTB7‐Th, it is proposed that an efficient charge generation mechanism is possible because PTB7‐Th predominantly orients around PDCBT filaments, allowing energy to be effectively relayed from PDCBT to PTB7‐Th. Fullerene can be replaced by a nonfullerene acceptor without sacrifices in charge generation, achieving a PCE above 11%. These results support the idea that thermodynamic mixing and energetics of the polymer–polymer interface are critical design parameter for realizing highly efficient ternary solar cells with variable electron acceptors.

One of the problems that restrict the further development of perovskite solar cells (PSCs) is hysteresis, making it difficult to evaluate the reliable performance of PSCs. Recent process regarding the strategies to efficiently reduce hysteresis in PSCs is reviewed. The influential factors and possible reasons are also outlined.

Abstract

Organic–inorganic hybrid perovskite solar cells (PSCs) have become a promising candidate in the photovoltaic field due to their high power conversion efficiency and low material cost. However, the development of PSCs is limited by their poor stability under practical conditions in the presence of oxygen, moisture, sunlight, heat, and the current–voltage (I–V) hysteresis. In particular, the hysteretic I–V issue casts doubt on the validity of the photovoltaic performance results that are achieved, making it difficult to evaluate the authentic performance of PSCs. This review article focuses on understanding the I–V hysteresis behavior in PSCs and on exploring the possible reasons leading to this hysteresis phenomenon. The various strategies attempted to suppress the I–V hysteresis in PSCs are summarized, and a brief future recommendation is provided.

A negligible‐Pb‐waste and upscalable perovskite film processing method combining raster ultrasonic spray coating and chemical vapor deposition is developed. Perovskite solar module shows a power conversion efficiency of 14.7% on 12 cm² active area, much lower substrate size dependence than the spin‐coating method, and outstanding operational stability near the maximum power point under 1 sun illumination (T ₈₀ lifetime of 388 h).

Abstract

An upscalable perovskite film deposition method combining raster ultrasonic spray coating and chemical vapor deposition is reported. This method overcomes the coating size limitation of the existing stationary spray, single‐pass spray, and spin‐coating methods. In contrast with the spin‐coating method (>90% Pb waste), negligible Pb waste during PbI₂ deposition makes this method more environmentally friendly. Outstanding film uniformity across the entire area of 5 cm × 5 cm is confirmed by both large‐area compatible characterization methods (electroluminescence and scattered light imaging) and local characterization methods (atomic force microscopy, scanning electron microscopy, photoluminescence mapping, UV–vis, and X‐ray diffraction measurements on multiple sample locations), resulting in low solar cell performance decrease upon increasing device area. With the FAPb(I_0.85Br_0.15)₃ (FA = formamidinium) perovskite layer deposited by this method, champion solar modules show a power conversion efficiency of 14.7% on an active area of 12.0 cm² and an outstanding shelf stability (only 3.6% relative power conversion efficiency decay after 3600 h aging). Under continuous operation (1 sun light illumination, maximum power point condition, dry N₂ atmosphere with <5% relative humidity, no encapsulation), the devices show high light‐soaking stability corresponding to an average T ₈₀ lifetime of 535 h on the small‐area solar cells and 388 h on the solar module.

A linear hole‐transporting material (HTM) based on 9,9‐dihexyl‐9H‐fluorene and N,N‐di‐p‐methylthiophenylamine (denoted as FMT) is synthesized. The p‐i‐n perovskite solar cells (pp‐PSCs) with the indium‐doped tin oxide (ITO)/FMT/CH₃NH₃PbI₃ (MAPbI₃)/PCBM/Al structure shows a high power conversion efficiency (PCE) of 19.06%. Hence, FMT is one of the simplest HTMs applied in pp‐PSCs, which shows a PCE of over 19% without dopants.

Abstract

For commercial applications, it is a challenge to find suitable and low‐cost hole‐transporting material (HTM) in perovskite solar cells (PSCs), where high efficiency spiro‐OMeTAD and PTAA are expensive. A HTM based on 9,9‐dihexyl‐9H‐fluorene and N,N‐di‐p‐methylthiophenylamine (denoted as FMT) is designed and synthesized. High‐yield FMT with a linear structure is synthesized in two steps. The dopant‐free FMT‐based planar p‐i‐n perovskite solar cells (pp‐PSCs) exhibit a high power conversion efficiency (PCE) of 19.06%, which is among the highest PCEs reported for the pp‐PSCs based on organic HTM. For comparison, a PEDOT:PSS HTM‐based pp‐PSC is fabricated under the same conditions, and its PCE is found to be 13.9%.

A specific bidentate molecule, 2‐mercaptopyridine, is demonstrated to substantially enhance anchoring strength at surface of metal halide perovskites, which improves the passivation efficacy and stability synchronously relative to monodentate counterparts. The highly stable bidentate anchoring based passivation on CH₃NH₃PbI₃ not only advances power conversion efficiency from 18.35% to 20.28%, but also leads to a champion lifetime in humid air.

Abstract

Chemical passivation is an effective approach to suppress the grain surface dominated charge recombination in perovskite solar cells (PSCs). However, the passivation effect is usually labile on perovskite crystal surface since most passivating agents are weakly anchored. Here, the use of a bidentate molecule, 2‐mercaptopyridine (2‐MP), to increase anchoring strength for improving the passivation efficacy and stability synchronously is demonstrated. Compared to monodentate counterparts of pyridine and p‐toluenethiol, 2‐MP passivation on CH₃NH₃PbI₃ film results in twofold improvement of photoluminescence lifetime and remarkably enhanced tolerance to chlorobenzene washing and vacuum heating, which improve the power conversion efficiency of n–i–p planar structured PSCs from 18.35% to 20.28%, with open‐circuit voltage approaching 1.18 V. Moreover, the CH₃NH₃PbI₃ films passivated with 2‐MP exhibit unprecedented humid‐stability that they can be exposed to saturated humidity for at least 5 h, mainly due to the passivation induced surface deactivation, which renders the unencapsulated devices retaining 93% of the initial efficiency after 60 days aging in air with relative humidity of 60–70%.

Layered 2D perovskite solar cells often suffer from poor carrier transport. Herein, the authors propose a homo‐tandem structure to extract the photogenerated carriers efficiently while retaining the optical density of the absorbers. It thus improves the power conversion efficiency of resultant devices by 30% without the penalty of moisture stability.

Layered two dimensional (layered 2D) organic–inorganic metal halide perovskites have attracted tremendous interest in photovoltaics due to its acceptable materials stability, especially the moisture resistance, when compared with their three dimensional counterparts. However, the limited carrier transport capability, which originates from the insulativity of bulky organic molecules, has significantly affected the resultant device efficiency. To create a shorter carrier pathway with sufficient optical density, the homo‐tandem device structure by using layered 2D perovskite absorbers is proposed. Following this strategy, the semi‐transparent device and filter bottom cells have been investigated and optimized using the same layered 2D perovskite absorber (BA₂MA₃Pb₄I₁₃). The corresponding four‐terminal tandem device is successfully demonstrated with the champion power conversion efficiency of 14.42%, which is 30% higher than that of single BA₂MA₃Pb₄I₁₃ perovskite devices (11.02%). A stabilized efficiency of 13.57% in the optimized champion tandem device also have been achieved. These results suggest alternatives to develop layered 2D perovskite based solar cells and other optoelectronic devices.

By introducing a CsPbBr₃ cluster into a triple cation perovskite film to form an inorganic perovskite‐passivated hybrid perovskite film, ion migration is largely inhibited and defect states are greatly passivated. The open‐circuit voltage of passivated solar cells increases from 1.15 to 1.195 V. More importantly, the T ₉₀ operational stability under light soaking of the device is significantly improved to 500 h.

Abstract

Ion migration and phase segregation, in mixed‐cation/anion perovskite materials, raises a bottleneck for its stability improvement in solar cells operation. Here, the synergetic effect of electric field and illumination on the phase segregation of Cs_0.05FA_0.80MA_0.15Pb(I_0.85Br_0.15)₃ (CsFAMA) perovskite is demonstrated. CsFAMA perovskite with a CsPbBr₃‐clusters passivated structure is realized, in which CsPbBr₃‐clusters are located at the surface/interface of CsFAMA grains. This structure is realized by introducing a CsPbBr₃ colloidal solution into the CsFAMA precursor. It is found that CsPbBr₃ passivation greatly suppresses phase segregation in CsFAMA perovskite. The resultant passivated CsFAMA also exhibits a longer photoluminescence lifetime due to reduced defect state densities, produces highly efficient TiO₂‐based planar solar cells with 20.6% power conversion efficiency and 1.195 V open‐circuit voltage. The optimized devices do not suffer from a fast burn‐in degradation and retain 90% of their initial performance at maximum power under one‐sun illumination at 25 °C (65 °C) exceeding 500 h (100 h) of continuous operation. This result represents the most stable output among CsFAMA solar cells in a planar structure with Spiro‐OMeTAD.

A 1D ultrabroadband (>450 nm) optical cavity is designed following an inverse electromagnetic computational approach to optimally trap light in a thin film absorber layer. When this novel cavity concept is applied to a low bandgap organic solar cell, a broadband absorption enhancement is demonstrated beyond the conventional limit resulting from light trapping in an ergodic optical geometry.

Abstract

In the subwavelength regime, several nanophotonic configurations have been proposed to overcome the conventional light trapping or light absorption enhancement limit in solar cells also known as the Yablonovitch limit. It has been recently suggested that establishing such limit should rely on computational inverse electromagnetic design instead of the traditional approach combining intuition and a priori known physical effect. In the present work, by applying an inverse full wave vector electromagnetic computational approach, a 1D nanostructured optical cavity with a new resonance configuration is designed that provides an ultrabroadband (≈450 nm) light absorption enhancement when applied to a 107 nm thick active layer organic solar cell based on a low‐bandgap (1.32 eV) nonfullerene acceptor. It is demonstrated computationally and experimentally that the absorption enhancement provided by such a cavity surpasses the conventional limit resulting from an ergodic optical geometry by a 7% average over a 450 nm band and by more than 20% in the NIR. In such a cavity configuration the solar cells exhibit a maximum power conversion efficiency above 14%, corresponding to the highest ever measured for devices based on the specific nonfullerene acceptor used.

Recent progress in antimony chalcogenide‐based photovoltaic materials and devices including Sb₂S₃ solar cells, Sb₂Se₃ solar cells, and Sb₂(S _x Se_1−x)₃ solar cells is comprehensively reviewed. The fundamental properties and preparation techniques of antimony chalcogenides are discussed. The achievements and challenges in antimony chalcogenide solar cells are highlighted. In addition, the outlook for future research in this field is provided.

Antimony chalcogenides such as Sb₂S₃, Sb₂Se₃, and Sb₂(S_xSe_1−x)₃ have emerged as very promising alternative solar absorber materials due to their high stability, abundant elemental storage, nontoxicity, low‐cost, suitable tunable bandgap, and high absorption coefficient. Remarkable achievements have been made in antimony chalcogenide solar cells in the past few decades, with the power conversion efficiency (PCE) currently reaching 9.2%, which is close to the PCE level required for industrial applications. To facilitate the realization of highly efficient antimony chalcogenide solar cells in the future, a comprehensive review of antimony chalcogenide‐based materials and photovoltaic devices is presented. First, the fundamental physical properties and preparation methods of antimony chalcogenide‐based materials are outlined, and then, notable recent developments in antimony chalcogenide‐based photovoltaic devices with various architectures are highlighted. Finally, the most prominent limitations are described, and approaches to achieving remarkable advances in antimony chalcogenide solar cells in the future are provided.