JIALINGBO

A Lewis acid tris(pentafluorophenyl)borane and nonhygroscopic lithium salt (LiClO₄) codoping strategy is introduced to tailor C₆₀ and fabricate highly efficient inorganic CsPbI₂Br perovskite solar cells with reduced hysteresis. Consequently, square‐centimeter inorganic CsPbI₂Br perovskite solar cells yield a record power conversion efficiency (PCE) of 14.44%. In addition, the first inorganic perovskite solar module with an efficiency exceeding 12% is reported, using a self‐developed quasi‐curved heating method.

Abstract

Although inorganic perovskite solar cells (PSCs) are promising in thermal stability, their large open‐circuit voltage (V _OC) deficit and difficulty in large‐area preparation still limit their development toward commercialization. The present work tailors C₆₀ via a codoping strategy to construct an efficient electron‐transporting layer (ETL), leading to a significant improvement in V _OC of the inverted inorganic CsPbI₂Br PSC. Specifically, tris(pentafluorophenyl)borane (TPFPB) is introduced as a dopant to lower the lowest unoccupied molecular orbital (LUMO) level of the C₆₀ layer by forming a Lewis acidic adduct. The enlarged free energy difference provides a favorable enhancement in electron injection and thereby reduces charge recombination. Subsequently, a nonhygroscopic lithium salt (LiClO₄) is added to increase electron mobility and conductivity of the film, leading to a reduction in the device hysteresis and facilitating the fabrication of a large‐area device. Finally, the as‐optimized inorganic CsPbI₂Br PSCs gain a champion power conversion efficiency (PCE) of 15.19%, with a stabilized power output (SPO) of 14.21% (0.09 cm²). More importantly, this work also demonstrates a record PCE of 14.44% for large‐area inorganic CsPbI₂Br PSCs (1.0 cm²) and reports the first inorganic perovskite solar module with the excellent efficiency exceeding 12% (10.92 cm²) by a self‐developed quasi‐curved heating method.

Conductive atomic force microscopy can realize a real‐space visualization of topography coupled with electronic properties on the microscopic scale and thereby demonstrates a unique ability to probe local effects of perovskite materials and devices. This manuscript comprehensively reviews the applications in perovskite solar cells for electronic transport behavior, ion migration and hysteresis, ferroelectric polarization, and facet orientation investigation.

Abstract

Metal halide perovskite materials, benefiting from a combination of outstanding optoelectronic properties and low‐cost solution‐preparation processes, show tremendous potential for optoelectronics and photovoltaics. However, the nanoscale inhomogeneities of the electronic properties of perovskite materials cause a number of difficulties, such as recombination, stability, and hysteresis, all of which seriously restrict device performance. Scanning probe microscopy, as a high‐resolution imaging technique, has been widely used to connect local properties and micro‐area morphologies to overall device performance. Conductive atomic force microscopy (C‐AFM) can realize a real‐space visualization of topography coupled with optoelectronic properties on a microscopic scale and thereby is uniquely suited to probe the local effects of perovskite materials and devices. The fundamental principles, alternative operation modes, and development of C‐AFM are comprehensively reviewed, and applications in perovskite solar cells (PSCs) for electronic transport behavior, ion migration and hysteresis, ferroelectric polarization, and facet orientation investigation are discussed. A comprehensive understanding and summary of up‐to‐date applications in PSCs is beneficial to further fully exploit the potential of such an emerging technique, so as to provide a novel and effective approach for perovskite materials analysis.

A comparative investigation of single‐donor component and different donor:acceptor blend ratio‐based organic solar cells (OSCs) is conducted using BTID‐0F as the donor and PC₇₁BM as the acceptor. The highest PCEs of 1.61% for single‐donor and 8.47% for BTID‐0F:PC₇₁BM‐based OSCs are obtained. Herein, the mechanism of charge generation in organic materials, thus obtaining high‐efficient single‐component OSCs, is analyzed.

Organic solar cells (OSCs) require a bulk heterojunction of a donor and an acceptor for efficient charge generation, whereas other types of solar cells normally use the p‐i‐n device structure. Herein, a comparative investigation of the p‐i‐n‐structured OSCs is conducted based on single‐donor‐component BTID‐0F and the bulkheterojuction OSCs with different donor:acceptor blend ratios using BTID‐0F as the donor and PC₇₁BM as the acceptor. The highest power conversion efficiency (PCE) of 1.61% is obtained for single‐donor‐based OSCs. The impact of PC₇₁BM weight ratio in BTID‐0F:PC₇₁BM‐based OSCs upon blend morphology, material energetics, photogenerated charge dynamic process, and photovoltaic device performance is investigated, and the highest PCE reaches 8.47%. Results indicate that even when the acceptor sites are highly diluted and the acceptor phase is discontinuous, electron transport can occur with a reasonable electron mobility. The PCE of 1.61% is the highest PCE reported for p‐i‐n structure OSCs based on a single‐donor component, which is helpful to understand the mechanism of charge generation in organic materials and thus obtainhigh‐efficient OSCs using the p‐i‐n structure.

Highly efficient mixed‐halide perovskite light‐emitting diodes with an external quantum efficiency over 20% are achieved through dual passivation of both lead and halide defects. A bi‐functional additive, 4‐fluorophenylmethylammonium‐trifluoroacetate, is designed to simultaneously passivate both lead and halide defects. Benefitting from the dual passivation effect, the phase segregation and device hysteresis are suppressed, and the stability is greatly improved.

Abstract

Solution‐processed metal halide perovskites (MHPs) have attracted much attention for applications in light‐emitting diodes (LEDs) due to their wide color gamut, high color purity, tunable emission wavelength, balanced electron/hole transportation, etc. Although MHPs are very tolerant to defects, the defects in solution‐processed perovskite LEDs (PeLEDs) still cause severe nonradiative recombination and device instability. Here, molecular design of additives for dual passivation of both lead and halide defects in perovskites is reported. A bi‐functional additive, 4‐fluorophenylmethylammonium‐trifluoroacetate (FPMATFA), is synthesized by using a simple solution process. The TFA anions and FPMA cations can bond with undercoordinated lead and halide ions, respectively, resulting in dual passivation of both lead and halide defects. In addition, the bulky FPMA group can constrain the grain growth of 3D perovskite, enhancing electron–hole capture rates and radiative recombination rates. As a result, high‐performance PeLEDs with a peak external quantum efficiency reaching 20.9% and emission wavelength at 694 nm are achieved using formamidinium‐cesium lead iodide‐bromide (FA_0.33Cs_0.67Pb(I_0.7Br_0.3)₃). Furthermore, the operational lifetime of PeLEDs is also greatly improved due to the low trap density in the perovskite film.

Two hydroxyl‐functionalized nonfullerene acceptors, IT‐OH and IT‐DOH, are synthesized, showing improved molecular arrangements and crystallinity compared to the parent ITIC molecule. This is attributed to intermolecular hydrogen bonds elongating conjugated planes and thus leading to long‐range‐ordered structures via π–π stacking. A best efficiency of 12.5% is achieved from the IT‐DOH‐based nonannealed solar cell with good device stability.

Abstract

Various substituents have been incorporated into nonfullerene acceptors (NFAs) to modulate absorption scopes and energy levels for boosting efficiencies of organic solar cells (OSCs). The manipulation of the NFAs' molecular order and crystallinity via those substitutions is equally crucial to OSC performances, which yet remains interesting and challenging. The hydroxyl group, which can potentially form strong intermolecular hydrogen bonds (H‐bonds) for improving molecular arrangements, has, however, never been considered. Herein, two hydroxyl‐functionalized NFAs, IT‐OH with one hydroxyl and IT‐DOH with two hydroxyls, are synthesized to tune the molecular packing and crystallinity. The ordered molecular arrangement and higher crystallinity are observed for the IT‐OH and IT‐DOH than the parent ITIC. This is assigned to the formation of intermolecular H‐bonds induced by the hydroxyls, which elongates molecular conjugated planes leading to long‐range‐ordered structures via π–π stacking. By the appropriate crystallinity and miscibility with donor polymer, an IT‐DOH‐based nonannealed OSC affords an efficiency of 12.5% with good device stability. This work provides a promising strategy to tune the molecular packing and crystallinity to design NFAs by introducing hydroxyl groups.

The significant advances in chlorinated photovoltaic materials have boosted the performances of organic solar cells (OSCs) from 4% to 17% only in 7 years. The design approaches utilizing chlorination as an effective tool to achieve high performance in OSCs are summarized. Furthermore, future challenges and prospects of these materials to realize the successful commercialization of OSCs are presented.

Abstract

The pursuit of low‐cost, flexible, and lightweight renewable power resources has led to outstanding advancements in organic solar cells (OSCs). Among the successful design principles developed for synthesizing efficient conjugated electron donor (ED) or acceptor (EA) units for OSCs, chlorination has recently emerged as a reliable approach, despite being neglected over the years. In fact, several recent studies have indicated that chlorination is more potent for large‐scale production than the highly studied fluorination in several aspects, such as easy and low‐cost synthesis of materials, lowering energy levels, easy tuning of molecular orientation, and morphology, thus realizing impressive power conversion efficiencies in OSCs up to 17%. Herein, an up‐to‐date summary of the current progress in photovoltaic results realized by incorporating a chlorinated ED or EA into OSCs is presented to recognize the benefits and drawbacks of this interesting substituent in photoactive materials. Furthermore, other aspects of chlorinated materials for application in all‐small‐molecule, semitransparent, tandem, ternary, single‐component, and indoor OSCs are also presented. Consequently, a concise outlook is provided for future design and development of chlorinated ED or EA units, which will facilitate utilization of this approach to achieve the goal of low‐cost and large‐area OSCs.

A highly efficient organic solar cell is demonstrated by applying a chlorine‐functionalized graphdiyne (GCl) multifunctional solid additive. A record‐high efficiency of 17.3%, with certified efficiency of 17.1%, is obtained along with the simultaneous increase of short‐circuit current (J _sc) and fill factor (FF), displaying state‐of‐the‐art binary organic solar cells at present.

Abstract

Morphology tuning of the blend film in organic solar cells (OSCs) is a key approach to improve device efficiencies. Among various strategies, solid additive is proposed as a simple and new way to enable morphology tuning. However, there exist few solid additives reported to meet such expectations. Herein, chlorine‐functionalized graphdiyne (GCl) is successfully applied as a multifunctional solid additive to fine‐tune the morphology and improve device efficiency as well as reproductivity for the first time. Compared with 15.6% efficiency for control devices, a record high efficiency of 17.3% with the certified one of 17.1% is obtained along with the simultaneous increase of short‐circuit current (J _sc) and fill factor (FF), displaying the state‐of‐the‐art binary organic solar cells at present. The redshift of the film absorption, enhanced crystallinity, prominent phase separation, improved mobility, and decreased charge recombination synergistically account for the increase of J _sc and FF after introducing GCl into the blend film. Moreover, the addition of GCl dramatically reduces batch‐to‐batch variations benefiting mass production owing to the nonvolatile property of GCl. All these results confirm the efficacy of GCl to enhance device performance, demonstrating a promising application of GCl as a multifunctional solid additive in the field of OSCs.

Bioinspired hydrogels with abilities of simultaneous fluorescence color and brightness changes, as well as complex shape deformation under pH stimulus by utilizing aggregation‐induced emission luminogens (AIEgens) and the bilayer hydrogel technique are designed and fabricated.

Abstract

Development of stimuli‐responsive materials with complex practical functions is significant for achieving bioinspired artificial intelligence. It is challenging to fabricate stimuli‐responsive hydrogels showing simultaneous changes in fluorescence color, brightness, and shape in response to a single stimulus. Herein, a bilayer hydrogel strategy is designed by utilizing an aggregation‐induced emission luminogen, tetra‐(4‐pyridylphenyl)ethylene (TPE‐4Py), to fabricate hydrogels with the above capabilities. Bilayer hydrogel actuators with the ionomer of poly(acrylamide‐r‐sodium 4‐styrenesulfonate) (PAS) as a matrix of both active and passive layers and TPE‐4Py as the core function element in the active layer are prepared. At acidic pH, the protonation of TPE‐4Py leads to fluorescence color and brightness changes of the actuators and the electrostatic interactions between the protonated TPE‐4Py and benzenesulfonate groups of the PAS chains in the active layer cause the actuators to deform. The proposed TPE‐4Py/PAS‐based bilayer hydrogel actuators with such responsiveness to stimulus provide insights in the design of intelligent systems and are highly attractive material candidates in the fields of 3D/4D printing, soft robots, and smart wearable devices.

Innovative time–temperature indicators with superior performance and extreme stability are engineered using self‐healing nanofibers. Owing to the intrinsic response of the self‐healable elastomer, highly sensitive, reliable, and tunable operation is enabled through morphological conversion. The self‐responsive working principle is driven by thermodynamic stability and liberates these indicators from the physical limitations and chemical hazards of existing devices.

Abstract

Perishable foods at undesired temperatures can generate foodborne illnesses that present significant societal costs. To certify refrigeration succession in a food‐supply chain, a flexible, easy‐to‐interpret, damage‐tolerant, and sensitive time‐temperature indicator (TTI) that uses a self‐healing nanofiber mat is devised. This mat is opaque when refrigerated due to nanofiber‐induced light scattering, but becomes irreversibly transparent at room temperature through self‐healing‐induced interfibrillar fusion leading to the appearance of a warning sign. The mat monitors both freezer (−20 °C) and chiller (2 °C) successions and its timer is tunable over the 0.5–22.5 h range through control of the polymer composition and film thickness. The thin mat itself serves as both a temperature sensor and display; it does not require modularization, accurately measures localized or gradient heat, and functions even after crushing, cutting, and when weight‐loaded in a manner that existing TTIs cannot. It also contains no drainable chemicals and is attachable to various shapes because it operates through an intrinsic physical response.

A new strategy using an abundant and colorful organic dye as the additive to passivate defect states and to produce more n‐type perovskite film is proposed, which remarkably enhances both efficiency and humidity/thermal stability of the perovskite solar cells.

Perovskite solar cells are a highly competitive candidate for next‐generation photovoltaic technology. Defects in the perovskite grain boundaries and on the film surfaces however have significant impacts on both the device efficiency and environmental stability. Herein, a strategy using organic dyes as additives to passivate the defect states and produce more n‐type perovskite films, thereby improving charge transport and decreasing charge recombination, is reported. Based on this strategy, the power conversion efficiency of the perovskite solar cell is significantly increased from 18.13% to 20.18% with a negligible hysteresis. Furthermore, the rich hydrogen bonds and carbonyl structures in the organic dye can significantly enhance device stability both in terms of humidity and thermal stress. The results present a promising pathway using abundant and colorful organic dyes as additives to achieve high‐performance perovskite solar cells.

In article number https://doi.org/10.1002/aenm.2019033691903369, Yoon‐Bong Hahn and co‐workers present highly stable perovskite solar cells fabricated with perovskite/Ag‐graphene and SrTiO₃/Al₂O₃‐graphene composites, achieving remarkably high photocurrent density of 25.75 mA cm⁻² and power conversion efficiency of 20.6%. This composites‐based device exhibits not only remarkable thermal‐ and photo‐stability but also long‐term stability, retaining 97–99% of the initial values of photovoltaic parameters, sustaining ≈93% of initial efficiency after 300 days under ambient conditions.

A Lewis acid tris(pentafluorophenyl)borane and nonhygroscopic lithium salt (LiClO₄) codoping strategy is introduced to tailor C₆₀ and fabricate highly efficient inorganic CsPbI₂Br perovskite solar cells with reduced hysteresis. Consequently, square‐centimeter inorganic CsPbI₂Br perovskite solar cells yield a record power conversion efficiency (PCE) of 14.44%. In addition, the first inorganic perovskite solar module with an efficiency exceeding 12% is reported, using a self‐developed quasi‐curved heating method.

Abstract

Although inorganic perovskite solar cells (PSCs) are promising in thermal stability, their large open‐circuit voltage (V _OC) deficit and difficulty in large‐area preparation still limit their development toward commercialization. The present work tailors C₆₀ via a codoping strategy to construct an efficient electron‐transporting layer (ETL), leading to a significant improvement in V _OC of the inverted inorganic CsPbI₂Br PSC. Specifically, tris(pentafluorophenyl)borane (TPFPB) is introduced as a dopant to lower the lowest unoccupied molecular orbital (LUMO) level of the C₆₀ layer by forming a Lewis acidic adduct. The enlarged free energy difference provides a favorable enhancement in electron injection and thereby reduces charge recombination. Subsequently, a nonhygroscopic lithium salt (LiClO₄) is added to increase electron mobility and conductivity of the film, leading to a reduction in the device hysteresis and facilitating the fabrication of a large‐area device. Finally, the as‐optimized inorganic CsPbI₂Br PSCs gain a champion power conversion efficiency (PCE) of 15.19%, with a stabilized power output (SPO) of 14.21% (0.09 cm²). More importantly, this work also demonstrates a record PCE of 14.44% for large‐area inorganic CsPbI₂Br PSCs (1.0 cm²) and reports the first inorganic perovskite solar module with the excellent efficiency exceeding 12% (10.92 cm²) by a self‐developed quasi‐curved heating method.

A series of electron transporting chiral stereoisomers of naphthalene diimide crystalline materials having N‐substituted two chiral groups is rationally designed and synthesized for the simultaneous achievement of low‐temperature solution processability, high device performance, and long‐term temporal (and high‐temperature) device stability.

Abstract

A series of chiral stereoisomers of electron transporting materials with two chiral substituents is rationally designed and synthesized, and the influence of stereoisomerism on their physical and electronic properties is investigated to demonstrate highly efficient and stable perovskite solar cells (PSCs). Compared to mesomeric naphthalene diimide (NDI) derivatives, which have heterochiral side groups with centrosymmetric molecular packing of symmetric‐shaped conformers in the crystalline state, enantiomeric NDI derivatives have homochiral side groups that exhibit non‐centrosymmetric molecular packing of asymmetric‐shaped conformers in the crystalline state and exhibit better solution processability based on one order of magnitude higher solubility. A similar trend is observed in different rylene diimide stereoisomers based on larger semiconducting core perylene diimide. The PSCs based on NDI enantiomers with good film‐forming ability and a very high lowest phase transition temperature (T _lowest) of 321 °C exhibit a high and uniform average power conversion efficiency (PCE) of 19.067 ± 0.654%. These PSCs also have a high temporal device stability, with less than 10% degradation of the PCE at 100 °C for 1000 h without encapsulation. Therefore, chiral stereoisomer engineering of charge transporting materials is a potential approach to achieve high solution processability, excellent performance, and significant temporal stability in organic electronic devices.

A new indacenothiophene‐based electron transporting material ITCP‐M with near‐infrared (NIR) absorption is developed and applied in inverted perovskite solar cells (PSCs). Interestingly, ITCP‐M can extend absorption to the NIR region in addition to electron extraction and electron transporting, which contributes to the enhanced photovoltaic performance of MAPbI₃‐based inverted PSCs.

Lead‐based organic–inorganic hybrid perovskite solar cells (PSCs) usually show an absorption edge around 800 nm, while the near‐infrared (NIR) wavelength beyond 800 nm cannot be utilized. Herein, a new indacenothiophene‐based electron transporting material (ETM), namely, ITCP‐M, is developed, which works to enhance electron extraction and electron transporting, and simultaneously extends photoresponses to the NIR region in MAPbI₃‐based inverted PSCs. Notably, the ITCP‐M‐based device exhibits a prominent photoresponse beyond 800 nm as observed from the external quantum efficiency (EQE) spectra, contributing to enhanced short‐circuit current density (J _sc) without sacrificing the open‐circuit voltage and fill factor. As a result, inverted PSCs using ITCP‐M ETM delivers a high efficiency of 19.15%, representing one of the highest efficiencies in inverted PSCs using nonfullerene ETMs. This work provides a new and simple strategy to extend photoresponses to the NIR absorption region for MAPbI₃‐based inverted PSCs that can significantly improve device performance.

The use of two precursor preparation methods for the deposition of phenethylammonium‐containing organic‐inorganic hybrid perovskite films for photovoltaic applications is reported. It is found that film properties, photovoltaic device performance, and stability differ depending on the precursor preparation methods. These new insights are important for optimizing precursor preparations for lower dimensional perovskite films to achieve the best device performance and stability.

For the fabrication of low‐dimensional perovskite solar cells, understanding the effect of precursor preparation on film formation is critical to achieve high‐quality perovskite film and, therefore, high efficiency in related solar devices. Herein, the two methods to prepare phenethylammonium‐based mixed perovskite precursors with the same chemical composition are reported. These methods are called 1) different phase (DP) and 2) same phase (SP) methods as the former involves the mixing of a 3D perovskite precursor with a 2D perovskite precursor, whereas the latter involves the mixing of quasi‐2D perovskite precursors. The films prepared by these methods are characterized by X‐ray diffraction, Kelvin probe force microscopy, and scanning electron microscopy, revealing different perovskite structures. The power conversion efficiency (PCE) of the champion cells by DP and SP methods reaches 19.1% and 18.9%, respectively. Results of the aging test show a dramatic improvement in the stability of SP perovskite devices maintaining 86% of its initial performance after exposure to a relative humidity (RH) 8 ± 5% for 1000 hr and over 80% of its initial PCE after continuous 1 sun illumination (including UV) at RH 70%. The new insights provided by this work are important to design perovskite precursor preparation methods for the best device performance and stability.

A dopant‐free alkoxy‐PTEG device processed with 3‐methylcyclohexanone exhibits 19.9% efficiency and a device with 2‐methyl anisole, which is a reported aromatic food additive, exhibits 21.2% efficiency. In addition, tetraethylene glycol groups can chelate lead ions with moderate strength (K _binding = 2.76), and this strength is considered to be nondestructive to the perovskite lattice to prevent lead leakage.

Abstract

With the recent developments in the efficiency of perovskite solar cells (PSCs), diverse functionalities are necessary for next‐generation charge‐transport layers. Specifically, the hole‐transport layer (HTL) in the various synthesized materials modified with functional groups is explored. A novel donor–acceptor type polymer, alkoxy‐PTEG, composed of benzo[1,2‐b:4,5:b′]dithiophene and tetraethylene glycol (TEG)‐substituted 2,1,3‐benzothiadiazole is reported. The alkoxy‐PTEG exhibits high solubility even in nonaromatic solvents, such as 3‐methylcyclohexanone (3‐MC), and can prevent possible lead leakage via chelation. The optical and electronic properties of alkoxy‐PTEG are thoroughly analyzed. Finally, a dopant‐free alkoxy‐PTEG device processed with 3‐MC exhibits 19.9% efficiency and a device with 2‐methyl anisole, which is a reported aromatic food additive, exhibits 21.2% efficiency in a tin oxide planar structure. The PSC device shows 88% stability after 30 d at ambient conditions (40–50% relative humidity and room temperature). In addition, nuclear magnetic resonance reveals that TEG groups can chelate lead ions with moderate strength (K _binding = 2.76), and this strength is considered to be nondestructive to the perovskite lattice to prevent lead leakage. This is the first report to consider lead leakage and provide solutions to reduce this problem.

Interfaces provide reactive zones and interphases stabilize electronic device operation. Understanding and designing interfaces and interphases represent an effective and efficient way for developing high‐performance rechargeable batteries and perovskite solar cells.

Abstract

The ever‐increasing demand for clean sustainable energy has driven tremendous worldwide investment in the design and exploration of new active materials for energy conversion and energy‐storage devices. Tailoring the surfaces of and interfaces between different materials is one of the surest and best studied paths to enable high‐energy‐density batteries and high‐efficiency solar cells. Metal‐halide perovskite solar cells (PSCs) are one of the most promising photovoltaic materials due to their unprecedented development, with their record power conversion efficiency (PCE) rocketing beyond 25% in less than 10 years. Such progress is achieved largely through the control of crystallinity and surface/interface defects. Rechargeable batteries (RBs) reversibly convert electrical and chemical potential energy through redox reactions at the interfaces between the electrodes and electrolyte. The (electro)chemical and optoelectronic compatibility between active components are essential design considerations to optimize power conversion and energy storage performance. A focused discussion and critical analysis on the formation and functions of the interfaces and interphases of the active materials in these devices is provided, and prospective strategies used to overcome current challenges are described. These strategies revolve around manipulating the chemical compositions, defects, stability, and passivation of the various interfaces of RBs and PSCs.

A steric engineering strategy to impede ion migration in perovskite thin films is demonstrated where ion migration is effectively hindered by localized lattice distortions induced by incorporation of oversized A site cations. The steric engineering approach improves the operational lifetime of perovskite solar cells by more than nine‐fold from 222 h to 2011 h.

Abstract

The operational instability of perovskite solar cells (PSCs) is known to mainly originate from the migration of ionic species (or charged defects) under a potential gradient. Compositional engineering of the “A” site cation of the ABX₃ perovskite structure has been shown to be an effective route to improve the stability of PSCs. Here, the effect of size‐mismatch‐induced lattice distortions on the ion migration energetics and operational stability of PSCs is investigated. It is observed that the size mismatch of the mixed “A” site composition films and devices leads to a steric effect to impede the migration pathways of ions to increase the activation energy of ion migration, which is demonstrated through multiple theoretical and experimental evidence. Consequently, the mixed composition devices exhibit significantly improved thermal stability under continuous heating at 85 °C and operational stability under continuous 1 sun illumination, with an extrapolated lifetime of 2011 h, compared to the 222 h of the reference device.

Au@CdS fills in the perovskite grain boundaries to form an Au@CdS–PbI₂ intermediate, which increases the valence band maximum of Spiro‐OMeTAD for a more favorable energy alignment with perovskite. With the help of the localized surface plasmon resonance of Au@CdS, the holes easily overcome the interface barrier through the bridge of the intermediate Au@CdS–PbI₂. The corresponding device shows high performance.

Abstract

The plasmonic characteristic of core–shell nanomaterials can effectively improve exciton‐generation/dissociation and carrier‐transfer/collection. In this work, a new strategy based on core–shell Au@CdS nanospheres is introduced to passivate perovskite grain boundaries (GBs) and the perovskite/hole transport layer interface via an antisolvent process. These core–shell Au@CdS nanoparticles can trigger heterogeneous nucleation of the perovskite precursor for high‐quality perovskite films through the formation of the intermediate Au@CdS–PbI₂ adduct, which can lower the valence band maximum of the 2,2,7,7‐tetrakis(N,N‐di‐p‐methoxyphenyl‐amine)9,9‐spirobifluorene (Spiro‐OMeTAD) for a more favorable energy alignment with the perovskite material. With the help of the localized surface plasmon resonance effect of Au@CdS, holes can easily overcome the barrier at the perovskite/Spiro‐OMeTAD interface (or GBs) through the bridge of the intermediate Au@CdS–PbI₂, avoiding the carrier accumulation, and suppress the carrier trap recombination at the Spiro‐OMeTAD/perovskite interface. Consequently, the Au@CdS‐based perovskite solar cell device achieves a high efficiency of over 21%, with excellent stability of ≈90% retention of initial power conversion efficiencies after 45 days storage in dry air.

Highly efficient mixed‐halide perovskite light‐emitting diodes with an external quantum efficiency over 20% are achieved through dual passivation of both lead and halide defects. A bi‐functional additive, 4‐fluorophenylmethylammonium‐trifluoroacetate, is designed to simultaneously passivate both lead and halide defects. Benefitting from the dual passivation effect, the phase segregation and device hysteresis are suppressed, and the stability is greatly improved.

Abstract

Solution‐processed metal halide perovskites (MHPs) have attracted much attention for applications in light‐emitting diodes (LEDs) due to their wide color gamut, high color purity, tunable emission wavelength, balanced electron/hole transportation, etc. Although MHPs are very tolerant to defects, the defects in solution‐processed perovskite LEDs (PeLEDs) still cause severe nonradiative recombination and device instability. Here, molecular design of additives for dual passivation of both lead and halide defects in perovskites is reported. A bi‐functional additive, 4‐fluorophenylmethylammonium‐trifluoroacetate (FPMATFA), is synthesized by using a simple solution process. The TFA anions and FPMA cations can bond with undercoordinated lead and halide ions, respectively, resulting in dual passivation of both lead and halide defects. In addition, the bulky FPMA group can constrain the grain growth of 3D perovskite, enhancing electron–hole capture rates and radiative recombination rates. As a result, high‐performance PeLEDs with a peak external quantum efficiency reaching 20.9% and emission wavelength at 694 nm are achieved using formamidinium‐cesium lead iodide‐bromide (FA_0.33Cs_0.67Pb(I_0.7Br_0.3)₃). Furthermore, the operational lifetime of PeLEDs is also greatly improved due to the low trap density in the perovskite film.

Hole transport material (HTM) plays important roles in n–i–p type perovskite solar cells. It affects both efficiency and the stability. After the recognition of its importance, a number of HTMs have been developed. This review summarizes various types of HTMs and discusses their development.

Abstract

With the application of organic–inorganic hybrid perovskites to liquid‐type solar cells, the unprecedented development of perovskite solar cells (Per‐SCs) has been boosted by the introduction of solid‐state hole transport materials (HTMs). The removal of liquid electrolyte has lead to improved efficiency and stability. Supported by high‐quality perovskite films, the certified efficiency of Per‐SCs has reached 25.2%. For Per‐SCs assembled in a conventional structure (n–i–p), the hole transport layer (HTL) plays an extra role in preventing the perovskite layer from external stimuli. In summary, the successful design and fabrication of the HTL must meet various requirements in terms of solubility, hole transport, recombination prevention, stability, and reproducibility, to name but a few. Many research strategies are focused on the development of high‐performance HTMs to meet such requirements. Such strategies for the development of HTMs employed in conventional n–i–p solar cells are reviewed herein. A vision of the future HTMs is proposed in this review based on the already proposed solutions and current trends.

Mixed‐halide perovskites are essential for use in all‐perovskite or perovskite–silicon tandem solar cells. Through photoluminescence measurements and electric field application, three distinct defect species are found responsible for charge‐carrier trapping, halide segregation, and electric field screening, respectively, within MAPb(Br_0.5I_0.5)₃ materials. External quantum efficiency measurements highlight that charge‐carriers can be extracted from the low‐bandgap regions of the phase‐segregated perovskite formed under illumination.

Abstract

Mixed‐halide perovskites are essential for use in all‐perovskite or perovskite–silicon tandem solar cells due to their tunable bandgap. However, trap states and halide segregation currently present the two main challenges for efficient mixed‐halide perovskite technologies. Here photoluminescence techniques are used to study trap states and halide segregation in full mixed‐halide perovskite photovoltaic devices. This work identifies three distinct defect species in the perovskite material: a charged, mobile defect that traps charge‐carriers in the perovskite, a charge‐neutral defect that induces halide segregation, and a charged, mobile defect that screens the perovskite from external electric fields. These three defects are proposed to be MA⁺ interstitials, crystal distortions, and halide vacancies and/or interstitials, respectively. Finally, external quantum efficiency measurements show that photoexcited charge‐carriers can be extracted from the iodide‐rich low‐bandgap regions of the phase‐segregated perovskite formed under illumination, suggesting the existence of charge‐carrier percolation pathways through grain boundaries where phase‐segregation may occur.

Molecules with controlled electron affinity processed at low temperature are used to tailor conductivity and the energy levels of hole transporting materials (HTMs), enabling fast holes extraction at the HTM/perovskite interface. This method with novel 3,6‐difluoro‐2,5,7,7,8,8‐hexacyanoquinodimethane enables the highest reported power conversion efficiency (PCE) of 22.13% and 20.01% for NiO _x ‐based rigid and flexible perovskite solar cells, respectively.

Abstract

Inverted perovskite solar cells (PSCs) with low‐temperature processed hole transporting materials (HTMs) suffer from poor performance due to the inferior hole‐extraction capability at the HTM/perovskite interfaces. Here, molecules with controlled electron affinity enable a HTM with conductivity improved by more than ten times and a decreased energy gap between the Fermi level and the valence band from 0.60 to 0.24 eV, leading to the enhancement of hole‐extraction capacity by five times. As a result, the 3,6‐difluoro‐2,5,7,7,8,8‐hexacyanoquinodimethane molecules are used for the first time enhancing open‐circuit voltage (V _oc) and fill factor (FF) of the PSCs, which enable rigid‐and flexible‐based inverted perovskite devices achieving highest power conversion efficiencies of 22.13% and 20.01%, respectively. This new method significantly enhances the V _oc and FF of the PSCs, which can be widely combined with HTMs based on not only NiO _x but also PTAA, PEDOTT:PSS, and CuSCN, providing a new way of realizing efficient inverted PSCs.

By introduction of a multiple ligand (pentaerythritol tetrakis(3‐mercaptopropionate)), uncoordinated Pb²⁺ and Pb⁰ defects are simultaneously passivated. Meanwhile, better energy level matching between the valence band of perovskite and the highest occupied molecular orbital of the HTM is achieved. As a result, perovskite solar cell efficiency increases from 19.0% to 21.4% after surface passivation by multiple ligands.

Abstract

In the past decade, the efficiency of perovskite solar cells quickly increased from 3.8% to 25.2%. The quality of perovskite films plays vital role in device performance. The films fabricated by solution‐process are usually polycrystalline, with significantly higher defect density than that of single crystal. One kind of defect in the films is uncoordinated Pb²⁺, which is usually generated during thermal annealing process due to the volatile organic component. Another detrimental kind of defect is Pb⁰, which is often observed during the film fabrication process or solar cell operation. Because the open circuit voltage has a close relation with the defect density, it is thus desirable to passivate these two kinds of defects. Here, a molecule with multiple ligands is introduced, which not only passivates the uncoordinated Pb²⁺ defects, but also suppresses the formation of Pb⁰ defects. Meanwhile, such a treatment improves the energy level alignment between the valence band of perovskite and the highest occupied molecular orbital of spiro‐OMeTAD. As a result, the performance of perovskite solar cells significantly increases from 19.0% to 21.4%.