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All‐inorganic cesium lead halide flexible perovskite solar cells (f‐PSCs) exhibit superior thermal stability compared to their organic‐inorganic hybrid counterparts. However, their flexibility and efficiency are still below‐par for practical viability. This study presents an approach involving the introduction of multifunctional molecule ammonium benzenesulfonate (ABS) to selectively etch 0D‐Cs4Pb(IBr)6 from the mixed‐dimensional perovskite film surface, to attain more contact area between the perovskite and hole transport layer for improved hole extraction and transport. It is found that the ABS molecules bind to the perovskite lattice surface via O atoms and NH4+, effectively passivating surface defects and enhancing phase stability. The hydrophobic nature of the benzene ring in ABS further contributes to operational stability, leading to high cell efficiency of 15.00%, accompanied by enhanced operational stability. Even after undergoing 60 000 flexing cycles at a curvature radius of 5 mm, the ABS‐treated f‐PSC still retains over 98.5% of its initial efficiency. This multifunctional strategy for modifying typical mixed‐dimensional perovskite compositions significantly enhances the photovoltaic performance and stability of flexible all‐inorganic f‐PSCs. [ABSTRACT FROM AUTHOR]

Deep defects often act as Shockley–Read–Hall recombination centers in semiconductor materials, degrading the photoelectric performance and long‐term stability of assembled photovoltaic devices. In this report, deep level transient spectroscopy is probed to determine defect concentrations and defect energy levels in all‐inorganic CsPbI3−xBrx perovskite solar cells. Combining that data with the density functional theory calculation, the dominant deep defect states are assigned to antisite defect pairs (PbI and IPb) and interstitial defects (Pbi) in freshly prepared CsPbI3−xBrx films. Astonishingly, all these defects are reduced by approximately one or two orders of magnitude after resting the films overnight, in excellent agreement with the defect‐reduced trends from the fluorescence spectra, transient photovoltage, and space‐charge‐limited current measurements. The reduced defect concentrations are proposed to be connected with their self‐regulation during the storage. To assess the thermodynamics possibilities, two reaction procedures are designed to calculate their formation enthalpies and negative Gibbs energy change revealed their spontaneous processes. Then, strain relief is the direct driving force for ion migration, thus defect‐regulation by tracing the X‐ray diffraction patterns. Furthermore, the power conversion efficiency is improved and the J–V hysteresis is suppressed due to reduced ion migration via relaxed strain. [ABSTRACT FROM AUTHOR]

Inorganic CsPbI2Br perovskite solar cells (PSCs) have gained enormous research interest due to their excellent thermal and light stabilities. However, their unsatisfactory power‐conversion efficiency and poor intrinsic phase stability remain roadblocks to their further development. Herein, Cs2PbI2Cl2 nanosheets (NSs) with the Ruddlesden–Popper (RP) structure are synthesized, and an NSs/CsPbI2Br/NSs heterostructure is employed to enhance both the stability and efficiency of CsPbI2Br solar cells. The novel Cs2PbI2Cl2 NSs can not only passivate the top and bottom surfaces of the perovskite film and top surface of the TiO2 film but also enhance the stability of the perovskite film. Based on the heterostructured NSs/CsPbI2Br/NSs inorganic perovskite film, the efficiency of the CsPbI2Br PSCs is improved from 15.02% to 16.65%. Moreover, the unencapsulated CsPbI2Br devices with the NSs/CsPbI2Br/NSs heterostructure sustain over 90% of their original efficiencies after being exposed to ambient conditions (≈25 °C and ≈35% RH) for 648 h. Both the UV‐light‐soaking stability (100 mW cm−1 365 nm UV light) and thermal stability (T = 85 °C) of the optimized devices are dramatically improved in comparison with their counterparts with only a 3D active layer. Therefore, this work promotes the application of RP inorganic perovskite nanocrystals in a range of perovskite optoelectronic devices. [ABSTRACT FROM AUTHOR]

High temperature stable inorganic CsPbX3 (X: I, Br, or mixed halides) perovskites with their bandgap tailored by tuning the halide composition offer promising opportunities in the design of ideal top cells for high‐efficiency tandem solar cells. Unfortunately, the current high‐efficiency CsPbX3 perovskite solar cells (PSCs) are prepared in vacuum, a moisture‐free glovebox or other low‐humidity conditions due to their poor moisture stability. Herein, a new precursor system (HCOOCs, HPbI3, and HPbBr3) is developed to replace the traditional precursors (CsI, PbI2, and PbBr2) commonly used for solar cells of this type. Both the experiments and calculations reveal that a new complex (HCOOH•Cs+) is generated in this precursor system. The new complex is not only stable against aging in humid air ambient at 91% relative humidity, but also effectively slows the perovskite crystallization, making it possible to eliminate the popular antisolvent used in the perovskite CsPbI2Br film deposition. The CsPbI2Br PSCs based on the new precursor system achieve a champion efficiency of 16.14%, the highest for inorganic PSCs prepared in ambient air conditions. Meanwhile, high air stability is demonstrated for an unencapsulated CsPbI2Br PSC with 92% of the original efficiency remaining after more than 800 h aging in ambient air. [ABSTRACT FROM AUTHOR]

Abstract: All‐inorganic perovskite CsPbI3 quantum dots (QDs) offer much better stability for photovoltaic applications. Unfortunately, their cell efficiencies are hindered by the low carrier transport efficiency of QD‐assembled films. In addition, agglomeration‐induced phase change of QDs poses another problem for material and device degradation. Herein, the use of µ‐graphene (µGR) to crosslink QDs to form µGR/CsPbI3 film is demonstrated. It is found that the resultant QDs film provides not only an effective channel for carrier transport, as witnessed by much improved conductivity but also significantly better stability against moisture, humidity, and high temperature stresses. The µGR/CsPbI3 based solar cell shows increased device performance. More specifically, compared to the solar cell without the µGR treatment, VOC is improved to 1.18 from 1.16 V, JSC to 13.59 from 13.17 mA cm−2, and FF to 72.6 from 68.1%, and overall power conversion efficiency to as high as 11.40 from 10.41%, a 12% increase. In addition, the instability originating from the thermal/moisture‐induced QD agglomeration is also greatly suppressed by the µGR crosslinking. The optimized device retains >98% of its initial efficiency after being stored in N2 atmosphere for one month. Importantly, under 60% humidity and 100 °C thermal stresses, the µGR/CsPbI3 devices show much better stability. [ABSTRACT FROM AUTHOR]

Abstract: All‐inorganic CsPbBrI2 perovskite has great advantages in terms of ambient phase stability and suitable band gap (1.91 eV) for photovoltaic applications. However, the typically used structure causes reduced device performance, primarily due to the large recombination at the interface between the perovskite, and the hole‐extraction layer (HEL). In this paper, an efficient CsPbBrI2 perovskite solar cell (PSC) with a dimensionally graded heterojunction is reported, in which the CsPbBrI2 material is distributed within bulk–nanosheet–quantum dots or 3D–2D–0D dimension‐profiled interface structure so that the energy alignment is optimized in between the valence and conduction bands of both CsPbBrI2 and the HEL layers. Specifically, the valence‐/conduction‐band edge is leveraged to bend with synergistic advantages: the graded combination enhances the hole extraction and conduction efficiency with effectively decreased recombination loss during the hole‐transfer process, leading to an enhanced built‐in electric field, hence a high VOC of as much as 1.19 V. The profiled structure induces continuously upshifted energy levels, resulting in a higher JSC of as much as 12.93 mA cm−2 and fill factor as high as 80.5%, and therefore record power conversion efficiency (PCE) of 12.39%. As far as it is known, this is the highest PCE for CsPbBrI2 perovskite‐based PSC. [ABSTRACT FROM AUTHOR]

Abstract: Each component layer in a perovskite solar cell plays an important role in the cell performance. Here, a few types of polymers including representative p‐type and n‐type semiconductors, and a classical insulator, are chosen to dope into a perovskite film. The long‐chain polymer helps to form a network among the perovskite crystalline grains, as witnessed by the improved film morphology and device stability. The dewetting process is greatly suppressed by the cross‐linking effect of the polymer chains, thereby resulting in uniform perovskite films with large grain sizes. Moreover, it is found that the polymer‐doped perovskite shows a reduced trap‐state density, likely due to the polymer effectively passivating the perovskite grain surface. Meanwhile the doped polymer formed a bridge between grains for efficient charge transport. Using this approach, the solar cell efficiency is improved from 17.43% to as high as 19.19%, with a much improved stability. As it is not required for the polymer to have a strict energy level matching with the perovskite, in principle, one may use a variety of polymers for this type of device design. [ABSTRACT FROM AUTHOR]

The complete phase transition from DMAPbI3 and Cs4PbI6 intermediates to the final CsPbI3 perovskite phase is pivotal for fabricating high‐quality inorganic perovskite films. In this study, the reaction energy barrier between DMAPbI3 and Cs4PbI6 is sought to be reduced by increasing their surface energy, where a perfluorinated compound is designed using DFT modeling to saturate the surface of the intermediates to effectively prevent their crystalline growth. Consequently, the smaller intermediates with ultrahigh surface energy react more energetically to facilitate a rapid conversion to the desired perovskite phase. It is found that the resultant inorganic perovskite shows improved crystallinity and morphology, as demonstrated by suppressed non‐radiative recombination and prolonged carrier lifetimes. As a result, the optimized inorganic perovskite solar cells (PSCs) achieve a power conversion efficiency (PCE) of over 20%, along with significantly improved light and thermal stability. This work provides a way to regulate crystallization dynamics for advanced quality of inorganic perovskites. [ABSTRACT FROM AUTHOR]

Trap‐mediated nonradiative charge recombination poses a significant obstacle to achieving high‐efficiency and stability in metal‐halide perovskite solar cells (PSCs). Utilizing the interactions between functional groups of molecules and perovskite defects as surface defect passivation strategies is a common approach in addressing this challenge. Nevertheless, the challenge lies in developing a comprehensive molecule capable of effectively depressing and passivating different charged defects. This study explores a multifunctional organic salt neostigmine methyl sulfate (NMS), to finely regulate the crystallization of perovskite film, thereby minimizing defects and passivating surface defects. The C═O and S═O of NMS coordinate with Pb2+, while the oxygen atoms of S═O interact with FA+ through hydrogen bonds (O∙∙∙H─N). The interactions involving S─O− with Pb2+ ions and ─N(CH3)3+ with the negative halide ions are predominantly electrostatic interactions. Therefore, through NMS treatment, the crystallization process of perovskite film is delayed, energy levels are optimized, and the surface defects are effectively passivated. This leads to a notable decrease in defect density and an improved alignment of perovskite energy levels, enhancing carrier transfer and extraction within the device. Consequently, a stabilized power conversion efficiency (PCE) of 24.95% is achieved. Even after 50 d, the device maintains its environmental stability retaining 89.39%. [ABSTRACT FROM AUTHOR]

BiVO4 faces significant challenges for widespread application in photoelectrochemical (PEC) water oxidation due to its poor hole transport ability, high surface defect density, and sluggish water oxidation reaction kinetics. Employing interfacial engineering to assist in energy level modulation is an effective strategy to address these challenges. Herein, a CuCrO2 hole transport layer (HTL) is coupled and further grew NiCo‐MOF in situ to prepare a NiCo‐MOF‐CuCrO2‐BiVO4 composite photoanode. The novel composite photoanode not only achieves a photocurrent density of 5.75 mA cm−2 at 1.23 V versus a reversible hydrogen electrode (vs RHE) but also maintains stable operation for over 24 h. Comprehensive physicochemical characterization and density‐functional theory calculations confirm that the built‐in electric field generated by the p–n heterojunction formed between the CuCrO2 HTL and BiVO4 photoanode enhances the hole transport ability. Moreover, the NiCo‐MOF chelated on the photoanode surface not only passivates the surface defect states but also accelerates the kinetics of the water oxidation reaction. Under the synergistic effect of dual modification, the PEC water oxidation performance of the BiVO4 photoanode is dramatically improved. This pioneering work presents a MOF/HTL/BiVO4 configuration that provides a blueprint for the future development of integrated photoanodes for efficient solar energy conversion. [ABSTRACT FROM AUTHOR]

The highest certified power conversion efficiency (PCE) of black phase based CsPbI3 perovskite solar cells has exceeded 18%, and become a hotspot in recent progress. However, the black phase of CsPbI3 rapidly transforms to yellow phase in ambient conditions due to its thermodynamic instability. Here, a Ruddlesden–Popper 2D structure is introduced into γ‐CsPbI3 film to stabilize the black phase via reducing dimensionality. It is found that a judicious amount of phenylethylammonium iodide can adjust the dimensionality of γ‐CsPbI3 film from 2D to quasi‐2D and 3D phase. Comprehensive consideration to obtain both the stability and high PCE, quasi‐2D (n = 40) γ‐CsPbI3 delivers a reproducible PCE of 13.65% with negligible hysteresis. By utilizing femtosecond transient absorption and time‐resolved PL decay, similar carrier kinetics in n = 40 and ∞ samples are observed, meaning an efficient charge extraction. More importantly, when the device is placed at 80 °C in N2 condition or in air with RH of 25–30%, its PCE keeps ≈88% and ≈89% of its initial PCE after 12 days, respectively. Such results are better than the 3D one (≈69% and ≈16%, respectively). [ABSTRACT FROM AUTHOR]

The Cs‐based inorganic perovskite solar cells (PSCs), such as CsPbI2Br, have made a striking breakthrough with power conversion efficiency (PCE) over 16% and potential to be used as top cells for tandem devices. Herein, I− is partially replaced with the acetate anion (Ac−) in the CsPbI2Br framework, producing multiple benefits. The Ac− doping can change the morphology, electronic properties, and band structure of the host CsPbI2Br film. The obtained CsPbI2−xBr(Ac)x perovskite films present lower trap densities, longer carrier lifetimes, and fast charge transportation compared to the host CsPbI2Br films. Interestingly, the CsPbI2−xBr(Ac)x PSCs exhibit a maximum PCE of 15.56% and an ultrahigh open circuit voltage (Voc) of 1.30 V without sacrificing photocurrent. Notably, such a remarkable Voc is among the highest values of the previously reported CsPbI2Br PSCs, while the PCE far exceeds all of them. In addition, the obtained CsPbI2−xBr(Ac)x PSCs exhibit high reproducibility and good stability. The stable CsPbI2−xBr(Ac)x PSCs with high Voc and PCE are desirable for tandem solar cell applications. [ABSTRACT FROM AUTHOR]

Inorganic cesium lead halide perovskite solar cells (PSCs) have received enormous attention due to their excellent stability compared with that of their organic–inorganic counterparts. However, the lack of optimization strategies leads the inorganic PSCs to suffer from low efficiency arising from significant recombination. To overcome this dilemma, a surface modification of the electron transport layer (ETL)/perovskite interface is undertaken by using SmBr3 to improve the crystallization and morphology of the perovskite layer for enhanced ETL/perovskite interface interaction. Encouragingly, a gradient energy band is created at the interface with an outstanding hole blocking effect. As a result, both the charge recombination occurring at the interface and the nonradiative recombination inside the perovskite are suppressed, and, simultaneously, the charge extraction is improved successfully. Therefore, the power conversion efficiency of the CsPbIBr2 PSCs is increased to as high as 10.88% under one sun illumination, which is 30% higher than its counterparts without the modification. It is logically inferred that this valuable optimization strategy can be extended to other analogous structures and materials. [ABSTRACT FROM AUTHOR]