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Although the highest power conversion efficiency of an all-inorganic perovskite solar cell has surpassed 20%, the efficiency gap compared with the hybrid perovskite device is still noticeable. The main electronic deficiency of all-inorganic perovskite for improving high efficiency is its larger energy band value. By studying the change of bandgap of inorganic perovskite with the composition ratio, it can help us to optimize the photoelectron performance of perovskite solar devices. Based on first-principles calculations, it is found that the degree of band curvature of the mixed CsSn1−xPbxI3 bandgap is small due to the joint effect of spin–orbit coupling and atomistic disorder, which is different from the bandgap evolution of a hybrid perovskite system. The bandgap bowing parameter gradually augments with an increasing MA+ ratio. Our results indicate that component engineering and electronic structure modulation can optimize the photovoltaic performance appropriately. [ABSTRACT FROM AUTHOR]

Perovskite light‐emitting diodes (PeLEDs) have shown great potential for low‐cost display and lighting technologies, and all‐inorganic blue PeLEDs are recognized as a promising substitute for blue fluorescent/phosphorescent organic light‐emitting diodes (OLEDs) owing to their superior color purity and great stability potential. However, confined by the solution fabrication process, depositing multi‐layered white PeLEDs remains a challenge. Here, a newly designed hybrid perovskite/organic tandem white LED (POTWLED), integrated with a bottom blue PeLED unit and a top orange/(orange + red) OLED unit, to prevent damage to the underlying perovskite layer caused by the deposition of the top emitting layers, is reported. To optimize the performance of POTWLEDs, a conductive passivator of 2,8‐bis(diphenylphosphoryl)dibenzo[b,d] thiophene, with a strong surface binding group of P═O, is introduced to passivate perovskite defects, which promotes a maximum external quantum efficiency (EQE) of 17.3% for blue PeLEDs with an emission peak at 488 nm. As a result, based on the optimized blue PeLED units, a maximum EQE of 23.9% with a low color temperature of 2522 K is obtained for POTWLEDs, which is the highest efficiency for perovskite‐based WLEDs, illustrating the great potential of the hybrid tandem device in fabricating high‐performance perovskite‐based WLEDs. [ABSTRACT FROM AUTHOR]

Vacancy related defects play a crucial role in optoelectronic properties and carrier transport for photovoltaic materials, especially for its structural evolution becoming non-radiative defects induced by strain. Thus far, the evolution phenomena of vacancy defects in halide perovskite triggered by energy or strain have not been systematically investigated. Herein, we study the change in defect levels occurred in different inorganic perovskite systems and the situation caused by strain in varied strength based on density functional theory calculations. We discover that VI deep levels are easily transformed from shallow levels due to the formation of Pb–Pb dimers and octahedral distortion in all-inorganic perovskites, especially in CsPbI3. Moreover, strain can be quantitatively applied to control the suppression or enhancement of the formation of dimer in CsBI3 (B = Pb/Ge) perovskites. Eventually, our calculation results unravel that the defect physics of VI defect and the formation mechanism of non-radiative center in all inorganic perovskites, which depends on the strain strength and the accompanying octahedral distortion. The strain modulation and its quantitation effect on defect evolution of dominant vacancy map a pioneering route toward fabricating high performance inorganic photovoltaics. [ABSTRACT FROM AUTHOR]

Heterostructures based on layered materials are considered next-generation photocatalysts due to their unique mechanical, physical, and chemical properties. In this work, we conducted a systematic first-principles study on the structure, stability, and electronic properties of a 2D monolayer WSe2/Cs4AgBiBr8 heterostructure. We found that the heterostructure is not only a type-II heterostructure with a high optical absorption coefficient, but also shows better optoelectronic properties, changing from an indirect bandgap semiconductor (about 1.70 eV) to a direct bandgap semiconductor (about 1.23 eV) by introducing an appropriate Se vacancy. Moreover, we investigated the stability of the heterostructure with Se atomic vacancy in different positions and found that the heterostructure was more stable when the Se vacancy is near the vertical direction of the upper Br atoms from the 2D double perovskite layer. The insightful understanding of WSe2/Cs4AgBiBr8 heterostructure and the defect engineering will offer useful strategies to design superior layered photodetectors. [ABSTRACT FROM AUTHOR]

Monolithic perovskite/organic tandem solar cells (POTSCs) have significant advantages in next‐generation flexible photovoltaics, owing to their capability to overcome the Shockley–Queisser limit and facile device integration. However, the compromised sub‐cells performance challenges the fabrication of high‐efficiency POTSCs. Especially for all‐inorganic wide‐bandgap perovskite front sub‐cells (AIWPSCs) based n‐i‐p structured POTSCs (AIPOTSCs), for which the power conversion efficiency (PCE) is much lower than organic–inorganic mixed‐halide wide‐bandgap perovskite based POTSCs. Herein, an ionic liquid, methylammonium formate (MAFm), based dual‐interface engineering approach is developed to modify the bottom and top interfaces of wide‐bandgap CsPbI2Br films. In particular, the Fm− group of MAFm can effectively passivate the interface defects, and the top interface modification can facilitate the formation of uniform perovskite films with enlarged grain size, thereby mitigating the defects and perovskite grain boundaries induced carrier recombination. As a result, CsPbI2Br‐based AIWPSCs with a high PCE of 17.0% and open‐circuit voltage (VOC) of 1.347 V are achieved. By integrating these dual‐interface engineered CsPbI2Br‐based front sub‐cells with the narrow‐bandgap PM6:CH1007‐based rear sub‐cells, a record PCE of 23.21% is obtained for AIPOTSCs, illustrating the potential of AIPOTSCs for achieving high‐efficiency tandem solar cells. [ABSTRACT FROM AUTHOR]

Monolithic perovskite/organic tandem solar cells (POTSCs) have attracted increasing attention owing to ability to overcome the Shockley–Queisser limit. However, compromised sub‐cells performance limits the tandem device performance, and the power conversion efficiency (PCE) of POTSCs is still lower than their single‐junction counterparts. Therefore, optimized sub‐cells with minimal energy loss are desired for producing high‐efficiency POTSCs. In this study, an ionic liquid, methylammonium acetate (MAAc), is used to modify wide‐bandgap perovskite sub‐cells (WPSCs), and bathocuproine (BCP) is used to modify small‐bandgap organic solar cells. The Ac− group of MAAc can effectively heal the Pb defects in the all‐inorganic perovskite film, which enables a high PCE of 17.16% and an open‐circuit voltage (Voc) of 1.31 V for CsPbI2.2Br0.8‐based WPSCs. Meanwhile, the BCP film, inserted at the ZnO/organic bulk‐heterojunction (BHJ) interface, acts as a space layer to prevent direct contact between ZnO and the BHJ while passivating the surface defects of ZnO, thereby mitigating ZnO defect‐induced efficiency loss. As a result, PM6:CH1007‐based SOSCs exhibit a PCE of 15.46%. Integrating these modified sub‐cells enable the fabrication of monolithic n–i–p structured POTSCs with a maximum PCE of 22.43% (21.42% certified), which is one of the highest efficiencies in such type of POTSCs. [ABSTRACT FROM AUTHOR]

To fabricate stable neat FAPbI3 perovskite with a pure α‐phase (pure α‐FAPbI3) is important in the field of photovoltaic commercialization because of its better bandgap than its alloying counterpart with cesium (Cs) or methylammonium (MA) cations. In this study, the first vapor deposited pure α‐FAPbI3 thin film solar cell with a power conversion efficiency (PCE) over 20% is achieved by regulating the phase transition process. It is found that under high humidity conditions, a fast phase transition between high‐purity α‐ and δ‐phase FAPbI3 can be realized. Moreover, theoretical calculations interestingly reveal a phase transition shortcut induced by the abnormal volume contraction that is ascribed to the formation of double hydrogen bonds at a certain H2O concentration. Therefore, a high‐humidity post‐treatment strategy is proposed to fabricate α‐FAPbI3 solar cells with a champion PCE of 20.19% (0.1 cm2) and 18.91% (1 cm2), which is currently the highest recorded value in vapor deposited pure α‐FAPbI3 perovskite solar cells. This study helps to redefine the effect of a water molecule on FAPbI3 solar cells. In addition, the demonstrated scaling‐up possibility provides another perspective for fabricating uniform high‐performance pure α‐FAPbI3 perovskite solar cells. [ABSTRACT FROM AUTHOR]

Organic‐free and lead‐free CsSnI3 perovskite solar cells (PSCs) have recently gained growing attention as a promising template to mitigate the thermal instability and lead toxicity of hybrid lead‐based PSCs. However, the relatively low device efficiency due to the high content of Sn(II)‐related defects hinders its further development. Herein, highly performed CsSnI3−xBrx compositional perovskite‐based PSCs are achieved by using dimethyl ketoxime (C3H7NO, DMKO) as a multifunctional additive. As a commercially used deoxidant, DMKO can effectively neutralize the oxygen molecule and reduce Sn4+ back to Sn2+, enhancing the oxidation resistance of the film. Besides, the electron‐rich oxime group (NOH) in DMKO tends to interact with Sn2+ ions with extremely low adsorption energy less than −15 eV and inhibits defect formation, resulting in films with low defect density. The corresponding PSCs deliver a considerable open‐circuit voltage (Voc) of 0.75 V with a record efficiency as high as 11.2%, which represents the highest reported efficiency for lead‐free all‐inorganic PSCs thus far. More importantly, the grain surface distributed DMKO provides an in situ encapsulation of the perovskite, which results in greatly enhanced ambient stability of the un‐encapsulated devices. [ABSTRACT FROM AUTHOR]

Perovskite solar cells (PSCs) via two‐step sequential method have received great attention in recent years due to their high reproducibility and low processing costs. However, the relatively high trap‐state density and poor charge carrier extraction efficiency pose challenges. Herein, highly efficient and stable PSCs via a two‐step sequential method are fabricated using organic—inorganic (OI) complexes as multifunctional interlayers. In addition to reduce the under‐coordinated Pb2+ ions related trap states by forming interactions with the functional groups, the complexes interlayer tends to form dipole moment which can enhance the built‐in electric field, thus facilitating charge carrier extraction. Consequently, with rational molecular design, the resulting devices with a vertical dipole moment that parallels with the built‐in electric field yield a champion efficiency of 23.55% with negligible hysteresis. More importantly, the hydrophobicity of the (OI) complexes contributes to an excellent ambient stability of the resulting device with 91% of initial efficiency maintained after 3000 h storage. [ABSTRACT FROM AUTHOR]

Vacancy defects are universally regarded to be the main defect that limits the photoelectric conversion efficiency of perovskite solar cells. In perovskite, iodine vacancy dominates the defect proportion due to its low formation energy. However, the defect property of iodine vacancy (VI) is still in dispute. Ideally, the VI defect is considered to be a shallow level defect near conduction band minimum, meaning that it does not act as a Shockley–Read–Hall (SRH) nonradiative recombination center. Herein, we find a direct correlation between compressive strain and VI defect behavior. The compressive strain along the lattice vector b/c direction will drive the VI defect from shallow level to deep level defect, which is related to the formation of Pb-dimer. In addition, the influence of extra electrons is also considered during the structural evolution of VI, which is often observed in the experiments. Therefore, we find that the elimination of compressive strain and extra electrons can be of great significance for improving the photoelectric performance of perovskite solar cells. Our work reveals the defect properties of VI from shallow level one to the SRH recombination center and the inherent physics mechanism of defect evolution under external factors, which provides a strategy to control device defects and eliminate recombination losses. [ABSTRACT FROM AUTHOR]

The Dion–Jacobson (DJ) perovskites solar cells (PSCs) demonstrate impressive humidity stability compared with 3D counterparts and have aroused extensive attention recently. However, it has not been investigated yet, how the humidity condition influences the photovoltaic performances. Herein, the effect of the humidity condition on the crystallization behavior, charge dynamics, photovoltaic and stability performances of BDAFAn‐1PbnI3n+1 DJ perovskite is systematically investigated. Humidity‐assisted annealing process can lead to reduced trap concentration and fast charge transfer process between different‐n DJ phases. The BDAFA5Pb6I19 PSC with the assistance of moisture achieves an efficiency as high as 17.17%, which is the highest value ever reported for methylammonium‐free DJ PSCs. In addition, the humidity‐, thermal‐, and photo‐stability properties of the DJ film and devices are significantly boosted. Further, first‐principles calculation indicates that water molecules occupy the iodide vacancies through a strong bonding with Pb ions during the crystallization process under humidity and increase the decomposition energy of the DJ phase, which corresponds to the improved photoelectronic and stability properties. These results show that humidity‐assisted deposition of 2D/3D multidimensional perovskite can be further explored to reduce the high demand of the production environment and enhance the performances. [ABSTRACT FROM AUTHOR]

Distinct from CsSnI3 perovskite systems, the most stable non-centrosymmetric trigonal structure (space group of R3m) of the CsGeI3 perovskite system was found in our calculations. We systematically studied the differences between two all-inorganic perovskites (CsSnI3 and CsGeI3) and proposed an unexpected distorted stable structure of the mixed Sn–Ge perovskite system (CsSn0.5Ge0.5I3). All calculations of structural configuration and electronic properties were performed in the projector augmented-wave density-functional theory framework via the generalized gradient approximation (GGA). We found that the energy band evolutions of all-inorganic perovskites CsSnxGe1−xI3 are completely different from those of the Sn–Pb perovskite compounds. After considering the spin–orbit coupling (SOC) effect, the bandgap evolution of the stable structure shows a linear change. The results unravel the previous controversial understanding of the atomic and electronic properties of Ge-based perovskite solar cells. [ABSTRACT FROM AUTHOR]

With respect to three‐dimensional (3D) perovskites, quasi‐two‐dimensional (quasi‐2D) perovskites have unique advantages in light‐emitting devices (LEDs), such as strong exciton binding energy and good phase stability. Interlayer ligand engineering is a key issue to endow them with these properties. Rational design principles for interlayer materials and their processing techniques remain open to investigation. A co‐interlayer engineering strategy is developed to give efficient quasi‐2D perovskites by employing phenylbutylammonium bromide (PBABr) and propylammonium bromide (PABr) as the ligand materials. Preparation of these co‐interlayer quasi‐2D perovskite films is simple and highly controllable without using antisolvent treatment. Crystallization and morphology are readily manipulated by tuning the ratio of co‐interlayer components. Various optical techniques, including steady and ultrafast transient absorption and photoluminescence spectroscopies, are used to investigate their excitonic properties. Photoluminescence quantum yield (PLQY) of the perovskite film is dramatically improved to 89% due to the combined optimization of exciton binding energy and suppression of trap state formation. Accordingly, a high current efficiency of 66.1 cd A−1 and an external quantum efficiency of 15.1% are achieved for green co‐interlayer quasi‐2D perovskite LEDs without using any light out‐coupling techniques, indicating that co‐interlayer engineering is a simple and effective approach to develop high‐performance perovskite electroluminescence devices. [ABSTRACT FROM AUTHOR]

Vapor reaction is one of the major methods used for large-scale fabrication of high-quality organic–inorganic halide perovskite solar cells, but its detailed process is rarely investigated. In this study, the thermal and illumination effects on PbI2 and its transformation to CH3NH3PbI3 (MAPbI3) under CH3NH3I (MAI) vapor were investigated. Atomic shifting of the PbI2 layer was observed, which caused the generation of defects and distortion in PbI2 without breaking the phase structure. The reaction with MAI started with decoupling of PbI2 layers and formation of nanoislands and then, the transformation of PbI2 to MAPbI3 proceeded randomly on the surface from top to bottom. Additional illumination of the reaction suppressed the transformation, causing the generation of PbI2 nano-walls along [100] and [010] directions, leading to decrease in power conversion efficiency. [ABSTRACT FROM AUTHOR]

[Display omitted] • Spontaneous formation of defect states in γ-InSe/(C 4 H 9 NH 3) 2 (CH 3 NH 3)Pb 2 I 7 van der Waals heterostructures. • Theoretical calculation and experiment suggest the dynamic generation of iodine vacancy and charge states. • Electron–phonon coupling of the 2D perovskite is weakened from −127 meV to −90 meV in the heterostructure. • The band offset causes the built-in electrical field, then strengthens the optoelectrical response of heterostructure. Van der Waals (vdW) heterostructure composed of two-dimensional (2D) materials and 2D perovskite has shown excellent optoelectrical properties recently, while the interfacial coupling is less investigated. Here, van der Waals InSe/(C 4 H 9 NH 3) 2 (CH 3 NH 3)Pb 2 I 7 heterostructure is fabricated and systemically investigated by photoluminescence (PL) spectroscopy. An optical broadband emission is generated due to the formation of heterostructure. The first principle calculation and variable PL spectra suggest the dynamic generation of defects such as iodine vacancy and charge states. Electron–phonon coupling of the 2D perovskite is weakened from −127 meV to −90 meV in the heterostructure. The band offset causes the built-in electrical field, which strengthens the optoelectrical response of heterostructure devices. The results deepen the understanding of the interfacial optoelectrical dynamic of 2D perovskite-related vdW heterostructure and help develop superior optoelectrical vdW heterostructure devices. [ABSTRACT FROM AUTHOR]

Distinct from CsSnI3 perovskite systems, the most stable non-centrosymmetric trigonal structure (space group of R3m) of the CsGeI3 perovskite system was found in our calculations. We systematically studied the differences between two all-inorganic perovskites (CsSnI3 and CsGeI3) and proposed an unexpected distorted stable structure of the mixed Sn–Ge perovskite system (CsSn0.5Ge0.5I3). All calculations of structural configuration and electronic properties were performed in the projector augmented-wave density-functional theory framework via the generalized gradient approximation (GGA). We found that the energy band evolutions of all-inorganic perovskites CsSnxGe1−xI3 are completely different from those of the Sn–Pb perovskite compounds. After considering the spin–orbit coupling (SOC) effect, the bandgap evolution of the stable structure shows a linear change. The results unravel the previous controversial understanding of the atomic and electronic properties of Ge-based perovskite solar cells. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) all-inorganic metal halide perovskites capture more attentions due to its superior stability compared with three-dimensional (3D) perovskites. However, the power conversion efficiency of 2D all-inorganic perovskite is needed to be largely improved and few theoretical research focuses on its structural stability and optoelectronic properties in depth. Herein, we exploit the electronic structure, thermodynamically stable phase, effective masses, and optical properties of Ruddlesden-Popper (RP) 2D inorganic perovskites Cs n+1 M n I n+1 Cl 2n (M = Pb or Sn, n = 1–4 and ∞) by employing density functional theory calculations. It is found that the most stable configuration is closely related to the specific position of the halogen atoms. Moreover, the thermodynamic stability of Pb-based 2D perovskites is further calculated based on the phase diagram, which is notably more stable than that of Cs 2 SnI 2 Cl 2. In addition, our calculated results show that the band gaps decrease as the number of layers increase in both Sn- and Pb-based perovskites. Moreover, Sn-based 2D perovskites can be adjusted to superior electronic properties with the optimal bandgap ranging from 0.9 to 1.6 eV and small effective mass of carriers considering its future application. This systematic theoretical study provides a significant methodology for fabricating stable, new-type 2D inorganic photoelectric materials according to a reasonable stoichiometric ratio. [ABSTRACT FROM AUTHOR]

Proton-conducting solid oxide fuel cells (H + -SOFCs) have attracted considerable interest recently. However, the overall cell performance of H + -SOFCs is still low due to the lack of a promising cathode material. In this study, SrSc 0.175 Nb 0.025 Co 0.8 O 3-δ (SSNC) was synthesized for evaluation as a cathode material in H + -SOFCs based on a BaZr 0.1 Ce 0.7 Y 0.2 O 3-δ (BZCY) electrolyte. The chemical compatibility and stability of the SSNC cathode with the BZCY electrolyte in humidified air were studied. In addition, the electrochemical behavior of the SSNC cathode on the BZCY electrolyte was investigated using SSNC/BZCY/SSNC symmetrical cells at 600 °C in dry air and humidified air at various H 2 O partial pressures. Promising electrocatalytic activity was observed for the SSNC cathode in humidified air. The area specific resistance obtained on symmetrical cells at 600 °C in a 10% H 2 O-air atmosphere was 0.26 Ω cm 2 . A promising peak power density of 498 mW cm −2 was obtained using an anode-supported cell with a 46 μm-thick BZCY electrolyte layer at 700 °C. [ABSTRACT FROM AUTHOR]

[Display omitted] Recently, hybrid two-dimensional (2D) Ruddlesden-Popper (RP) phase layered halide perovskite structures of (BA) 2 Cs n-1 Pb n Br 3n+1 (BA is the butylammonium organic chain and n is the number of inorganic perovskite-like layers) have been experimental synthesized and indicated superior optical properties. Here, we reported an investigation of the above series of layered halide perovskites (n = 1, 2, 3 and ∞). Their structural, electronic and optical properties were calculated using first-principle approaches, including the bond angles, band structures, formation energy, carrier effective masses, density of states, differential charge densities, Bader charge analysis, optical absorption spectra and transition dipole moment. As a consequence of these findings, with the increase in the number of inorganic layers, perovskite materials showed lower bandgaps, improved light absorption and poorer stability. Hence, tuning the inorganic layer thickness of layered 2D RP phase perovskites is a suitable method to enhance their optoelectronic properties. This work provides a theoretical basis for layered 2D perovskite materials with large-scale and low-cost applications in the photoluminescent device light-emitting diodes. [ABSTRACT FROM AUTHOR]

Metal-halide perovskite solar cells (PSCs) now show excellent efficiencies with record values in excess of 25%. However, the uncoordinated Pb2+ ions on the surface of perovskite films are usually generated due to the easily volatile organic component during thermal annealing, which commonly induce deep level traps on perovskite films. These defects heavily influence the device performance and stability by acting as nonradiative recombination centers and ionic migration channels. Therefore, it is thus desirable to passivate uncoordinated Pb2+ ions. Here, a dual-active-site isonicotinic acid (INA) containing nitrogen (N) atom and C=O group electron donors is employed to passivate uncoordinated Pb2+ defects on the surface of perovskite films. Experimental results confirm strong chemical interaction between INA molecule and perovskite film, thereby significantly improving charge transport and reducing defect density. Upon INA passivation, the devices (with an active area of 0.1 cm2) performance is boosted from 19.19% to 20.34% with less hysteresis. Meanwhile, benefiting from the passivation effect, the passivated devices exhibit much longer stability, retaining 80% of its initial efficiency after 20 days of constant illumination. This work provides a promising strategy to achieve high performance and stable PSCs. • Undercoordinated Pb2+ defects of perovskite film were passivated using innovative molecules with dual-active-site. • We first demonstrate N atom at pyridine has stronger electronic interaction with Pb2+ compared with the carboxyl in experimental route. • The device performance was boosted from 19.19% to 20.34% with less hysteresis by INA passivation. • It provides a new way to optimize perovskite films and fabricate high-efficiency PSCs with Mulit-Active Site molecules. [ABSTRACT FROM AUTHOR]