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Cubic zinc metatitanate (ZTO) is identified as an excellent electron transport material with interface engineering treatment of dezincification for high efficient perovskite solar cells (PSCs). By integrating an inorganic hole transport layer and rGO protection, the ZTO electron transport layer‐based PSCs exhibit strong resistance to moisture, heat, and ultraviolet light, demonstrating high efficiency and stability toward practical applications.

Perovskite solar cells (PSCs) have experienced considerable development in the past few years. The stability issue has become a focus of research efforts toward their commercial applications. The development and interface engineering of electron transport materials (ETMs) to build up stable interfaces with perovskites has been emerging as a powerful strategy to enhance PSCs' stability. Herein, cubic zinc metatitanate (ZTO) is identified as an excellent ETM with interface engineering treatment of dezincification for fabricating PSCs with much better overall performances than those fabricated from TiO₂, a popularly used ETM. The high electron mobility of ZTO helps minimize the hysteresis. Together with the use of CuSCN as inorganic hole transport material and further protecting the PSCs with reduced graphene oxide, the ZTO‐based PSCs exhibit remarkable enhancement in stability, retaining 95% of initial power conversion efficiency under AM 1.5 G illumination at 85 °C and 85% relative humidity in air for 1000 h at open circuit.

An effective polar molecule of (2‐aminothiazole‐4‐yl)acetic acid (ATAA) is incorporated onto a ZnO electron transport layer to simultaneously achieve defect passivation and work function modulation by forming permanent interface dipoles. It minimizes the charge recombination loss in perovskite solar cells, and the ZnO–ATAA‐based device ultimately achieves an enhanced efficiency of 19.74% while suppressing the device hysteresis.

The intrinsic characteristics of a ZnO electron transport layer (ETL) lead to severe charge loss in perovskite solar cells (PSCs), such as photogenerated charge accumulation recombination in the perovskite layer due to the low electron extraction capacity, and defect‐induced charge recombination at the interface due to the unfavorable defects, causing efficiency loss and device hysteresis. Here, the polar molecule of (2‐aminothiazole‐4‐yl)acetic acid (ATAA) is self‐assembled onto a ZnO layer with the help of oxygen vacancy defects, combining the advantages of lowering the work function by forming the permanent interface dipole and simultaneously passivating defect states. It effectively strengthens the electron extraction capacity and reduces the density of defect states. Therefore, the resulting PSCs with a ZnO–ATAA ETL yield an enhanced efficiency of 19.74% with evidently reduced device hysteresis.

A simple low‐temperature‐processed In₂O₃/SnO₂ bilayer electron‐transport layer (ETL) is used for fabricating efficient perovskite solar cells (PSCs). The bilayer ETL with appropriate energy alignment is beneficial for charge transfer, thus minimizing open‐circuit voltage (V _OC) loss. An optimized planar PSC with a power conversion efficiency (PCE) of 23.24% is obtained. In contrast, devices based on single SnO₂ only achieve efficiency of 21.42%.

Abstract

An electron‐transport layer (ETL) with appropriate energy alignment and enhanced charge transfer is critical for perovskite solar cells (PSCs). However, interfacial energy level mismatch limits the electrical performance of PSCs, particularly the open‐circuit voltage (V _OC). Herein, a simple low‐temperature‐processed In₂O₃/SnO₂ bilayer ETL is developed and used for fabricating a new PSC device. The presence of In₂O₃ results in uniform, compact, and low‐trap‐density perovskite films. Moreover, the conduction band of In₂O₃ is shallower than that of Sn‐doped In₂O₃ (ITO), enhancing the charge transfer from perovskite to ETL, thus minimizing V _OC loss at the perovskite and ETL interface. A planar PSC with a power conversion efficiency of 23.24% (certified efficiency of 22.54%) is obtained. A high V _OC of 1.17 V is achieved with the potential loss at only 0.36 V. In contrast, devices based on single SnO₂ layers achieve 21.42% efficiency with a V _OC of 1.13 V. In addition, the new device maintains 97.5% initial efficiency after 80 d in N₂ without encapsulation and retains 91% of its initial efficiency after 180 h under 1 sun continuous illumination. The results demonstrate and pave the way for the development of efficient photovoltaic devices.

La_0.5Sr_0.5Mn_0.5Co_0.5O_{3− δ} strained epitaxial thin films are characterized using X‐ray diffraction, X‐ray absorption near edge spectroscopy and ion scattering techniques. The induced strain resulted in correlated structural and chemical changes with selectivity to the transition metal. In‐plain tensile strain promotes preferential reduction of Mn cations due to the higher Mn‐O/Ti‐O mismatch and favors a greater segregation of Sr secondary phases.

Abstract

Understanding the effects of lattice strain on oxygen surface and diffusion kinetics in oxides is a controversial subject that is critical for developing efficient energy storage and conversion materials. In this work, high‐quality epitaxial thin films of the model perovskite La_0.5Sr_0.5Mn_0.5Co_0.5O_{3− δ} (LSMC), under compressive or tensile strain, are characterized with a combination of in situ and ex situ bulk and surface‐sensitive techniques. The results demonstrate a nonlinear correlation of mechanical and chemical properties as a function of the operation conditions. It is observed that the effect of strain on reducibility is dependent on the “effective strain” induced on the chemical bonds. In‐plain strain, and in particular the relative BO length bond, is the key factor controlling which of the B‐site cation can be reduced preferentially. Furthermore, the need to use a set of complimentary techniques to isolate different chemically induced strain effects is proven. With this, it is confirmed that tensile strain favors the stabilization of a more reduced lattice, accompanied by greater segregation of strontium secondary phases and a decrease of oxygen exchange kinetics on LSMC thin films.

Tetraethyl orthosilicate processed silica oligomer is in situ introduced into perovskite films to serve as a passivation agent (PA) for perovskite solar cells (PVSCs). Silica oligomer PA can enlarge perovskite grain sizes, prolong carrier lifetime, enhance charge carrier dynamics, and reduce trap state densities, resulting in highly efficient PVSCs with good humid and thermal stability.

Abstract

Perovskite solar cells (PVSCs) have achieved excellent power conversion efficiency (PCE) but still suffer from instability issues. Defect passivation is an important route to simultaneously increase the efficiency and stability of PVSCs. Here, a strategy of incorporating silica oligomer in perovskite films for surface and grain boundary defect passivation is reported. Silica oligomer passivation agent (PA) is in situ formed through hydrolysis and condensation reaction of tetraethyl orthosilicate additive in perovskite precursor. The passivation mechanism is elucidated by density functional theory calculation, revealing stable chelating interaction and hydrogen bond interaction between PA and perovskite. Spectroscopic and electrical characterizations demonstrate that silica oligomer can enlarge grain sizes, prolong carrier lifetime, enhance charge carrier dynamics, and reduce trap state densities in perovskite films. Planar PVSCs with passivation achieve a highly improved PCE of 19.64% with a stabilized efficiency of 18.81%. More importantly, unencapsulated perovskite devices with passivation retain nearly 90% of original efficiency after 1000 h storage under ambient condition and sustained 87% of initial performance after high‐temperature (120 °C) thermal accelerated aging, showing highly enhanced moisture and thermal stability. Therefore, the present study provides a pathway to the future design and optimization of PVSCs with higher efficiency and greater stability.

A solution‐processed, organic‐modulated perovskite quantum dots photodetector is designed, which exhibits ultrasensitive photoresponse abilities with detectivity (4.6 × 10¹³ J), noise equivalent power (1 × 10⁻¹⁶ W Hz^−0.5) and I _Light/I _Dark ratio (2 × 10³). This device is fabricated by adding a protecting layer deposited from hydrofluoroether solution (M7100) between the quantum dots film and the organic layer to solve the challenge of solvent orthogonality.

Abstract

The integration of organic materials with colloidal quantum dots (QDs) has the merits the advantages of the molecular diversity and photoelectric tunability for ultrasensitive photodetector applications. Herein, a uniform CsPbBr₃ QD layer is sandwiched between the same poly‐(N, N′‐bis‐4‐butylphenyl‐N, N′‐bisphenyl) benzidine (Poly‐TPD) and phenyl‐C61‐butyric acid methyl ester (PCBM) (1:1) organic blend films. The CsPbBr₃ QD layer efficiently absorbs the excitation light, where the generated exciton can sufficiently diffuse to the interface of QD and organic blend layers for efficient charge separation and effective gate modulation. Owing to the desirable heterojunction at the interface, the dark current is substantially suppressed, while the photocurrent is increased in comparison with those of pristine QDs photodetectors. The ultrafast charge transfer time (≈300 ps) from QDs to organic blend layer measured by the time‐resolved transient absorption spectroscopy is potentially benefit the enhanced electron–hole pair dissociation. The solution‐processed, organic (Poly‐TPD:PCBM blend)‐modulated CsPbBr₃ QDs photodetector are exhibited ultrasensitive photoresponse abilities in terms of in terms of noise equivalent power (NEP = 1 × 10⁻¹⁶ W Hz^−0.5), I _Light/I _Dark ratio (2 × 10³), and the a specific detectivity (D* = 4.6 × 10¹³ Jones). The results will be a starting point for ultrasensitive next‐generation light detection technologies.

The effects of adding different Lewis bases on the composition of quasi‐2D crystal phases are investigated. The introduction of stable intermediate complexes not only enhances spatial uniformity of crystallization but also modulates the orientation. Weak dative bonding and strong hydrogen bonding combine to enhance device performance.

Abstract

Crystallographic orientation has a significant impact on the optoelectronic properties of films of quasi‐2D perovskite quantum wells. Here, oxygen‐bearing Lewis bases are employed as additives to explore their ability to modulate spatial uniformity of crystallization and orientation of crystal phases. Different Lewis bases added into the precursor solutions incorporating the large organic ammonium cation, phenethylammonium (PEA⁺), lead to different crystallization kinetics, which are attributed to the varying stability of intermediate complexes. The microscopic photoluminescence heterogeneity and 2D X‐ray diffraction patterns of the thin films reveal that inclusion of Lewis bases can lead to spatially more uniform crystallization and random orientation, resulting in an enhancement in light‐emitting diode performance. In contrast, quasi‐2D phases formed without Lewis bases show poorer uniformity and preferentially vertical orientation. Comparing the Lewis base properties such as Mayer order unsaturation and polarizability suggests that the ability to weakly coordinate with lead and strongly interact with the large organic ammonium is a key factor in controlling the phase composition favorably toward highly luminescent light‐emitting diodes. This work may be of help to provide insight of what kinds of Lewis bases can be helpful to realize the desired phase composition for high performance of optoelectronic applications.

In this Review, the important role of the interface in tin‐based perovskites and their PSCs device is demonstrated. The up‐to‐date studies on interface engineering of tin‐based PSCs are summarized. At last, a future perspective and remaining challenges in this field are given to provide some new thoughts on interface engineering for efficient tin‐based PSCs device.

Abstract

As a rising star of lead‐free perovskite solar cells (PCSs), tin‐based PSCs have drawn much attention and made promising progress during the past few years. Notably, interfaces in the tin‐based PSCs device have great impacts on performance enhancements. In this Review, the authors first demonstrate why the interface is especially crucial for tin‐based PSCs device. It is proposed that the engineering of i) interface between perovskite grains in the film and ii) interface within the PSCs device are of great significance on the improvement of device functionality and stability. Then, the up‐to‐date studies on interface engineering of tin‐based PSCs are reviewed, including the following strategies: i) passivation of trap states; ii) modification of interfacial layers; iii) construction of 2D/3D structure. At last, a future perspective and remaining challenges in this field are given, aiming to provide a comprehensive understanding of interfaces in tin‐based PSCs and give some new thoughts on interface engineering for efficient PSCs device.

The biaxial strains originating from the lattice mismatch endow the monolayer SnS an indirect‐to‐direct bandgap transition. Moreover, the interface effect in turn reduces the band offset of the CsPbI₃/SnS heterostructure and enhances its optical absorption ability. Therefore, forming heterostructure can promote the properties of CsPbI₃‐based devices.

Abstract

Different 2D materials can be stacked by the weak van der Waals (vdW) force, forming the vdW heterostructures and devices, which opens a new field of engineering regulation of electronic and optical properties at the atomic level. The asymmetric strain‐introduced interface effect is studied on the electronic and optical properties of CsPbI₃/SnS vdW heterostructure by employing first‐principles calculations. The biaxial strains deriving from the interface mismatch reduce the work function of the monolayer SnS to a low‐energy level, and lead to monolayer SnS an indirect‐to‐direct bandgap transition. The different charge transfer behaviors in the PbI₂‐ (CsI‐) surface indicate that monolayer SnS can act as the promising hole‐ (electron‐) transport material of perovskite solar cells (PSCs). Moreover, the interface effect causes the absorption spectrum of the CsPbI₃/SnS heterostructure an obvious redshift and enhances its absorption ability, which is more suitable for photovoltaic devices. This work suggests that the strain‐introduced interface effect plays a significant role in the interface engineering of the vdW heterostructure between perovskite and 2D materials, which provides a new way to fabricate the high performance perovskite/2D materials heterostructure‐based solar cells and optoelectronic devices.

The present study reveals a strong influence of sputtered NiO _x on the perovskite crystallization and the appearance of residual PbI₂ grains resulting in low photovoltaic device performance. Among different methylammonium (MA⁺) halide additives and vapor treatment (to improve the perovskite crystallization) only MA⁺ halide vapor‐treated perovskite shows suppressed recombination, enhanced carrier lifetime, and device efficiency.

Abstract

Investigating the low efficiency issue of radio frequency‐sputtered nickel oxide (sp‐NiO _x )‐based perovskite solar cells (PSCs) due to a limited understanding of the correlation between perovskite growth and sp‐NiO _x on the optoelectronic properties and photovoltaic device performance is critical. Herein, the crystallization of methylammonium (MA) lead iodide (MAPbI₃) thin film (obtained from stoichiometric precursor ratio) on sp‐NiO _x is shown, resulting in appearance of residual PbI₂ grains. This is in contrast to perovskite growth on solution‐processed NiO _x . The amount of residual PbI₂ is suppressed by 1) adding excess MACl/MAI additives and 2) annealing the perovskite film in MACl/MAI vapor atmosphere. Structural and morphological results reveal significant reduction in the amount of residual PbI₂ and enhanced grain size for all the cases while photophysical measurements reveal mitigation of trap/defect sites (within the bulk and at the interfaces) only for MACl/MAI vapor annealing case. As a result, photovoltaic devices exhibit improved performance only for the vapor annealing case. These results elucidate the critical role of maintaining stoichiometric ratio in perovskite and its crystallization on sp‐NiO _x by eliminating the associated defects (influenced by sp‐NiO _x ) in rendering improved performance, which can be insightful to further enhance the performance of PSCs.

The epitaxial mechanism of perovskite SrTiO₃ on fluorophlogopite mica substrate is understood by the atomic scale observation, accompanied by confirmation, and understanding from the atomistic calculations, of the interfaces. The epitaxy of the film is strongly related to the oxygen sublattices in the (111) Sr–O₃ atomic plane of SrTiO₃ and in the (001) (SiAl)₂–O₃ plane of the mica.

Abstract

The excellent functionalities of perovskite oxides and the growing demands for flexible devices lead to great interests on epitaxial growth of functional oxide films on flexible mica substrates. Understanding the film epitaxy on the substrate with a very different crystal structure is a key issue for the optimization of the film growth and hence properties. Such understanding largely depends on knowing the atomic structure of the interfaces between the films and the substrates. Here, the interface between the epitaxial films of SrTiO₃ on the fluorophlogopite mica substrate is studied in detail. Two types of interfaces, clean or with secondary phase, exist in this system, leading to two types of crystallographic orientation relationships. Atomic‐resolution scanning transmission electron microscopy images reveal that at the clean interface the (111) Sr–O₃ atomic plane of SrTiO₃ interacts with the (001) (SiAl)₂–O₃ plane of mica. This interface structure and thus the epitaxy of the film are understood in light of the strong similarity of the oxygen sublattices in these two atomic planes. First‐principles calculations demonstrate strong bonding of the atoms at the interface, which is also corroborated by the observation of misfit dislocations at the interfaces.

The nontoxic carbon spheres synthesized with uniform morphology and controllable size and used as a template to generate the tunable porous TiO₂ films. The effect of porosity modification of TiO₂ film, as an efficient ETL in the perovskite solar cells, on the formation of CH₃NH₃PbI₃ films with large grain size is studied in ambient atmosphere with humidity higher than 50%.

Abstract

Crystallization and nucleation of the perovskite layer in the mesoscopic perovskite solar cells (PSCs) depend on the nucleation sites of the electron transport layer (ETL). The porosity optimization of TiO₂ film as an efficient ETL plays an important role in the performance improvement of PSCs. In the present study, nontoxic carbon spheres synthesized with uniform morphology and controllable size under hydrothermal conditions and used as a template to generate the tunable porous TiO₂ films. Furthermore, the effect of porosity modification of TiO₂ on the formation of perovskite films with large grain size is studied in an ambient atmosphere with humidity higher than 50%. The best TiO₂ film is produced with carbon spheres 8 wt% (C8), which results in the formation of a pinhole‐free, and compact‐packed perovskite layer. The fully air processed PSC device with the ETL made of C8 film exhibits an efficiency of 16.66% with reduced hysteresis, which is much superior in performance compared to the standard cell (11.72%). It is believed that this porosity optimization of TiO₂ layer is a simple practical strategy for improved stability of fully air processed efficient perovskite solar cells and usable for the fabrication of reproducible compact perovskite layers in uncontrolled laboratories.

The nontoxic carbon spheres synthesized with uniform morphology and controllable size and used as a template to generate the tunable porous TiO₂ films. The effect of porosity modification of TiO₂ film, as an efficient ETL in the perovskite solar cells, on the formation of CH₃NH₃PbI₃ films with large grain size is studied in ambient atmosphere with humidity higher than 50%.

Abstract

Crystallization and nucleation of the perovskite layer in the mesoscopic perovskite solar cells (PSCs) depend on the nucleation sites of the electron transport layer (ETL). The porosity optimization of TiO₂ film as an efficient ETL plays an important role in the performance improvement of PSCs. In the present study, nontoxic carbon spheres synthesized with uniform morphology and controllable size under hydrothermal conditions and used as a template to generate the tunable porous TiO₂ films. Furthermore, the effect of porosity modification of TiO₂ on the formation of perovskite films with large grain size is studied in an ambient atmosphere with humidity higher than 50%. The best TiO₂ film is produced with carbon spheres 8 wt% (C8), which results in the formation of a pinhole‐free, and compact‐packed perovskite layer. The fully air processed PSC device with the ETL made of C8 film exhibits an efficiency of 16.66% with reduced hysteresis, which is much superior in performance compared to the standard cell (11.72%). It is believed that this porosity optimization of TiO₂ layer is a simple practical strategy for improved stability of fully air processed efficient perovskite solar cells and usable for the fabrication of reproducible compact perovskite layers in uncontrolled laboratories.

A sandwich heterostructure made of PVK/ZnO nanorods/graphene is designed for building ultraviolet photodetector. The device shows enhanced photoresponse and an increased responsivity of ≈440% under strain‐induced piezopolarization charges. More details can be found in article number https://doi.org/10.1002/admi.2019013651901365 by Xinglai Zhang, Baodan Liu, and co‐workers.