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A compact TiO₂/WO₃ bilayer film is fabricated as electron transport layer (ETL) in perovskite solar cells. Compared to the single WO₃ layer, the bilayer efficiently covers the fluorine‐doped tin oxide (FTO), avoids the direct contact between perovskite and FTO, decreases the risk of recombination. Finally, the bilayer ETL based device achieves a superior power conversion efficiency of 20.14%.

Abstract

It is crucial to retard the carrier recombination and minimize the energy loss at the transparent electrode/electron transport layer (ETL)/perovskite absorber interfaces to improve the performance of the perovskite solar cells (PSCs). Here, a bilayered TiO₂/WO₃ film is designed as ETL by combining atomic layer deposition (ALD) technology and spin‐coating process. The ALD‐TiO₂ underlayer fills the fluorine‐doped tin oxide (FTO) valleys and makes the surface smoother, which effectively avoids the shunt pathways between perovskite layer and FTO substrate and thereby suppresses electron–hole recombination at the interface. Moreover, the presence of hydrophilic TiO₂ underlayer is helpful in forming a uniform and compact WO₃ layer which is beneficial for extracting electron from perovskite to ETL. Meanwhile, the lower valance band minimum level of TiO₂ relative to WO₃ can efficiently enhance the hole‐blocking ability. By employing the optimized TiO₂ (7 nm)/WO₃ bilayer as ETL, the resulting cell exhibits an obviously enhanced power conversion efficiency of up to 20.14%, which is much better than the single WO₃ or TiO₂ ETL based device. This work is expected to provide a viable path to design ultrathin and compact ETL for efficient PSCs.

A postdeposition treatment is designed to modify the photoactive layer of perovskite solar cell (PSC) by spin‐coating p‐aminobenzoic acid (PABA). The PABA treatment can enhance V _OC, fill factor, and power conversion efficiency. The performance improvement is attributed to the suppression of carrier trap states. PABA post‐treatment provides a promising strategy and potential option for high performance solar cells.

Abstract

Various approaches of interface engineering are shown to be effective in improving the device performance of organic–inorganic hybrid perovskite solar cells (PSCs). The modification of the photoactive layer of PSC, CH₃NH₃PbI₃ (MAPbI₃), by spin‐coating a layer of p‐aminobenzoic acid (PABA), which can significantly enhance the open‐circuit voltage (V _OC), the fill factor (FF), and the power conversion efficiency (PCE) of PSCs, is herein reported. The champion device shows a short‐circuit current (J _SC) of 22.83 mA cm⁻², V _OC of 1.167 V, FF of 0.768, and PCE of 20.47%. The improvement in photovoltaic performance is attributed to the suppression of carrier trap states and the improvement in the morphologies of perovskite films. This work demonstrates a simple and effective protocol to enhance the device performance, and provides an insight into the influence of PABA post‐treatment on the charge carrier dynamics.

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 efficiency and stability of 2D perovskite solar cells are synergistically improved through metal ion doping. The hole extraction and transport abilities are significantly enhanced by Cu ion doping in the NiO _x layers, while the optoelectronic properties of the BA₂MA₃Pb₄I₁₃ (BA = butylamine; MA = methylammonium) layers are effectively improved with Cs ion doping.

Abstract

2D perovskites hold a great prospective to create highly efficient and stable solar cell devices. In order to explore their full potential, every component of 2D perovskite solar cells (PSCs) has to be carefully designed and engineered. Herein, the metal ion doping strategy is taken to optimize both the hole transport layers (HTLs) and the light absorbing layers of the BA₂MA₃Pb₄I₁₃ (BA = butylamine; MA = methylammonium) based 2D PSC devices. The hole extraction and transport abilities are significantly enhanced by Cu ion doping in the nickel oxide layers, while the optoelectronic properties of the BA₂MA₃Pb₄I₁₃ layers are effectively improved with Cs ion doping. The synergistic incorporations of Cu and Cs ions have boosted the device power conversion efficiency to 13.92%, the highest for 2D PSCs based on inorganic HTLs. In addition, the inorganic nature of the Cu doped nickel oxide film and the high quality of the Cs doped 2D perovskite film also endow the PSC device with extraordinary humidity and thermal stabilities.

In article number https://doi.org/10.1002/admi.2019007181900718, Kai Wang, Bin Hu, and co‐workers report spin‐polarized electronic transport through Ni/CH₃NH₃PbI_3−x Cl _x spinterfaces at room temperature. Both anisotropic magnetoresistance (AMR) and spin‐valve based magnetoresistance (MR) are highly decided by the formations of the spinterfaces. The spin accumulation and the change of magnetic moment are further studied by the capacitancefrequency (C‐f) and electron paramagnetic (EPR) spectroscopies.