Hybrid organic–inorganic perovskites have attracted intensive interest as light absorbing materials in solid‐state solar cells. Herein, we demonstrate a high‐performance CH3NH3PbI3‐based perovskite photodetector constructed on the flexible indium tin oxide (ITO) coated substrate even after 200 bending cycles. The as‐fabricated devices show high responsivity, broad spectrum response from ultraviolet to whole visible light, long‐term stability, and high on‐off ratio. Particularly, atomic layer deposition technique was used to deposit the ultrathin Al2O3 film on devices, functioning as a protection layer to effectively enhance the stability and durability of perovskite photodetectors. The first all‐perovskite self‐powered nanosystem was successfully assembled by integrating a perovskite solar cell with a perovskite photodetector. Driven by the perovskite solar cell, the photodetector exhibits fast and stable response to illuminated light at a low working voltage less than 1.0 V. This stable integrated nanosystem has promising applications in which photodetectors can work in harsh environments without external power sources.

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The fabrication of pinhole-free and compact electron transport layer is crucial for achieving high power conversion efficiency of perovskite solar cells. In this work, we report efficient perovskite solar cells using ultrathin TiO 2 films (5-20 nm) as high-quality electron transport layers deposited by atomic layer deposition technique.The as-prepared solar cells on FTO substrates show a high efficiency of 13.6% employing the optimum 10 nm TiO 2 layer thickness. Furthermore, the flexible cells on PET substrates give an efficiency of 7.2% with low-temperature-processed TiO 2 layers at 80 o C. The effects of layer thicknesses on the cell performance are investigated to reveal the mechanism of high-performance, which is mainly attributed to high transmittance, low leakage current, low charge transfer resistance and recombination rate. Our major findings are expected to provide a guide to design the ultrathin compact electron transport layers for efficient perovskite solar cells.

Organic–inorganic hybrid perovskite solar cells have undergone an unprecedented development as the next‐generation photovoltaic devices in recent years. The power conversion efficiency and stability are the key factors attracting great attentions from both academic and industrial communities. Here, a nonoxide CdS layer is inserted between TiO2 and perovskite to passivate the TiO2 interface in planar‐type perovskite solar cells. After introducing the CdS layer, significantly enhanced air stability and suppressed recombination between the trapped electrons and perovskite related to inverse transport are observed. At the optimum CdS thickness, a champion power conversion efficiency of 14.26% is achieved compared with 10.31% for the reference CdS‐free devices. This impressive efficiency also surpasses that of previously reported perovskite solar cells based on CdS. The largely improved performance is ascribed to the increased Fermi level of the electron transport layer, more efficient charge transport, and lower recombination rates.

In planar perovskite solar cells, it is vital to engineer the extraction and recombination of electron-hole pairs at the electron transport layer/perovskite interface for obtaining high performance. This study reports a novel titanium oxide (TiO ) bilayer with different Fermi energy levels by combing atomic layer deposition and spin-coating technique. Energy band alignments of TiO bilayer can be modulated by controlling the deposition order of layers. The TiO bilayer based perovskite solar cells are highly efficient in carrier extraction, recombination suppression, and defect passivation, and thus demonstrate champion efficiencies up to 16.5%, presenting almost 50% enhancement compared to the TiO single layer based counterparts. The results suggest that the bilayer with type II band alignment as electron transport layers provides an efficient approach for constructing high-performance planar perovskite solar cells.