Recently, lead‐free double perovskites have emerged as a promising environmentally friendly photovoltaic material for their intrinsic thermodynamic stability, appropriate bandgaps, small carrier effective masses, and low exciton binding energies. However, currently no solar cell based on these double perovskites has been reported, due to the challenge in film processing. Herein, a first lead‐free double perovskite planar heterojunction solar cell with a high quality Cs2AgBiBr6 film, fabricated by low‐pressure assisted solution processing under ambient conditions, is reported. The device presents a best power conversion efficiency of 1.44%. The preliminary efficiency and the high stability under ambient condition without encapsulation, together with the high film quality with simple processing, demonstrate promise for lead‐free perovskite solar cells.

Photodetectors that capture light and convert it into electricity have been used in many applications, such as imaging systems, environmental surveillance, communications, and biological sensing. [1][2][3] UV detectors play an important role in practical applications, many devices have been prepared with wide bandgap semiconductors, such as ZnO, NiO, and TiO 2 etc. [4][5][6][7][8][9] However, these heterojunction self-powered detectors often exhibit low responsivity and slow response times.

Compared with silicon-based solar cells, organic-inorganic hybrid perovskite solar cells (PSCs) possess a distinct advantage, i.e., its application in the flexible field. However, the efficiency of the flexible device is still lower than that of the rigid one. First, it is found that the dense formamidinium (FA)-based perovskite film can be obtained with the help of N-methyl-2pyrrolidone (NMP) via low pressure-assisted method. In addition, CH 3 NH 3 Cl (MACl) as the additive can preferentially form MAPbCl 3−x I x perovskite seeds to induce perovskite phase transition and crystal growth. Finally, by using FAI·PbI 2 ·NMP+x%MACl as the precursor, i.e., ligand and additive synergetic process, a FA-based perovskite film with a large grain size, high crystallinity, and low trap density is obtained on a flexible substrate under ambient conditions due to the synergetic effect, e.g., MACl can enhance the crystallization of the intermediate phase of FAI·PbI 2 ·NMP. As a result, a record efficiency of 19.38% in flexible planar PSCs is achieved, and it can retain about 89% of its initial power conversion efficiency (PCE) after 230 days without encapsulation under ambient conditions. The PCE retains 92% of the initial value after 500 bending cycles with a bending radii of 10 mm. The results show a robust way to fabricate highly efficient flexible PSCs.

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A novel and facile protocol for the rapid synthesis of flower-like Cu(2)O architectures is reported in the presence of ionic liquid 1-n-butyl-3-methyl imidazolium tetrafluoroborate ([BMIM]BF(4)) with the assistance of microwave irradiation. The hierarchical structures are assembled from many thin nanosheets with tunable sizes by adjusting the amount of [BMIM]BF(4) in the reaction solution. Noticeably, the flower-like Cu(2)O architectures present a high surface area of 65.77 cm(2) g(-1) with a band gap of about 2.25 eV, and exhibit high and stable photochemical activity for the reduction of Cr(VI) to Cr(III) under visible light irradiation. A reasonable model of an absorption and diffusion-limited aggregation process is proposed for explaining the possible formation mechanism of the flower-like Cu(2)O. The approach described in this study provides a feasible and rapid method to synthesize flower-like Cu(2)O with a hierarchical structure that is ready for application in the fields of photocatalytic hazard pollutants.