Wang, SiyangTan, LiguoZhou, JunjieLi, MinghaoZhao, XingLi, HangTress, WolfgangDing, LimingGraetzel, MichaelYi, Chenyi2022-07-182022-07-182022-07-182022-06-1510.1016/j.joule.2022.05.002https://infoscience.epfl.ch/handle/20.500.14299/189352WOS:000819196200005Methylammonium (MA)-free perovskites such as Cs(x)FA(1-x)PbX(3) (CsFA) show excellent thermal stability, favoring their use in perovskite solar cells (PSCs). However, the power conversion efficiency (PCE) of CsFA lags behind that of MA-containing formulations due to the difficulty in controlling the film morphology. Herein, we report innovative morphology engineering using solution deposition of a mixture of CsBr, Pbl(2), and PbCl2 followed by vacuum evaporation of formamidinium iodide (FAI) to fabricate CsFA films. The introduction of a chloride precursor leads to larger grain sizes, forming a high-quality CsFA film under annealing. This enables the realization of robust CsFA-based PSCs with the highest reported PCE up to 24.1% (certified 23.9%) for 0.1 cm(2) and 22.8% for 1 cm(2) devices. Moreover, the unencapsulated evaporation device shows excellent stability with negligible efficiency decline after 20,000 h of storage in dry air or 1,000 h of exposure to 50% humidity, which is much better than the device prepared using the solution procedure.Chemistry, PhysicalEnergy & FuelsMaterials Science, MultidisciplinaryChemistryEnergy & FuelsMaterials Sciencehalide perovskitesformamidiniumperformancemodulesareastabilizationstabilitycesiumtext::journal::journal article::research article