Over 24% efficient MA-free CsxFA1-xPbX3 perovskite solar cells

Methylammonium (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.

Automated summary

In this study, CsFA films with high quality were fabricated using innovative morphology engineering method, which combines solution deposition and vacuum evaporation. The CsFA-based perovskite solar cells demonstrated excellent thermal stability and high power conversion efficiency, making them a promising candidate for applications in solar energy conversion.