The disappearing additive: introducing volatile ethyl acetate into a perovskite precursor for fabricating high efficiency stable devices in open air.

In recent years, organic-inorganic halide perovskite solar cells (PSCs) have attracted massive attention because of their high power conversion efficiency (PCE). However, it is difficult to prepare perovskite films with good performance in open air due to the poor stability of perovskite materials in high humidity, which is seriously hindering the practical application and development of PSCs. Herein, ethyl acetate (EA) is introduced into the perovskite precursor to enhance the crystallinity of perovskite for fabricating high efficiency stable devices in the atmospheric environment. Interestingly, volatile EA, which is often used as an anti-solvent, could quickly evaporate and accelerate the nuclei formation during perovskite crystallization. More impressively, the Lewis base nature of EA can form strong chemical bonding interactions with perovskite to passivate the defects during crystallization. As a result, the EA-modified perovskite film demonstrates dense and defect-less morphology with large grain size (the maximum achieves 0.9 μm). The EA-treated device has a dramatic efficiency of 19.53% and negligible hysteresis of the photocurrent. Furthermore, both the temperature and humidity resistances of EA-modified PSC are significantly improved. The normalized PCE of the EA-modified device without encapsulation can still retain over 80% of its initial value after being stored in 60% relative humidity (RH) in the dark for 500 hours. This contribution provides a promising channel for facilitating the commercialization of PSCs.