High-air-flow-velocity assisted intermediate phase engineering for controlled crystallization of mixed perovskite in high efficiency photovoltaics

Mixed-composition perovskites (m-perovskites) are emerging as one of the hottest materials in the field of photovoltaics. However, a satisfactory m-perovskite film cannot always be attained even through a standard operating procedure. The formation of a m-perovskite film during transitory one-step spin-coating is a train of complex dynamic processes which are intimately bound up with solvent evaporation and anti-solvent interdiffusion. In these processes, many underappreciated variables that will greatly alter the mode of solvent behavior have rarely been taken into serious consideration. In this paper, the air flow velocity during spin-coating is proved to be a very important factor. A precise control over the formation as well as the decomposition of the intermediate phase can be realized through high-air-flow-velocity assisted spin-coating, which guarantees a subsequent controllable and high-quality crystallization of the m-perovskite. Finally, the planar-structured device exhibits the best efficiency of 20.24% (19.58% stabilized) with alleviated hysteresis and better long-term stability.