Superiority of two-step deposition over one-step deposition for perovskite solar cells processed in high humidity atmosphere

Abstract

Perovskite solar cells (PSC) are currently experiencing rapid development due to the potential for achieving high efficiency but the fabrication process is strictly restricted inside an inert environment. This is because high relative humidity (RH) condition may cause irreversible degradation or low quality of perovskite film. Since the film quality and device performance depend strongly on the deposition protocol, a systematic investigation about the impact of one-step and two-step spin coating on perovskite film prepared in high-humidity is needed. Hereby, we developed PSC in humid atmosphere (RH40-50%) using both deposition techniques to find the most easily-adopted coating method for PSC fabrication in high-humidity. Results show that one-step-based sample has numerous pinholes and smaller grain size whereas two-step-based counterpart exhibits compact surface coverage and large grains. Hence, the two-step-based film has higher light absorption, better charge transfer and lower charge recombination. The employment of PCBM as a secondary electron transport layer underneath the perovskite layer in one-step-based sample causes both layers to be washed away by chlorobenzene anti-solvent. However, such undesirable phenomenon is not seen for the two-step-based sample. Therefore, the use of two-step method is strongly recommended for the development of efficient PSC in open atmosphere without humidity restriction.