Organometal halide perovskites solar cells (PSCs) are very promising for cost effective solar energy conversion and have attracted tremendous attention recently. Remarkable progress on PSCs has been made and the highest certified power conversion efficiency (PCE) exceeds 20% to date. PSCs can be structured in either mesosuperstructure-type or planar-type. Planar-type devices are particularly interesting because their simple layer design can be feasibly prepared with low-temperature processing. Various methods have been developed for the preparation of the perovskite layers, including evaporation, vapor-assisted solution process and solution process in either one step or two steps. Among these different techniques, one-step solution processing is potentially the lowest-cost one and may be adaptable to large-area production. Combined with low-temperature solution processing, planar-type PSCs can be fabricated on low-cost, flexible substrates to exploit the cost effectiveness of high throughput continuous fabrication technologies such as roll-to-roll processing.
In our research, a modified surface rinsing method in which the rinsing solvent is allowed to soak the whole surface of the as-coated perovskite layer to form the precipitation before the treated films are subject to spinning to drain the solvents. Besides the enhanced crystallinity and surface morphology due to the rinsing induced surface precipitation that constrains the grain growth underneath in the precursor films, large-area uniformity with film thickness determined exclusively by the rotational speed of rinsing spinning for solvent draining was observed. With the use of chloroform (CF) in this solvent soaking and rinsing process, mirror-like perovskite layer of 8 cm × 8 cm was obtained and highly uniform planar PSC devices with PCE of 10.6 ± 0.2% and greatly enhanced reliability were achieved even with very simple layer structure of ITO/PEDOT:PSS/perovskite/PC61BM/Al. Moreover, since the surface precipitation forms before the solvent draining, this solvent soaking and rinsing method may be adapted to spinless process and may thus be compatible with large-area and continuous production.
