Ammonium-iodide-salt additives induced photovoltaic performance enhancement in one-step solution process for perovskite solar cells

Abstract Unordered aggregation of perovskite particles on TiO 2 mesoporous film surface is a common problem in one-step solution process for fabricating perovskite solar cells (PSCs). This phenomenon is harmful for homogeneous dispersion of perovskite in mesoporous TiO 2 film and responsible for the low photovoltaic performance of corresponding perovskite solar cells at the same time. Delicate control of perovskite nucleation and growth is an effective route to solve this problem. In this work, we proposed a facile strategy to improve perovskite (CH 3 NH 3 PbI 3 ) growth by adding C 6 H 5 CH 2 NH 3 I (BAI) or NH 4 I ionic compounds in perovskite precursor solution. We investigated perovskite crystal structure and morphology, optical and electrochemical properties of perovskite films or devices using different additives by XRD, SEM, UV–Vis, IPCE, and EIS. We found that these additives could decrease the grain size of perovskite crystal and diminish perovskite particle aggregation on TiO 2 film surface. This effect is benefit for electron transfer on perovskite/TiO 2 interface. Finally, perovskite solar cells using BAI or NH 4 I additives obtain the best solar-to-electricity conversion efficiency of 9.05% and 9.49%, respectively, which are much higher than that of the pristine one, 6.83%.