Direct formed tri-iodide ions stabilizing colloidal precursor solution and promoting the reproducibility of perovskite solar cells by solution process

Solution process is the most widely used method to prepare perovskite films for efficient solar cells due to its facile fabrication and low-cost. However, the aged perovskite precursor solutions usually suffer from degradation, which impedes the reproducibility of the solution. In this paper, we demonstrate the direct formed tri-iodide ions stabilizing colloidal precursor solution for efficient halide perovskite solar cells. The added I-2 molecules dissolved in perovskite precursor sustain the dynamic balance between I- ions and I-3(-) ions by the reversible reaction: I- + I-2 (sic) I-3(-), which effectively stabilizes the whole I- ion concentration in perovskite solution and prevents the colloidal particles from aggregation. The resulting perovskite films with better crystallization have less bulk defects that act as carrier recombination centers. As a result, the devices using the aged solution with the additional tri-iodide ions show the less efficiency drop from similar to 19% to similar to 16% with the increased aging time up to 15 days, compared with the devices using the as-prepared precursor solution degrading from similar to 18% to similar to 6%. Our results represent an important advance in the stabilization of perovskite colloidal precursor and promote the reproducibility of perovskite solar cells by solution process. (C) 2019 Elsevier Ltd. All rights reserved.