Perovskites on ice : an additive-free approach to increase the shelf-life of triple-cation perovskite precursor solutions

The development of stable perovskite precursor solutions is critical if solution-processable perovskite solar cells (PSCs) are to be practically manufacturable. Ideally, such precursors should combine high solution stability without using chemical additives that might compromise PSC performance. Here, we show that the shelf-life of high-performing perovskite precursors can be greatly improved by storing solutions at low-temperature without the need to alter chemical composition. We find that devices fabricated from solutions stored for 31-days at 4°C achieve a champion PCE of 18.6% (97% of original PCE). The choice of precursor solvent also impacts solution shelf-life, with DMSO-based solutions having enhanced solution stability compared to those including DMF. We explore the compositions of aged precursors using NMR spectroscopy and analyse films made from these solutions using X-ray diffraction. We conclude that the improvement in precursor solution stability is directly linked to the suppression of an addition-elimination reaction and the preservation of higher amounts of methylammonium within solution.