Unravelling the solvent-solute interactions between γ-valerolactone and FAPbI3 for realization of perovskite solar cells from green solvents

To avoid environmental impact and health concerns arising from fabrication of perovskite solar cells, it is paramount to replace conventional perovskite precursor solvent systems with more eco-friendly and safe solvents. In this study, γ -valerolactone (GVL) was employed as green solvent and the implications of its use for coating of photoactive perovskite thin films were assessed by a combination of solution characterization, COSMO-RS calculations and comparison of photovoltaic performance of devices processed from GVL and DMF:DMSO. The potential of GVL to solubilize the perovskite precursor could be explained by calculation of the solvent’s σ-surface, highlighting it as a promising alternative to conventional perovskite precursor solvents. A strong tendency for perovskite formation in the photoactive α-phase was found when processing from GVL, opening ways for perovskite coating without antisolvent quenching and with only mild annealing steps. Finally, the same high power conversion efficiency of > 21 % could be demonstrated for perovskite solar cells processed from both types of solvents, demonstrating the feasibility to use GVL as green solvent for perovskite PV fabrication.