Improving the Ecological Index in the Solution Processing of Hybrid Perovskites

Abstract

Lead halide perovskites are on the center stage in photoactive materials due to their highly tunable properties and potential applications in photovoltaics and light-emitting devices. Hybrid perovskites have demonstrated exceptionally high solar cell efficiencies, which have quickly approached those of silicon photovoltaics; however, their technology readiness suffers from limited environmental stability and the use of toxic solvents, such as N,N-dimethylformamide (DMF). This research presents a new green solvent system that combines biodegradable dihydrolevoglucosenone (Cyrene^TM) and 2-Methyltetrahydrofuran (2-MeTHF) as sustainable alternative to the hazardous DMF. This eco-friendly solvent system reduces reliance on conventional aprotic solvents in perovskite solar cells processing. Additionally, ethyl acetate was employed as a green antisolvent in the one-step spin coating process to enhance crystallization, selected for its lower toxicity compared to other common solvents. Investigation on solvent-solute interactions by various characterization techniques led to an optimized solvent blend of Cy-THF:DMSO (70:30 vol%) with an added 7.5 vol% acetonitrile that resulted in a desirable viscosity and a stable perovskite precursor solution. Additives, including methylammonium chloride (MACl, CH₃NH₃Cl) and thiourea (SC(NH₂)₂), were incorporated to improve crystallinity and surface coverage of the perovskite films. The resulting thin films of cubic perovskite exhibited enhanced film quality and superior stability under ambient conditions, with optoelectronic properties comparable to those of DMF-based perovskites to achieve 95 % of the DMF-reference device efficiency. These results demonstrate the promise of green solvent systems, derived from recyclable carbon, for sustainable perovskite processing.