Sustainable Solvent Selection for Perovskite Solar Cells

Perovskite solar cells have emerged as a promising and highly efficient solar technology. Despite efficiencies continuing to climb, reaching a new record of 25.7%1, the prospect of industrial manufacture is in part hampered by concerns regarding the safety and sustainability of the solvents used in lab scale manufacture. Here, we aim to present a methodology for green solvent selection informed by EHS considerations from the CHEM-21 solvent guide for succesful methylammonium lead triiodide (MAPbI3) precursor dissolution2. Through the use of this methodology we present a N,N-dimethylformamide (DMF)-free alternative solvent system for deposition of MAPbI3 precursors (MAI and PbI2) consisting of dimethyl sulfoxide (DMSO), dimethylpropyleneurea (DMPU), 2-methyltetrahydrofuran (2-MeTHF) and ethanol (EtOH). Perovskite films cast from the three candidate solutions show improved crystallinity, higher fluorescence emission, and improved crystal size uniformity than those cast from DMF/DMSO and similar photovoltaic performance (16.2% for DMF/DMSO, 16.1% for candidate A solvent system2). We will cover the key solvent parameters which determine effective MAPbI3 precursor dissolution; provide a set of criteria for appropriate alternative solvent selection; and demonstrate the application of green chemistry principles to solvent selection for perovskite photovoltaic manufacturing. Due to significant advancement in the perovskite research sphere, more thermally stable and efficient perovskite compositions have risen to prominence. This includes the now ubiquitous ‘triple cation’ perovskite (Cs0.05(MA0.17FA0.83)0.95Pb(I0.83Br0.17)3)3, providing increased impetus to study solvent interactions in these more complex colloidal dispersions. We will discuss recent progress towards ‘green’ solvent engineering strategies specifically tailored towards these compositions, further highlighting key parameters requiring control to potentially improve the optoelectronic properties of this promising material.