Water-Based Recycling Process of FTO/SnO₂ Substrate for Sustainable Perovskite Solar Cell Technology

Fluorine-doped tin oxide (FTO) substrate is an important and expensive component in perovskite solar cells (PSCs), which accounts for up to 40 % of a typical PSC raw material cost. In this study, we investigated the recyclability of SnO₂/FTO in PSCs by washing the spent PSCs using different solvent such as dimethylformamide (DMF), dimethylsulfoxide (DMSO), acetone, water, and acetone/water mixture. Characterisation of properties of the SnO₂/FTO substrates recovered from the PSC show the surface wettability of SnO₂/FTO is largely unchanged with water washing while a higher hydrophobicity is obtained with organic solvent washing. Comparison of electronic properties of the SnO₂/FTO substrate shows a downward shift of the conduction band by 180 meV with water washing, creating favourable energy alignment with adjacent perovskite for efficient interfacial charge injection. Consequently, PSCs using the water-based recycled SnO₂/FTO substrates produced a high power conversion efficiency (PCE) of 19.33 % which is comparable to the device using fresh SnO₂/FTO substrate (PCE=19.85 %). Furthermore, we demonstrated that the water washing process could retain property of SnO₂/FTO substrate for decent PSC performance up to four recycling cycles. This study opens new avenues towards recycling of valuable FTO substrates in PSCs for increased sustainability and cost-effectiveness.