Unravelling Recombination Processes in Bifacial Guanidinium-Incorporated Perovskite Solar Cells with SnO₂ and TiO₂...

Maximising the energy yield of perovskite solar cells (PSCs) through bifacial architectures is a promising route toward commercialisation. However, optimising charge extraction at the interfaces remains a critical challenge. In this study, we systematically compare tin dioxide (SnO₂) and titanium dioxide (TiO₂) electron transport layers (ETLs) in bifacial guanidinium-incorporated PSCs with a transparent gold (10 nm) back electrode. While the bulk perovskite crystallinity remains invariant on both substrates, SnO₂ provides a distinct optical advantage through enhanced UV-blue transmittance. Beyond these optical benefits, comprehensive recombination process analyses reveal that SnO₂ drastically suppresses non-radiative recombination. The SnO₂ layer effectively mitigates defect states, significantly reducing both bulk and surface trap-assisted recombination rates without disrupting intrinsic bimolecular charge transport. Ultimately, these findings underscore the critical importance of rational interfacial engineering to neutralise defects, proving SnO₂ to be an indispensable component for realising highly efficient and commercially viable bifacial perovskite optoelectronics.