SnO₂/TiO₂ Electron Transporting Bilayers: A Route to Light Stable Perovskite Solar Cells

Perovskite solar cells have driven a paradigm shift in the research domain of photovoltaics. Although the field has progressed tremendously, device stability holds back further progress and application to the market. In this work, we aim to gain insights into electron transport layer (ETL)/perovskite interfacial degradation by characterizing perovskite films with TiO2, SnO2, and TiO2/SnO2 ETLs. Our results demonstrate that SnO2 and TiO2/SnO2 maintained long-term stability of 1000 h under maximum power point tracking, while the TiO2 sample degraded upon onset. We attempt to link this analogy to the perovskite film properties by monitoring the optoelectronic and morphological features under light soaking for each electron transporting layer configuration. Our results demonstrate reduced photoluminescent emission and decay, perovskite film morphological degradation, and a surge in PbI2 in TiO2 samples, trends that were not found in SnO2 and TiO2/SnO2 samples. We highlight the passivation effect of SnO2 films in the bilayered ETL configuration (TiO2/SnO2) that results in stability enhancement phenomena as speculated from our constructed energy diagram. The results show that the SnO2 layer could suppress charge recombination with the perovskite layer and improves the optical durability.