Jeonbuk National University, a South Korea-based public research university, has reported a new interface engineering strategy for BC perovskite solar cells using a bilayer tin oxide electron transport layer. In BC-PSCs, the perovskite absorber layer is positioned at the top of the stack, allowing direct sunlight exposure. Electron and hole-collection contacts are positioned at the back, and generated charge carriers are transported to their respective layers. They have fabricated this bilayer SnO₂ structure via a spin-coating process that combines nanoparticle and sol-gel layers on indium tin oxide substrates. According to the published study, the bilayer device has achieved the highest average photocurrent of 33.67 pA, surpassing sol-gel SnO₂ at 26.69 pA and colloidal SnO₂ at 14.65 pA. The bilayer device has reached a maximum power conversion efficiency of 4.52% with improved operational stability.