Optimization of Halide Composition and Interfacial Passivation for High-Performing Indoor Flexible Perovskite Solar Cells on PET

Flexible perovskite solar cells (FPSCs) are ideal for indoor applications due to their lightweight and bendable nature. Polyethylene terephthalate (PET) is the preferred substrate for its cost-effectiveness and chemical stability. Our study presents highly efficient FPSCs on PET with two optimizations: anion mixing of the perovskite composition and interfacial engineering using tetrabutylammonium bromide (TBAB). This approach results in high efficiencies of 28.9% at $230 \pm 30$ lx and a record 32.5% at $1150\pm 150$ lx. The spectroscopic techniques demonstrated the formation of a low-dimensional phase at the interface between the deposited perovskite material and the TBAB over-layer. This low-dimensional phase resulted in a more stable device, retaining 72% of its initial efficiency after 118 days of storage (ISOS-D1), compared to 29% for reference devices. Moreover, the cells maintained over 80% of their initial PCE after 1000 bending cycles.