Ultraflexible and biodegradable perovskite solar cells utilizing ultrathin cellophane paper substrates and TiO₂/Ag/TiO₂ transparent electrodes

Flexible perovskite solar cells (PSCs) on paper are promising biodegradable power sources for wearable and portable electronics, while fabrication of paper-based PSCs with high mechanical flexibility and efficiency is still challenging due to the limited optimization of paper-based PSCs. Herein, flexible PSCs were demonstrated using 25 μm cellophane paper substrates combined with TiO₂/ultrathin Ag/TiO₂ (OMO) electrodes, composing the typical structure of cellophane/OMO/C60 pyrrolidinetris-acid (CPTA)/CH₃NH₃PbI₃/Spiro-OMeTAD/Au. PSCs on cellophane paper exhibited a high power conversion efficiency (PCE) of 13.00%. More interesting, the performance of paper-based PSCs showed minor degradation after bending with the radius in the range of 0.3–10 mm: they retained 97.6% of the initial PCE after bending with a radius of 0.3 mm and even preserved 95.8% of the initial PCE after bending with a radius of 1 mm for 1000 cycles. The ultraflexibility of PSCs was ascribed to the ultrathin substrates to relieve strain in bended devices and superior flexibility of OMO electrodes. The ultraflexible and efficient PSCs on paper are promising for application in self-powered paper-based electronics.