Highly efficient flexible perovskite solar cells and their photo-stability

We report here a simple method to fabricate highly efficient and robust flexible perovskite solar cells (F-PSCs) along with their photo-stability. The solar cells were prepared on indium tin oxide (ITO) coated polyethylene terephthalate (PET) substrates. The solar cells incorporated methylammonium lead iodide chloride (CH3NH3PbI3-xClx) mixed halide perovskite as the light absorber, tin oxide (SnO2) as electron transport layer (ETL), Spiro-MeOTAD as hole transport layer (HTL) and Ag as the top electrode. This structure exhibited very high external quantum efficiency (EQE) of ~80% at 500 nm and power conversion efficiency (PCE) of 12.7±0.6% (active area 9.6 mm2) with no effect of multiple bending cycles on the performance even after 100 bending cycles. For the evaluation of their lifetime in dark and under actual operating conditions, a systematic study was performed on the unsealed devices. The solar cells showed half life (T50) of about 340 hrs when stored in dark in ambient environment, but they degraded very rapidly in direct sunlight. The main reason behind their degradation was found to be the rapid degradation in their short circuit current density (Jsc). The same device design was processed to fabricate large area flexible solar modules in 5×5 cm2 area (active area 15.84 cm2) and the solar modules exhibited PCE of 5.6±0.2%. Substantial loss of PCE in the modules compared to small area devices has been attributed to larger series resistance of longer ITO electrodes used in the modules.