Low-temperature processed high-performance flexible perovskite solar cells via rationally optimized solvent washing treatments

High performance planar-heterojunction (PHJ) perovskite (CH₃NH₃PbI₃) solar cells fabricated through low-temperature annealing are demonstrated. Simple spin-coating with an optimized solvent washing process readily forms homogeneous and crystalline perovskite thin films. The perovskite films fabricated via this solvent washing process show a low dependence on annealing temperature in achieving high crystallinity and large grain size, prerequisites for high efficiency perovskite solar cells. The solar cell device fabricated by solvent washing and 100 °C annealing exhibited a high power conversion efficiency (PCE) over 14% with high short circuit current density (J_SC) of 19.3 mA cm^-2 and fill factor (FF) of 0.80. More importantly, the device annealed at low temperature (<90 °C) also yields high PCEs of over 12%. This enables us to fabricate flexible solar cells at low-temperatures with promising PCE as high as 9.43%. This study demonstrates that this optimized solvent washing process is highly relevant for low-cost roll-to-roll (R-2-R) processing of high performance perovskite solar cells.