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 degrees 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 degrees 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.