Multi-Influences of Ionic Migration on Illumination-Dependent Electrical Performances of Inverted Perovskite Solar Cells

ZnO films are employed as the electron transport layers for perovskite solar cells. Such a device exhibits an ultralong time increase in V_oc (∼100 s) and J_sc (∼1000 s) and a weakening hysteresis under continuous illumination. Besides, a slow (∼20 s) V_oc decay when illumination is switched off is also observed. The electrical measurements performed under illumination and under voltage bias before being illuminated, suggest the influences of ionic accumulation/redistribution in causing above phenomena. Ionic accumulation happening in dark and ionic redistribution under illumination lead to band bending which affects the excitons separation and carrier extraction. These can account for the ultralong time increase in V_oc and J_sc as well as the slow V_oc decay. Also, the time-dependent photocurrent response under stepwise scan proves the presence of a capacitive effect in the device which can be dramatically reduced by the ionic redistribution under illumination. The ionic redistribution is also an important reason for the weakening hysteresis. (Graph Presented).