The effect of storage cycle on improvement in the photovoltaic parameters of planar triple cation perovskite solar cells

One of the important challenges in the field of perovskite solar cells is to investigate the competitive mechanisms of humidity and oxygen which improve the efficiency of cells at moderate humidity and cause the degradation of perovskites at high levels of moisture. We found that when an un-encapsulated standard planar architecture, glass/ITO/SnO2/triple cation perovskite/Spiro-OMeTAD/Au, was realized, exposure to moderate humid air was always needed for proper functioning. We investigated the fabrication and storage procedures of thin (∼320 nm) triple cation perovskite solar cells showing, for the first time, to the best of our knowledge, a remarkable enhancement of all photovoltaic parameters compared to those of pristine cells (with the fill factor exceeding 80%, a short circuit current density of about 24 mA cm−2 and an open circuit voltage of 1121 mV, for champion devices) and, particularly, an impressive increase of power conversion efficiency (PCE) from 13.2% to 20.8% after 72 h of storage in air with moderate humidity. A slight PCE increase to 20.9% was also achieved after subsequent low vacuum storage and after 720 h from the fabrication day. Moreover, devices exhibiting hysteresis-free behavior after storage were characterized for evaluating the mechanism of charge carrier recombination by means of dark and light current density–voltage and illumination-dependent photovoltaic parameters. The storage cycle shown in this work could be a possible route to improve the performance of pristine perovskite solar cells and consequently to proceed with encapsulation procedures.