Defect states influencing hysteresis and performance of perovskite solar cells

Abstract

Here we explore the origin of hysteresis behavior in perovskite solar cells by investigating the defects density of states. In order to reveal this anomalous characteristic, low-temperature capacitance spectroscopy and current-voltage analysis are performed. The present study shows that the open-circuit voltage and hysteresis tend to decrease as the temperature falls below ~200 K. For temperature range of ~300 K to ~180 K, the hysteresis index under dark condition remains almost unaltered whereas, under illuminated condition, the hysteresis index increases with a decrease in temperature. The average hysteresis index under the dark and illuminated conditions is ~71% and ~18% in the tetragonal phase, whereas it becomes ~4% and ~24% in the orthorhombic phase, respectively. Further, below ~180 K, both hysteresis index decreases mutually with the identical rate with a decrease in temperature. Two inflection points have been observed in forward and reverse current cross over-voltage points, indicating rearrangement of internal built-in field distribution and defects at different temperatures. In the tetragonal phase, the Gaussian profile of defect density extends towards lower energy as temperature decreases that refer to a shift in quasi-Fermi level which changed the open-circuit voltage. The increased distribution defect leads to unfavorable accumulation of mobile ions at the electrode and grain boundaries interfaces lead to hysteresis effect in the device.