Tunable hysteresis effect for perovskite solar cells

Perovskite solar cells (PSCs) usually suffer from a hysteresis effect in current-voltage measurements, which leads to an inaccurate estimation of the device efficiency. Although ion migration, charge trapping/detrapping, and accumulation have been proposed as a basis for the hysteresis, the origin of the hysteresis has not been apparently unraveled. Herein we reported a tunable hysteresis effect based uniquely on open-circuit voltage variations in printable mesoscopic PSCs with a simplified triple-layer TiO2/ZrO2/carbon architecture. The electrons are collected by the compact TiO2/mesoporous TiO2 (c-TiO2/mp-TiO2) bilayer, and the holes are collected by the carbon layer. By adjusting the spray deposition cycles for the c-TiO2 layer and UV-ozone treatment, we achieved hysteresis-normal, hysteresis-free, and hysteresis-inverted PSCs. Such unique trends of tunable hysteresis are analyzed by considering the polarization of the TiO2/perovskite interface, which can accumulate positive charges reversibly. Successfully tuning of the hysteresis effect clarifies the critical importance of the c-TiO2/perovskite interface in controlling the hysteretic trends observed, providing important insights towards the understanding of this rapidly developing photovoltaic technology.