Effect of TiO2 structure on hysteretic behaviors in CH3NH3PbI3 perovskite solar cells

This work explores a mechanism behind hysteresis in CH3NH3PbI3 perovskite solar cells. The solar cells in this work employed either compact TiO2, mesoporous TiO2, or a combination of compact and mesoporous TiO2 as an electron transport layer. The solar cells using compact TiO2 layer displayed the most pronounced hysteresis compared to those which made use of mesoporous TiO2. Different hysteretic behavior is attributed to difference in the built-in electric fields present in the architecture of perovskite solar cell. The solar cells with a compact TiO2 layer have a built-in field which allows for iodide ions to migrate and accumulate near to the interface of indium-tin-oxide electrode, ultimately causing a reduction in the measured power conversion efficiency for forward bias scans. In case of the cells with a mesoporous TiO2 layer, they have the built-in fields configured in such a way that iodide ions are blocked from migrating on a large scale to the vicinity of the ITO electrode. This results in the reduced hysteresis in perovskite solar cells when a mesoporous TiO2 electron transport layer is employed.