Interface structure between titania and perovskite materials observed by quartz crystal microbalance system

Abstract

Adsorption of PbI2 onto a titania layer was monitored by a quartz crystal microbalance system in solution. The amount of PbI2 adsorbed on the titania layer increased with an increase in the PbI2 concentration in dimethylformamide (DMF). However, PbI2 remained after being rinsed with DMF, suggesting that PbI2 is rigidly bonded to the surface of the titania. The x-ray photoelectron spectroscopy measurement of PbI2 adsorbed on the titania substrate showed that the Pb compound has a composition of PbI0.33, not PbI2, suggesting that part of the Pb-I reacts with the HO-Ti moieties of titania to form Pb-O-Ti linkages. Trap density as measured by the thermally stimulated current method decreased after PbI2 passivation. Perovskite solar cells consisting of porous titania passivated with PbI2 had a higher efficiency than those without the passivation. It was concluded that PbI2 passivation of porous titania surfaces is one of the crucial approaches for enhancing the efficiency of perovskite solar cells with a scaffold layer of porous titania.