Thickness of AVA⁺ Controls the Direction of Charge Transfer at TiO₂/PbI₂ Interfaces

Abstract

Theoretical density functional theory analysis of 5-ammonium valeric acid (AVA+, HOOC–(CH2)4–NH3+) resulted in self-limitation of the length of AVA+ chains and in a redistribution of the electron density in the lowest unoccupied molecular orbital states of TiO2 and PbI6 clusters depending on the number of AVA+ ions between the clusters. This behavior had strong consequences for the direction of charge transfer at TiO2/PbI2 interfaces as demonstrated experimentally by a combined study of infrared spectroscopic ellipsometry and modulated surface photovoltage spectroscopy.