Influence of interfacial Sn-doping on band alignment of ZnO-nanorods/MAPbI3 interface: The density functional calculation

Abstract

This work used density functional theory to investigate both electronic and atomic structures at the interface between MAPbI3 and Sn-doped ZnO-nanorods. In the model, we considered two possible surfaces of ZnO-nanorod in forming interfaces with MAPbI3 layers, i.e. polar (0001) and non-polar (1010) surfaces. From the results, the undoped ZnO(1010)/MAPbI3 interface presents type-II band alignment, whereas the undoped ZnO(0001)/MAPbI3 presents type-I band alignment. The partial density of state analysis reveals that the trap state only occurs in ZnO(0001)/MAPbI3. However, when Sn atoms substitute the Zn atoms at the interface, the band alignment was found to change from type-II to type-I in Sn-doped ZnO(1010)/MAPbI3, and the band gap of ZnO was found reduced. However, for the Sn-doped ZnO(0001)/MAPbI3, the band alignment is still type-I and the band gap is almost unchanged. This means that how the band structure of Sn-doped ZnO/MAPbI3 realigns depends on how ZnO terminates at the interface (i.e. polar or non-polar), when Sn-doping is introduced. In addition, this band alignment modification of Sn-doped ZnO/ MAPbI3 was found to be originated from the contribution of Sn 5s-orbital at the band edge, which adjusts the band structure of ZnO at the interface. These therefore suggest that using Sn-doped ZnO nanorods as electron transporting layers may be useful for band engineering. Specifically, the band alignment and band offsets can be tuned with controlling of Sn concentration.