Band-Edge Engineering at the Carbon Dot–TiO2 Interface by Substitutional Boron Doping

Abstract

We investigated the heterostructures of pristine and boron-doped carbon dots (CDs) with TiO2 using a first principles approach. Heterojunctions of CDs and TiO2 demonstrated type II band alignments that promote spatial separation of charge carriers and were well suited for sensitizer configuration. However, large CD band gaps severely restricted their optical efficiencies. Substitutional boron doping of the CDs introduced new electronic states and pulled the CDs’ conduction band minimum (CBM) down, resulting in dramatic reduction of CD band gaps (by 48–57%). The resulting band alignment of the boron-doped CD–TiO2 heterostructures were found to be type I, in which CBM and valence band maximum of TiO2 straddled those of CDs and photoexcited carriers could migrate to CD side. This indicated better suitability for device configurations where conducting channel lies through the CDs but elevated the chance of recombination loss. However, the internal electric fields at these heterojunctions were found to selecti...