Graphene Oxide/Perovskite Interfaces For Photovoltaics

Graphene-based materials hold a promising prospect for their utilization in perovskite solar cell devices as electron-extraction or hole-transport layers. Here, we investigate the role of oxidized graphene when interfaced with the perovskite MAPbI. Using first-principles calculations based on density functional theory, we study the change in the structural and electronic properties of the heterostructures with the oxidation level. We show that, depending on the concentration of the epoxy functional groups, only reduced graphene oxide would be advantageous for the extraction of photogenerated charge carriers. For oxygen concentration up to 33%, both hole and electron carriers could be extracted, whereas for concentrations between 33 and 66%, electron transfer is favored. For concentrations above 66%, it should not be possible to extract carriers. Moreover, the analysis of the charge density rearrangement at the interface due to the oxidization of graphene shows that the interfacial dipole decreases with the increase in the oxygen content. Finally, we report the modification of the band gap and the work-function in the oxidized graphene for different rearrangements of the epoxy groups on the graphene sheet. This study shows that the reduced graphene oxide with specific oxidation levels could effectively be incorporated as a selective contact in heterojunction devices for applications in perovskite solar cells.