In-depth photocarrier dynamics in a barrier variable iron-oxide and vertically aligned reduced-graphene oxide composite

A key requirement for semiconductors operating in light-harvesting devices, is to efficiently convert the absorbed photons to electronic excitations while accommodating low loss pathways for the photogenerated carrier’s transport. The quality of this process corresponds to different relaxation phenomena, yet primarily it corresponds to minimized thermalization of photoexcited carriers and maximum transfer of electron-hole pairs in the bulk of semiconductor. However, several semiconductors, while providing a suitable platform for light-harvesting applications, pose intrinsic low carrier diffusion length of photoexcited carriers. Here we report a system based on a vertical network of reduced graphene oxide (rGO) embedded in a thin-film structure of iron oxide semiconductor, intended to exploit fast electron transport in rGO to increase the photoexcited carrier transfer from the bulk of the semiconductor to rGO and then to the external circuit. Using intermodulation conductive force microscopy, we locally monitored the fluctuation of current output, which is the prime indication of successful charge transfer from photoexcited semiconductor to rGO and efficient charge collection from the bulk of the semiconductor. We reveal the fundamental properties of vertical rGO and semiconductor junction in light-harvesting systems that enable the design of new promising materials for broad-band optical applications.