Reconstruction of Solar Fuel Ultrathin Films via Periodically Microbending for Efficient Photoelectrochemical Water Splitting

Tackling the conflict between the optical and electronic properties of the ultrathin optoelectronic films is of critical importance for the development of highly efficient photoenergy conversion devices. We show in this report a proof of concept for designing an ultrathin photoelectrode film that compensates intrinsic low absorption coefficients and limited charge-carrier transport properties. To enhance light absorption under these conditions a light trapping structure using coupled optical properties was designed on the basis of an array of hollow half spheres generated by periodically microbending the deposited thin film, yielding well-defined two-dimensional ordered microspaces. Exemplified by α-Fe₂O₃, this film structure is able to generate an approximately 4.5-fold increase in photocurrent at a bias of 1.23 V versus RHE under simulated solar radiation conditions compared to that of a flat film with the same thickness. Both the experimental results and the theoretical simulations prove that modulating the periodicity of the ordered microspaces can further improve the PEC properties of the microbending photoelectrode. The numerical 3D simulations of optical properties of the microbent films indicate a clearly superior absorption compared to that of the planar Fe₂O₃ film, and the nanoarch diameter influences the PEC water splitting performance, both of which are in good agreement with our experimental results. Our results indicate that periodic microbending of ultrathin solar fuel films can be considered as a viable strategy to develop high-performance photoelectrodes for light-driven water splitting, which is of special relevance for photosensitive semiconductors characterized by relatively low absorption coefficients and moderate diffusion lengths of light-excited electron-hole pairs.