Crystallographic Anisotropies in α-SnWO₄ Photoelectrodes and Their Effects on Electronic Properties and Photoelectrochemical Performances

Multinary metal oxide photoelectrodes remain fundamentally limited by poor charge transport despite theoretical promise for solar fuel production. α-SnWO₄ exemplifies this challenge: while density functional theory predicts highly anisotropic charge transport with orientation-dependent band-edge positions, synthetic barriers to achieving phase-pure films with controlled crystallographic orientation have prevented its exploitation. Here, we demonstrate that rapid thermal processing (RTP) of pulsed-laser-deposited films overcomes these synthetic limitations, creating percolation networks of co-oriented grains. Multiscale characterization reveals that aligned crystallographic orientations produce well-aligned band edges, lowering contact potential difference by 0.35 eV and enhancing the local conductivity by more than 2 orders of magnitude compared to furnace heating (FH). These results directly correlate enhanced transport properties with previously reported improved photoelectrochemical performance of the RTP-treated films compared to those treated by FH and suggest a microscopic mechanism for this improvement. Our findings establish that controlling grain orientation connectivity, not simply grain size, provides a scalable pathway for exploiting anisotropic transport in multinary metal oxide photoelectrodes, directly linking the microstructure to the enhanced charge transport required for practical solar fuel devices.