Included in the dataset are detailed information into the crystallography, morphology, electronic properties, (photo)electrochemical and carrier dynamics of both single-crystal Cu2O thin films and polycrystalline Cu2O with favored crystal orientations. Multiple intruments, including Empyrean X-ray Diffractometer, Zeiss Merlin Scanning Electron Microscope, Tecnai Osiris Transmission Electron Micrisocope, Newport LCS-100 Solar Simulator, Biologic SP-200, GC9790plus Gas Chromatograph, Keithley 2450 SourceMeter, Shimadzu UV-3600 Plus Double-beam Spectrophotometer, were applied to collect the data. Abstract of associated publication: Solar fuels offer a promising approach to provide sustainable fuels by harnessing sunlight. Following a decade of advancement, Cu2O photocathodes are capable of delivering a performance comparable to that of photoelectrodes with established photovoltaic materials. However, considerable bulk charge carrier recombination that is poorly understood still limits further advances in performance. Here we demonstrate performance of Cu2O photocathodes beyond the state-of-the-art by exploiting a new conceptual understanding of carrier recombination and transport in single-crystal Cu2O thin films. Using ambient liquid-phase epitaxy, we present a new method to grow single-crystal Cu2O samples with three crystal orientations. Broadband femtosecond transient reflection spectroscopy measurements were used to quantify anisotropic optoelectronic properties, through which the carrier mobility along the [111] orientation was found to be an order of magnitude higher than those along other orientations. Driven by these findings, we developed a polycrystalline Cu2O photocathode with an extraordinarily pure (111) orientation and (111) terminating facets using a simple and low-cost method, which delivers 7 mA cm−2 current density (more than 70% improvement compared to that of state-of-the-art electrodeposited devices) at 0.5 V versus a reversible hydrogen electrode under air mass 1.5 G illumination, and stable operation over at least 120 h.