This study reports on the high carrier mobility along the [111] orientation in Cu₂O photoelectrodes, demonstrating significant improvements in performance and stability. The research team used ambient liquid-phase epitaxy to grow single-crystal Cu₂O thin films with three crystal orientations. Broadband femtosecond transient reflection spectroscopy revealed that carrier mobility along the [111] direction is an order of magnitude higher than in other orientations. This finding led to the development of a polycrystalline Cu₂O photocathode with a pure (111) orientation and (111) terminating facets, achieving a current density of 7 mA cm⁻² at 0.5 V versus RHE under AM1.5G illumination, with stable operation over at least 120 hours. The study highlights the importance of anisotropic properties in Cu₂O for efficient charge transport and separation. Single-crystal thin films offer superior optoelectronic properties due to the absence of grain boundaries and lower defect density. The research team also investigated ultrafast carrier dynamics, finding that the [111] orientation has the longest exciton lifetime and the longest hole diffusion length, which contributes to the high performance of the photocathode. The study demonstrates that the anisotropic properties of Cu₂O can be exploited to enhance the performance of photoelectrochemical devices. The polycrystalline Cu₂O photocathode with a preferred (111) orientation achieved a current density of 7 mA cm⁻², a 75% improvement over state-of-the-art electrodeposited devices. The photocathode also showed excellent stability, with less than 15% current loss after 120 hours of operation. The research team also investigated the electronic and optical properties of Cu₂O, finding that the [111] orientation has the lowest trap density and the highest carrier mobility. These properties contribute to the high performance and stability of the photocathode. The study also highlights the importance of surface and interface engineering in optimizing charge separation and transport in photoactive materials. Overall, the study demonstrates the potential of Cu₂O as a promising material for solar fuel production, with the ability to achieve high performance and stability through the exploitation of anisotropic properties. The findings provide a foundation for further improvements in the performance and stability of photoelectrochemical devices.This study reports on the high carrier mobility along the [111] orientation in Cu₂O photoelectrodes, demonstrating significant improvements in performance and stability. The research team used ambient liquid-phase epitaxy to grow single-crystal Cu₂O thin films with three crystal orientations. Broadband femtosecond transient reflection spectroscopy revealed that carrier mobility along the [111] direction is an order of magnitude higher than in other orientations. This finding led to the development of a polycrystalline Cu₂O photocathode with a pure (111) orientation and (111) terminating facets, achieving a current density of 7 mA cm⁻² at 0.5 V versus RHE under AM1.5G illumination, with stable operation over at least 120 hours. The study highlights the importance of anisotropic properties in Cu₂O for efficient charge transport and separation. Single-crystal thin films offer superior optoelectronic properties due to the absence of grain boundaries and lower defect density. The research team also investigated ultrafast carrier dynamics, finding that the [111] orientation has the longest exciton lifetime and the longest hole diffusion length, which contributes to the high performance of the photocathode. The study demonstrates that the anisotropic properties of Cu₂O can be exploited to enhance the performance of photoelectrochemical devices. The polycrystalline Cu₂O photocathode with a preferred (111) orientation achieved a current density of 7 mA cm⁻², a 75% improvement over state-of-the-art electrodeposited devices. The photocathode also showed excellent stability, with less than 15% current loss after 120 hours of operation. The research team also investigated the electronic and optical properties of Cu₂O, finding that the [111] orientation has the lowest trap density and the highest carrier mobility. These properties contribute to the high performance and stability of the photocathode. The study also highlights the importance of surface and interface engineering in optimizing charge separation and transport in photoactive materials. Overall, the study demonstrates the potential of Cu₂O as a promising material for solar fuel production, with the ability to achieve high performance and stability through the exploitation of anisotropic properties. The findings provide a foundation for further improvements in the performance and stability of photoelectrochemical devices.