Vertically aligned biphase Cu2O/Cu4O3 heterojunctions for enhanced charge extraction and broad−spectrum solar energy conversion

Cuprous oxide (Cu₂O) is a promising p-type semiconductor for solar energy conversion owing to its direct bandgap (2.1−2.5 eV), earth abundance, and environmental benignity. However, conventional Cu₂O-based solar cells are typically based on single-phase structures, and their conversion efficiencies remain significantly below the theoretical limit of 20 % due to limitations in light absorption wavelength range and carrier transport length. This study proposes a strategy for the precise fabrication of vertically aligned biphase Cu₂O/Cu₄O₃ solar cells via reactive magnetron sputtering under controlled oxygen flux modulation. The results demonstrate that atomically sharp phase interfaces and vertically ordered nanostructures within the Cu₂O/Cu₄O₃ system facilitate continuous carrier transport pathways and effectively suppress recombination losses at grain boundaries, resulting in a 22 % improvement in carrier collection efficiency. Moreover, the type−II staggered band alignment at the Cu₂O/Cu₄O₃ heterojunction enables complementary bandgap synergy, extending the photoresponse threshold from 518 nm to 623 nm and enhancing light absorption by 53 %, ultimately yielding a power conversion efficiency of 1.06 %, which represents a 193 % improvement over single-phase Cu₂O devices. Our work establishes a universal design paradigm for vertically ordered nanocomposites, advancing the development of high-performance copper-oxide photovoltaics and offering insights for broader optoelectronic and artificial photosynthesis systems.