Carbon/Silicon Heterojunction Solar Cells: Status and Perspectives

Carbon/silicon (C/Si) heterojunction solar cells have recently achieved power conversion efficiencies exceeding 23% for small‐area (6 cm²) devices. The development pathway toward these results highlights the critical requirements for engineering efficient contacts and heterojunction structures in next‐generation photovoltaic technologies. If current performance trends continue, C/Si heterojunctions could provide a viable route to affordable, high‐efficiency solar cells. This review examines the main carbon allotropes explored for C/Si junctions, that is, amorphous carbon (a‐C), C₆₀ fullerene, graphene, and carbon nanotubes (CNTs) and evaluates their optoelectronic properties, deposition strategies, and device performance. The a‐C approach enables low‐temperature, scalable processing but suffers from high defect densities and limited carrier mobility. Fullerene derivatives offer favorable energy‐level alignment for electron extraction, yet their low conductivity and photochemical instability remain obstacles. Graphene provides reasonable optical transparency, mechanical flexibility, and a tunable work function; however, its relatively high sheet resistance, parasitic optical absorption, and interface recombination cast doubt over its use in high‐efficiency solar cells. By contrast, CNTs combine outstanding electrical conductivity, one‐dimensional carrier transport, and simple solution‐based fabrication, supporting efficient charge separation and extraction when integrated with optimized passivation layers. As a result, CNT/Si heterojunctions consistently outperform other carbon‐based architectures, positioning CNTs as the leading candidate for future low‐cost, high‐efficiency C/Si photovoltaic devices. The review concludes by outlining research priorities in interface optimization and scalable large‐area processing.