Functional Carbon Nanotube Contacts for Silicon Photovoltaics: From Transparent Conductive Films to Selective and Passivating Interfaces.

Carbon nanotube/silicon (CNT/Si) heterojunction solar cells have emerged as a promising low-temperature photovoltaic platform, combining the strong light-harvesting capability of Si with the transparency, processability, and mechanical compliance of CNT-based contacts. Recent advances have pushed laboratory-scale efficiencies to about 23% and extended device operation to centimeter-scale areas. These advances reflect a functional evolution of CNT contacts from transparent conductive films in early front-junction devices to chemically and structurally engineered contacts and further to selective/passivating interfaces integrated with architectures that decouple optical management from CNT transport constraints. This review examines how CNT composition, doping, morphology, Si absorber design, interfacial passivation, and optical management collectively regulate carrier extraction, recombination, photon utilization, and mechanical form factor. It then discusses the key barriers to practical implementation, including CNT film uniformity, area scaling, contact stability, and mechanical reliability. By linking device-performance advances with the remaining materials and engineering challenges, this review provides a materials and interface perspective on the requirements for scalable and reliable CNT/Si photovoltaics.