Low-cost nanocarbon electrodes on arbitrary fibrous substrates as efficient bifacial photovoltaic wires

The emergence of wearable electronics has demanded advances in efficient flexible/wearable energy devices. Photovoltaic wires (PVWs) have unique 3D light-harvesting capabilities and available electrode materials that are attractive for this purpose. Developing low-cost and efficient Pt-free fibrous counter electrodes (CEs) for PVWs is essential. Herein, ultralow-cost nanocarbon, with considerable electrochemical activity, was deposited onto arbitrary fibers, including TiO2 semiconductor, metal wires, and polymeric carbon fibers, using a facile dip-coating method. These fibers were then used as efficient catalytic fibrous CEs in PVWs. The influence of nanocarbon loading and charge transfer resistance on electrocatalytic activity were investigated in nanocarbon-penetrated Ti/TiO2 nanotube array CEs and dummy cells based on SS wire/nanocarbon CEs. Due to the balanced influences of conductive substrate and nanocarbon electrocatalytic film, PVWs assembled from SS wire/nanocarbon CE and an all-carbon carbon fiber/nanocarbon CE achieved efficiencies of 6.09% and 5.10% under AM1.5G illumination (100 mW cm−2), respectively. Furthermore, a double-sided illuminated PVW had an apparent efficiency of 10.8%. This work demonstrates innovative cost-efficient photovoltaic wires that may help boost low-cost, bifacial and highly flexible/wearable photovoltaics toward practical applications.