Flexible lignin-derived electrospun carbon nanofiber mats as a highly efficient and binder-free counter electrode for dye-sensitized solar cells

A series of flexible carbon nanofiber (CNF) mats have been successfully fabricated via electrospinning of aqueous alkaline lignin-based solutions containing poly(vinyl alcohol) as a spinning-assisted agent, thermal stabilization, and subsequent carbonization at different temperatures. When the carbonization is performed at the temperatures higher than 1000 °C, both graphitizing degree and specific surface area are found to be remarkably enlarged. At the carbonization temperature of 1500 °C, the specific surface area is even as high as 941 m² g⁻¹. A series of dye-sensitized solar cells (DSSCs) are then assembled using the as-obtained CNF mats as the binder-free counter electrodes (CEs) and their electrochemical and photovoltaic properties are studied. At carbonization temperature of 1500 °C, the maximum photoelectric conversion efficiency is achieved up to 7.60%, almost equal to that of the DSSCs with a conventional platinum CE (7.67%) as a reference. The excellent photoelectric performance is attributed to the very high specific surface area and low charge transfer resistance of lignin-based CNF mats as a CE. The cost-effective and flexible features make the sustainable CNF mats as a promising alternative CE to replace conventional and expensive platinum for DSSCs.