Enhanced performance by heteroatom-doped reduced graphene oxide-TiO₂-based nanocomposites as photoanodes in dye-sensitised solar cells

The photoanode in a dye-sensitised solar cell (DSSC) plays a crucial role in achieving a high power conversion efficiency (PCE). It supports the sensitiser and acts as a transporter of photo-excited electrons from the sensitiser to the external circuit. These two functions are enhanced by a large surface area and a fast charge transport rate. Typically, the photoanode consists of titanium dioxide (TiO₂) nanoparticles. If the nanoparticles are deposited on a carbonaceous substrate, it facilitates the transport of photogenerated electrons. This study compared the photoanode performance of boron- or nitrogen-doped reduced graphene oxide (B- or N-rGO) nanocomposites integrated with TiO₂. All nanocomposites exhibited mainly the anatase TiO₂ phase, and N-rGO-TiO₂ exhibited the lowest bandgap of 2.1 eV, which was attributed to the formation of Ti-O-C and Ti-O-N bonds. Also, N-rGO-TiO₂ displayed good charge carrier separation ability and electron transfer. The low TiO₂ content in the nanocomposites led to the suppression of electron-hole recombination, reduction in the bandgap energy and improvement in electron transport, resulting in higher current density. Two photo-harvesting dyes (sensitisers) were investigated, that is, eosin B and Sudan II. A higher light-harvesting efficiency was obtained from eosin B, indicating the presence of more dye molecules anchored onto the TiO₂. Photoanodes fabricated from N-rGO-TiO₂ and B-rGO-TiO₂ showed enhanced photo-exciton generation, higher short-circuit current densities and significantly better PCEs of 3.94% and 2.55%, respectively, than their undoped rGO-TiO₂ counterparts (1.78%). This work demonstrates that heteroatom-doped rGO-TiO₂-based nanocomposites can improve the rate of transportation and collection of electrons, thereby enhancing the performance of DSSCs.