Carbon Nanotubes versus Graphene as Flexible Transparent Electrodes in Inverted Perovskite Solar Cells

Transparent carbon electrodes, carbon nanotubes, and graphene were used as the bottom electrode in flexible inverted perovskite solar cells. Their photovoltaic performance and mechanical resilience were compared and analyzed using various techniques. Whereas a conventional inverted perovskite solar cells using indium tin oxide showed a power conversion efficiency of 17.8%, the carbon nanotube- and graphene-based cells showed efficiencies of 12.8% and 14.2%, respectively. An established MoO₃ doping was used for  carbon electrode-based devices. The difference in the photovoltaic performance between the carbon nanotube- and graphene-based cells was due to the difference in morphology and transmittance. Raman spectroscopy, and cyclic flexural testing revealed that the graphene-based cells were more susceptible to strain than the carbon nanotube-based cells, though the difference was marginal. Overall, despite higher performance, the transfer step for graphene has lower reproducibility. Thus, the development of better graphene transfer methods would help maximize the current capacity of graphene-based cells.