Graphene compared to fluorine-doped tin oxide as transparent conductor in ZnO dye-sensitized solar cells

Graphene could replace widely used transparent conductors (TC) like tin oxides due to its high transparency and electrical conductivity. This work focuses on the technical feasibility of graphene produced by chemical vapor deposition (CVD) to replace tin oxides in the photoanode of dye-sensitized solar cells (DSSCs). This is the first study in which graphene is used as photoanode TC in a tin oxide-free DSSC with ZnO as mesoporous semiconductor. The stability of graphene towards hybridization with ZnO was investigated using electrical measurements and Raman spectroscopy. A thorough comparison of performance between FTO- and graphene-DSSCs fabricated with otherwise identical methods was performed with linear voltammetry, electrochemical impedance spectroscopy and electron lifetime calculations. The higher optical transmittance of graphene resulted in larger open circuit voltage and short circuit current density than FTO devices. However, the larger sheet resistance of graphene caused a lower fill factor in the graphene-DSSCs. Graphene- and FTO-DSSCs yielded similar power conversion efficiencies of 0.4%, despite graphene being ∼250 times thinner than FTO. The findings have important cost and environmental implications for large scale production, not only for DSSCs, but for the photovoltaic technologies derived from them, such as perovskites and quantum dot-SSCs, and other photoelectrochemical devices. Tin oxides replacement with graphene is promising for development of lighter, and more flexible, sustainable and resilient PV technology.