Design of CoNi alloy/graphene as an efficient Pt-free counter electrode in liquid junction photovoltaic devices

CoxNi1-x alloys (0 <= x <= 1) are successfully synthesized and immobilized on a reduced graphene oxide (RGO) surface using the dry plasma reduction method. HRSEM and XPS measurements are used to analyze the morphology and chemical composition of the developed materials. Then, the developed materials are applied as Pt free counter electrodes (CEs) in liquid junction photovoltaic devices. In order to obtain efficient CEs, the chemical composition of the CoxNi1-x/RGO is controlled through optimizing the volume ratio of the Co and Ni precursors during the synthesizing process. It is found that the highest efficiency was 6.75% for the device using Co0.3Ni0.7/RGO CE, which is also higher than those of the devices using Pt CE (6.63%), Co/RGO (6.33%), and Ni/RGO (5.52%). The obtained results can be explained through the optimization of the charge-transfer resistance and diffusion impedance values of the developed materials. The strategy is simple and efficient; thus, it is promising for fabricating cost-effective CE materials for dye-sensitized solar cells.