FeSn alloy/graphene as an electrocatalyst for the counter electrode of highly efficient liquid-junction photovoltaic devices

This study presents the synthesis of FexSn1-x alloys (0 ≤ x ≤ 1)/reduced graphene oxide (RGO) using a dry plasma reduction method. The formation of bimetallic FeSn nanoparticles on the surface of RGO was confirmed through TEM and XRD measurements. In the results, FeSn ranging from 1 to 5 nm in size is shown to be successfully immobilized on the RGO surface. The developed materials are then applied as Pt-free counter electrodes (CEs) in liquid-junction photovoltaic devices. To get efficient CEs, we have carefully controlled the chemical composition of the FexSn1-x/RGO through changing the volume ratio of the Fe and Sn precursors during synthesis. The catalytic activity of the electrodes follows the sequence of Fe0.1Sn0.9/RGO > Fe0Sn1/RGO > Fe0.3Sn0.7/RGO > Fe0.5Sn0.5/RGO > Fe0.7Sn0.3/RGO > Fe0.9Sn0.1/RGO > Fe1Sn0/RGO, with the Zw values of the developed electrodes lower than those of Sn/RGO and Fe/RGO electrodes. Accordingly, the highest efficiency was 5.0% for the device using Fe0.1Sn0.9/RGO CE, which is also higher than those of devices using Sn/RGO (4.6%) and Fe/RGO (3.8%). The proposed strategy is simple and efficient and is, therefore, promising for the fabrication of cost-effective CE materials for next-generation solar cells and lithium-ion batteries.