A new insight into solar paint concept: regeneration of CuS nanoparticles for paintable counter electrodes in QDSSCs

Copper sulfide (CuS) counter electrodes (CEs) fabricated by chemical bath deposition (CBD) are commonly employed CEs in quantum-dot-sensitized solar cells (QDSSCs). This article focuses on regenerating crystalline CuS nanoparticles (NPs) from residual solution of CBD and then utilizing them for paintable CEs. Our strategy eliminates the underuse of CuS NPs in conventional CBD and provides a simplistic and economically viable approach to develop efficient CEs from regenerated CuS NPs. Affirmatively, we transformed regenerated CuS NPs into paint with and without binder to make CEs having substantial electrochemical performance. Such paintable CEs revitalize the concept of a solar paint that was previously limited to photoanodes only. While demonstrating the feasibility of paintable CEs, we also prepared CEs via spin coating and drop casting using the same regenerated CuS NPs to draw a comparison with originally produced CE from CBD. The higher surface roughness, homogeneous porosity, and hydrophilicity offered by the CE prepared by paint without binder made it electrochemically more active with least charge transfer resistance (Rct), and hence, a significant power conversion efficiency of ~ 0.7% was obtained for a QDSSC having painted photoanode as well as CE. Graphic abstract: [Figure not available: see fulltext.].