Composite films of metal doped CoS/carbon allotropes; efficient electrocatalyst counter electrodes for high performance quantum dot-sensitized solar cells.

This study reports the enhanced catalytic ability of metal ions-doped CoS and CoS/carbon allotrope counter electrodes (CEs) (synthesized using a successive ionic layer adsorption and reaction (SILAR) method) to improve the power conversion efficiency (η) in quantum dot-sensitized solar cells (QDSSCs). Firstly, doping effects of different metal ions (Mg2+, Ca2+, Sr2+ and Ba2+) in the CoS CE on the QDSSCs performance have been investigated. Overall, among the different metal doped CoS CEs, the best energy conversion efficiency of 2.19%, achieved for Sr, is the highest reported for QDSSCs constructed with metal doped CoS. A sandwich structural Sr- and Ba-CoS/carbon allotrope (graphene sheet (GS), graphene oxide (GO) and carbon nanotube (CNT)) composite CEs have been prepared by repeating electrophoretic deposition (EPD) of carbon materials and deposition of CoS nanoparticles. Dramatic enhancements of η have been observed with the Sr- and Ba-CoS/GO CEs based QDSSCs (∼76% and ∼41%, respectively), which is higher than that of the bare CoS CE. Because of the large specific surface area and superior electrical conductivity of GS, GO and CNT and the high electrocatalytic activity of CoS, these CEs show an improvement in the photocurrent density in the cells, as revealed from electrochemical and spectral data.