Quasi-solid state cadmium sulfide quantum dots embedded photovoltaic cells with gel electrolyte

Abstract

Quantum dots (QDs) are semiconductor nanoparticles exhibiting unique optical and electrical properties due to quantum confinement, which differ from those of the bulk material because of their nano-size. Quantum dot-sensitized solar cells (QDSSCs) belong to the third generation of solar cells and incorporate QDs into the photoanode, acting as photosensitizers. The structure of a QDSSC consists of a photoanode, an electrolyte and a counter electrode. The present study is focused on the preparation of quasi-solid state QDSSC with new polysulfide gel polymer electrolytes. A polysulfide electrolyte is used because it is more suitable for Cadmium Sulfide (CdS) quantum dot solar cells compared to other common electrolytes like I⁻/I³⁻. In this study, multilayer Titanium Dioxide (TiO₂) photoanodes were fabricated using spin coating and doctor blade methods on Fluorine-doped Tin Oxide substrates. TiO₂ acts as the nanostructured metal oxide semiconductor layer, which mediates the electron transportation through the photoanode. CdS QDs, which are the light-harvesting species, were gradually grown on the mesoporous TiO₂ films using Successive Ionic Layer Adsorption and Reaction (SILAR) method. The room temperature conductivity of gel polymer electrolyte was 20.78 Ms/cm, and it increases with temperature. The cell performances were investigated by applying 10 SILAR cycles of CdS to the photoanode. In this study, 2-layer and 4-layer TiO₂ photoanodes were used with polysulfide gel electrolyte along with a Platinum counter electrode. The maximum efficiency of 0.76% was observed in CdS QDs-embedded solar cells with a 4-layer TiO₂ photoanode, with an open circuit voltage (Voc) of 0.49 V and a short circuit current density (Jsc) of 3.71 mA/cm². The maximum efficiency of the cells fabricated with a 2-layer TiO₂ photoanode was 0.71% together with Voc of 0.40 V and Jsc of 4.70 mA/cm². The higher efficiency of cells with a 4-layer TiO₂ photoanode demonstrates that increasing the number of TiO₂ layers enhances solar cell efficiency.