Zinc-diffused silver indium selenide quantum dot sensitized solar cells with enhanced photoconversion efficiency

Abstract

Alloying of quantum dots (QDs) with suitable metal ions is one of the efficient tools to enhance the power conversion efficiency (PCE) of QD sensitized solar cells (QDSSCs). Ternary AgInX₂ (X = S, Se) based liquid-junction QDSSCs have low PCEs due to the presence of defect states at internal atom vacancies. However, Zn²⁺ diffusion at these vacant sites can improve the carrier mobility of the QDs. The QDSSCs with Zn²⁺-diffused AgInSe₂ (ZAISE) QDs have a broad light harvesting range up to the near-infrared (NIR) range. PCE was enhanced from a merely 1.67% for pristine AgInSe₂ QDs (AISE) to 3.07% for ZAISE with a Zn/(Ag + In) ratio of 48.2%, aided by an optimized ZnS passivation layer on the photoanode. The device efficiency was further improved to 3.57% by applying dual passivation of amorphous TiO₂ and SiO₂ layers. This approach could effectively suppress the recombination pathways at the QD surface and thereby minimize back electron transfer from photoexcited electrons of QDs and from the conduction band of TiO₂ to the polysulfide electrolyte. The combined strategy of alloying with Zn²⁺ and inorganic passivation could achieve the highest ever PCE of environmentally friendly AgInX₂ based QDSSCs.