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