Cubic AgBiS₂ Colloidal Nanocrystals for Solar Cells

Recent progress in colloidal quantum dot (CQD)-based solar cells indicates that low-toxicity materials such as AgBiS2 nanocrystals (NCs) show potential in replacing toxic PbS and CdS CQDs in solar cell applications. In this study, an investigation on the importance of the composition and sensitivity toward synthesis conditions was performed by adjusting concentrations and ratios of Ag and Bi precursors-first, by varying the ratio of Ag toward Bi precursors and, second, by varying the concentration of Ag with a constant ratio toward Bi precursors in the solution. Furthermore, elemental XPS studies and TEM imaging together with solar cell analysis indicated a strong correlation between the concentration of Ag precursor and the NC properties and, moreover, the solar cell properties based on these NCs. In short, a large amount of Ag precursor resulted in smaller Ag-rich NCs, which resulted in solar cells with high photovoltage but low photocurrent density, while a lower amount of Ag precursor resulted in larger NCs and solar cells with a lower photovoltage. The Ag:Bi:S ratio of 0.72:0.9:1 resulted in almost stoichiometric NCs but with a slight excess of Ag, which in turn resulted in solar cells with the highest performance. This work therefore gives insight into how the elemental composition and size of the NCs can be tuned by the precursor ratios and how this, in turn, affects the performance of the solar cell devices.