Tailoring Energy Structure of Low-toxic Ternary Ag–Bi–S Quantum Dots through Solution-phase Synthesis for Quantum-Dot-Sensitized Solar Cells

Abstract

Low-toxic multinary semiconductor quantum dots (QDs) showing a photoresponse in a wide range from visible to near-IR have been intensively investigated for fabricating efficient solar light conversion systems. Recently, AgBiS2 QDs have attracted much attention to improve the performance of QD solar cells because they have a large absorption coefficient in visible and near-IR. In this report, we describe the solution-phase preparation of ternary Ag-Bi-S QDs with different sizes and with different Ag/Bi ratios. The average size of resulting spherical Ag-Bi-S QDs was controllable from 2.7 to 8.1 nm by adjusting the reaction temperature from 373 to 473 K, while the Ag fraction of obtained QDs also increased with an increase in the particle size. The absorption onset wavelength shifted from 850 to 1200 nm in the near-IR region as the particle size increased. AgBiS2 QDs with almost the stoichiometric composition, obtained at the reaction temperatures of 423 and 473 K, contained no deep intragap states and exhibited a p-type semiconductor behavior. Sensitized solar cells fabricated with stoichiometric AgBiS2 QDs exhibited a relatively high photoresponse in the visible and near-IR regions, the optimal PCE being 0.74% with AgBiS2 QDs of 6.2 nm in diameter that were prepared at 423 K.