One-pot synthesis of colloidal Cdx:CuInS2 quaternary quantum dots used as sensitizers in photovoltaic cells

Abstract

In this work, we present the synthesis of Cd_x:CuInS₂ quaternary quantum dots (q-QDs) using a one-pot non-injection approach of alloying CuInS₂ with Cd²⁺. Photoluminescence measurements showed that an increase in the Cd mole fraction in Cd_x:CuInS₂ q-QDs caused a systematic blue-shift in the QD emission wavelength. The as-prepared Cd_x:CuInS₂ q-QDs exhibited emissions in the range of 560–645 nm, and a maximum fluorescence quantum yield of 22%. Time-resolved photoluminescence measurements indicated that the average lifetime of Cd_x:CuInS₂ q-QDs became shorter compared to that of the CuInS₂ ternary QDs (t-QDs), clearly indicating that a certain amount of Cd²⁺ defects exist inside the CuInS₂ host. The photovoltaic performance of QD-sensitized solar cells (QDSSCs) was investigated by sandwiching a polysulfide electrolyte between Cd_x:CuInS₂ q-QDs photoanodes and Cu₂S photocathodes. A maximum energy conversion efficiency of 1.74% was obtained under AM1.5 G simulated solar light for the cell fabricated with Cd_x:CuInS₂ q-QDs (x = 1) as the sensitizer, which is about 70% and 35% better than the cells sensitized with pristine CuInS₂ t-QDs and Zn:CuInS₂ q-QDs, respectively. More interestingly, it was noted that J_SC systematically improved as the quantum yields of Cd_x:CuInS₂ q-QDs increased, resulting in an enhancement in power conversion efficiency. Furthermore, the power conversion efficiency of the solar cells co-sensitized with Cd:CuInS₂ and CdSe can be elevated further to an encouraging 2.86%.