Photophysics and photovoltaic properties of Zn-alloyed Ag-In-S quantum dots sensitized solar cells

Abstract

Quantum dots (QDs) have attracted attention for use in photovoltaic applications. However, till now, QDs sensitized liquid junction solar cells (QDSCs) are primary concentrated on binary QDs that contain toxic elements which limit their practical applications in regarding of environmental issues. Hence, the study of less-toxic ternary such as AgInS2 (AIS) and CuInS2 (CIS) or core/shell AIS/ZnS and CIS/ZnS QDs with high power conversion efficiency (PCE) is the most common way for commercial applications. Although significant improvement has been realized for AIS (CIS) QDSCs by overgrowth of wide bandgap ZnS to form quasi type-I core/shell structure for eliminating surface trapping defects where the PCE is comparable or even better than toxic QDs, simultaneously the shell could also cause impeding electron injection from QDs to metal oxide matrix (TiO2) and hole scavenge. For resolving this problem, diffusion of Zn2+ into QDs forming alloyed QDs is a better strategy to improve the conductivity and thus the PCE owing to alloyed QDs could not only reduce the density of trap defects but also regulate the bandgap and contribute to electron injection. Herein, the highly luminescent heavy-metal free and hydrophilic Ag-In-S-Zn alloyed QDs with broad light harvesting range to near infrared (NIR) were synthesized as effective sensitizer for constructing QDSCs, where the optimal PCE of 3.12% was achieved. Moreover, surface passivation by deposition of ZnS layer over the sensitized electrode was also primarily studied to decrease the QDs/electrolyte/TiO2 interface recombination and a champion PCE of 3.78% was obtained.