Copper indium sulphide:zinc sulphide (CIS:ZnS)-alloyed quantum dots as an eco-friendly absorber in solar cells

Synthesis and characterization of less toxic copper indium zinc sulphide (CIS:ZnS)-alloyed quantum dots (QDs) were carried out and the ligand exchange process towards the efficiency enhancement in CIS:ZnS QD-sensitized solar cell was demonstrated. The colloidal CIS:ZnS QDs were synthesized by an inexpensive heat up method with oleic acid as the capping ligand. The optical properties were analysed through ultraviolet-visible absorption and photoluminescence emission spectroscopy. The influence of the ligand exchange process on the CIS:ZnS QD-based solar cells was analysed with the fabrication of two batches of solar cells. The ligand exchange process was confirmed from Fourier transform infrared and thermogravimetric analyses. The QD-sensitized solar cells were fabricated using a CIS:ZnS QD-loaded titania photoanode and by employing copper sulphide as the counter electrode. The photovoltaic performance of the fabricated QD solar cells was analysed through photovoltaic characterization methods (current density-voltage characteristics of the devices under the simulated solar light conditions and external quantum efficiency measurements). The ligand-exchanged QD-loaded solar cells show enhanced power conversion efficiency compared to the long chain ligand-capped CIS:ZnS QD-sensitized solar cells.