Hot injection synthesis of CuInS2 nanocrystals using metal xanthates and their application in hybrid solar cells

Abstract

Copper indium sulfide (CuInS₂) nanocrystals with a size of 3–4 nm and a chalcopyrite crystal structure were synthesized from copper and indium xanthates as precursors in a hot injection synthesis performed at a temperature of 200 °C. Dioleamide molecules served as stabilizing ligands and were exchanged to 1-hexanethiol after the synthesis. TEM images reveal that after the ligand exchange process, the inter-particle distance is significantly reduced and the nanocrystals agglomerate slightly, which is also indicated by small angle X-ray scattering and AFM measurements. Information about charge transfer between the conjugated polymer PCDTBT and the nanocrystals was gained from photoluminescence quenching measurements. Furthermore, the prepared CuInS₂ nanoparticles with an optical band gap of 1.57 eV were applied as acceptors in polymer/nanocrystal bulk heterojunction solar cells and their performance was evaluated. The obtained solar cells showed high open circuit voltages up to 730 mV and overall power conversion efficiencies of 0.23%.