A hybrid ink of binary copper sulfide nanoparticles and indium precursor solution for a dense CuInSe2 absorber thin film and its photovoltaic performance

A newly developed hybrid ink of binary CuS nanoparticles and In precursor solution was prepared to form a CuInSe2 (CIS) thin film. Previously, we have shown a CIS thin film solar cell with 4.19% conversion efficiency using the hybrid ink of Cu2-xSe nanoparticles and In precursor. Deposition using hybrid ink offers advantages including the provision of stress-relief and crack-deflection centers by pure material based nanoparticles and effective binding with the nanoparticles by precursor solutions without other organic binders. Here, we demonstrate volume expansion of a thin film for forming a well-grown absorber layer using CuS nanoparticles instead of Cu2-xSe. Binary nanoparticles were synthesized by a low temperature colloidal process and a precursor solution was prepared by using a non-toxic chelating agent to disperse the In component stably. The band gap of the CIS thin film was 1.08 eV, as determined by external quantum efficiency (EQE) measurements, and the reproducible conversion efficiency of the fabricated device was 6.23%.