Facile and eco-friendly synthesis of water-soluble Cu2-xSe nanoparticles for photovoltaic applications

Water-soluble Cu2-xSe (x = 0.2) nanoparticles (NPs) were synthesized by an eco-friendly modified chemical co-precipitation method at 70 °C within a short reaction time of 15 min using ascorbic acid. Cu2-xSe NPs showed pseudo-spherical and hexagonal shapes with sizes in the range of 20–50 nm. XRD analysis showed cubic structure to Cu2-xSe NPs. Thin films of Cu2−xSe were deposited by drop-casting the synthesized Cu2-xSe NPs solution using polyvinylpyrrolidone binder and their physical properties were investigated. The annealed Cu2-xSe NPs thin film showed a direct optical band gap of 1.82 eV and an indirect band gap of 1.69 eV. Hall Effect measurements of the annealed films showed p-type conductivity with a carrier concentration of 3.18 × 1019cm−3, resistivity of 1.31 × 10−1 Ω-cm, and hole mobility of 1.5 cm2/V-s. In order to investigate the potential of Cu2-xSe NPs as an absorber, solar cells with a device configuration of soda-lime glass (SLG)/Mo/Cu2-xSe NPs/CdS/i-ZnO/Al:ZnO/Ni/Ag were fabricated and tested, which showed a power conversion efficiency (PCE) of 0.095%. Even though the Cu2-xSeNPs solar cell showed low PCE, the use of environmentally benign reducer like ascorbic acid offers the benefit of eco-friendliness and compatibility of water-soluble Cu2-xSe NPs synthesis, and its ultimate use in solar cell as well as other applications.