Chemical synthesis of Cu(In) metal inks to prepare CuInS2 thin films and solar cells

We report a chemical method to prepare Cu/In inks or Cu–In inks, from which CuInS2 films are formed. Cu, In and Cu–In nanoparticles are initially synthesized by a polyol method, and then dispersed in solvents to form inks. Metal films are subsequently obtained by drop-casting the Cu inks and In inks in sequence or Cu–In inks directly. The sulfurization of the metal films is carried out in a tube with high sulfur vapors. The obtained CuInS2 films are compact with large grains and pure phases. The band gap of the CuInS2 film is determined to be ∼1.45 eV, which is near the optimal band gap of the solar cell materials. Tentative CuInS2 solar cell with an efficiency of 0.7% is fabricated.

Research highlights▶ CuInS2 (CIS) thin films with optical band gap of 1.5 eV are favored for the production of high-efficiency single-cell systems with large open circuit voltage and of top cells in tandem systems. To reduce the cost of the thin-film solar cells non-vacuum techniques are intensively studied. Among a variety of non-vacuum techniques, nanoparticle-based ink printing is attractive, given the convenience for large-scale production and sufficient utilization of materials. Thereinto, nanoparticles play an important role in the preparation of inks. Although some methods have been proposed to prepare the CIS related nanoparticles, rare examples have been succeed in the fabrication of Cu, In and Cu–In nanoparticles. ▶ In this paper, we present a novel low-cost method to prepare Cu, In or Cu–In nanoparticles, which then are used to fabricate CIS films. Modified polyol method is successfully employed to synthesis metal nanoparticles. The metal nanoparticles are then dispersed in solvents to form inks. Later on, metal films can be subsequently obtained by drop-casting Cu inks and In inks in sequence or Cu–In inks, analogous to the subsequent or simultaneous evaporation in industry, respectively. Finally, the sulfurization of the metal films leads to the formation of CIS films, which are compact with large grains and pure phases. CIS solar cell with an efficiency of 0.7% is also prepared and investigated.