Rapid microwave synthesis of Cu2ZnSnS4 nanocrystals for photovoltaic junctions

Abstract

Copper zinc tin sulfide (CZTS) nanocrystal (NC) ink was prepared using thiourea as sulphur source by microwave assisted process. Thin films fabricated by doctor blading technique were then used to analyze the structure and morphology of the CZTS NCs. Variation in the properties of the NCs with varying Zn content in the precursor solution was studied. A Zn/Sn ratio of 1.4 with a Cu/(Sn + Zn) ratio of 0.8 in the starting solution was identified as an optimum compositional ratio to get good optoelectronic properties. Synthesis of CZTS NCs was done in ethylene glycol solvent and in a solvent which is a 1:1 mixture of isopropanol and poly ethylene glycol. The films developed from the latter ink showed better morphological and optoelectronic properties. CZTS thin films show absorption coefficient of the order of 104 cm−1 and optical band gap of 1.5 eV. The electrical resistivity was found to be 2.5 × 102 Ω/cm and hole mobility 0.051 cm2/ (Vs). Glass/FTO/CdS/CZTS multilayer structures were fabricated to form P-N junctions. A knee voltage of 0.8 V from the I-V characteristics of the PN junction indicates that a good Voc can be expected from a solar cell constructed with CZTS ink as absorber layer.