Preparation of Cu2ZnSnS4 thin films with high carrier concentration and high carrier mobility by optimized annealing

Abstract

The Cu2ZnSnS4 (CZTS) thin film with both high carrier concentration of 3.10 × 1020 cm−3 and high mobility of 19.8 cm2/V/s was prepared with optimization of heat treatment technique. In this work, different heat treatment techniques have been applied for the as-deposited CZTS by electrodeposition method. The as-deposited CZTS thin films have suitable Cu-poor and Zn-rich chemical composition, determining the high carrier concentration. The grain boundaries were designed for enhancement of carrier mobility of the CZTS thin films. Multi-step annealing refined the grains and increased the area of the grain boundaries in the films, resulting in the slight decrease of carrier mobility. Based on multi-step annealing, long and narrow particles and the preferential orientation of the grain boundaries formed by the decrease of Ar flow rate in 550 °C annealing. With such structure, the direct transportation of the holes along the vicinity of the grain boundaries increased carrier mobility.