Investigation of Optimum Mg Doping Content and Annealing Parameters of Cu(2)Mg(x)Zn(1−x)SnS(4) Thin Films for Solar Cells

Cu(2)Mg(x)Zn(1−x)SnS(4) (0 ≤ x ≤0.6) thin films were prepared by a simple, low-temperature (300 °C) and low-cost sol–gel spin coating method followed by post-annealing at optimum conditions. We optimized the annealing conditions and investigated the effect of Mg content on the crystalline quality, electrical and optical performances of the Cu(2)Mg(x)Zn(1−x)SnS(4) thin films. It was found that the Cu(2)Mg(x)Zn(1−x)SnS(4) film annealed at 580 °C for 60 min contained large grain, less grain boundaries and high carrier concentration. Pure phase kesterite Cu(2)Mg(x)Zn(1−x)SnS(4) (0 ≤ x ≤ 0.6) thin films were obtained by using optimal annealing conditions; notably, the smaller Zn(2+) ions in the Cu(2)ZnSnS(4) lattice were replaced by larger Mg(2+) ions. With an increase in x from 0 to 0.6, the band gap energy of the films decreased from 1.43 to 1.29 eV. When the ratio of Mg/Mg + Zn is 0.2 (x = 0.2), the grain size of Cu(2)Mg(x)Zn(1−x)SnS(4) reaches a maximum value of 1.5 μm and the surface morphology is smooth and dense. Simultaneously, the electrical performance of Cu(2)Mg(x)Zn(1−x)SnS(4) thin film is optimized at x = 0.2, the carrier concentration reaches a maximum value of 3.29 × 10(18) cm(−3).