*Article* **Investigation on the Selenization Treatment of Kesterite Cu2Mg0.2Zn0.8Sn(S,Se)4 Films for Solar Cell**

**Dongyue Jiang 1, Yu Zhang 1, Yingrui Sui 1,\*, Wenjie He 1, Zhanwu Wang 1, Lili Yang 1, Fengyou Wang <sup>1</sup> and Bin Yao <sup>2</sup>**


Received: 27 May 2019; Accepted: 21 June 2019; Published: 29 June 2019

**Abstract:** High-selenium Cu2Mg0.2Zn0.8Sn(S,Se)4 (CMZTSSe) films were prepared on a soda lime glass substrate using the sol–gel spin coating method, followed by selenization treatment. In this work, we investigated the effects of selenization temperature and selenization time on the crystal quality, and electrical and optical properties of CMZTSSe films. The study on the micro-structure by XRD, Raman, X-ray photoelectron spectroscopy (XPS), and energy-dispersive X-ray spectroscopy (EDS) analysis showed that all CMZTSSe samples had kesterite crystalline structure. In addition, the crystalline quality of CMZTSSe is improved and larger Se takes the site of S in CMZTSSe with the increase of selenization temperature and selenization time. When increasing the selenization temperature from 500 to 530 ◦C and increasing the annealing time from 10 to 15 min, the morphological studies showed that the microstructures of the films were dense and void-free. When further increasing the temperature and time, the crystalline quality of the films began to deteriorate. In addition, the bandgaps of CMZTSSe are tuned from 1.06 to 0.93 eV through adjusting the selenization conditions. When CMZTSSe samples are annealed at 530 ◦C for 15 min under Se atmosphere, the crystal quality and optical–electrical characteristics of CMZTSSe will be optimal, and the grain size and carrier concentration reach maximums of 1.5–2.5 <sup>μ</sup>m and 6.47 <sup>×</sup> 1018 cm<sup>−</sup>3.

**Keywords:** CMZTSSe films; sol–gel; electrical properties; optical properties; selenization treatment; solar cells
