In the recent years, thin film solar cells (TFSCs) have emerged as a viable replacement for crystalline silicon solar cells and offer a variety of choices, particularly in terms of synthesis processes and substrates (rigid or flexible, metal or insulator). Among the thin-film absorber materials, SnS has great potential for the manufacturing of low-cost TFSCs due to its suitable optical and electrical properties, non-toxic nature, and earth abundancy. However, the efficiency of SnS-based solar cells is found to be in the range of 1 ~ 4 % and remains far below those of CdTe-, CIGS-, and CZTSSe-based TFSCs. Aside from the improvement in the physical properties of absorber layer, enormous efforts have been focused on the development of suitable buffer layer for SnS-based solar cells. Herein, we investigate the device performance of SnS-based TFSCs by introducing double buffer layers, in which CdS is applied as first buffer layer and ZnMgO films is employed as second buffer layer. The effect of the composition ratio (Mg/(Mg+Zn)) of RF sputtered ZnMgO films on the device performance is studied. The structural and optical properties of ZnMgO films with various Mg/(Mg+Zn) ratios are also analyzed systemically. The fabricated SnS-based TFSCs with device structure of SLG/Mo/SnS/CdS/ZnMgO/AZO/Al exhibit a highest cell efficiency of 1.84 % along with open-circuit voltage of 0.302 V, short-circuit current density of 13.55 mA cm−2, and fill factor of 0.45 with an optimum Mg/(Mg + Zn) ratio of 0.02.

ZnO thin films co-doped with Mg and Ga (MxGyZzO, x+y+z=1, x=0.05, y=0.02 and z=0.93) were preparedon glass substrates by RF magnetron sputtering with different sputtering powers ranging from 100W to 200W at a substratetemperature of 350oC. The effects of the sputtering power on the structural, morphological, electrical, and optical propertiesof MGZO thin films were investigated. The X-ray diffraction patterns showed that all the MGZO thin films were grown asa hexagonal wurtzite phase with the preferred orientation on the c-axis without secondary phases such as MgO, Ga2O3, orZnGa2O4. The intensity of the diffraction peak from the (0002) plane of the MGZO thin films was enhanced as the sputteringpower increased. The (0002) peak positions of the MGZO thin films was shifted toward, a high diffraction angle as thesputtering power increased. Cross-sectional field emission scanning electron microscopy images of the MGZO thin filmsshowed that all of these films had a columnar structure and their thickness increased with an increase in the sputtering power.MGZO thin film deposited at the sputtering power of 200W showed the best electrical characteristics in terms of the carrierconcentration (4.71×1020cm−3), charge carrier mobility (10.2cm2V−1s−1) and a minimum resistivity (1.3×10−3Ωcm). A UV-visible spectroscopy assessment showed that the MGZO thin films had high transmittance of more than 80% in the visibleregion and that the absorption edges of MGZO thin films were very sharp and shifted toward the higher wavelength side, from270nm to 340nm, with an increase in the sputtering power. The band-gap energy of MGZO thin films was widened from3.74eV to 3.92eV with the change in the sputtering power.