Synthesis of Cu2ZnSn(Sx,Se1-x)4 thin films by sputtering based Cu/SnS2/ZnS precursors and their solar cell applications

Abstract

Quaternary Cu2ZnSnS4 (CZTS), which is a promising candidate absorber materials that contains neither In nor Ga, has been attracted much attention for thin film solar cells due to its cheap element, high absorption coefficient over 104 cm-1 in the visible region, direct band gap energy of 1.5 eV, high chemical stability, and p-type conductivity [1-4]. In addition, W. Hillhouse et al. reported the maximum efficiency for single junction Cu2ZnSnS4 and Cu2ZnSnSe TFSCs devices and use photon balance calculations (Shockley-Queisser style detailed balances, CZTSe, η = 31.0%, and CZTS, η = 32.4%) [5]. These outstanding materials characteristics indicate that low cost thin film solar cells (TFSCs) with high power conversion efficiency (PEC) can be fabricated by utilizing a CZTS material[6, 7]. Recently, T.K. Todorov et al. reported the best PCE (~ 11.1 %) for the CZTSSe-based TFSCs device using a hybrid solution-particle approach in a hydrazine-based solution [8] while vacuum-based processes provide a lower efficiency of 9.15% using the CZTSe absorber layer by the co-evaporation method [9]. These lower efficiency for CZTS-based TFSCs than that of Cu(In,Ga)Se2 TFSCs is indicated the more detail researches should be required to improve efficiency of CZTS-based TFSCs. In this work, the CZTS absorber thin films were prepared by sulfurization of sputtering stacked precursor and the CZTS-based TFSCs were fabricated using Al/AZO/i-ZnO/CdS/CZTS/Mo/SLG multi-structure. The synthesis and characterization of CZTS-based thin films and TFSCs will be discussed. First, it presents the effect of stacking orders in the precursor thin films on the properties of CZTS thin films in order to well synthesis the CZTS thin films with voids between CZTS absorber and Mo thin films. The sulfurized thin film from Cu/SnS2/ZnS stacking order indicated the more dense microstructure and uniform morphology than that of other stacking orders. The sulfurized thin films from other stacking order showed th...