Optimization Of Cds Buffer Layer For High Efficiency Earth-Abundant Cu2znsn(S, Se)(4) Thin Film Solar Cells

Earth-abundant kesterite, copper-zinc-tin-sulfo-selenide (CZTSSe) compound is an attractive absorber material for thin-film solar cells (TFSCs). However, the open circuit voltage deficit (V-oc-deficit) resulting from high recombination rate at buffer/absorber interface is one of the major challenges that must be overcome to improve the performance of kesterite-based TFSCs. Herein, we have correlated the performances of Cu2ZnSn(S,S)e(4) (CZTSSe) based solar cell as a function of chemically bath deposited CdS buffer layer thickness. By tuning the CdS buffer layer thickness from 22 to 48 nm, the conversion efficiency of CZTSSe thin film solar cells were improved from 8 to similar to 10%. The ideal factors resulting from diode parameters showed improved performance with the CdS layer thickness. The devices fabricated with thin buffer layers exhibited slightly higher open circuit voltages indicating less interfacial recombination at the buffer/absorber interface. The results indicated that the device parameters and hence the performances are strongly dependent on the CdS buffer thickness. Solar cells with thicker CdS buffer layers showed increased series resistance (R-s), shunt conductance (G(sh)) and reverse saturation current (I-0), as well as V-oc-deficit in the kesterite solar cells. The best conversion efficiencies of 9.87 and 5.5% were achieved with a 22 nm and 64 nm thick CdS buffer layers deposited at 60 and 80 degrees C, respectively. The study shows that further improvement of interface between absorber and buffer layer may reduce the open circuit voltage deficit which in turn improves the conversion efficiency of CZTSSe TFSCs.