Highly stable ethanol-based Cu2ZnSnS4 (CZTS) low-cost thin film absorber: Effect of solution aging

Aging is an important factor that can affect the grain size, surface morphology and optical band gap of the thin films. Especially, it is thought that these important parameters will have a strong impact on the solar cell energy conversion ratio in Cu2ZnSnS4 (CZTS) absorber based photovoltaic devices. With this aim the presented study reports the effect of the aging time on the structural, morphological and optical characteristics of p-type quaternary CZTS absorber materials, produced by using a solution assisted dip-coating process on the glass substrate and annealed at 515 °C without using any dangerous environment (such as sulphurization or selenization). The kesterite crystal structure was determined by X-ray diffraction (XRD) analyses for all the CZTS samples. To support the observed kesterite crystal structure of the CZTS, the main vibration modes and chemical composition of the samples were investigated by Raman and XPS tools. Besides, the comprehensive surface analyses were conducted to better understanding of the morphology variation within the CZTS thin films depending on the aging time of the CZTS precursor solution by using SEM and AFM tools. Generally, large grain size and solution stability of absorber material have important impacts on the solar cell energy conversion solar cells. Furthermore, the band gap of the CZTS thin film shifts toward the optimal energy value (from 1.82 eV to 1.56 eV), observed from the optical studies. This last result is highly attractive for the CZTS based solar cell applications. [Display omitted] •Highly stable kesterite-based Cu2ZnSnS4 (CZTS) was obtained by green sol-gel process.•One of the most important factors is the solution stability of the CZTS absorber for the thin film solar cells.•Band gap shifts from 1.82 eV to ~1.56 eV was observed with the effect of aging.•Triethanolamine (TEA) additive agent improves the decomposition of thiourea (TU) into the sulphur anion over time.