Performance enhancement of flexible CZTSSe solar cells on optimized roughness substrate

Flexible Cu2ZnSn(S,Se)(4) (CZTSSe) thin film solar cells are fabricated on titanium substrate by magnetron sputtering with a composition gradient precursor followed by selenization. By varying polishing time with diluted HNO3 and HF from 0 to 90 s, an atomic force microscope shows that the substrate with the minimal surface roughness of 8.6 nm is obtained with the polishing time of 60 s. X-ray diffraction and Raman spectroscopy reveal a highly crystalline structure for the prepared CZTSSe thin films. The gradual grown up grain size of CZTSSe thin film is observed with the increasing polishing time of the substrate. Compared with the CZTSSe solar cells on untreated titanium substrates, a maximum power conversion efficiency enhancement of 56% is achieved for solar cells on polished substrates, which can be attributed to the reduction of recombination at the interface and isolated defects in devices. External quantum efficiency curves show an enhancement in the visible and near-infrared region after optimizing substrate roughness. On the basis of Ti substrate with a minimum roughness, the percentage reduction of efficiency is found to exhibit the minimum value of 5% after bending for five times. (C) 2018 Society of Photo-Optical Instrumentation Engineers (SPIE).