Flexible CZTSSe thin film solar cells fabricated at low temperature with relieved residual stress by Sb incorporation

Abstract

The troublesome residual stress is always a stumbling block that drags the progress pace of flexible CZTSSe thin film solar cells, which urgently needs to be noticed and solved. In this paper, low-temperature prepared CZTSSe absorber with relieved residual stress (0.558 GPa) is realized by Sb incorporation. Owing to the evaporated 20 nm Sb layer under CZTS precursor, the crystalline quality and band mismatching of CZTSSe/CdS interface are simultaneously improved. Additionally, the spatial potential fluctuation extracted from the PL results is found to decrease from 63.26 meV to 41.57 meV, indicating a reduction in band tailing and disorder of CZTSSe absorber. Compared with the general solar cells fabricated at 580 °C, flexible devices with Sb incorporation can maintain a slightly higher performance at a lower temperature about 60 °C. The best power conversion efficiency (PCE) of 4.41% is obtained in the solar cell with 550 °C-selenized CZTSSe absorber after incorporating 20 nm Sb layer, featuring 351.20 mV Voc, 25.73 mA/cm2 Jsc and 48.79% FF. Finally, low-temperature prepared flexible CZTSSe thin film solar cell can retain over 83% of the original PCE after bending at 180° for 40 cycles. The mechanical durability paves a promising way for flexible CZTSSe thin film solar cell in roll-to-roll production.