Effect of CZTS/CCZTS Stacked Structures Prepared through Split-Cycle on the Performance of Flexible Solar Cells

Abstract

Flexible CZTS solar cells have attracted significant attention in recent years owing to their high earth element composition and high photovoltaic conversion efficiency. However, these cells are associated with limitations common in compound thin-film solar cells, such as heterojunction interface combination centers, material defects, and energy level mismatch. In the current study, a green and simple solution spin-coating method is proposed for the preparation of flexible solar cells with multicycle CZTS/CCZTS absorber stacked structures to effectively circumvent the limitations of flexible devices. The results showed that the optimized Zn/Cd ratio results in CCZTS films with large grain longitudinal growth. However, lots of small broken grains were formed at the bottom of the absorber owing to the large lattice spacing, leading to the formation of cell leakage channels. The surface morphology of the absorber film was improved by preparing a stacked structure of CZTS and CCZTS with different periods while suppressing the longitudinal grain delamination. The stacked structure also helps to match the energy band of CZTS/CCZTS/CdS heterojunction. The top layer of CCZTS forms a buffered “energy band ladder” in the energy band of the CZTS/CdS heterojunction, thus suppressing the rapid carrier recombination caused by the Cliff-type energy band bending. A flexible solar cell was thus prepared to obtain a high photoelectric conversion efficiency of 6.51%, and the cells showed excellent resistance to mechanical bending.