The structural, electrical, chemical, and optical properties of ternary Zn(O,S) thin films formed by atomic layer deposition (ALD) were investigated. It was revealed that the films characteristics were highly influenced by the O/(O+S) ratio. The n-type Zn(O,S) layer was applied to both S-rich and Se-rich Cu2ZnSn(S,Se)4 (CZTSSe) absorbers as an alternative buffer layer to conventional CdS. The device performance relationship to the O/(O+S) ratio was examined. The highest power-conversion efficiency (PCE) of 2.75% and 3.30% was achieved using an actual O/(O+S) ratio of ∼0.67 in the buffer layer for S-rich and Se-rich CZTSSe solar cells, and these PCEs correspond to 77% and 67% of the standard CdS-based solar cells, respectively. Further improvement in Se-rich CZTSSe was demonstrated by using NH4OH solution instead of pure H2O as oxygen source during ALD process. The dependence of the solar cell performance on the O/(O+S) ratio was investigated using dark current density-voltage (J-V), external quantum efficiency (EQE), transmission electron microscopy (TEM), and energy-dispersive X-ray spectroscopy (EDX).
Bibliographical noteFunding Information:
J. Heo thanks Prof. B. Shin (KAIST, Rep. of Korea) for helpful discussion on EQE analysis. This work was supported by the New & Renewable Energy Core Technology Program of the Korea Institute of Energy Technology Evaluation and Planning (KETEP) granted financial resource from the Ministry of Trade, Industry & Energy, Republic of Korea ( 20143030011950 ). This research was also supported by Basic Science Research Program ( NRF-2015R1C1A1A02036616 ) through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT & Future Planning .
© 2016 Elsevier B.V. All rights reserved.
Copyright 2016 Elsevier B.V., All rights reserved.
- Atomic layer deposition
- Buffer layer