Interface engineering of CdS/CZTSSe heterojunctions for enhancing the Cu2ZnSn(S,Se)4 solar cell efficiency

Wei Chao Chen, Cheng Ying Chen, Yi Rung Lin, Jan Kai Chang, Chun Hsiang Chen, Ya Ping Chiu, Chih I. Wu, Kuei Hsien Chen, Li Chyong Chen

Research output: Contribution to journalArticle

Abstract

Interface engineering of CdS/CZTS(Se) is an important aspect of improving the performance of buffer/absorber heterojunction combination. It has been demonstrated that the crossover phenomenon due to the interface recombination can be drastically eliminated by interface modification. Therefore, in-depth studies across the CdS/CZTS(Se) junction properties, as well as effective optimization processes, are very crucial for achieving high-efficiency CZTSSe solar cells. Here, we present a comprehensive study on the effects of soft-baking (SB) temperature on the junction properties and the corresponding optoelectronic and interface-structural properties. Based on in-depth photoemission studies corroborated with structural and composition analysis, we concluded that interdiffusion and intermixing of CZTSSe and CdS phases occurred on the Cu-poor surface of CZTSSe at elevated SB temperatures, and the interface dipole moments induced by electrostatic potential fluctuation were thus significantly eliminated. In contrast, with low SB temperature, the CdS/CZTSSe heterojunction revealed very sharp interface with very short interdiffusion, forming interface dipole moments and drastically deteriorating device performance. These post thermal treatments also significantly suppress defect energy level of interface measured by admittance spectroscopy from 294 to 109 meV due to CdS/CZTSSe interdiffusion. Meanwhile, the interdiffusion effects on the shift of valence band maximum, conduction band minimum and band offset across the heterojunction of thermally treated CdS/CZTSSe interface are spatially resolved at the atomic scale by measuring the local density of states with cross-sectional scanning tunneling microscopy and spectroscopy. A significant enhancement in the power conversion efficiency from 4.88% to 8.48% is achieved by a facile interface engineering process allowing a sufficient intermixing of CdS/Cd and CZTSSe/Se phases without detrimental recombination centers.

Original languageEnglish
Pages (from-to)256-266
Number of pages11
JournalMaterials Today Energy
Volume13
DOIs
Publication statusPublished - 2019 Sep

    Fingerprint

Keywords

  • CZTSSe
  • CdS
  • Heterojunction
  • Soft-baking

ASJC Scopus subject areas

  • Renewable Energy, Sustainability and the Environment
  • Materials Science (miscellaneous)
  • Nuclear Energy and Engineering
  • Fuel Technology
  • Energy Engineering and Power Technology

Cite this

Chen, W. C., Chen, C. Y., Lin, Y. R., Chang, J. K., Chen, C. H., Chiu, Y. P., Wu, C. I., Chen, K. H., & Chen, L. C. (2019). Interface engineering of CdS/CZTSSe heterojunctions for enhancing the Cu2ZnSn(S,Se)4 solar cell efficiency. Materials Today Energy, 13, 256-266. https://doi.org/10.1016/j.mtener.2019.05.015