Visualization of Anion Vacancy Defect Annihilation in CZTSe Solar Cells by Hydrogen-Assisted Selenization with In Operando X-ray Nanoprobe Studies

Chih-Yang Huang; Shao-Chin Tseng; Wei-Chao Chen; Gung-Chian Yin; Bo-Yi Chen; Kuei-Hsien Chen; Li-Chyong Chen; Cheng-Ying Chen

doi:10.1021/acsami.4c11127

Visualization of Anion Vacancy Defect Annihilation in CZTSe Solar Cells by Hydrogen-Assisted Selenization with In Operando X-ray Nanoprobe Studies

ACS Appl Mater Interfaces. 2024 Nov 15. doi: 10.1021/acsami.4c11127. Online ahead of print.

Authors

Chih-Yang Huang^{1

2

3}, Shao-Chin Tseng⁴, Wei-Chao Chen^{3

5}, Gung-Chian Yin⁴, Bo-Yi Chen⁴, Kuei-Hsien Chen^{3

5}, Li-Chyong Chen^{3

6

7}, Cheng-Ying Chen^{3

8}

Affiliations

¹ International Graduate Program of Molecular Science and Technology, National Taiwan University (NTU-MST), Taipei 10617, Taiwan.
² Molecular Science and Technology Program, Taiwan International Graduate Program (TIGP), Academia Sinica, Taipei 11529, Taiwan.
³ Center for Condensed Matter Sciences, National Taiwan University, Taipei 10617, Taiwan.
⁴ National Synchrotron Radiation Research Center (NSRRC), Hsinchu 30092, Taiwan.
⁵ Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan.
⁶ Department of Physics, National Taiwan University, Taipei 10617, Taiwan.
⁷ Center of Atomic Initiative for New Materials (AI-MAT), Taipei 10617, Taiwan.
⁸ Department of Optoelectronics and Materials Technology, National Taiwan Ocean University, Keelung 202301, Taiwan.

PMID: 39547793
DOI: 10.1021/acsami.4c11127

Abstract

The traditional sulfur selenization process in Cu₂ZnSn(S,Se)₄ (CZTSSe) solar cell fabrication often results in the creation of localized anion vacancies (V_S and V_Se). These vacancies are considered harmful defects as they can trap carriers generated by light, leading to reduced solar cell efficiency. Moreover, concrete evidence has been lacking on the extent of the impact caused by these anion vacancies. Our research introduces a novel approach: the hydrogen-assisted selenization (HAS) process, specifically designed to minimize localized anion vacancies in Cu₂ZnSnSe₄ (CZTSe) solar cells. Our investigation, utilizing current-voltage (I-V) and admittance spectroscopy measurements, provides clear insights. We observed notable improvements in carrier collection efficiency and a discernible reduction in defect states. Furthermore, there was a significant decrease in the activation energy required within the solar cell device, dropping from 184 to 145 meV. To delve deeper into the structural and compositional aspects, we employed synchrotron-based X-ray nanoprobes. Through nanoscale X-ray fluorescence and hard X-ray beam-induced current measurements, we can directly observe and document the relationship between the local compositional distribution and photocurrent activity in operando. These comprehensive results furnish strong evidence that mitigating anion vacancies in the CZTSe layer can substantially improve the power conversion efficiency of the CZTSe solar cells. This advancement not only sheds light on the critical role of anion vacancies in solar cell performance but also underscores the effectiveness of the HAS process in enhancing overall device efficiency.

Keywords: CZTSe; Solar Cells; anion vacancy; nano-XBIC; nano-XRF.