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Engineering of interface band bending and defects elimination via a Ag-graded active layer for efficient (Cu,Ag)2ZnSn(S,Se)4 solar cells

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Abstract

Although the substitution of Cu by Ag to suppress CuZn defects offers several advantages in overcoming the large open-circuit voltage (Voc) deficit for Cu2ZnSn(S,Se)4 (CZTSSe) solar cells, an excellent performance has not been achieved to date primarily due to the Fermi level pinning at the CdS/absorber interface and large recombination at the absorber/Mo interface. Herein, we developed a composition grading strategy to achieve a V-shaped Ag-graded structure with a higher Ag content on both the back and front surfaces of the (Cu,Ag)2ZnSn(S,Se)4 (CAZTSSe) layer. The key advantages of this Ag-graded structure are as follows: the higher content towards the CdS/absorber interface can create weak n-type donor defects and retard Fermi level pinning, whereas the lower content at the interlayer maintains the conductivity and light absorption; moreover, the other higher content towards Mo back contact can effectively suppress the recombination and improve the utilization of long-wave incident light. By appropriately adjusting the Ag gradient, we demonstrated a significant increase in Voc, and an unexpected conversion efficiency of 11.2% was achieved. This is the highest efficiency achieved to date for Ag-substituted CZTSSe solar cells, and the result supports a new aspect that synthesis of a composition-graded CAZTSSe absorber has great potential for future research.

Graphical abstract: Engineering of interface band bending and defects elimination via a Ag-graded active layer for efficient (Cu,Ag)2ZnSn(S,Se)4 solar cells

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Publication details

The article was received on 21 May 2017, accepted on 18 Sep 2017 and first published on 18 Sep 2017


Article type: Paper
DOI: 10.1039/C7EE01405H
Citation: Energy Environ. Sci., 2017, Advance Article
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    Engineering of interface band bending and defects elimination via a Ag-graded active layer for efficient (Cu,Ag)2ZnSn(S,Se)4 solar cells

    Y. Qi, D. Kou, W. Zhou, Z. Zhou, Q. Tian, Y. Meng, X. Liu, Z. Du and S. Wu, Energy Environ. Sci., 2017, Advance Article , DOI: 10.1039/C7EE01405H

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