Efficient (Cu_1−xAg_x)₂ZnSn(S,Se)₄ solar cells on flexible Mo foils

Abstract

Cation substitution plays a crucial role in improving the efficiency of Cu 2 ZnSn(S,Se) 4 (CZTSSe) solar cells. In this work, we report a significant efficiency enhancement of flexible CZTSSe solar cells on Mo foils by partial substitution of Cu + with Ag + . It is found that the band gap (E g ) of (Cu 1Àx Ag x ) 2 ZnSn(S,Se) 4 (CAZTSSe) thin films can be adjusted by doping with Ag with x from 0 to 6%, and the minimum E g is achieved with x ¼ 5%. We also found that Ag doping can obviously increase the average grain size of the CAZTSSe absorber from 0.4 to 1.1 mm. Additionally, the depletion width (W d ) at the heterojunction interface of CAZTSSe/CdS is found to be improved. As a result, the open-circuit voltage deficit (V oc,def ) is gradually decreased, and the band tailing is suppressed. Benefiting from the enhanced open-circuit voltage (V oc ), the power conversion efficiency (PCE) is successfully enhanced from 4.34% (x ¼ 0) to 6.24% (x ¼ 4%), and the V oc,def decreases from 915 to 848 mV.

Homogeneous and Graded Ag Alloying in (Cu1‐xAgx)2ZnSnSe4 Solar Cells

“…This representation has been chosen to evidence that the incorporation of Ag is not beneficial for kesterite devices despite numerous attempts to optimize the performances of CAZTSe-based solar cells. At first sight, this result is in contradiction with numerous previous studies [6][7][8][9][10][11][12][13] in which an optimum is found at low (but not null) ACA ratios. All the literature data concerning Ag alloying for kesterite solar cells have been shown in Figure 6b along with the state-of-the-art PCE for sulfur, selenium, and sulfoselenium Ag-free absorbers.…”

“…b) Literature review of the maximum PCE for CAZTS(S)(e) as a function of the ACA ratio. [6][7][8][9][10][11][12][13] Stars represent the state-of-the-art efficiency for CZTS, CZTSSe, and CZTSe solar cells respectively. [17][18][19] The dashed line is a guide for the eye.…”

“…[4] Some recent studies have shown an improvement of the kesterite-based solar cell PV properties with the introduction of Ag in the lattice. [5][6][7][8][9][10][11][12][13] In almost all cases, the CAZTSSe absorbers (containing both S and Se) have been fabricated with solution-based processes and show an optimum ACA ratio between 3% and 20%. In the studies by Yan et al and Yang et al, [8,12] physical vapor deposition (PVD) methods have been used to fabricate pure sulfide CAZTS absorbers, whereas in the study by Gershon et al, [9] a pure selenide CAZTSe absorber synthesized by a chemical method exhibits a small PCE improvement for a 10% ACA ratio.…”

Raman and X-ray Photoelectron Spectroscopic Study of Aqueous Thiol-Capped Ag-Zn-Sn-S Nanocrystals

“…Theoretical calculations demonstrated that due to a substantially larger ionic radius of Ag + (1.14 Å) in comparison with Cu + (0.74 Å) or Zn 2+ (0.74 Å), the formation energy of the AgZn defect (at 0.2 eV above the valence band edge) is much larger than that of the CuZn defect (0.12 eV). Many reports indeed showed an improved lattice (cationic) order in (Cu1-xAgx)2ZnSn(S,Se)4 (CAZTS) or Ag2ZnSn(S,Se)4 (AZTS), as well as a concomitant increase of the photovoltaic device efficiency [5,7,8], although also adverse effects of the substitution were reported [9]. It should be noted that embedding a high Ag concentration into the (intrinsically p-type) CZTS alters the conductivity to n-type [8].…”

“…The latter problem is generally believed to originate from band tails caused by Cu-Zn antisite defects [4]. Partial substitution of Cu for Ag is supposed to be a promising approach to reduce the antisite defect density and thus the band tailing [5,6]. Theoretical calculations demonstrated that due to a substantially larger ionic radius of Ag + (1.14 Å) in comparison with Cu + (0.74 Å) or Zn 2+ (0.74 Å), the formation energy of the AgZn defect (at 0.2 eV above the valence band edge) is much larger than that of the CuZn defect (0.12 eV).…”