Substitution of Ag for Cu in Cu2ZnSn(S,Se)4: Toward Wide Band Gap Absorbers with Low Antisite Defects for Thin Film Solar Cells

Abstract

Cation substitution is a promising approach to reduce the antisite defects and further improve the efficiency of Cu2ZnSn(S,Se)4 (CZTSSe) cells. In this paper, silver (Ag) has been introduced into Cu2ZnSn(S,Se)4 (CZTSSe) thin film to replace Cu partially and form (Cu1-xAgx)2ZnSn(S,Se)4 (0 ≤ x ≤ 1) (CAZTSSe) alloy films by combination of solution method and a rapid annealing technique. The fundamental properties of the mixed Ag-Cu kesterite compound are systematically reported as a function of the Ag/(Ag+Cu) ratio. The results show that band gap of kesterite CAZTSSe is incessantly increased by adjusting the Ag doping content, indicating that the CAZTSSe alloy film is a potentially applicable bandgap grading absorption layers material to obtain higher CZTSSe device. Furthermore, CAZTSSe alloy films with better electrical performance were also obtained by adjusting the Ag content during film fabrication. Finally, we also observed an increment in open circuit voltage (Voc) by 160 mV and an accompanying rise in device efficiency from 4.24 to 5.95%. The improvement is correlated to the improved grain size and decreased antisite defects of Cu instead of Zn site (CuZn) in the lattice. The Voc enhancement evidences that the solution method is facile and viable to achieve proper cation substitution toward higher efficiency kesterite solar cells. In addition, the CAZTSSe cell also displays better charge collection performance because of the higher fill factor (FF) and power conversion efficiency (PCE). Therefore, it can be concluded that the doping of Ag is a potentially appropriate method to reduce the Cuzn antisite defects of CZTSSe and improve efficiency of CZTSSe device.

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

“…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 reducing 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 Ag Zn defect (at 0.2 eV above the valence band edge) is much larger…”

Enhancing the Performance of Aqueous Solution-Processed Cu2ZnSn(S,Se)4 Photovoltaic Materials by Mn2+ Substitution

“…The reduction of R S and the improvement of R Sh for the CMZTSSe device are mostly due to the increase of grain size and the decrease of defect density. The decrease in R S and improved R Sh result in the improvement of J SC and FF [ 14 ]. The V OC of CMZTSSe device increases from 356 to 385 mV in comparison with the CZTSSe device.…”

“…The replacement of Cd for Zn can significantly increase the PCE of CZTSSe devices from 5.3% to 9.24%, which indicates that cation replacement of Zn has great potential for improving the PCE of CZTSSe solar cells [ 11 , 12 ]. Replacing Cu with Ag in CZTSSe is also an efficacious method to decrease the concentration of anti-site defects, which, thereby, improves device performance [ 13 , 14 , 15 ]. However, the general substitution elements such as Ag and Cd are mostly rare or toxic, which deviates from the profit of CZTSSe.…”

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

“…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).…”

“…There is a noticeable discrepancy in the literature regarding the dependence of the phonon Raman peak position and width on the Ag content in CAZTS, the NC size, or non-stoichiometry [5,39]. With the growing number of reports on the synthesis and applications of colloidal AZTS NCs [6,9,11,33,40,41], the physics and chemistry of defects and structural phases in such NCs need to be explored.…”