Maarja Grossberg-Kuusk1,Idil Mengü1,Jüri Krustok1,Mati Danilson1,Maris Pilvet1,Kristi Timmo1,Katri Muska1,Valdek Mikli1,Reelika Kaupmees1,Marit Kauk-Kuusik1
Tallinn University of Technology1
Maarja Grossberg-Kuusk1,Idil Mengü1,Jüri Krustok1,Mati Danilson1,Maris Pilvet1,Kristi Timmo1,Katri Muska1,Valdek Mikli1,Reelika Kaupmees1,Marit Kauk-Kuusik1
Tallinn University of Technology1
With the aim to reduce recombination losses in the kesterite based solar cells, the Ag alloying was performed on Cu<sub>2</sub>ZnSn(S,Se)<sub>4</sub> monograins, leading to the formation of (Ag<sub>1-x</sub>Cu<sub>x</sub>)<sub>2</sub>ZnSn(S,Se)<sub>4</sub> (ACZTSSe) solid solution. Ag is known to partially replace Cu in ACZTSSe, reducing the influence of Cu-Zn disordering and improving the open circuit voltage (<i>V<sub>OC</sub></i>) of the solar cells. Controversial results on the influence of the substitution of Cu by Ag in kesterite thin films have been reported in the literature. However, Ag alloyed kesterite thin film solar cells have been shown to have improved performance due to the reduced defect concentrations compared to the pure Cu<sub>2</sub>ZnSnSe<sub>4</sub> and Cu<sub>2</sub>ZnSnS<sub>4</sub> absorbers. Recently, Yuancai Gong et al. reported 13 % efficient thin film solar cells based on Ag alloyed kesterite CZTSSe<sup>[1]</sup>.<br/>We have previously studied the influence of Ag alloying on the properties of Cu<sub>2</sub>(Zn,Cd)SnS<sub>4</sub> monograin powders and on the performance of the corresponding monograin layer solar cells<sup>[2]</sup>. The incorporation of Ag into the Cu<sub>1.85</sub>(Zn<sub>0.8</sub>Cd<sub>0.2</sub>)<sub>1.1</sub>SnS<sub>4</sub> monograin absorber material improved the efficiency of monograin layer solar cells from 6.62% (x = 0) to 8.73% (x = 0.01) resulting from the changes in the defect structure, which led to reduced non-radiative recombination losses in the absorber.<br/>Here, we report the influence of Ag incorporation into the Cu<sub>2</sub>ZnSn(S,Se)<sub>4</sub> monograins on the structural, optical and electrical properties of the absorber material as well as on the performance of the monograin layer solar cells. Various ratios of [Ag]/ ([Cu] + [Ag]) were used in the synthesis process and losses of outcome Ag concentrations in the resulting material compared to the input were observed. The formation of ACZTSSe solid solutions is determined by X-ray diffraction as well as Raman spectroscopy. Changes in the defect structure and related radiative recombination mechanisms were studied by temperature dependent photoluminescence spectroscopy and correlated to the defects detected by admittance spectroscopy of the corresponding solar cells. Reduced recombination of photoexcited charge carriers as well as improved device performance of the ACZTSSe compared to the CZTSSe monograin layer solar cell devices is reported.<br/><br/>References:<br/>[1] Yuancai Gong et al. Nat Energy 7, 966–977 (2022). https://doi.org/10.1038/s41560-022-01132-4<br/>[2] Kristi Timmo et al. J. Mater. Chem. A, 2019, 7, 24281–24291, DOI: 10.1039/c9ta07768e