Ag Alloying in Cu2−yAgyBa(Ge, Sn)Se4 Films and Photovoltaic Devices. Issue 7 (27th January 2023) - Kim, Yongshin
Abstract : Trigonal Cu2 BaGe1− x Sn x Se4 (CBGTSe) has recently gained interest as a potential photovoltaic absorber to target mitigation of antisite defect formation in Cu2 ZnSn(S, Se)4 . This study examines partial substitution of Cu by Ag as a potential approach to tune the properties of Ag‐incorporated CBGTSe in the following aspects: 1) phase stability and crystal structure as a function of Ag content; 2) film morphology and grain structure; 3) charge carrier properties; 4) band positions; and 5) charge carrier kinetics and recombination. Up to 20% of Cu can be substituted by Ag in CBGTSe, while above 20% a phase mixture appears. Increasing Ag content induces larger average grain size and reduced hole carrier densities. In contrast, photoelectron spectroscopy and photoluminescence measurements reveal negligible impact of Ag substitution on ionization potential (≈5.4 eV) and electron affinity (≈3.7 eV). Also, Ag content offers negligible impact on carrier lifetimes (few ns). Consistent with these fundamental properties, solar cells based on two different Ag/(Ag + Cu) ratios (≈0% and ≈20%) show comparable power conversion efficiencies (≈2.7–2.8%). These results indicate that CBGTSe films and solar cells may be less sensitive to Ag substitution compared to Cu2 ZnSn(S, Se)4, at least at the current level of absorber and device optimization. Abstract : This study examines Ag alloying as a potential approach to tune the properties of Cu2 Ba(Ge, Sn)Se4 (CBGTSe) films. It is found that up to 20% of Cu in CBGTSe can be replaced with Ag while maintaining the trigonal crystal structure. While Ag does not noticeably change the band positions and carrier lifetimes, it can significantly affect film morphologies and carrier densities.