Band Gap Tuning of Cu2ZnGeSxSe4-x Absorbers for Thin-Film Solar Cells

From sputtered metal precursors towards Cu2Zn(Sn1-x,Gex)Se4 thin film solar cells with shallow back grading

“…From first principle calculations for Cu 2 ZnGeSe 4 a bandgap of 1.5 eV was calculated when replacing Sn with Ge [5], which is close to the experimentally found value of 1.52 eV [6]. For the solid solution with sulfur (Cu 2 Zn(Sn 1-x Ge x )(S,Se) 4 the bandgap can be increased even further [7]. For pure selenide (Cu 2 Zn(Sn 1-x Ge x )Se 4 ) compounds, it was shown that the bandgap increases linear for x=0-1 [8].…”

Investigation on limiting factors affecting Cu2ZnGeSe4 efficiency: Effect of annealing conditions and surface treatment

“…It is worthwhile to mention that the calculated E U in this study is smaller than the one found for the same absorber synthesized by co-evaporation with a value of ~28 meV corresponding to E g ~1.4 eV [44]. E U of about 33 meV was encountered within the best efficiency reported for CZTGSe material with E g ~1.31 eV [41]. These values stay far below the Sn kesterite case, estimated to be around 60 meV in the case of CZTSSe, and 70 meV for CZTS [45].…”

“…The V oc deficit witnesses a drop from 0.83 V for the unetched sample to 0.61 V for the sample etched with KCN with unchanged bandgap (~1.45 eV) as mentioned in Table 2. However, these values are still high compared to efficient CZTSSe and CZTGSe ones, found to be around 0.37 V and 0.35 V for a bandgap of 1.13 eV and 1.11 eV, respectively [39,40], which is expected to happen by widening the band gap [41].…”

Wide band gap kesterite absorbers for thin film solar cells: potential and challenges for their deployment in tandem devices

“…The most obvious procedure would be to anneal the sample in the simultaneous presence of Se and S. However, the boiling point of S is 445°C [21], considerably lower than the annealing temperature of 550°C, and thereby does not allow a constant S supply during the annealing. Therefore, GeS is used as an additional sulfur source [22], which is expected to release S into the gas phase via the following reaction:…”

“…[S]/([S]+[Se])-ratio can be estimated based on this data, revealing that it varies in a range between 0.27 and 0.50[22]. However, the peak shape of the 112-reflections slightly changeswith the amount of GeS.…”