First-principles study of indium-free photovoltaic compounds Ag<inf>2</inf>ZnSnSe<inf>4</inf> and Cu<inf>2</inf>ZnSnSe<inf>4</inf>

Synthesis and Characterization of Nanostructured Stannite Cu2ZnSnSe4 and Ag2ZnSnSe4 for Thermoelectric Applications

“…Room temperature UV–vis spectra (Figure ) indicated a band gap of 1.4 eV for Ag 2 ZnSnSe 4 and 1.2 eV for Cu 2 ZnSnSe 4 . This opening of the band gap in stannites with Ag instead of Cu may be due to a lowering of the energy level of the VBM, as has been observed in kesterite compounds, due to the longer bond lengths of Ag–Se (2.632 Å) as compared with that of Cu–Se (2.393 Å) . In addition, it was reported that Ag 2 ZnSnSe 4 (Δ H r = −28.6 kJ/mol) is easier to decompose than Cu 2 ZnSnSe 4 (Δ H r = −84.1 kJ/mol) .…”

“…By replacing Ag with Cu, the size of the unit cell increases, from 5.69 and 11.34 Å (for a and c , respectively, lattice constants that are in agreement with that reported previously) to 5.79 and 11.45 Å, due to the larger size of the Ag atom compared with that of the Cu atom. The bond length of Ag–Se in Ag 2 ZnSnSe 4 is longer than that of Cu–Se in Cu 2 ZnSnSe 4 and results in a lowering of the energy level of the valence band maximum (VBM) which results in a larger band gap, as will be discussed below.…”

“…Room temperature four-probe Hall measurements were conducted at multiple positive and negative magnetic fields in order to eliminate voltage probe misalignment. 35 and results in a lowering of the energy level of the valence band maximum (VBM) which results in a larger band gap, as will be discussed below.…”

“…50 This opening of the band gap in stannites with Ag instead of Cu may be due to a lowering of the energy level of the VBM, as has been observed in kesterite compounds, due to the longer bond lengths of Ag−Se (2.632 Å) as compared with that of Cu−Se (2.393 Å). 35 In addition, it was reported that Ag 2 ZnSnSe 4 (ΔH r = −28.6 kJ/mol) is easier to decompose than Cu 2 ZnSnSe 4 (ΔH r = −84.1 kJ/mol). 35 Our DTA results indicated a decomposition temperature of 470 °C for the Cu 2 ZnSnSe 4 nanocrystals and 365 °C for the Ag 2 ZnSnSe 4 nanocrystals, in agreement with that report.…”

“…35 In addition, it was reported that Ag 2 ZnSnSe 4 (ΔH r = −28.6 kJ/mol) is easier to decompose than Cu 2 ZnSnSe 4 (ΔH r = −84.1 kJ/mol). 35 Our DTA results indicated a decomposition temperature of 470 °C for the Cu 2 ZnSnSe 4 nanocrystals and 365 °C for the Ag 2 ZnSnSe 4 nanocrystals, in agreement with that report.…”