What is the bandgap of kesterite?

Optical properties of Cu_2ZnSnSe_4 thin films and identification of secondary phases by spectroscopic ellipsometry

“…PL spectra can also be used to determine the band gap of a semiconductor if the material has no tailing and the emission is dominated by band to band transition. However, it is not the case for CZTSe and the main PL peak is usually observed around 100 to 150 meV below the band gap energy due to tailing and the contribution of defects [31,32].…”

Nanometre-scale optical property fluctuations in Cu2ZnSnS4 revealed by low temperature cathodoluminescence

“…2a) does not show a sharp onset at long wavelengths, indicating that the CZTS has significant band tails [5]. At energies close to the onset the absorption coefficient is approximately given by log[1/(1-EQE)] [3,5]; strictly speaking the internal quantum efficiency must be used instead of the EQE, although a comparison with optical reflection-transmission measurements shows that this approximation is still reasonable for the selenide variant, Cu 2 ZnSnSe 4 [5]. The EQE Tauc plot gave a room temperature band gap of 1.63 ± 0.03 eV (Fig.…”

“…The open circuit voltage (V OC ) deficit is however large compared to the structurally similar Cu(In,Ga)Se 2 (CIGS) photovoltaic devices [2,3], and is the main reason for a relatively modest record cell efficiency of 12.6% for the S, Se variant Cu 2 ZnSn (S,Se) 4 or CZTSSe [4]. A key difference between CZTS and CIGS is the extensive band tailing in the former [3,5]. Band tailing in CZTS is related to: (i) Urbach tails in absorption and quantum efficiency spectra [5], (ii) broadening of Raman vibration modes [6,7], (iii) S-shaped temperature dependence of the photoluminescence peak [8,9] and (iv) an anomalously long carrier lifetime at low temperature [3,10].…”

“…A key difference between CZTS and CIGS is the extensive band tailing in the former [3,5]. Band tailing in CZTS is related to: (i) Urbach tails in absorption and quantum efficiency spectra [5], (ii) broadening of Raman vibration modes [6,7], (iii) S-shaped temperature dependence of the photoluminescence peak [8,9] and (iv) an anomalously long carrier lifetime at low temperature [3,10]. Band tailing is common in highly doped, highly compensated semiconductors and is due to statistical fluctuations in the local dopant (i.e.…”

Influence of Amorphous Silicon Carbide Intermediate Layer in the Back-Contact Structure of Cu2ZnSnSe4Solar Cells

“…As it can be observed in that figure, the samples with a-SiC layers show a steeper EQE dependence for photons with wavelengths beyond 1000 nm. The absorption edge in CZTSe material is dominated by tail states [32]; thus, the steeper EQE dependence is related to a lower tail state density, i.e. a higher quality absorber.…”