Excitonic and Band‐to‐Band Transitions in Temperature‐Dependent Optical Absorption Spectra of Cu2SnS3 Thin Films

摘要: Temperature-dependent optical absorption spectra from transmittance and reflectance measurements of Cu2SnS3 (CTS) thin films which are promising material for solar cells were investigated. Thin film CTS samples with Cu-poor, near-stoichiometric, Cu-rich compositions prepared on glass substrates by thermal co-evaporation sulfurization. At low temperature, three band-to-band (BB) transitions that allowed between triple upper valence bands a single lower conduction band observed all samples. The square the product coefficient photon energy was plotted to estimate gap Cu-poor sample. On other hand, excitonic (EX) corresponded near-stoichiometric BB EX resolved using simplified fitting equation Lorentzian functions as transitions. gap, transition, exciton binding energies lowest sample determined be 0.945 eV, 0.936 eV, 8.9 meV at 6 K, respectively. In low-temperature region, anomalous blue-shifts estimated increasing temperature obtained