Browsing by Author "Sousa, R. A."
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- Comparison of fluctuating potentials and donor-acceptor pair transitions in a Cu-poor Cu2ZnSnS4 based solar cellPublication . Teixeira, J. P.; Sousa, R. A.; Sousa, M. G.; Cunha, A. F. da; Fernandes, P. A.; Salomé, P. M. P.; González, J. C.; Leitão, J. P.The structure of the electronic energy levels of a single phase Cu2ZnSnS4 film, as confirmed by Raman Scattering and x-ray diffraction, is investigated through a dependence on the excitation power of the photoluminescence (PL). The behavior of the observed asymmetric band, with a peak energy at ∼1.22 eV, is compared with two theoretical models: (i) fluctuating potentials and (ii) donor-acceptor pair transitions. It is shown that the radiative recombination channels in the Cu-poor film are strongly influenced by tail states in the bandgap as a consequence of a heavy doping and compensation levels. The contribution of the PL for the evaluation of secondary phases is also highlighted.
- Influence of defects on photoluminescence from a Cu2ZnSnS4 thin filmPublication . Teixeira, J. P.; Sousa, R. A.; Leitão, J. P.; Sousa, M. G.; Cunha, A. F. da; Fernandes, P. A.; Salomé, P. M. P.GubZnSnS2 VCZTS0 p re sent s p romi sing p rope rtie s fo r thin film photovoltaics VPV0 technology [;]Z • non toxic character and availability of the constituentsS • high absorption coefficient VR;M2 cm-;0 in the near-infrared and visible spectral regionsS • almost optimal direct bandgap energy V;F3 eV0F
- Radiative transitions in highly doped and compensated chalcopyrites and kesterites: The case of Cu2ZnSnS4Publication . Teixeira, J. P.; Sousa, R. A.; Sousa, M. G.; Cunha, A. F. da; Fernandes, P. A.; Salomé, P. M. P.; Leitão, J. P.The theoretical models of radiative recombinations in both CuIn1−xGaxSe2 chalcopyrite and Cu2ZnSnS4 kesterite, and related compounds, were revised. For heavily doped materials, electrons are free or bound to large donor agglomerates which hinders the involvement of single donors in the radiative recombination channels. In this work, we investigated the temperature and excitation power dependencies of the photoluminescence of Cu2ZnSnS4-based solar cells in which the absorber layer was grown through sulphurization of multiperiod structuresofprecursorlayers.Forbothsamplestheluminescenceisdominatedbyanasymmetricbandwithpeak energy at∼1.22 eV, which is influenced by fluctuating potentials in both conduction and valence bands. A value of ∼60 meV was estimated for the root-mean-square depth of the tails in the conduction band. The radiative transitions involve the recombination of electrons captured by localized states in tails of the conduction band with holes localized in neighboring acceptors that follow the fluctuations in the valence band. The same acceptor level with an ionization energy of∼280 meV was identified in both absorber layers. The influence of fluctuating potentials in the electrical performance of the solar cells was discussed