Structural defects and recombination behavior of excited carriers in Cu(In,Ga)Se2 solar cells.

The carriers' behavior in neutral region (NTR) and space charged region (SCR) of Cu(In,Ga)Se₂ thin film based solar cells has been investigated by temperature dependent photoluminescence (PL-T), electroluminescence (EL-T) and current-voltage (IV-T) from 10 to 300 K. PL-T spectra show that three kinds of defects, namely V_Se, In_Cu and (In_Cu+V_Cu), are localized within the band gap of NTR and SCR of CIGS layer, corresponding to the energy levels of E_C-0.08, E_C-0.20 and E_C-0.25 eV, respE_Ctively. The In_Cu and (In_Cu+V_Cu) deep level defects are non-radiative recombination centers at room temperature. The IV-T and EL-T analysis reveals that the injection modes of electrons from ZnO conduction band into Cu(In,Ga)Se2 layer are tunneling, thermally-excited tunneling and thermionic emission under 10-40, 60-160, and 180-300 K, respectively. At 10-160 K, the electrons tunnel into (In_Cu+V_Cu) and Vse defect levels in band gap of SCR and the drifting is involved in the emission bands at 0.96 and 1.07 eV, which is the direct evidence for a tunneling assisted recombination. At 180-300 K, the electrons are directly injected into the Cu(In,Ga)Se₂ conduction band, and the emission of 1.13 eV are ascribed to the transitions from the conduction band to the valence band. [ABSTRACT FROM AUTHOR]