Bandlike and Localized Defect States in CuInSe2 Solar Cells

We used the deep-level transient spectroscopy (DLTS) to investigate the electronic properties of p-type CuInSe₂ (CIS) polycrystalline thin-film solar cells. We detected electron (or minority) traps with activation energies ranging from E_c-0.1 to E_c-0.22 eV (where E _c is the energy of electrons at the conduction band minimum). While varying the filling pulse duration, we observed the gradual increase in the amplitude of the DLTS signal for these states until it apparently saturates at a pulse duration ∼1 s. Increasing the duration of the filling pulse also results in broadening the DLTS signals and shifting the maximum of these signals towards lower temperature, whereas the high-temperature sides coincide. We also detected a hole (or majority) trap around a temperature of 190 K. Using a model that allows us to distinguish between bandlike states and localized ones based on the dependence of the shape of their DLTS-signal on the filling-pulse duration, we relate the electron trap to bandlike states and the hole trap to localized ones.