Optical response of deep defects as revealed by transient photocapacitance and photocurrent spectroscopy in CdTe/CdS solar cells

• We measured transient photocapacitance and photocurrent spectra in CdTe/CdS solar cells.
• The spectra show a defect band at 1.28 eV above the valence band.
• Such a defect band is not indicated in admittance spectroscopy, capacitance–voltage profiling, and drive level capacitance profiling.
• Using a thermal quenching model for the TPC temperature dependence, we find a corresponding thermal energy of 0.22 eV below the conduction band.

Transient photocapacitance (TPC) and photocurrent (TPI) spectroscopy were used to characterize defects in CdTe/CdS solar cells. A broad defect band is observed at an optical energy of 1.28 eV above the valence band, and such a defect is not indicated by admittance spectroscopy and drive-level capacitance profiling. Temperature-dependent TPC measurements of the defect band follow a thermal quenching model in which the defect׳s energy, 0.22 eV below the conduction band, is consistent with the optical response. We provide a theoretical basis for the use of a thermal quenching model in TPC.