Characterization of solar cells by optical spectroscopic techniques

Photoreflectance (PR), electroreflectance (ER), photoluminescence (PL), and surface photovoltage spectroscopy (SPV) were applied at room temperature (RT) to characterize ZnO/CdS/CuGaSe2 based solar cells deposited on Mo/glass substrates. These techniques are complementary and yield information about structural, optical and electronic properties of the cell. The PL and ER bands showed contributions of both the CdS and the underlying CuGaSe2 layer. The valence band edge structure was obtained from the ER spectra and was confirmed by low temperature (LT) PR spectroscopy. The band gap of CuGaSe2 was estimated by fitting the LT PR spectra and from the absorption edge of the SPV spectrum. Moreover, the CuGaSe2 layer thickness was calculated from the interference fringes of the PR and ER spectra in the spectral region below the material band gap.