Evaluation of Optical Absorption in Cu 2 ZnSn(S,Se) 4 Absorber Within Cell Structure by Fourier Transform Photocurrent Spectroscopy

We demonstrated to evaluate optical absorption spectra of Cu 2 ZnSn(S,Se) 4 (CZTSSe) photo-absorbers within cell structure by Fourier transform photocurrent spectroscopy (FTPS). FTPS measurements were carried out for two series of CZTSSe thin film solar cells using window layer with different thickness. In the spectra, exponential tail was found below photon energy of 1.2 eV. We indicated that band gap energy and Urbach energy of CZTSSe photo-absorbers were determined from the spectra obtained by FTPS measurements for CZTSSe thin film solar cells.