Temperature dependent electroreflectance study of Cu2ZnSnSe4 solar cells

Electroreflectance measurements (ER) of Cu2ZnSnSe4 (CZTSe) solar cell were performed in the temperature range of T=100-300 K. ER spectra were fitted using the Lorentzian line shape functional form. The broadening parameter did not change with temperature and had very high value of 125 meV. High concentration of charged defects and spatial fluctuations of bandgap energy caused by the presence of both ordered and disordered crystal structures and/or different defect clusters are the main reasons for broadening of the ER spectra. The temperature dependence of the band-gap energy for CZTSe was determined from ER data. The overall shift of the bandgap energy was found to be only about 13 meV from room temperature to T=0 K.