Evaluation of Solar Cell Using Terahertz Time-Domain Spectroscopy

Terahertz time-domain spectroscopy (THz-TDS) has been used to investigate the optical properties of mono silicon solar cell. The sample was optically excited using continuous-wave (CW) light of wavelengths of 800 nm and 365 nm and the carrier density and mobility were extracted from the THz-TDS data by fitting with the simple Drude model. The conductivity shows nonlinear increase with the optical excitation power. The mobility of the photo-excited carriers also increases nonlinearly with the CW light power. However, the mobility shows tendency to saturate with the increase of illumination power, which can be explained by carrier trapping effect to the impurity states existing in the band-gap region of the base material of solar cell. In addition, it is observed that the carrier density and mobility are smaller for 365 nm light illumination due to surface recombination.