Advanced optical characterization of disordered semiconductors by Fourier transform photocurrent spectroscopy

The paper summarizes progress in the Fourier transform photocurrent spectroscopy (FTPS) since 2001 when it was introduced for the first time for evaluation of the spectral dependence of the optical absorption coefficient in microcrystalline silicon thin films. We concentrate on the appropriate measuring conditions and evaluation procedures for a correct data interpretation of various thin films and solar cell structures. We show how the measured and finally evaluated absorption spectra differ in case of single junction amorphous and microcrystalline silicon solar cells as well as for a micromorph tandem. The key issue of the tandem structure diagnostics is a separation of FTPS signals from amorphous and microcrystalline parts of a stacked structure and their correct interpretation. For an appropriate simulation of the light propagation within the structure and confirmation of our measuring approach the computer model cell has been used.