USING SPECTROSCOPY TO PROBE THE BAND ENERGETICS OF TRANSPARENT NANOCRYSTALLINE SEMICONDUCTOR-FILMS

Transparent polycrystalline semiconductor films are formed on a conducting glass substrate by sintering nanocrystallites in air at high temperatures. Incorporation in an electrochemical cell, as the working electrode, permits potentiostatic control of the Fermi energy within the semiconductor film. On applying a potential more negative than the flatband potential electrons accumulate in the conduction band. Spectral changes assigned to accumulation of free carriers and the associated Burstein shift have been characterized. Calculation of the flatband potential is possible from the measured relationship between either the free electron absorbance or the Burstein shift, and the applied potential at several different pHs. These methods are finding applications in optimization of regenerative photoelectrochemical cells based on polycrystalline semiconductor films.