Physical properties of disordered chalcogenide solar cell from Pb₂₀Ge _x Se_{80 − x} thin films

Abstract

The preparation and study of homogeneous p-n junctions from amorphous chalcogenide Pb₂₀Ge _x Se_{80 − x} by thermal evaporation are presented. Such p-n junction is a novel module since no one had fabricated such homogeneous cell from these amorphous compounds yet. The p-type layer is Pb₂₀Ge₂₀Se₆₀ and the n-type is Pb₂₀Ge₂₅Se₅₅ elemental analysis of n- and p-types of Pb₂₀Ge _x Se_{80 − x} is confirmed by energy dispersive X-ray analysis. Optical energy gaps were determined from transmission spectra in the range of 300 to 2500 nm; these values was 1.9 eV for p-Pb₂₀Ge₂₀Se₆₀ and 2.0 eV for n-Pb₂₀Ge₂₅Se₅₅ thin films. The J-V characteristics in the dark are exhibited rectification in the reverse voltage resulting from junction. The reverse current under illumination shows no saturation with voltage. From I-V characteristics under illumination and the spectral response the open circuit voltage V _oc and I _sc were measured. Capacitance measurements are the main method to evaluate doping concentration through the solar cell. The distribution of charged carriers across the depletion region was calculated and interpreted.