Temperature Dependence of Minority Carrier Diffusion Length in Solar Cells Prepared from Lower Purity Silicon

V. Schlosser

• Ludwig Boltzmann Institut für Festkörperphysik, Wien

• Institut für Festkörperphysik University of Vienna

• A-1060 Wien, Kopernikusgasse 15 (AUSTRIA)

ABSTRACT. Minority carrier diffusion length L_n in solar cells prepared from different samples of crystalline lower purity silicon - p-Si, resistivity 0.03 Ohm.cm - 0.3 Ohm.cm - was determined from steady state photoresponse measurements under monochromatic light conditions. In order to estimate the influence of the back side of a 0.3 mm thick device n⁺pp⁺-solar cells were illuminated from front side and from back side. The resulting diffusion length at room temperature and the temperature dependence of L_n are considerably different in both cases thus suggesting that majority carriers contribute to the total light generated current in a solar cell. In order to minimize the influence of majority carriers on the determination of electron diffusion length n⁺p-junctions and MIS structures without a back surface field were used to calculate the room temperature value of L_n for differently heat treated samples. A dependence of L_n on the concentration of a point defect at E_v+E_t = 0.32eV was observed. The temperature dependent evaluation of the capture cross section of point defects from L_n measurements shows that more than one Coulomb attractive center is present in our samples.