Preparation of Solar Cells from Lower Purity Silicon

V. Schlosser, K. Wendl

• Institut für Festkörperphysik der Universität Wien

• Ludwig Boltzmann Institut für Festkörperphysik, Wien^*)

Summary
Lower purity silicon made from different metallurgical feedstock has been characterized by means of deep levd transient spectroscopy and determination of minority carrier diffusion length. The latter ranging between 10 Micrometer and 50 Micrometer. Influence of processing temperature on minority carrier diffusion length has been observed and was interpreted by redistribution and complexing of residual impurities during heat treatment of the silicon samples. In order to take advantage of diffusion length enhancement by thermal annealing during solar cell processing different preparation techniques were applied to lower purity silicon wafers: Inversion layer MIS-structures exhibit poor current-voltage characteristics. pn-junctions, made by thermal diffusion require temperatures above 850 degress Centigrade. Deposition of a thin polycrystalline silicon layer onto wafers of lower purity silicon below 750 degrees Centigrade is leading to an improvement of current losses across the pn-junction.

^*)Work supported by Shell Austria AG and Forschungsförderungsfonds der Gewerblichen Wirtschaft Wien (Austria).