Grain size and its influence on efficiency in polycrystalline GaAs solar cells

Abstract

Several variations of the metal-organic chemical vapor deposition process for growth of polycrystalline GaAs films have been developed. The grain size of the films ranged from less than one to several hundred microns, yet the air mass zero efficiencies of the best Schottky barrier solar cells made from films grown by each procedure were all only about 1–2%. The short-circuit current was quite high, as predicted, for large grain films but in nearly all cases where extra processing and higher temperatures were introduced in order to obtain larger grains the open-circuit voltage and fill factor were reduced. Clearly enhancement of grain size alone is insufficient to yield high quality devices, and the roles of contamination and/or process-induced defects must be thoroughly investigated in order to understand and improve the low efficiencies.