Characterization of thin epitaxial emitters for high-efficiency silicon heterojunction solar cells

We report silicon heterojunction solar cells with conversion efficiencies exceeding 21% using appropriately designed emitter structures comprised of highly doped thin epitaxial layers grown by plasma-enhanced chemical vapor deposition at temperatures close to 200 degrees C. We show that at a given doping concentration, there is an optimum epitaxial layer thickness, above which the conversion efficiency is limited by Auger recombination and bandgap narrowing within the epitaxial layer. In contrast, below the optimum thickness, the conversion efficiency is limited by carrier recombination at the emitter surface of the crystalline silicon substrate. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4751339]