Boron Diffusion with Boric Acid for High Efficiency Silicon Solar Cells

A boron diffusion process using boric acid as a low cost, nontoxic spin-on source is introduced. Using dilute solutions of boric acid, sheet resistances ranging from 20 to 200 Omega/square were achieved, along with saturation current densities as low as 85 fA/cm(2). These results indicate that boric acid is a suitable source for forming both p(+) emitters and back surface fields for high efficiency n- and p-type solar cells. The degradation of the minority carrier bulk lifetime, which is a common efficiency-limiting characteristic of low cost boron sources, was also minimized through the use of a high purity boric acid source. The ability to achieve low sheet resistances, high bulk lifetimes and low saturation current densities with boric acid were exploited to achieve a 19.7% efficient screen printed solar cell exhibiting a bulk lifetime >400 mu s. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3392364] All rights reserved.