Isotextured Silicon Solar Cell Analysis and Modeling 2: Recombination and Device Modeling

We extend our analysis of isotextured silicon solar cells by 1) examining experimentally the role played by isotexture in determining the surface recombination velocity at silicon surfaces and 2) combining these experimental results with our model for photogeneration in order to simulate in one dimension typical solar cell devices with isotextured surfaces. We examine both undiffused and diffused
$n$
-type isotextured silicon surfaces, and we find that the rate of surface recombination usually decreases with increasing isotexture etch depth. However, when undiffused surfaces are passivated with hydrogenated
$\hbox{SiO}_2$
or
$\hbox{SiN}_x$
, surface recombination velocity is, counterintuitively perhaps, found to be independent of surface texture—this is despite a surface area that is up to 1.9-fold larger than a planar equivalent. We demonstrate the utility of our analysis of isotextured surfaces by simulating various device structures in one dimension. In one case, where device parameters are chosen to approximate a typical screen-printed cell with full-area back surface field, simulation results indicate that the optimal isotexture etch depth is
$1\hbox{--}3\,\mu\hbox{m}$
. This optimum etch depth is slightly below the one deduced from published experimental results, indicating that surface recombination on samples observed in this study is uniquely independent of isotexture morphology.