20.1% Efficient Silicon Solar Cell With Aluminum Back Surface Field

We present a standard
$\hbox{p}^{+}\hbox{pn}^{+}$
solar cell device exhibiting a full-area aluminum back surface field (BSF) and a conversion efficiency of 20.1%. The front side features a shallow emitter which has been exposed to a short oxidation step and reduces the emitter dark saturation current density
$j_{0{e}}$
to 160
$\hbox{fA/cm}^{2}$
on a textured surface. The front contact is formed by light-induced nickel and silver plating. Also, devices featuring screen-printed front contacts have been realized that reach a conversion efficiency of 19.8%. PC1D simulations are presented in order to extract the electronic parameters of the BSF. Therefore, external quantum efficiency and reflectance have been determined for modeling the internal quantum efficiency by adapting surface recombination and lifetime of the PC1D-simulated silicon device. As a result, a recombination velocity of
$S_{\rm BSF} = \hbox{283}\ \hbox{cm/s}$
and a dark saturation current density of
$j_{\rm BSF} = \hbox{274}\ \hbox{fA/cm}^{2}$
in the Al BSF are determined. This results in an effective diffusion length
$L_{\rm eff} = \hbox{1150}\ \mu\hbox{m}$
.