Heavily doped transparent-emitter regions in junction solar cells, diodes, and transistors

Abstract

An analytical treatment of heavily doped transparentemitter devices is presented that includes the effects of bandgap narrowing, Fermi-Dirac statistics, a doping concentration gradient, and a finite surface recombination velocity S at the emitter surface. Transparency of the emitter to minority carrier is defined by the condition that the transit time τtis much smaller than the minority carrier lifetime in the emitter τp,\tau_{t} \ll \tau_{p}. As part of the analytical treatment, a self-consistency test is formulated that checks the validity of the assumption of emitter transparency for any given device. The transparent-emitter model is applied to calculate the dependence of the open-circuit voltage VOCof n+-p junction silicon solar cells made on low-resistivity substrates. The calculated VOCagrees with experimental values for highS_{P}( \geq5 \× 10^{4}cm/s) provided the effects of bandgap narrowing (modified by Fermi-Dirac statistics) are included in the transparent-emitter model.