Assessment of design approaches for high-efficiency GaAs solar cells

A comprehensive, two-dimensional numerical simulation program for GaAs-based solar cells is used to project achievable efficiency limits for concentrator cells. With lifetimes characteristic of high-quality GaAs, it is projected that conventional p/n heteroface cells can achieve just over 30% conversion efficiency under 500 AM1.5 direct suns. The n/p cell should achieve just under 30% efficiency. These projections assume no shadowing or reflection losses. Simulations show that bandgap-narrowing effects degrade cell performance, but the effects can be largely overcome in n/p cells by using heterojunction back-surface fields. GaAs cells with lightly doped base regions are also investigated, but simulations show that they offer no substantial performance advantage over more conventional designs and are especially sensitive to surface recombination. The simulations suggest that heteroface cells can achieve efficiencies only a few percentage points below the approximately 35% thermodynamic limit under 50 AM1.5 suns.