Improving the performance of GaInP solar cells through rapid thermal annealing and delta doping

We show that the effect of rapid thermal annealing (RTA) on carrier lifetime in GaInP grown by molecular beam epitaxy depends strongly on both doping type and density, and that these disparities must be accounted for to realize high-performance GaInP solar cells. Although the photoluminescence intensity and lifetime of lightly doped p- and n-GaInP improved greatly with RTA, heavily doped n(+)-GaInP showed sharp degradation upon RTA, preventing the realization of GaInP front-junction solar cells with low emitter sheet resistance. Since a low series resistance is important to achieve high fill factor (FF), we designed a front-junction cell utilizing a thin, lightly doped n-type emitter with delta doping to enhance conductivity, attaining an open-circuit voltage (V-OC) of 1.40 V and FF of 86%. We then designed rear-heterojunction solar cells to further leverage the relatively long lifetime of lightly n-doped GaInP (similar to 19 ns). With the help of delta doping in the n-AlInP window to improve surface passivation, we attained a V-OC of 1.42 V, similar to cells grown by metal-organic vapor phase epitaxy.