Miniaturization of InGaP/InGaAs/Ge solar cells for micro-concentrator photovoltaics

Micro-concentrator photovoltaic (CPV), incorporating micro-scale solar cells within concentrator photovoltaic modules, promises an inexpensive and highly efficient technology that can mitigate the drawbacks that impede standard CPV, such as resistive power losses. In this paper, we fabricate micro-scale multijunction solar cells designed for micro-CPV applications. A generic process flow, including plasma etching steps, was developed for the fabrication of complete InGaP/InGaAs/Ge microcells with rectangular, circular, and hexagonal active areas down to 0.089 mm(2) (0.068-mm(2) mesa). Large cells (>1 mm(2)) demonstrate good electrical performance under one sun AM1.5D illumination, but a degradation in the open-circuit voltage (V-OC) is observed on the smallest cells. This effect is attributed to perimeter recombination for which a passivation effect by the antireflective coating partially recovers the V-OC. The V-OC penalty for small cells is also reduced under high-intensity illumination, from 3.8% under sun to 1.0% at 974 suns. High intensity illumination yields an efficiency of 33.8% under 584 suns for a 0.25-mm(2) and microcells are expected to show higher efficiency than standard cells under very high concentration.