• Energy Research

AbstractA core issue in concentrator photovoltaic technology (CPV) is the resistive losses in cells that usually limits the maximum photoconversion efficiency under high concentration. We propose the use of three‐junction monolithic interconnected modules (MIM) to mitigate resistive losses by providing high‐voltage low‐current power. First, we present the fabrication of InGaP/InGaAs/Ge front‐contacted microcells with various designs and dimensions. Front‐contacted cells are the key enabler for the MIM fabrication and demonstrate good electrical characteristics under one sun, similar to standard‐contacted cells. The base front contact size is minimized to limit the unutilized area on the wafer. Second, fabrication techniques for interconnecting cells in MIM are described. Finally, electrical measurements show a record conversion efficiency of 35.1% under 798 suns for the first three‐junction MIM reported (17.8% when considering the entire device area). Versatility and further optimization of the devices are discussed to enlarge their field of application.

AbstractMicro‐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 mm2 (0.068‐mm2 mesa). Large cells (>1 mm2) demonstrate good electrical performance under one sun AM1.5D illumination, but a degradation in the open‐circuit voltage (VOC) 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 VOC. The VOC 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‐mm2 and microcells are expected to show higher efficiency than standard cells under very high concentration.