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

Abstract

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 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.

Tunable Photovoltaics: Adapting Solar Cell Technologies to Versatile Applications

“…These tuning capabilities in adjustable SCs cover a multitude of aspects such as bandgap, [22] transparency, [17,20] color, [21] thermal management, [23][24][25] mechanical flexibility, [26][27][28] weight, [29] and size. [30][31][32][33] Tunable PV can be defined as SC technologies that present a manipulation of inherent properties through material design of the functional components and retrofits or via device architecture engineering. The primary aim is to enable suitable customization and adaptation to the specific requirements of a given application.…”

Multijunction solar cell mesa isolation: Correlation between process, morphology and cell performance

“…As hundreds of multijunction solar cells can be fabricated from a single wafer, each component must be electrically isolated from one to another, at the end of the fabrication cycle. This step is commonly referred as mesa isolation and it can be performed by saw-dicing [de Lafontaine et al (2021a); de Lafontaine et al (2016)], wet etching [Kim et al (2014); Raappana et al (2021); Bennett et al (2015); de Lafontaine et al (2021a); Malevskaya et al (2019); Turala et al (2013); Geisz et al (2020); Helmers et al (2011)] or plasma etching [Raappana et al (2021); Albert et al (2021); de Lafontaine et al (2021a); de Lafontaine et al (2016); Lafontaine et al (2019); de Lafontaine et al (2021b)]. Saw-dicing relies on physical abrasion, wet etching uses chemical reaction and plasma etching uses a combination of chemical reactions and ion-assisted sputtering to consume the target material.…”

“…The solar cell performance is affected by recombinations at the sidewalls of the cells (perimeter recombination) [de Lafontaine et al (2021a); Espinet-Gonzalez et al (2014); Belghachi and Khelifi (2006)]. Understanding these mechanisms is especially important considering the fact that the performance loss increases when the cell dimension is reduced towards the submillimetric range needed for micro-concentrator photovoltaics (Micro-CPV) [Espinet-Gonzalez et al (2014); Belghachi and Khelifi (2006); Albert et al (2021); Wiesenfarth et al (2020)]. One can expect the cell performance to depend on the sidewall fabrication method, herein, the mesa isolation etching.…”

“…Despite the improvement provided by plasma etching, the underlying mechanisms and the morphological characteristics of mesa isolation and their impact on III-V/Ge solar cell performance have yet to be investigated. Therefore, identifying the critical mesa isolation characteristics and the optimization pathways represent the keystone for the development of smaller (<200x200 µm 2 ) micro-multijunction solar cells for Micro-CPV applications [Albert et al (2021); Dominguez et al (2017); Wiesenfarth et al (2020)]. In this study, III-V/Ge triple junction solar cells were fabricated with the three different mesa isolation techniques and their open-circuit voltages were assessed under AM1.5D illumination.…”

“…The post-isolation wet clean enables to reduce even more the roughness down to a Sdr value below 1.5 %. Plasma etching offers an interesting pathway for multijunction solar cell miniaturization[Albert et al (2021)]. Despite the fact that this study is focussed on triple junction solar cells, all mesa isolation methods could be relevant for other III-V-based devices such as four, five or six junction solar cells, phototransducers and light-emitting diodes.6.…”