Plasma etching applications in concentrated photovoltaic cell fabrication

Abstract

Abstract. Photovoltaic cells are conventionally electrically isolated (isolation) and then separated from the wafer (singulation) by saw dicing at the end of the fabrication process. However, saw dicing presents limitations in terms of cell shapes and causes excessive material losses. We propose isolation and singulation by plasma etching as an alternative to saw dicing. The etching process proposed also allows via hole etching for through cell via contacts (TCVC) [1]. This technology uses isolated metallized vias to carry front-side generated carriers to the backside. This new architecture could increase the efficiency and increase the energy production per wafer for concentrated photovoltaic (CPV) cells. In this paper, those two plasma etching applications for CPV cell fabrication are discussed. More precisely, triple junction solar cells have been fabricated with either a plasma singulation or with via holes and compared with reference cells (without via hole and saw dicing singulation). One sun IV measurements, external quantum efficiency (EQE) and 100 suns IV characteristics show that no performance losses can be observed on cells with plasma singulation. Via hole etching induces open circuit voltage (V OC ) and fill factor (FF) losses below 3 % that can be recovered with a surface passivation.

Integrated Micro‐Scale Concentrating Photovoltaics: A Scalable Path Toward High‐Efficiency, Low‐Cost Solar Power

“…Insolight achieved exceptionally large acceptance with a biconvex aspheric lens array. [ 52,55 ] Other optical architectures have also been proposed. [ 160 ]…”

“…Another factor is the material loss during wafer dicing when singulating the solar cells. Standard technologies such as diamond sawing and laser ablation have lane widths (lost area between active dies) in the micron range [50][51][52] (Figure 2B). These technologies also contribute to the aforementioned perimeter recombination losses for solar cells, by causing mechanical defects during the dicing process.…”

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

“…Accordingly, isolation of microcells requires a soft advanced microfabrication technique such as plasma etching, as developed in the recent years in our group 32–36 . In this work, a Cl 2 /SiCl 4 /H 2 ‐based inductively coupled plasma etch was chosen for isolating the whole heterostructure of Figure 1D.…”

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.…”

“…Wet mesa etching can be performed with variety of different solutions such as Lafontaine et al (2021a)], K 2 Cr 2 O 7 /HBr and KOH/glycerol [Malevskaya et al (2019)], Br 2 /2-propanol and H 2 O 2 [Turala et al (2013)], HBr/Br/H 2 O [Geisz et al (2020)], H 3 PO 4 /H 2 O 2 /H 2 O and HBr/H 3 PO 4 [Helmers et al (2011)]. Plasma mesa etching can be performed with different chlorine-based chemistries such as BCl 3 /Cl2 2 [de Lafontaine et al (2016); Lafontaine et al (2019)], SiCl 4 /Cl 2 [Lafontaine et al (2019)] and SiCl 4 /H 2 [ de Lafontaine et al (2021a,b)] as most chlorine-based subproducts from III-V semiconductors etching are volatile (GaCl x , AsCl x , etc), with the exception of InCl x at room temperature. In this case, desorption can be stimulated by energetic ion bombardment.…”