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

• Published in: Solar energy materials and solar cells 2022-06, Vol.239, p.111643, Article 111643
• Main Authors: de Lafontaine, Mathieu, Ayari, Farah, Pargon, Erwine, Gay, Guillaume, Petit-Etienne, Camille, Turala, Artur, Hamon, Gwenaelle, Jaouad, Abdelatif, Volatier, Maïté, Fafard, Simon, Aimez, Vincent, Darnon, Maxime
• Format: Article
• Language: English
• Subjects: Atomic force microscopy; Circuits; Concentrated photovoltaics; Cytology; Electric power; Engineering Sciences; Etching; Fabrication; III–V; Mesa isolation; Micro and nanotechnologies; Microelectronics; Microscopy; Multijunction solar cells; Photovoltaic cells; Plasma etching; Roughness; Saw dicing; Scanning electron microscopy; Solar cells; Wet etching
• ISSN: 0927-0248; 1879-3398
• DOI: 10.1016/j.solmat.2022.111643

Multijunction solar cells must be electrically isolated from one to another at the end of the fabrication process; a step known as mesa isolation. In this study, three different techniques are assessed to perform this step: saw-dicing, wet etching and plasma etching. Triple junction solar cells were fabricated with each process and the open-circuit voltages were measured in order to compare the impact of each technique on the device performance. An optional wet treatment is also proposed to clean the sidewalls after the mesa isolation process. The mesa sidewalls were characterized by scanning electron microscopy and atomic force microscopy to assess the profile length and roughness respectively. The cell performance was then correlated to the sidewall length and roughness for all three isolation techniques. This study indicates that a plasma etching process followed by a wet clean is the process that maximizes the solar cell performance, thanks to a short profile length and a low sidewall roughness. •Plasma etching and saw-dicing enable an anisotropic mesa isolation that reduces the sidewall profile length.•Wet etching reduces the sidewall roughness.•Saw dicing damage can be significantly recovered by a cleaning process.•Plasma etching followed by a wet clean is the best technique thanks to a short sidewall length and low roughness.