Sodium enhances indium-gallium interdiffusion in copper indium gallium diselenide photovoltaic absorbers

• Published in: Nature communications 2018-02, Vol.9 (1), p.826-12, Article 826
• Main Authors: Colombara, Diego, Werner, Florian, Schwarz, Torsten, Cañero Infante, Ingrid, Fleming, Yves, Valle, Nathalie, Spindler, Conrad, Vacchieri, Erica, Rey, Germain, Guennou, Mael, Bouttemy, Muriel, Manjón, Alba Garzón, Peral Alonso, Inmaculada, Melchiorre, Michele, El Adib, Brahime, Gault, Baptiste, Raabe, Dierk, Dale, Phillip J., Siebentritt, Susanne
• Format: Article
• Language: English
• Subjects: 140/133; 140/58; 147/135; 147/137; 639/301/299/946; 639/4077/909/4101/4096/946; 639/766/119/544; Chemical Sciences; Condensed Matter; Copper; Copper converters; Diffusion; Energy conversion; Engineering Sciences; Gallium; Gallium arsenide; Grain boundaries; Humanities and Social Sciences; Indium; Interdiffusion; Material chemistry; Materials; Materials Science; Micro and nanotechnologies; Microelectronics; multidisciplinary; Photovoltaic cells; Photovoltaics; Physics; Science; Science (multidisciplinary); Sodium; Solar cells; Solar energy; Solar energy conversion; Substrates; Thin films
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-018-03115-0

Copper indium gallium diselenide-based technology provides the most efficient solar energy conversion among all thin-film photovoltaic devices. This is possible due to engineered gallium depth gradients and alkali extrinsic doping. Sodium is well known to impede interdiffusion of indium and gallium in polycrystalline Cu(In,Ga)Se 2 films, thus influencing the gallium depth distribution. Here, however, sodium is shown to have the opposite effect in monocrystalline gallium-free CuInSe 2 grown on GaAs substrates. Gallium in-diffusion from the substrates is enhanced when sodium is incorporated into the film, leading to Cu(In,Ga)Se 2 and Cu(In,Ga) 3 Se 5 phase formation. These results show that sodium does not decrease per se indium and gallium interdiffusion. Instead, it is suggested that sodium promotes indium and gallium intragrain diffusion, while it hinders intergrain diffusion by segregating at grain boundaries. The deeper understanding of dopant-mediated atomic diffusion mechanisms should lead to more effective chemical and electrical passivation strategies, and more efficient solar cells. Sodium doping is necessary to achieve high performance in polycrystalline chalcopyrite solar cells, but retards gallium interdiffusion, and thus efficiency optimisation. Here, Colombara et al. show that in contrast to the polycrystalline case, sodium accelerates atomic interdiffusion in monocrystalline samples.