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Nanoco Technologies Limited

Paul Kirkham

Stephen Whitelegg

Cary Allen

Ombretta Masala

Christopher Paul Newman

A method for the preparation of copper indium gallium diselenide/disulfide (CIGS) nanoparticles utilizes a copper-rich stoichiometry. The copper-rich CIGS nanoparticles are capped with organo-chalcogen ligands, rendering the nanoparticles processable in organic solvents. The nanoparticles may be deposited on a substrate and thermally processed in a chalcogen-rich atmosphere to facilitate conversion of the excess copper to copper selenide or copper sulfide that may act as a sintering flux to promote liquid phase sintering and thus the growth of large grains. The nanoparticles so produced may be used to fabricate CIGS-based photovoltaic devices.

Preparation of copper-rich copper indium (gallium) diselenide/disulfide nanoparticles

A method for preparing CIGS absorber layers using CIGS nanoparticles on a substrate comprises one or more annealing steps that involve heating the CIGS nanoparticle film(s) to dry the film and possibly to fuse the CIGS nanoparticles together to form CIGS crystals. Generally, at least the final annealing step will induce particle fusion to form CIGS crystals. Reactive gas annealing has been found to facilitate the growth of larger grains in the resulting CIGS absorber layers and lead to improved photovoltaic performance of those layers. It is suspected that the presence of carbon in CIGS nanoparticle films hinders grain growth and limits the size of crystals which can be obtained in CIGS films upon annealing. It has been discovered that exposing the CIGS nanoparticle films to a reactive atmosphere containing sulfur can decrease the amount of carbon in the film, resulting in the growth of larger CIGS crystals upon annealing.

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Lancashire, United Kingdom

Paul Kirkham