Film Flip and Transfer Process to Enhance Light Harvesting in Ultrathin Absorber Films on Specular Back-Reflectors.

Kay, Asaf; Scherrer, Barbara; Piekner, Yifat; Malviya, Kirtiman Deo; Grave, Daniel A; Dotan, Hen; Rothschild, Avner · Adv Mater · 2018

basic_science · Level V

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Abstract

Optical interference is used to enhance light-matter interaction and harvest broadband light in ultrathin semiconductor absorber films on specular back-reflectors. However, the high-temperature processing in oxygen atmosphere required for oxide absorbers often degrades metallic back-reflectors and their specular reflectance. In order to overcome this problem, a newly developed film flip and transfer process is presented that enables high-temperature processing without degradation of the metallic back-reflector and without the need of passivation interlayers. The film flip and transfer process improves the performance of photoanodes for photoelectrochemical water splitting comprising ultrathin (<20 nm) hematite (α-Fe<sub>2</sub> O<sub>3</sub> ) films on silver-gold alloy (90 at% Ag-10 at% Au) back-reflectors. Specular back-reflectors are obtained with high reflectance below hematite films, which is necessary for maximizing the productive light absorption in the hematite film and minimizing nonproductive absorption in the back-reflector. Furthermore, the film flip and transfer process opens up a new route to attach thin film stacks onto a wide range of substrates including flexible or temperature sensitive materials.