Film flip and transfer process to enhance light harvesting in ultrathin absorber films on specular back-reflectors

TL;DR

This paper introduces a novel film flip and transfer process that enables high-temperature processing of ultrathin hematite films on metallic back-reflectors, significantly enhancing light harvesting for photoelectrochemical applications.

Contribution

The study presents a new film flip and transfer method that prevents degradation of metallic back-reflectors during high-temperature processing, improving light absorption in ultrathin semiconductor films.

Findings

Enhanced light absorption in ultrathin hematite films.

High reflectance of back-reflectors achieved.

Process applicable to flexible and temperature-sensitive substrates.

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, we present a newly developed film flip and transfer process that allows for 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 (Fe2O3) films on silver-gold alloy (90 at% Ag-10 at% Au) back-reflectors. We obtain specular back-reflectors with high reflectance below hematite films, which is necessary for maximizing the productive light absorption in the hematite film and minimizing non-productive 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.