(617ey) Engineering Interfaces for the Activation and Stabilization of Photovoltaic-Grade Thin Film Light Absorbers for Photoelectrochemical Hydrogen Production

Authors: 
Palm, D. W., Stanford University
Hellstern, T. R., Stanford University
Jaramillo, T. F., Stanford University
Gaillard, N., University of Hawaii at Manoa
The next key challenge for the proliferation of renewable energy technologies is scalable storage of the energy captured from these often intermittent and diffuse energy sources. One promising option for readily transportable energy storage is the production of a chemical fuel from an abundant feedstock. Toward this end, our work focuses on the development of stable photoelectrochemical (PEC) materials for the light-induced catalytic decomposition of water to hydrogen gas. Such systems combine both energy capture and energy storage into one device, but currently suffer from either low efficiencies or poor stability under illumination. In collaboration with Dr. Nicolas Gaillard (U of Hawaii), photo-active electrocatalytic arrays that optimally match the solar spectrum and can sustain operation over technologically meaningful time scales are being developed. In the Jaramillo group, our focus has been on understanding the complex interfaces between the light-absorber, protective film, catalyst and electrolyte in the PEC device.

The chalcopyrite class of materials has shown promise for photovoltaic (PV) applications given these materialsâ?? utility as potentially scalable and bandgap-tunable thin film light absorbers. Accordingly, Dr. Gaillardâ??s group has developed thin films of CuGa(S,Se)2 that approach the ideal bandgap for the front absorber in a tandem dual-absorber array for PEC; as a p-type semiconductor, these films function well as photocathodes for carrying out the hydrogen evolution reaction (HER). However, the material is neither intrinsically stable in aqueous electrolyte nor intrinsically active as an HER catalyst. Accordingly, attempts have been made to activate and stabilize the photocathodes using thin films of oxides (such as TiO2) and sulfides (like MoS2) that have proven valuable as either protection layers, electrocatalysts, or both. Mechanisms for degradation have been probed via post-mortem electron microscopy and elemental analysis. Furthermore, work has been conducted to investigate the incorporation of n-type emitter layers (such as CdS and ZnOS) in order to maximize the photovoltage produced by the photoelectrode array.