Proceedings of nanoGe Fall Meeting 2018 (NFM18)
DOI: https://doi.org/10.29363/nanoge.nfm.2018.141
Publication date: 6th July 2018
The development of efficient photoelectrochemical (PEC) cells for solar hydrogen production is necessary for a prospective renewable energy supply of mankind. Semiconducting films in PEC cells are used as absorber layers in a triple system of electrolyte-catalyst-semiconductor for generating hydrogen which can be stored and afterwards reburned to water in gas turbines, fuel cells or for the production of chemicals [1]. Due to the low efficiency and poor stability of the absorber layers in the electrolyte their performance must be considerably improved.
We were successful in the preparation of highly (001)-textured polycrystalline WSe2+x thin films with a Pd-promoter on TiN:O back contact substrates [2]. In this process, in a first step X-ray amorphous Se-rich WSex films have been deposited at room temperature by a reactive magnetron sputtering onto a thin metal-promoter Pd film which were afterwards annealed in an H2S(e)/Ar atmosphere. During the crystallization process a liquid promoter PdSex forms and migrates to the surface of the growing WSe2 film. It acts as a solvent agent and accumulates at the non van-der-Waals-planes finally initiating the lateral growth of WSe2 platelets and their coalescence. A maximum hole mobility of 70 cm2 V-1s-1 was reached for our polycrystalline films, which is close to the value for a single crystalline WSe2 (100 cm2 V-1s-1).
Recently, we improved the photoelectrochemical performance using Pt [3], Rh and ammonium thiomolybdate (ATM: (NH4)2Mo3S13) layers on top of the WSe2 photocathode for hydrogen evolution reaction in an acidic solution. The surface states of WS2 and WSe2 crystallites can be passivated by photodeposition of the metal catalysts such as Pt, Rh and Ag. We show that the ATM can be used instead of expensive conventional metal catalysts on the WSe2 photocathode. In addition, the ATM layer forms a heterojunction with the WSe2 film, which improves the charge carrier separation, and allows lowering the prize for preparation of catalyst layers on top of different types of semiconductors.
1. Fichtner, M. J. Alloys Comp. 509S, S529-S534 (2012).
2. Bozheyev, F., Friedrich, D., Nie, M., Rengachari, M. & Ellmer, K. Phys. Stat. Sol. A 211, 2013-2019 (2014).
3. Bozheyev, F., Harbauer, Zahn, C., Friedrich D., & Ellmer, K. Sci. Rep. 7, 16003 (2017).
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