Photoelectrochemistry of Semiconducting Oxide Materials for Solar Water Splitting: Characterization of Charge Carrier Dynamics Using IMPS
Ingrid Rodríguez-Gutiérrez a, Manuel Rodríguez-Pérez b, Alberto Vega-Poot a, Geonel Rodríguez-Gattorno a, Gerko Oskam a
a Department of Applied Physics, CINVESTAV-IPN, Mérida, Yuc., México.
b Facultad de Ingeniería, Universidad Autónoma de Campeche, Campeche, Cam., México.
Proceedings of International Conference on Hybrid and Organic Photovoltaics (HOPV19)
Roma, Italy, 2019 May 12th - 15th
Organizers: Prashant Kamat, Filippo De Angelis and Aldo Di Carlo
Oral, Gerko Oskam, presentation 063
Publication date: 11th February 2019

Photoelectrochemical water splitting is an attractive method to convert solar energy to storable chemical energy in the form of hydrogen. In order to efficiently convert sunlight to hydrogen, the semiconducting material must absorb sunlight efficiently, must be capable of reducing and/or oxidizing water, and has to be stable under illumination under current flow in an aqueous electrolyte solution. In particular, for small bandgap semiconductors, stability is often an issue, and it is difficult to fully avoid degradation processes. In addition, the water reduction and oxidation processes need to effectively compete with recombination and surface degradation processes. The kinetic rate constants for charge transfer and surface recombination therefore are very important parameters. Intensity-modulated photocurrent spectroscopy (IMPS) is a powerful option to study the carrier dynamics in a photoelectrochemical cell. The frequency-dependent photocurrent admittance corresponds to the frequency-dependent external quantum efficiency, and time constants for charge transfer and surface recombination can be determined, provided a simple model can be applied [1].

We have used IMPS to study the charge transfer and recombination dynamics in a variety of systems including WO3, p-CuBi2O4 and WO3-BiVO4 heterojunctions. For CuBi2O4 photocathodes, an unfavorable balance between the rate constants for charge transfer and surface recombination limits the conversion efficiency [2]. On the other hand, IMPS analysis of screen-printed WO3 photoanodes shows that the recombination rate constant is significantly smaller than the charge transfer rate constant. The efficiency  limiting process appears to be the charge collection efficiency [3]. Recent results on WO3-BiVO4 heterojunctions, CuWO4, and electrocatalyzed Sn-doped Fe2O3 photoanodes are also discussed.

The authors gratefully acknowledge CONACYT, SENER and CICY for funding through the Renewable Energy Laboratory of South East Mexico (LENERSE; Project 254667; SP-4).

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