Charge Transport and Recombination in Nanostructured, Mesoporous Materials for Photoelectrochemical and Solar Cells
Gerko Oskam a, Julio Villanueva b, Juan Antonio Anta c
a Departamento de Física Aplicada, CINVESTAV-IPN, Mérida, 97310
b Instituto de Física, Benemérita Universidad Autónoma de Puebla, Puebla, Pue. 72570
c Area de Química Física, Departamento de Sistemas Físicos, Químicos y Naturales, Sevilla, 41013
Asia-Pacific International Conference on Perovskite, Organic Photovoltaics and Optoelectronics
Proceedings of International Conference Asia-Pacific Hybrid and Organic Photovoltaics (AP-HOPV17)
Yokohama-shi, Japan, 2017 February 2nd - 4th
Organizers: Tsutomu Miyasaka and Iván Mora-Seró
Oral, Gerko Oskam, presentation 095
Publication date: 7th November 2016



The electronic properties of nanostructured photoelectrodes have a strong influence on the efficiency of converting light to an electrical current in a variety of devices such as, for example, dye-sensitized solar cells and solar water splitting systems. In these mesoporous, nanostructured electrodes, charge transport and recombination can generally be described using a continuity equation incorporating activated diffusion-limited charge transport and charge density-dependent recombination. In a two-electrode configuration, the photoelectrodes are often represented by a diode equation including non-ideal behavior related to the influence of traps in both processes. In the analysis of the current - voltage curve, a 100% collection efficiency is generally assumed, which appears to be confirmed by small-signal perturbation methods, such as electrochemical impedance spectroscopy (EIS). However, related to the particular properties of mesoporous, nanostructured materials in a high ionic strength medium, the quasi-Fermi level of electrons in the photoelectrode is not equal to the Fermi level of the conducting oxide substrate under short-circuit conditions, and a significant driving force for recombination is present. By a careful analysis of these processes, we have found that the charge collection efficiency determined from small-perturbation methods is significantly overestimated if recombination under short-circuit conditions cannot be neglected, and this effect becomes more pronounced with increasing recombination losses. We propose a simple method to detect whether recombination losses under short-circuit conditions are important.




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