New Views on Carrier Diffusion and Recombination by Combining Small Perturbation Techniques: Application to BiVO₄ Photoelectrodes

Abstract

Impedance spectroscopy (IS), intensity‐modulated photocurrent spectroscopy (IMPS), and intensity‐modulated photovoltage spectroscopy (IMVS) are well‐established powerful modulated techniques to characterize optoelectronic devices. Their combined use has proven to provide an understanding of the behavior and performance of these systems, far beyond the output obtained from their independent analysis. However, this combination is shown to be challenging when applied to complex systems. Herein, IS, IMPS, and IMVS are cooperatively used, for the first time, to study the distributed photogeneration, diffusion, and recombination processes in a photoanode of zircon‐doped bismuth vanadate. The use of this methodology reveals that the carriers that determine the response of the device are the electrons when the device is illuminated from the hole‐collector side (electrolyte) and the holes when the illumination reaches the device from the electron‐collector side. Detailed quantitative information is obtained for each carrier, including recombination lifetime, diffusion coefficient and collectrion and separation efficiencies, identifying the latter as the main limitation of this device. This methodology is a powerful tool that can be used for the characterization and understanding of the operating processes of other photoconversion devices.

Correcting unintended changes in electroluminescence perturbation for reliable light intensity modulated spectroscopies

“…Light-perturbated transient techniques [1,2] and spectroscopic technique methods [3] are commonly used to characterize photosensitive devices, such as photoelectrodes [4], photodetectors [5] and photovoltaic (PV) cells [6], based on a broad range of materials, including silicon [3,7] to chalcopyrites [8], dyes [9], organic semiconductors [10,11], perovskites [12,13], and ternary oxide semiconductors [14]. Among the spectroscopic techniques, the intensity-modulated photocurrent and photovoltage spectroscopies, IMPS and IMVS, respectively, are commonly used to approach the transport properties and dissipation mechanisms [15,16] in photosensitive samples.…”

“…Commonly, IMPS and IMVS spectra are shown in Nyquist representation, where the respective transfer functions are plotted representing the negative imaginary parts -Q′' and -W′', as a function of the real parts, Q′ and W′ (see figure 1). In this representation, most typical spectra include one or several arcs in the first quadrant [3,4,19] and, in some cases, loops and/or tails in the second [4,20] and/or the fourth quadrant [21,22].…”