Considerations for the Accurate Measurement of Incident Photon to Current Efficiency in Photoelectrochemical Cells

Abstract

In this paper we review some of the considerations and potential sources of error when conducting Incident Photon to Current Efficiency (IPCE) measurements, with focus on photoelectrochemical (PEC) cells for water splitting. The PEC aspect introduces challenges for accurate measurements often not encountered in dry PV cells. These can include slow charge transfer dynamics and, depending on conditions (such as a white light bias, which is important for samples with non-linear response to light intensity), possible composition changes, mostly at the surface, that a sample may gradually undergo as a result of chemical interactions with the aqueous electrolyte. These can introduce often-overlooked dependencies related to the timing of the measurement, such as a slower measurement requirement in the case of slow charge transfer dynamics, to accurately capture the steady-state response of the system. Fluctuations of the probe beam can be particularly acute when a Xe lamp with monochromator is used, and longer scanning times also allow for appreciable changes in the sample environment, especially when the sample is under realistically strong white light bias. The IPCE measurement system and procedure need to be capable of providing accurate measurements under specific conditions, according to sample and operating requirements. To illustrate these issues, complications, and solution options, we present example measurements of hematite photoanodes, leading to the use of a motorized rotating mirror stage to solve the inherent fluctuation and drift-related problems. For an example of potential pitfalls in IPCE measurements of metastable samples, we present measurements of BiVO4 photoanodes, which had changing IPCE spectral shapes under white-light bias.

External Quantum Efficiency Spectra of BiVO4 Thin Film Photoanodes under Bias Illumination

“…For (F mono ,*) configurations, therefore, the low-wavelength peak can be considered to effectively be a nearsurface (within 10-20 nm) feature. This would be consistent with our previous measurements of ultrathin (10 nm, 30 nm) BiVO 4 films 19,22 which exhibited even more prominent low wavelength peaks than does the 100 nm film measured here. The optical absorption profile for back illumination, Fig.…”

“…This approach is discussed in more detail in Ref. 19. All aspects of the EQE scan were automated by software written in Labview.…”

“…With the above setup, current-voltage (CV) and EQE scans were performed over the course of 5 d. Distinguishing between days of measurement is of importance based on a previous experiment on similar BiVO 4 samples. 19 In the several hours break overnight, where the sample is kept in the dark and in open circuit, we can assume that the BiVO 4 sample has sufficient time to fully "recover" to its initial, unaltered state. The conditions for the various EQE scans, in terms of optical configuration, applied potential, and relative intensity of the LB source, are listed in sequential order in Table I below.…”

Reliable bi-functional nickel-phosphate /TiO2 integration enables stable n-GaAs photoanode for water oxidation under alkaline condition

“…( 1 ), compared with the quantitative J–V curve (Fig. 4a ) 35 : where J is the measured photocurrent density (mA·cm −2 ) at a particular wavelength, λ(nm) is the wavelength of incident light, and P light is the incident light (mW·cm −2 ). The photoresponse exhibited a sharp absorption edge at 870 nm, which corresponds to the bandgap (E g = 1.4 eV) of GaAs.…”

Surface‐Mediated Charge Transfer of Photogenerated Carriers in Diamond

“…When the quantum efficiency is computed, PCS is also referred as Incident Photon to Current Efficiency (IPCE). [ 39 ] The diamond materials properties affecting photoexcitation and charge transfer processes are investigated by comparing diamond materials with different surface terminations, doping, and surface nanostructuration. More precisely, nanostructured boron‐doped diamonds, referred to as diamond black (DB), [ 7 ] and (100) single crystal diamonds (SC) are compared.…”