Impact of Nanostructuring on the Photoelectrochemical Performance of Si/Ta₃N₅ Nanowire Photoanodes

Abstract

The nanostructuring of light-absorbing materials in photoelectrochemical applications can potentially improve the performance of charge transport limited semiconductors by increasing incident light absorption as well as the electrochemically active surface area. However, a drawback associated with an increase in electrode surface area is the increased effect of surface recombination on device performance. To understand the interplay of the positive and negative impacts of nanostructuring, we studied these effects by varying the nanowire length and thereby surface area on the photoelectrochemical performance of tandem core–shell Si/Ta3N5 photoanodes. Si/Ta3N5 nanowires of different lengths, 1.2–3.3 μm, were fabricated by changing the reactive ion etch duration by which the Si nanowires are formed and subsequently characterized by optical UV–vis reflectance measurements, effective charge carrier lifetime measurements, and photoelectrochemical ferrocyanide oxidation. Overall, we show that as the nanowire length is increased, the photovoltage decreases due to decreasing effective carrier lifetimes that arise from higher surface recombination. On the other hand, the device photocurrent increases as the nanowires become longer due to increasing electrochemically active surface area and decreased light reflection, which in turn increases absorption due to light trapping within the nanowires. Balancing these effects is crucial toward developing high performance devices.

A Spin Coating Method To Deposit Iridium-Based Catalysts onto Silicon for Water Oxidation Photoanodes

“…The photovoltage measurements are supported by the open-circuit potential (OCP) in the dark and under illumination measured in both sulfuric acid and potassium ferrocyanide electrolytes (Figure S8). 38 The lightlimited photocurrent is approximately the same for both IrO x | n-Si and SrCl 2 :IrO x |n-Si, around 15 mA/cm 2 , meaning that light absorption in the two catalyst films is similar. Thus, we postulate that SrCl 2 :IrO x facilitates improved charge carrier transport across the Si−catalyst−electrolyte interface compared to IrO x , leading to its improved photovoltage.…”

2D Oxide Nanomaterials to Address the Energy Transition and Catalysis

“…An example is represented by a thin film comprised of an array of vertically ordered TiO 2 nanotubes, modified by supported metal nanoparticles, which were successfully used as advanced photoanodes in new photoelectrocatalytic cells to produce solar fuels . Another example is photoanodes based on tantalum (oxy)nitride nanotube arrays, which can be used in PEC cells for the generation of solar fuels …”

Dynamic Photoelectrochemical Device with Open-Circuit Potential Insensitive to Thermodynamic Voltage Loss

“…33 When employing nanostructured Si photoelectrodes for improving light absorptance and interfacial charge transfer kinetics, high surface recombination losses due to the increased surface defects lead to V oc degradation. 34,35 Although many studies have been conducted to develop a dielectric passivation layer capable of surface defect treatment, it has not been easy to realize a sufficient surface passivation effect to avoid V oc degradation. 35−37 Despite many efforts for improving V oc , a fundamental understanding of why it is affected by the thermodynamic voltage loss has not been addressed so far.…”

“…Specifically, when utilizing only a long-wavelength absorber as the bottom cell in a tandem device, V oc is more degraded as compared with that obtained by using the full wavelength . When employing nanostructured Si photoelectrodes for improving light absorptance and interfacial charge transfer kinetics, high surface recombination losses due to the increased surface defects lead to V oc degradation. , Although many studies have been conducted to develop a dielectric passivation layer capable of surface defect treatment, it has not been easy to realize a sufficient surface passivation effect to avoid V oc degradation. − …”