Unassisted photoelectrochemical water splitting exceeding 7% solar-to-hydrogen conversion efficiency using photon recycling

Abstract

Various tandem cell configurations have been reported for highly efficient and spontaneous hydrogen production from photoelectrochemical solar water splitting. However, there is a contradiction between two main requirements of a front photoelectrode in a tandem cell configuration, namely, high transparency and high photocurrent density. Here we demonstrate a simple yet highly effective method to overcome this contradiction by incorporating a hybrid conductive distributed Bragg reflector on the back side of the transparent conducting substrate for the front photoelectrochemical electrode, which functions as both an optical filter and a conductive counter-electrode of the rear dye-sensitized solar cell. The hybrid conductive distributed Bragg reflectors were designed to be transparent to the long-wavelength part of the incident solar spectrum (λ>500 nm) for the rear solar cell, while reflecting the short-wavelength photons (λ<500 nm) which can then be absorbed by the front photoelectrochemical electrode for enhanced photocurrent generation.

Recent Advances in the BiVO4 Photocatalyst for Sun-Driven Water Oxidation: Top-Performing Photoanodes and Scale-Up Challenges

“…A similar dual OEC structure was employed by Shi et al [44,45] to produce high performing BiVO 4 photoanodes.…”

“…Synthesizing BiVO 4 photoanodes with high transparency is also essential for their use as light absorbers in tandem cell devices [45]. Thus, the thickness of the material deposited onto the substrate should be controlled and limited according to the chosen synthesis technique.…”

“…In a different work, Shi et al [45] synthesized a mesoporous WO 3 bottom layer that was spin-coated with a Mo-doped BiVO 4 . Natural doping of the W on the WO 3 layer occurred at the BiVO 4 , due to their intimate contact during the annealing process.…”

Enhancing Charge Carrier Lifetime in Metal Oxide Photoelectrodes through Mild Hydrogen Treatment

“…In contrast, metal oxide semiconductors are relatively cheap and stable in aqueous solutions, but photoelectrodes based on metal oxides have only shown moderate efficiencies (< 8%). [10][11][12][13] A major limitation of complex metal oxides is their poor charge carrier (electron and/or hole) transport properties. As an illustration, carrier mobilities can be as high as 8,500…”

Photocurrent Enhancement by Spontaneous Formation of a p–n Junction in Calcium‐Doped Bismuth Vanadate Photoelectrodes

“…[2a, 7] Tungsten (W) and molybdenum (Mo) are among the most effective dopants, withh igh AM1.5 photocurrents reported for W-and Mo-doped BiVO 4 photoanodes. [4c, 8] Codoping with, for example, Mo/W, [9] Fe/ Mo, [10] Mo/H, [11] and Fe/W [12] has also resultedi ne nhanced pho-tocurrents, although the exact nature of the synergistic effect of the codopants seems not yet fully understood.One issue associated with the high donor concentration in these photoanodes is that this also results in very narrow space chargeregions and, therefore, poor charge separation efficiencies.T oa ddress this, we proposed ag radient doping strategy that distributes the electric field over al arger region of the sample. [8d, 13] While this indeed enhances the separation efficiency,t he reported photocurrents for dense thin-film BiVO 4 photoelectrodes still fall short of the theoretical value of 7.3 mA cm À2 (based on the 2.4 eV band gapofBiVO 4 ).…”