Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userCounterbalancing light absorption and ionic transport losses in the electrolyte for integrated solar water splitting with III-V/Si dual-junctions
270
0
0.0
(
0
)
Authors
Moritz Kolbach
Ask ChatGPT about the research
No Arabic abstract
Recently, significant progress in the development of III-V/Si dual-junction solar cells has been achieved. This not only boosts the efficiency of Si-based photovoltaic solar cells, but also offers the possibility of highly efficient green hydrogen production via solar water splitting. Using such dual-junction cells in a highly integrated photoelectrochemical approach and aiming for upscaled devices with solar-to-hydrogen efficiencies beyond 20%, however, the following frequently neglected contrary effects become relevant: (i) light absorption in the electrolyte layer in front of the top absorber and (ii) the impact of this layer on the ohmic and transport losses. Here, we initially model the influence of the electrolyte layer thickness on the maximum achievable solar-to-hydrogen efficiency of a device with an Si bottom cell and show how the top absorber bandgap has to be adapted to minimise efficiency losses. Then, the contrary effects of increasing ohmic and transport losses with decreasing electrolyte layer thickness are evaluated. This allows us to estimate an optimum electrolyte layer thickness range that counterbalances the effects of parasitic absorption and ohmic/transport losses. We show that fine-tuning of the top absorber bandgap and the water layer thickness can lead to an STH efficiency increase of up to 1% absolute. Our results allow us to propose important design rules for high-efficiency photoelectrochemical devices based on multi-junction photoabsorbers.
rate research
Read More
Narrow-bandgap III-V semiconductor nanowires (NWs) with a suitable band structure and strong light-trapping ability are ideal for high-efficiency low-cost solar water-splitting systems. However, due to their nanoscale dimension, they suffer more severe corrosion by the electrolyte solution than the thin-film counterparts. Thus, short-term durability is the major obstacle for using these NWs for practical water splitting applications. Here, we demonstrated for the first time that a thin layer (~7 nm thick) of compact TiO$_2$ deposited by atomic layer deposition can provide robust protection to III-V NWs. The protected GaAs NWs maintain 91.4% of its photoluminescence intensity after 14 months of storage in ambient atmosphere, which suggests the TiO$_2$ layer is pinhole-free. Working as a photocathode for water splitting, they exhibited a 45% larger photocurrent density compared with un-protected counterparts and a high Faraday efficiency of 91%, and can also maintain a record-long highly-stable performance among narrow-bandgap III-V NW photoelectrodes; after 67 hours photoelectrochemical stability test reaction in strong acid electrolyte solution (pH = 1), they show no apparent indication of corrosion, which is in stark contrast to the un-protected NWs that are fully failed after 35-hours. These findings provide an effective way to enhance both stability and performance of III-V NW based photoelectrodes, which are highly important for practical applications in solar-energy-based water splitting systems.
Renewable energy conversion and storage, and greenhouse gas emission-free technologies are within the primary tasks and challenges for the society. Hydrogen fuel, produced by alkaline water electrolysis is fulfilling all these demands, however the technology is economically feeble, limited by the slow rate of oxygen evolution reaction. Complex metal oxides were suggested to overcome this problem being low-cost efficient catalysts. However, the insufficient long-term stability, degradation of structure and electrocatalytic activity are restricting their utilization. Here we report on a new perovskite-based self-assembling material BaCo0.98Ti0.02O3-$delta$:Co3O4 with superior performance, showing outstanding properties compared to current state-of-the-art materials without degeneration of its properties even at 353 K. By chemical and structural analysis the degradation mechanism was identified and modified by selective doping. Short-range order and chemical composition rather than long-range order are factors determining the outstanding performance. The derived general design rules can be used for further development of oxide-based electrocatalytic materials.
Semiconductor compounds are widely used for water splitting applications, where photo-generated electron-hole pairs are exploited to induce catalysis. Recently, powders of a metallic oxide (Sr$_{1-x}$NbO$_3$, 0.03 < x < 0.20) have shown competitive photocatalytic efficiency, opening up the material space available for finding optimizing performance in water-splitting applications. The origin of the visible light absorption in these powders was reported to be due to an interband transition and the charge carrier separation was proposed to be due to the high carrier mobility of this material. In the current work we have prepared epitaxial thin films of Sr$_{0.94}$NbO$_{3+{delta}}$ and found that the bandgap of this material is ~4.1 eV, which is very large. Surprisingly the carrier density of the conducting phase reaches 10$^{22}$ cm$^{-3}$, which is only one order smaller than that of elemental metals and the carrier mobility is only 2.47 cm$^2$/(V$cdot$s). Contrary to earlier reports, the visible light absorption at 1.8 eV (~688 nm) is due to the bulk plasmon resonance, arising from the large carrier density, instead of an interband transition. Excitation of the plasmonic resonance results in a multifold enhancement of the lifetime of charge carriers. Thus we propose that the hot charge carriers generated from decay of plasmons produced by optical absorption is responsible for the water splitting efficiency of this material under visible light irradiation.
Modifying the optoelectronic properties of nanostructured materials through introduction of dopant atoms has attracted intense interest. Nevertheless, the approaches employed are often trial and error, preventing rational design. We demonstrate the power of large-scale electronic structure calculations with density functional theory (DFT) to build an atlas of preferential dopant sites for a range of M(II) and M(III) dopants in the representative III-V InP magic sized cluster (MSC). We quantify the thermodynamic favorability of dopants, which we identify to be both specific to the sites within the MSC (i.e., interior vs surface) and to the nature of the dopant atom (i.e., smaller Ga(III) vs larger Y(III) or Sc(III)). These observations motivate development of maps of the most and least favorable doping sites, which are consistent with some known experimental expectations but also yield unexpected observations. For isovalent doping (i.e., Y(III)/Sc(III) or Ga(III), we observed stronger sensitivity of the predicted energetics to the type of ligand orientation on the surface than to the dopant type, but divergent behavior is observed for whether interior doping is favorable. For charge balancing with M(II) (i.e., Zn or Cd) dopants, we show that the type of ligand removed during the doping reaction is critical. We show that limited cooperativity with dopants up to moderate concentrations occurs, indicating rapid single-dopant estimations of favorability from DFT can efficiently guide rational design. Our work emphasizes the strong importance of ligand chemistry and surface heterogeneity in determining paths to favorable doping in quantum dots, an observation that will be general to other III-V and II-VI quantum dot systems generally synthesized with carboxylate ligands.
We present a method for low temperature plasma-activated direct wafer bonding of III-V materials to Si using a transparent, conductive indium zinc oxide interlayer. The transparent, conductive oxide (TCO) layer provides excellent optical transmission as well as electrical conduction, suggesting suitability for Si/III-V hybrid devices including Si-based tandem solar cells. For bonding temperatures ranging from 100$^{circ}$C to 350$^{circ}$C, Ohmic behavior is observed in the sample stacks, with specific contact resistivity below 1 $Omega$cm$^2$ for samples bonded at 200$^{circ}$C. Optical absorption measurements show minimal parasitic light absorption, which is limited by the III-V interlayers necessary for Ohmic contact formation to TCOs. These results are promising for Ga$_{0.5}$In$_{0.5}$P/Si tandem solar cells operating at one sun or low concentration conditions.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
