Dye Sensitization of n and p Type Gallium Phosphide Photoelectrodes

Choi, Daejin; Rowley, John G.; Parkinson, B. A.

doi:10.1149/2.005211jes

Cited by 9 publications

(13 citation statements)

References 27 publications

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“…To date, several organic and inorganic chromophores demonstrate the capacity for light-stimulated hole injection into p-GaP photoelectrodes. − However, the majority of studies have employed conditions where p-GaP is immersed in an electrolyte containing the dissolved dye, that is, the chromophore is not permanently adsorbed onto the electrode and is instead involved in some dynamic adsorption/desorption equilibrium. Although this tactic simplifies measurement, it does not address how the sensitizer–electrode combination would operate when the dye is adhered permanently to the semiconductor surface.…”

Section: Introductionmentioning

confidence: 99%

Sensitization of p-GaP by Physisorbed Triarylmethane Dyes

2018

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p-Type gallium phosphide (GaP) electrodes have been sensitized by triarylmethane dyes physisorbed from aqueous solutions. This work is the first to show light-stimulated hole injection from an adsorbed molecular chromophore on native GaP surfaces. Freshly etched p-GaP(100) and p-GaP(111)A electrodes were loaded with physisorbed dye by brief soaking in solutions of Fast Green. X-ray photoelectron spectroscopy, corroborated by Auger electron spectroscopy, indicated that such treatments yield undetectable surface coverages. However, steady-state photoelectrochemical responses consistently showed that sub-bandgap photoresponses were commensurate with light absorption by the adsorbed dye. The photoresponse characteristics were clearly insensitive to the identity and amount of intended redox mediators dissolved in solution at low light intensities. Instead, the data suggest electrochemically active surface states related to the cathodic degradation of GaP can accept electrons from photoexcited physisorbed dye. Measurements at high illumination intensities showed sensitivity toward redox mediators in solution, indicating that the conventional mode of dye regeneration by redox species in solution is possible with p-GaP. Separate measurements with covalently modified p-GaP(111)A photoelectrodes further suggested that deliberate modification to minimize/eliminate surface states is also possible. Collectively, this work indicates that although some types of dye readily adsorb onto native GaP interfaces, the low dye loadings and the susceptibility of the interface to chemical attack during the sensitization process argue against using bare p-GaP photocathodes with physisorbed triarylmethane dyes. Instead, these studies suggest that dye-sensitized photocathodes based on p-GaP require deliberate surface chemical modification methods to overcome the low loading and inhibit unwanted charge transfer between the surface and the photoexcited dye.

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Section: Introductionmentioning

confidence: 99%

Sensitization of p-GaP by Physisorbed Triarylmethane Dyes

2018

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“…To expand light-harvesting efficiencies, the hole injection into p-GaP can be sensitized using organic dyes ,− or quantum dots that absorb the light with wavelengths above 550 nm. Organic dyes, , such as triarylmethane, acridine, or xanthene compounds, are particularly promising sensitizers for p-GaP because they can be readily tailored to exhibit strong absorption in the red portion of the visible spectrum. , In addition, the excited-state reduction potentials of most dyes are sufficiently positive to allow the hole injection into p-GaP ,, and other semiconductors. , Finally, the lowest unoccupied molecular orbitals (LUMOs) of many organic dyes are sufficiently negative to enable the electron transfer to Pt, Fe, Ni, or Co-based H 2 -evolving catalysts. − …”

Section: Introductionmentioning

confidence: 99%

Sensitization of p-GaP with Monocationic Dyes: The Effect of Dye Excited-State Lifetime on Hole Injection Efficiencies

Ilić

Brown²,

Xie

et al. 2016

J. Phys. Chem. C

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The sensitized hole injection to the p-type gallium phosphide (p-GaP) electrode was evaluated for several triarylmethane (6O+), acridine (4O+, 2O+, Me2N-Acr+, T-Acr+), and flavin dyes (Et-Fl+). Thermodynamics for sensitized charge injection were evaluated using steady-state ultraviolet–visible absorption and cyclic voltammetry experiments. All dyes (except 4O+) had strong absorption at wavelengths above 550 nm (absorption cutoff for GaP), and their highest occupied molecular orbital energies were below the valence band of GaP (+1.20 V vs normal hydrogen electrode), indicating that the electron transfer from p-GaP electrode to the excited dye molecules was thermodynamically favorable. Photoelectrochemical measurement conducted on p-GaP electrodes immersed in aqueous electrolytes and dye showed sensitization for only two dyes (2O+ and Et-Fl+), and the sensitization efficiencies were found to depend on the chemical nature of differently prepared p-GaP electrodes. Femtosecond pump–probe measurements revealed that the “inefficient” dyes had short-lived excited states (few picoseconds), preventing the successful charge transfer into p-GaP surface. Collectively, this work provides insight on time scales of hole-injection rates during dye-sensitization processes.

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“…[1][2][3][4][5] In particular, considerable attention has been given to high-power AlGaInP-based LEDs that emit wavelengths ranging from 570 nm to 700 nm. AlGaInP LEDs have been shown to experience serious current crowding because of resistive p-AlGaInP layers.…”

Section: Introductionmentioning

confidence: 99%

Electrical Characteristics of Schottky Contacts to p-Type (001) GaP: Understanding of Carrier Transport Mechanism

Song¹,

Kim²,

Kang³

et al. 2016

Journal of Elec Materi

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Formation of low-resistance ohmic contacts to p-GaP is important for development of high-efficiency AlGaInP light-emitting diodes (LEDs), which emit light from red to yellow-green and have a wide variety of applications such as traffic light lamps, automobile tail lamps, and in biotherapy. The current flow behavior can be understood by investigating the effect of the Schottky barrier height (SBH; U B ) on the work function of metals (U M ). In this work, SBHs and their dependence on U M at (001) p-GaP surfaces were investigated. With increasing temperature, the SBH increased, while the ideality factor decreased. This behavior is explained by means of a thermionic field-emission (TFE) model. The SBH and ideal factor ranged from 0.805 eV to 0.852 eV and from 1.18 to 1.50, respectively, for different Schottky metals. The S-parameter (dU B /dU M ) was estimated to be 0.025, with this approximately zero value implying that the surface Fermi level is virtually perfectly pinned at the surface states at $0.85 eV above the valence-band edge.

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Dye Sensitization of n and p Type Gallium Phosphide Photoelectrodes

Cited by 9 publications

References 27 publications

Sensitization of p-GaP by Physisorbed Triarylmethane Dyes

Sensitization of p-GaP by Physisorbed Triarylmethane Dyes

Sensitization of p-GaP with Monocationic Dyes: The Effect of Dye Excited-State Lifetime on Hole Injection Efficiencies

Electrical Characteristics of Schottky Contacts to p-Type (001) GaP: Understanding of Carrier Transport Mechanism

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