Hole transfer dynamics from dye molecules to p-type NiO nanoparticles: effects of processing conditions

Abstract

Hole transfer dynamics of Atto647N sensitized p-type NiO nanoparticle (NP) thin films is investigated using both ensemble-averaged and single-molecule spectroscopy techniques. The rate of hole transfer is dependent on the processing conditions and is enhanced when the NiO is pre-annealed in air as compared to vacuum. This is possibly due to an upward shift of the valence band of the semiconductor and an increase in the free energy for hole transfer as more Ni(2)O(3) are formed in the presence of air. The stretched exponential fluorescence decay profile of Atto647N on NiO NP suggests the presence of a distribution of hole transfer rates. This is in agreement with the observed emission lifetime and intensity fluctuations and non-monoexponential fluorescence decays for individual Atto647N molecules on NiO NP films. A plausible explanation for the heterogeneous hole transfer rates is an inhomogeneous distribution of (defect) sites on the metal oxide due to the processing conditions and a fluctuation in the intermolecular interaction.

Other origins for the fluorescence modulation of single dye molecules in open-circuit and short-circuit devices

“…6b. The molecule experiences a maximum EF of 1.9 Â 10 5 V cm À1 when the voltage is adjusted to +10 V/À10 V. The emission intensity of the molecule does not modulate with the EF and is similar to those previously reported for single Atto647N molecules immobilized on a glass substrate 8,9 and PVA matrix. 10 Furthermore, the BEL intensity does not show any significant variation with the applied potential (Fig.…”

Interplay of Hole Transfer and Host–Guest Interaction in a Molecular Dyad and Triad: Ensemble and Single‐Molecule Spectroscopy and Sensing Applications

“…The quenched “dim” states are not attributed to cis isomer, which is known to have the same lifetime as the trans isomer 32. Therefore, hole transfer is responsible for the observed reduction in intensity and lifetimes, and the hole‐transfer rate undergoes dynamic fluctuation over time 34. Given the heterogeneous distribution of τ 0.5 , the fluorescence lifetime profile constructed from photons detected before photobleaching cannot be described by a mono‐exponential model and is instead best fitted to a stretched exponential decay function:34 …”

“…Its corresponding autocorrelation function is a double‐exponential decay with lifetimes of 167 μs and 270 ms (Figure 9 (B)), which suggests that the time durations of reactivity for the different hole transfer rates are not homogeneous and span across a large time range. This can be rationalized by considering the microenvironment surrounding each molecule to be in a perpetual state of dynamic change 34. Conditions such as local temperature and glass–molecule interaction, when sufficiently perturbed, are capable of inducing the necessary intramolecular conformational changes needed to cause fluctuations in the electronic coupling, hole transfer efficiency and reactivity between Cy5 and Fc.…”

“…This can be rationalized by considering the microenvironment surrounding each molecule to be in a perpetual state of dynamic change. [34] Conditions such as local temperature and glass-molecule interaction, when sufficiently perturbed, are capable of inducing the necessary intramolecular conformational changes needed to cause fluctuations in the electronic coupling, hole transfer efficiency and reactivity between Cy5 and Fc. This perturbation is stochastic in nature and gives rise to the observed erratic changes in the hole transfer rates throughout the molecule's survival time and the relatively complex G(t).…”

Hematite–NiO/α-Ni(OH)2 heterostructure photoanodes with high electrocatalytic current density and charge storage capacity

“…The hydrothermal modification of a NiO nanoparticle seeded pre-hydrothermally modified hematite film leads to the formation of this new kind of photoelectrode. NiO is a p-type semiconductor employed in dye sensitized solar cells [19][20][21][22][23] and as a water oxidation catalyst. 24a,b NiO has an indirect wide band gap of 3.3 eV.…”