Quantitative characterization of the long-term charge storage of a ZnO-based nanorod array film through persistent photoconductance

Abstract

Quo, Qus and η were derived from a photocurrent–time curve to quantitatively characterize the charge storage of a ZnO-based nanorod array film.

Long‐Standing Optically Excited Magnetic States in ZnO Nanoparticles

“…Under UV-vis illumination, the photogenerated holes neutralize the oxygen ions leading to O 2 desorption: the remaining photogenerated electrons then increase the n-type conductivity [17,18] . The persistent photocurrent (after illumination removal) has decay time of the order of several hours [18,19] , suggesting that a similar or analogous phenomenon is presently observed. The observed very long life-times are compatible with some spin-forbidden transitions, as would be expected for the quintet (J = 2) or triplet (J = 1) states of some dark bound excitons [20] .…”

Effects of Illumination and Ferroelectric Field on Nanoscale Al:ZnO Films: Implications for Nonvolatile Multistage Storage and Photosensor Devices

“…45 Generally, during the generation and recombination of photogenerated carriers, both the defects and the adsorption of surface oxygen in the films play important roles, which further affect the relaxation time. 46 Therefore, the longer relaxation time here may be due to the defects and surface oxygen adsorption of the nanoscale AZO films.…”

“…Therefore, under steady illumination, the photogenerated carriers rise exponentially (can be reflected by the surface potential rise curve in Figure b) Δ n = βαIτ (1 – e – t /τ ), where β represents the electron–hole pair generated per absorption of one photon, α is the absorption coefficient, and τ is the unbalanced carrier lifetime . Generally, during the generation and recombination of photogenerated carriers, both the defects and the adsorption of surface oxygen in the films play important roles, which further affect the relaxation time . Therefore, the longer relaxation time here may be due to the defects and surface oxygen adsorption of the nanoscale AZO films.…”

“…Since a recombination process is also present at the photoexcitation, until the recombination rate of the electron−hole is equal to the generation rate, the photogenerated carrier density and the photoconductivity of AZO films are saturated. Therefore, under steady illumination, the photogenerated carriers rise exponentially (can be reflected by the surface potential rise curve in Figure4b) Δn = βαIτ(1 − e −t/τ ), where β represents the electron−hole pair generated per absorption of one photon, α is the absorption coefficient, and τ is the unbalanced carrier lifetime.45 Generally, during the generation and recombination of photogenerated carriers, both the defects and the adsorption of surface oxygen in the films play important roles, which further affect the relaxation time 46. Therefore, the longer relaxation time here may be due to the defects and surface oxygen adsorption of the nanoscale AZO films.In a thermal equilibrium state for semiconductor, the carrier density is constant, but exerting an external effect (illumination, electrical bias) on it will break the equilibrium condition.…”

Insights into the Photocatalytic Memory Effect of Magneto-Plasmonic Ag–Fe3O4@TiO2 Ternary Nanocomposites for Dye Degradation and H2 Production under Light and Dark Conditions

“…This indicates that there could be some altered pathways defined by the amalgamated band structures of different materials in the composite that enabled the electrons to recombine slowly, or it could be due to the release of stored electrons leading to the slow decay of the photocurrent. 55 The electrochemical impedance (EI) spectra of the materials under dark and light conditions are displayed in Figure 11(b). The observed smaller semicircles for the ternary composite under both dark and light conditons indicate that there could be a reduced interfacial resistance in the ternary system as compared to the other materials, which suggests that there is an enhanced carrier transfer to the surface involved in the redox reactions with the surrounding molecules.…”