Photocurrent steady state

Fig. 34 Photocurrent (steady state) versus light intensity for PTS-polydiacetylene single crystals. Data for F II b taken under illumination with 457 nm line of Ar laser F L b measured using a tungsten lamp (457 nm). Electric field, F = 4 x 103 V cm-1. (After Lochner et al., 1976a)...

The basic idea of most diffusion length measurement techniques is to generate a certain number of minority carriers inside the bulk Si, for example by illumination, and to measure the fraction of these carriers that diffuse to a collecting interface. This fraction can be determined capacitively [Bo6], as well as by measurements of the steady-state photocurrent [Dr2, Lei 1], The parameter obtained by these measurements is the minority carrier diffusion length ID of electrons in... 

Steady-state wavelength-specific photocurrents were measured for the Ti-Fe-0 films in a two-electrode arrangement at different applied voltages. Incident photon-to-current efficiencies (IPCE) are calculated using the following equation ... 

Figure 6.1 Steady-state photocurrent in an a-As2Se3 sample at 700 nm illumination with approximate intensity of lO photons/cm /s as a function of inverse temperature (curve 1). Also shown is the effect induced hy laser irradiation (A = 633 nm) at 7 = 100 K (curve 2).

There is another compensating effect at a metal electrode as a consequence of such an electron transfer in the excited state. The species D+ and D which are generated have acceptor or donor levels below or above the Fermi level of the metal where a reverse electron transfer is now possible. In the steady state reached within the lifetime of the products D+ and D at the electrode the photocurrents are compensated by the reverse electron transition from the products. Only if a feist consecutive reaction brings one of the products to an energy state where no reverse electron transfer is possible a net photocurrent can be observed at a metal electrode. It is not clear whether up to now any reaction has been found which... 

When an ion-pair recombines, it may form an excited state which can luminesce. The intensity of luminescence is a direct monitor of the competing ratio of recombination and luminescence. With steady-state conditions, the luminescence intensity is proportional to the rate of recombination. For instance, Morrow et al. [380] have radio lysed solutions of pyrene in cyclohexane. Solvated electrons and pyrene cations are produced. On recombination, an excited singlet state is produced which can fluoresce. If two pyrene molecules are in (or near) contact when one or other molecule is in the excited singlet state, then excimer fluorescence may be observed. The intensity of fluorescence can be decreased by application of an electric field, since fewer ion-pairs recombine to form the excited state. Jarnagin [381] and Holroyd and Russell [382] have photoionised iVjA iV. iV -tetramethyl-p-phenylenedia-mine (TMPD) with light (of photon energy 5.5—6 eV) in hydrocarbon solvents and measured the photocurrent at various electric field strengths. 

Light is switched off at +0.5 V vs. SCE for the cathodic sweep. In (a) there is no added reductant (b), (c), and (d) contain 0.5mM ferrocene, 1, l -dimethylferrocene, and acetyl-ferrocene, respectively. Acetylferrocene does not attenuate the surface ferricenium surface ferrocene wave since it is not a sufficiently powerful reductant. Ferrocene and 1, l -dimelhylferrocene both attenuate the surface ferricenium - surface ferrocene wave. But l,l -dimethylferrocene is more effective under identical conditions despite the fact that the same, mass transport-limited, steady-state photocurrent is found for these two reductants. These data suggest that after the light is switched off the reduction of surface ferricenium is controlled partially by mass transport and partly by the electron transfer rate (see text). 

The acetylferrocene does not consume the (FeCp2+)surf., Figure Ad, because the reaction is not thermodynamically spontaneous. The conflict in our data is that steady-state photocurrents for the fast reductants is the same, but the (FeCp2+)surf. can be consumed at different rates in the dark for the various fast reductants. 

When an n-CdS electrode is suddenly illuminated with light capable of producing holes in the CdS, j, would almost immediately reach some large value (equal to or less than the saturation current of curve 1) and then decay to the steady state value of curve 1 as the steady state value of N is approached according to equation 3. If such a transient does not occurthe oxidized corrosion site acting as a recombination state is not the controlling factor in the photocurrent onset. 

All results which will be reported pertain to steady-state values of both IR and s. At relatively high values of the ratio of photocurrent density vs. concentration at pH = 3.8, an initial decrease of the photocurrent was observed, indicating the formation of some surface layer. Such cases have not been taken into consideration here. 

PET across a phospholipid bilayer was also shown to occur when triad molecules of the type pictured in Fig. 21a, were brought into BLM [167,185], A steady-state photocurrent across the membrane was observed in these experiments. 

In the presence of hydroquinone, the quasi-steady-state photocurrent sensitized by partially aggregated Dye II will be governed by the following relations ... 

The above-discussed photocurrent measurements were performed under the steady-state illumination of electrodes. In the pulse illumination mode, the photo-... 

Analysis of the ratio of the instantaneous to steady-state photocurrent. J. Phys. Chem., 89, 3863-3869. 

This section considers the competition between electron transfer and surface recombination under steady state conditions, and shows that no kinetic information can be obtained from the measured photocurrent. 

In the non steady-state experiment, the illumination is switched on at t = 0, defining the initial condition Qs(0) = 0. The transfer, recombination and charging components of the time dependent photocurrent are... 

At t = 0, Qs = 0 and the measured photocurrent is entirely due to charging. At longer times the surface charge tends towards its steady state value, and the charging current falls to zero. The current due to charge transfer is proportional to Q so it is zero at t = 0 and increases with time towards its final steady state value. Since the recombination term also depends on Qs, the fraction of charge carriers at the surface that are transferred is determined by the ratio ktr/(ktr + krcc) for all values of t. 

Sodergren et al. obtained the steady state solution of equation (8.52) by assuming that D and r are constant and 17 = 1. Under these conditions, the photocurrent due to photoinjected electrons is independent of voltage, and the steady state photocurrent is given by... 

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