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Photoexcitation recombination

Another common loss process results from electron—hole recombination. In this process, the photoexcited electron in the LUMO falls back into the HOMO rather than transferring into the conduction band. This inefficiency can be mitigated by using supersensitizing molecules which donate an electron to the HOMO of the excited sensitizing dye, thereby precluding electron—hole recombination. In optimally sensitized commercial products, dyes... [Pg.450]

The chapter is organized as follows in Section 8.2 a brief overview of ultrafast optical dynamics in polymers is given in Section 8.3 we present m-LPPP and give a summary of optical properties in Section 8.4 the laser source and the measuring techniques are described in Section 8.5 we discuss the fundamental photoexcitations of m-LPPP Section 8.6 is dedicated to radiative recombination under several excitation conditions and describes in some detail amplified spontaneous emission (ASE) Section 8.7 discusses the charge generation process and the photoexcitation dynamics in the presence of an external electric field conclusions are reported in the last section. [Pg.445]

Figure 18. Schematic illustration of slow charge recombination via lateral diffusion of electrons and holes in the A and the D layers, respectively, in the A-S-D triad monolayer. Radical anions and cations on A and S moieties were created by photoexcitation of the S moieties followed by the charge separation. Figure 18. Schematic illustration of slow charge recombination via lateral diffusion of electrons and holes in the A and the D layers, respectively, in the A-S-D triad monolayer. Radical anions and cations on A and S moieties were created by photoexcitation of the S moieties followed by the charge separation.
In photoexcited n-type semiconductor electrodes, photoexcited electron-hole pairs recombine in the electrodes in addition to the transfer of holes or electrons across the electrode interface. The recombination of photoexcited holes with electrons in the space charge layer requires a cathodic electron flow from the electrode interior towards the electrode interface. The current associated with the recombination of cathodic holes, im, in n-type electrodes, at which the interfadal reaction is in equilibrium, has already been given by Eqn. 8-70. Assuming that Eqn. 8-70 applies not only to equilibrium but also to non-equilibrium transfer reactions involving interfadal holes, we obtain Eqn. 10-43 ... [Pg.352]

The current i flowing in photoexcited n-type semiconductor electrodes equals the sum of the photoexcited hole current i >h, the limiting current of hole diffusion ip. itB, and the current of hole recombination inc as shown in Eqn. 10—44 ... [Pg.353]

Figure 3.32. Energy level scheme of the device in Figure 3.31. Photoinduced electron transfer takes place from the photoexcited ruthenium dye into the Ti02 conduction band. The recombination directly back to the dye has to be suppressed. Instead, the current is directed through the circuit to the counterelectrode and the hole conductor that brings the electrons back via hopping transport. HTM hole transport material. Figure 3.32. Energy level scheme of the device in Figure 3.31. Photoinduced electron transfer takes place from the photoexcited ruthenium dye into the Ti02 conduction band. The recombination directly back to the dye has to be suppressed. Instead, the current is directed through the circuit to the counterelectrode and the hole conductor that brings the electrons back via hopping transport. HTM hole transport material.
Still open also is the problem of para-products formation. Practically all comparable data are given in Table II. They exhibit a surprising independence of yields of para-product (63) from the polarity of the solvent. The not-too-convincing explanation that both Path A and Path B are equally participating in para-product formation is at hand. It is clear that more quantitative data are necessary to elucidate this problem. Experimentally found spin densities of photoexcited phenoxy radicals (Table III) would allow a preferential recombination of radicals in the para-position (cf. Eqs. 67 + 68 -> 73). [Pg.119]

Fig. 3 Charge transfer in DNA hairpins after photoexcitation of stilbene linker (St) by a laser pulse [45]. A hole, first, undergoes a transition from photoexcited St to the adjacent GC pair as shown by the solid arrow. Then it can either hop to next GC pairs (dot-dashed arrow) or return to St with the subsequent electron-hole recombination (dotted arrow)... Fig. 3 Charge transfer in DNA hairpins after photoexcitation of stilbene linker (St) by a laser pulse [45]. A hole, first, undergoes a transition from photoexcited St to the adjacent GC pair as shown by the solid arrow. Then it can either hop to next GC pairs (dot-dashed arrow) or return to St with the subsequent electron-hole recombination (dotted arrow)...
First, injection occurs from the photoexcited dye into the tin oxide conduction band, but is followed by very rapid trapping at a site that is energetically close to the conduction band and physically close to the dye. Trapping is accompanied by rapid, charge-compensating uptake of a proton—either from a hydronium ion or from a water molecule. Perhaps because of the proton uptake, the trapped electron remains proximal to the dye for at least a few hundred nanoseconds. The proximity enables each electron to return precisely to the dye that initially injected it. In other words, the recombination is geminate and the process is first... [Pg.115]


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