Polaron level

At higher doping levels the polaron states interact the authors calculated that a bipolaron level is 0.49 eV more stable than two polaron levels so unfavourable polaron interactions are avoided via the formation of a more stable bipolaron, in agreement with the epr data of Scott and colleagues (1983). 

These experiments yield an exciton binding energy of 0.5 eV relative to separate electron and hole. This is a large value. An important consequence, although one that is never mentioned, is that in such a case, the polaron binding energy u>p (see Fig. 7 of Chapter 11) must be larger than 0.25 eV for the absorption between polaron levels in the gap to occur below that of the exciton in practice, the polaron absorption, if it exists, will remain hidden under the excitonic absorption. 

Photoinduced optical studies show that positive (P+) and negative (P ) polaron levels exist inside the n-n bandgap of EB associated with benzenoid and quinoid levels, respectively.17 They are believed to play an important role in charge injection and transport. We propose the following mechanism for the SCALE device operation. Under low bias voltages, electrons and holes can be injected from the electrodes into the quinoid and benzenoid levels of EB and form negative and positive polarons, respectively. These polarons transport to the EB/PPy interfaces via... 

FIGURE 9.10. Energy diagram showing the role of positive (P+) and negative (P ) polaron levels of EB and the interface states in the SCALE device operation. 

Figure 11.1 Electronic band diagrams of a nondegenerate Jt-conjugated polymer related to different doping levels, (a) Undoped (neutral state) (b) Slightly doped polymer with localized polaronic levels (c) Moderately doped polymer with polaronic bands (d) Heavily doped polymer with bipolaronic bands. The benzenoid (e) and...

The polaronic level of holes on the conjugated polymer donor phase is sUghtly above the HOMO of the polymer, and the transport level of the electrons is closely related to the LUMO level of the acceptor (n-type semiconductor, e.g., the fullerene). Thus, their resulting energetic sphtting has to be related to the difference between the HOMO of the donor and the LUMO of the acceptor and conceptually determines the maximum open circuit po-... 

Similar to the case of transition to supersonic velocities discussed above, this interchain transport process is also nonadiahatic. To pass through the barrier, the electron has to undergo an electronic transition from the polaron level localized to chain 1 to the TT -level localized to chain 2. The energy needed for this transition, the activation energy, is taken from the phonon system. Actually, the process is very similar to that treated by the Holstein theory discussed in Section 2.2 the electronic coupling between the chains is weak enough to force the electronic states to localize on individual chains. 

Equation 22.2 shows that we can determine U from a single transition (5S ) if is known and charge conjugation symmetry exists. In more general case in which S is replaced by a polaron level, this transition should be associated with the SOMO level in the gap. We used this relation to determine Uin NDGS polymers from the optical transitions associated with the polaron and bipolaron levels in the gap [49]. 

Upon further oxidation, the subsequent loss of another electron can result in two possibilities the electron can come from either a different segment of the polymer chain thus creating another independent polaron, or from a polaron level (removal of an unpaired electron) to create a... 

Chemical or electrochemical doping (oxidation and incorporation of counterions) results in the generation of a polaron level at midgap. Further oxidation leads to the formation of bipolaron energy bands in... 

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