Contact staircase

Since we know the complete, explicit dependence of all quantities on Jf, it is not necessary to use the superscripts . To make contact with the discussion of Sects. 2 and 3, however, we display in Fig. 1 on the riser below the J/ = N0 tread of the Jf-p staircase the nucleophilic quantities following from Eqs. (33)-(35) which correspond to the - reactive indices of Sects. 2 and 3, and on the riser above those corresponding to the + or electrophilic indices. On the tread in between, corresponding to fixed Jf = N0 and fixed p(r) = pNo(r), we have displayed the corresponding isoelectronic reactivity indices with superscript zero. 

This equation differs from that for a spherical UME by the Zn2 term, which accounts for blocking of the diffusion path to the NP by the supporting planar surface. - In this situation, the current from each new NP contact adds to the previous one and a staircase response is observed as shown in Figure 8.31. 

Anode contacts to hole transporting molecular layers were discussed briefly in Section 9.3.2. To reiterate, it is often found that metal phthalocyanine compounds effectively mediate the injection of holes from ITO into hole transport layers. (One could also say oxidation of carbocations in the HTL with net transfer of an electron from the HTL into the ITO.) Some experiments have suggested that multiple layers of phthalocyanines based on different metals, and hence having different HOMO state energies, can further reduce the injection barrier. The basic method in use in these cases is to provide a staircase of small barriers up which a hole can climb more easily than would be the case for a single large step. The low mobility of holes in the organic interlayers comes in handy here as it reduces the rate at which holes return to the contact. 

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