Hole injection efficiencies values

Hole injection efficiencies (Jinj/Jscl) mobilities ratios in different energy barriers between phenylamine and PEDOT PSS. The open circles (O) and triangles (A) represent the ratios of mobility values from DISCLC (PDi/lt) and AS (PAs/mve)/ respectively. 

Hence, r is equal to 1 if the hole injection efficiency is 100%, and the contact can be viewed as truly ohmic. On the other hand, t) should be less than 1 if the contact is Schottky. Figure 3.24 shows t) (solid squares) vs the nominal hole injection barrier at a field strength f=0.1MV/cm. The open circles are the ratios of mobilities derived from DI experiments (Xdi to the TOF-derived hole mobilities p. Moreover, the open triangles are ratios of AS-derived mobilities Pas to the average hole mobilities derived from TOF For the ohmic contact of PEDOTPSS/MTDATA, rj 1 and the hole injection approaches an efficiency of nearly 100%. Meanwhile, the injection efficiency for NPB is lowered to about 70%, but the nominal hole mobilities derived from Dl and AS reach 90% and 100% of the TOF-derived mobility value respectively. For the contact of TPD, the injection efficiency and the nominal hole mobilities are less than 80%. Therefore, PEDOTPSS forms the worst contact with TPD among those PA compounds. 

The photoconductivity of USq-5 to -15 have been studied in bilayer xerographic devices [179]. Although fabrication effect, purity and hole-injection efficiency have been shown to be important factors that influence the photoconductivity, USq-13 was identified as the most outstanding squaraine so far. Specifically, USq-13 is shown to have a low dark-decay value (—15 V/s) and high sensitivity in xerographic devices, where Eo values of 3.1 and 1.9 ergs/cm at 600 nm and 790, respectively, are obtained [181]. The sensitivity appears to surpass all squaraines reported in the literature (Table 10.4). In fact, the sensitivity performance of USq-13... 

Based on extensive screening of hundreds of ruthenium complexes, it was discovered that the sensitizer s excited state oxidation potential should be negative of at least —0.9 V vs. SCE, in order to inject electrons efficiently into the Ti02 conduction band. The ground state oxidation potential should be about 0.5 V vs. SCE, in order to be regenerated rapidly via electron donation from the electrolyte (iodide/triiodide redox system) or a hole conductor. A significant decrease in electron injection efficiencies will occur if the excited and ground state redox potentials are lower than these values. 

In materials where the photogeneration involves the surface-enhanced dissociation of an exciton, as is generally the case for the phthalocanines, the photogeneration efficiency defined by Kanemitsu and Imamura represents the fraction of photons that create exitons that diffuse to the interface between the generation and transport layers. The injection efficiency then represents the fraction of pairs that dissociate into free electrons and free holes. The field dependence of the photogeneration efficiency was described by the Onsager theory. A primary quantum yield of 0.50 was reported. Values of the thermalization distance and the injection efficiency were not cited. 

Results for a 20 pm thick sample of polycarbonate containing 50 mass% TPD for a field of 1.5 x 107Vm-1 at 296 K with charges injected from an indium tin oxide (ITO) electrode coated with a 0.1 pm thick layer of PPV are shown in Fig. 8.30(b). The limiting current is close to the trap-free SCLC, indicating that the PPV-coated ITO acts as an efficient hole-injecting electrode. The lower curve is the TOF transient recorded under identical conditions. The arrow on the lower curve indicates the transit time and that on the upper curve is 0.8 of this value. The step-voltage response is therefore close to the theoretical prediction. 

Introduction of CFx thin film on top of the ITO anode as HTL via plasma polymerization of CHF3 can also enhance device performance of PFO-based PLED, as reported by us [79]. At the optimal C/F atom ratio using the radio frequency power 35 W (see Table 2) as determined by X-ray photoelectron spectrometer, the device performance based on the ITO/CFx(35 W)/PFO/CsF/Ca/Al configuration is optimal having maximum current efficiency of 3.1 cdA 1 and maximum brightness of8400 cdm 2 much better than 1.3 cd A-1 and 1800 cd m-2 for the device with PEDOT PSS as HTL. The improved device performance was attributed to a better balance between hole and electron fluxes because the CFx (35 W) layer possesses an Ip value of 5.6 eV (see Table 2), as determined by ultraviolet photoelectron spectroscopy data, and therefore causes a lower hole-injection barrier to the PFO layer (0.2 eV) than that of 0.7 eV for PEDOT PSS. 

Experiments were conducted on devices A-D to compare with analyses [20]. Electrical properties of these devices are almost identical despite very large variations in the thickness of the hole-injection layer (m-MTDATA F4-TCNQ), indicating the effectiveness of the conductive doping in enhancing conductivity. In Figure 9.8b and c, measured efficiencies of devices A-D (symbols) are compared with calculated efficiencies (lines). A reasonably good agreement is obtained between calculated and experimental values. 

Here we show that the polarity of polymer solar cells can be reversed by changing the position of two interfacial layers vanadium oxide (V2O5) layer as hole injection and cesium carbonate (CS2CO3) layer as electron injection, independent of the top and bottom electrodes. ° Since our first demonstration of inverted solar cells, more and more interests have focused on this new architecture. Waldauf et al. demonstrated inverted solar cells with a solution-processed titanium oxide interfacial layer. White et al. developed a solution-processed zinc oxide interlayer as efficient electron extraction contact and achieved 2.58% PCE with silver as a hole-collecting back contact. It is noteworthy to mention that EQE value for inverted solar cells approaches 85% between 500 and 550 nm, which is higher than that of normal polymer solar cells. This is possibly due to (i) the positive effect of vertical phase separation of active layer to increase the selection of electrode and (ii) lower series resistance without the PEDOT PSS layer. 

The value of y is related to the injection process and depends on electrode materials. InP-LJBD, a calcium electrode is used to increase the electron injection efficiency due to its low work function(12,13). The value of 7 e.h related to not only materials but also device structure. Multi-layer structure is commonly used to increase the value of 7, generating the hole and/or electron accumulation near a light-emitting layer surface(l,14). The maximum value of 7 1 has been suggested to be 25% because of the spin statistics of singlet exciton formation (11). Toin rove g, we have to use highly efficient materials or dye-doped materials(15). 

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