Single-Layer Diodes

Figure 12-13 compares j(L ) characteristics for a single layer diode of polylluor-enone sandwiched between an ITO anode and either an aluminum or an magnesium cathode ]45]. The increase of the current upon replacing Al by Mg proves that in the latter case the majority of the earners must be electrons. At the same... 

Fundamental studies established that simple single-layer diodes, as shown in Fig. 9.28(b), can exhibit reasonable internal quantum efficiency r iBU as given by ... 

Fig. 7. Schematic of light emitting diodes (a) single-layer device (b) single heteiostmctuie (c) double heteiostmctuie.

MIM or SIM [82-84] diodes to the PPV/A1 interface provides a good qualitative understanding of the device operation in terms of Schottky diodes for high impurity densities (typically 2> 1017 cm-3) and rigid band diodes for low impurity densities (typically<1017 cm-3). Figure 15-14a and b schematically show the two models for the different impurity concentrations. However, these models do not allow a quantitative description of the open circuit voltage or the spectral resolved photocurrent spectrum. The transport properties of single-layer polymer diodes with asymmetric metal electrodes are well described by the double-carrier current flow equation (Eq. (15.4)) where the holes show a field dependent mobility and the electrons of the holes show a temperature-dependent trap distribution. 

Comparison of the spectral response and of the power efficiency of these first conjugated polymer/fullerene bilayer devices with single layer pure conjugated polymer devices showed that the large potential of the photoinduced charge transfer of a donor-acceptor system was not fully exploited in the bilayers. The devices still suffer from antibatic behavior as well as from a low power conversion efficiency. However, the diode behavior, i.e. the rectification of these devices, was excellent. 

Light-Emitting Diodes 16.4.2.1 Single-Layer Devices... 

Z. Bao, Z. Peng, M.E. Galvin, and E.A. Chandross, Novel oxadiazole side chain conjugated polymers as single-layer light-emitting diodes with improved quantum efficiencies, Chem. Mater., 10 1201-1204, 1998. 

E.J.W. List, L. Holzer, S. Tasch, G. Leising, M. Catellani, and S. Luzzati, Efficient, single layer yellow light emitting diodes made of a blend of a ladder-type poly(p-phenylene) and polyalkylthio-phene, Opt. Mater., 12 311-314, 1999. 

J.P. Markham, S.C. Lo, S.W. Magnnis, P.L. Burn, and I.D.W. Samuel, High-efficiency green phosphorescence from spin-coated single-layer dendrimer light emitting diodes, Appl. Phys. Lett., 80 2645-2647 (2002). 

TD Anthopoulos, JPJ. Markham, EB Namdas, IDW Samuel, SC Lo, and PL Burn, Highly efficient single-layer dendrimer light-emitting diodes with balanced charge transport, Appl. Phys. Lett., 82 4824 1826, 2003. 

Fig. 20. Current-voltage (I-V) characteristics of the single-layer light-emitting diode of ITO/o-PBTMS-PPV/Al ( ), ITO/m-PBTMS-PPV/Al ( ), and ITO/p-PBTMS-PPV/Al ( )...

Fig. 22. Electroluminance (EL) spectra of the single-layer light-emitting diodes of (a) MEH-PPV, (b) p-PMEH-PPV, (c) p-PBTMS-PPV, and (d) o-PBTMS-PPV, which have ITO/poly-mer/Al configuration...

---