Light-emitting diodes polymer

The mechanism operating within a polymer LED involves injection, via a metal electrode, of electrons into the conduction band and holes into the valence band of the polymeric semi-conductor. The electrons and holes diffuse towards each other and then combine to form an exciton, which can move along the polymer chain. These excited states then decay to the ground state with a characteristic fluorescence. 

When the device is biased forward, the voltage drop across the polymer is compensated. In the case when the applied voltage equals the difference in the work functions of the two metals, the so called flat band condition is obtained (see Fig. 5.2b). When the applied voltage exceeds this value, the width of the potential barrier for charge injection decreases and, at some critical field, charge injection into the polymer becomes possible. 

In an ideal Schottky barrier, the width of the barrier is controlled by the width of the depletion layer (i.e., the concentration of dopants). The limiting factor in this case is the barrier height 

It should be noted that the rigid band model and the tunnelling process discussed above are an idealization of the real device. It is unlikely that the barrier is exactly triangular as sketched in Fig. 5.2. The results presented in this book are aimed to give a further insight into the microscopic features of the metal-polymer interfaces and how these can be related to the macroscopic models such as the relations above. 

Roderick and R. H. Williams, Metal-Semiconductor Contacts, 2nd Edition (Clarendon Press, Oxford, 1988). 

Schott, in Organic Conductors,. -P Farges (Ed.) (Marcel Dekker, Inc., New York, 1994) Chapter 12. 

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N. Tessler, N.T. Harrison, R.H. Friend, High peak brightness polymer light-emitting diodes, Adv. Mater., 1998, 10, 64. 

As a class of n-type organic semiconductors, PBI derivatives have received considerable attention for a variety of applications [312, 313], for example, for organic or polymer light-emitting diodes (OLEDs and PLEDs) [314, 315], thin-film organic field-effect transistors (OFETs) [316, 317], solar cells [318, 319], and liquid crystals [320]. They are also interesting candidates for single-molecule device applications, such as sensors [321], molecular wires [322], or transistors [141]. 

C Zhang, G Yu, and Y Cao, Long Operating Life for Polymer Light-Emitting Diodes, U.S. Patent... 

Y Yang, Q Pei, and AJ Heeger, Efficient blue polymer light-emitting diodes from a series of soluble poly(paraphenylene)s, J. Appl. Phys., 79 934—939, 1996. 

Z Shuai, D Beljonne, RJ Silbey, and JL Bredas, Singlet and triplet excitons formation rates in conjugated polymer light-emitting diodes, Phys. Rev. Lett., 84 131-134, 2000. 

C Zhang, S Hoger, K Pakbaz, F Wudl, and AJ Heeger, Improved efficiency in green polymer light-emitting diodes with air-stable electrodes, J. Electron. Mater., 23 453 458, 1994. 

Y Cao, G Yu, C Zhang, R Menon, and AJ Heeger, Polymer light-emitting diodes with polyethylene dioxythiophene polystyrene sulfonate as the transparent anode, Synth. Met., 87 171-174, 1997. 

DJ Pinner, RH Friend, and N Tessler, Transient electroluminescence of polymer light emitting diodes using electrical pulses, J. Appl. Phys., 86 5116-5130, 1999. 

ID Parker, Y Cao, and CY Yang, Lifetime and degradation effects in polymer light-emitting diodes, J. Appl. Phys., 85 2441-2447, 1999. 

Y Cao, G Yu, and AJ Heeger, Efficient, low operating voltage polymer light-emitting diodes with aluminum as the cathode material, Adv. Mater., 10 917-920, 1998. 

Y Cao, Electrically Active Polymer Compositions and Their Use in Efficient, Low Operating Voltage, Polymer Light-Emitting Diodes with Air-Stable Cathodes, U.S. Patent 5,965,281, 1999. 

MD McGehee, D Vacar, U Lemmer, D Moses, and AJ Heeger, Microplanar polymer light-emitting diodes, Synth. Met., 85 1233-1234, 1997. 

Making polymer light emitting diodes with polythiophenes O.Inganas Organic Electroluminescent Materials and Devices, S. Miyata and H.S. Nalwa, Eds., Gordon and Breach, Amsterdam, pp. 147-175... 

Polythiophenes for Structured and Polarized Polymer Light-Emitting Diodes... 

S.A. Carter, M. Angelopoulos, S. Karg, P.J. Brock, and J.C. Scott, Polymeric anodes for improved polymer light-emitting diode performance, Appl. Phys. Lett., 70 2067-2069, 1997. 

V. Blyznyuk, B. Ruhstaller, P.J. Brock, U. Scherf, and S.A. Carter, Self-assembled nanocomposite polymer light-emitting diodes with improved efficiency and luminance, Adv. Mater., 11 1257-1261, 1999. 

M.M. Alam, and S.A. Jenekhe, Polybenzobisazoles as efficient electron-transport materials for improving the performance and stability of polymer light-emitting diodes, Chem. Mater., 14 4775-4780, 2002. 

Y-H. Niu, J. Huang, and Y. Cao, High-efficiency polymer light-emitting diodes with stable saturated red emission use of carbazole-based copolymer blends in a poly(p-phenylene vinylene) derivative, Adv. Mater., 15 807-811, 2003. 

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