EFFECTS OF POLYMERIC ELECTRON TRANSPORTERS AND THE STRUCTURE OF POLY(P-PHENYLENEVINYLENE) ON THE PERFORMANCE OF LIGHT-EMITTING-DIODES

A series of new electroactive monomers containing 2,5-diphenyl-1,3-oxa zole, 2,5-diphenyl-1,3,4-oxadiazole, and 3,4,5-triphenyl-1,2,4-triazol e heterocycles have been synthesized in good yield. These monomers wer e incorporated as either pendant groups or directly into the backbone of 10 high molecular weight polymers [poly(arylmethacrylate), poly(ary lmethacrylamide), poly(aryl formal), and poly(aryl ether)]. The polyme rs appear to be amorphous and exhibit glass transition temperatures in the range 115-208 degrees C, and most have excellent thermal stabilit y in air (decomposition > 400 degrees C). Thin, clear, pinhole free-fi lms are readily deposited on a variety of substrates (e.g., silicon, q uartz) by spin coating. These materials were used as the electron tran sport (ET) layer in light-emitting diodes (LEDs) having an ET layer de posited on PPV with aluminum and indium tin oxide electrodes (i.e., Al /ET layer/PPV/ITO). The ET materials contain as much as 97 mol % of th e electroactive moiety, while conventional electron transporters (e.g. , PBD dissolved in PMMA) contain 46 mol %. LEDs containing these ET po lymers were much more stable than devices without an ET. Many were als o more stable than those having a conventional electron transporter. R elative to LEDs without ETs, the internal quantum efficiencies using E Ts were higher in some cases and lower in others. In addition to varyi ng the ET layer, two different types of PPV (crystalline and amorphous ) were also used to construct four different types of devices. In term s of diode efficiency, the most important factor is the PPV conjugatio n length and not the type of ET used. The internal quantum efficiencie s ranged from 0.2 to 0.0004%. Finally, the current/voltage curves of s ome of the LEDs were fitted to four different models in order to deter mine which best describes the device physics.