Novel PVK-based π-stacked Polymer Semiconductor Materials: Synthesis, Properties And Optoelectronic Devices

Polymer semiconductor materials promote the development and commercialization of optoelectronic devices due to their low cost solution processing technology. Compared with traditional conjugated polymers, π-stacked polymers have unique carrier transporting channel, and have been widely used in organic optoelectronics fields. Poly(N-vinylcarbazole)(PVK) is a classic π-stacked polymer with unique molecular configuration, higher triplet energy level(ET=3.0 eV) and excellent hole transporting properties and has been widely used as host material for blue phosphorescent polymer light-emitting devices(PhPLEDs) and also as organic memory material. To further improve the stability and expand the applications of π-stacked polymer materials, a series of new π-stacked polymers have been designed and synthesized by introducing bulky hindrance and electronic functionalized structures to PVK based on our previous work. The thermodynamics, photophysical and electrochemical properties of these new π-stacked polymers are studied, and then applied to blue phosphorescent light-emitting devices and transistor memories. The main findings are as follows:First, although PVK is an excellent host material, it is inclined to photoaging and degradation owing to the strong activaties of 3,6-position of carbazole units. A dumbbell-shaped polymer, poly(3,6-bis(9-phenyl- fluoren-9-yl)-9-vinyl-carbazole)(PVKDPF), was successfully synthesized via a fully end-capping strategy. PVKDPF exhibits great enhancement in terms of anti-photoaging ability against UV light irradiation and excellent electrochemical stability. When used as host materials for blue PhPLEDs in the FIrpic-doped devices, stable blue emission has been achieved with maximum luminous efficiency of 17.3 cd A-1 and power efficiency of 9.0 lmW-1.Second, PVK exhibits excellent film-forming properties and large HOMO-LUMO(highest occupied molecular orbital-lowest unoccupied molecular orbital) bandgap, and thus allowing it to be used to modify the interface of organic semiconductors and SiO2 in the organic field-effect transistor memories. A higher mobility can be gained, which is far greater than the value of devices without a PVK layer. But the devices could not well maintain the stability, especially for the erased state. A series of new π-stacked PVK derivatives PVKFPO, PVKFDPO and PVKDCNPPF have been designed and synthesized by introducing phosphorus oxygen and cyano groups through sp3 carbon of 9-phenylfluorenyl moieties(PFMs). Then the thermodynamics, photophysical and electrochemical properties are studied by conducting the TGA, DSC, UV, PL, CV tests for organic field-effect transistor(OFET) memory application. The devices stability has been effectively improved. Particularly, the introduction of cyano group not only significantly inhibites the decay of erased state, while maintaining Ion/off not less than 105, but also affords bidirectional memory properities.