Syntheis And Luminescence Properties Of Red-, Green-emitting Polylfuorenes

Based on two decades development, organic light-emitting devices (OLEDs) productsare now becoming commercially available. Especially, they have an extremely wideapplication in the small-size digital media such as cell phone, MP3, and so on. Even,large-size panels display products have been achieved, like30inch OLED TVs. However, allthe commercialized OLED products are made of small molecules and only realized byvacuum deposition technique, which suffered from many drawbacks, such as expensiveequipment, low yield, materials waste and difficult to realize large area display, while polymerlight-emitting diodes (PLEDs) can be realized by solution process. This solution processdraws considerable attention due to the fact that it can overcome the disadvantage mentionedabove.Polyfluorenes (PFs) and its derivatives have been considered to be the most prominentlight-emitting materials due to good thermal and electrochemical stability, high fluorescenceyield and facile chemical functionalization. Although PFs is blue light-emitter, we canintroduce narrow bandgap units into PFs main chain to tune the emission colors over thewhole visible range. Dibenzothiophene-S,S-dioxide (SO) unit is electron-deficient moietywith slightly higher electron affinity energy and a smaller band gap compared with PFs.Besides, SO unit has high fluorescence quantum efficiency.In Chapter2, Section1, benzothiadiazole were incorporated into the main chain ofpoly(fluorene-co-dibenzothiophene-S,S-dioxide) with the ratio of benzothiadiazole being1%and2%respectively and attain two polymers named as PPFSO15BT1and PPFSO15BT2.Based on these two copolymers, single layer devices were fabricated asITO/PEDOT:PSS/Polymer/CsF/Al. Taking PPFSO15BT2as light-emitting layer, the devicegives the best performance, showing a maximum luminous efficiency (LEmax), maximumexternal quantum efficiency (EQEmax), maximum luminance (Lmax) and turn-on voltage (Von)of21.42cd/A,5.79%,12080cd/m2and3.5V, respectively.In order to further optimize the efficience and color purity, we incorporate phenyl intothe two sides of2,1,3-benzothiadiazole, gaining4,7-diphenyl-2,1,3-benzothiadiazole, and we obtain series of green light-emitting materials named as PFSOxDPBTy by Suzuki couplingreaction. Single layer devices are fabricated as ITO/PEDOT:PSS/Polymer/CsF/Al. Amongthem, PFSO15DPBT5gives the best EL properties, showing the highest LEmaxof7.39cd/A,EQE of1.89%and Vonof4.0V. Referring to efficience stability, PFFSO20BT5’s LEmaxis4.85cd/A at100mA/cm2, and when current density increases to400mA/cm2, LE is4.02cd/A,just less than20%loss, indicating that these polymers have a good efficience stability.In chapter3, we introduce oxidazole into the main chain ofpoly(fluorine-co-4,7-di(4-hexyl-2-thienyl)-2,1,3-benzothiadiazole), and gain a series ofcopolymers named as PFOXD10DHTBTn. Single layer device are fabricated based on thesematerials as ITO/PEDOT:PSS/Polymer/CsF/Al. Among them, PFOXD10DHTBT2shows thehighest LEmax of0.71cd/A, and the highest luminance of1793.6cd/m2.