Novel Conjugated Polymers: Synthesis And Properties

During the past decade, conjugated polymers have been the focus ofboth scientific research and industrial application, because of theirpotential applications in large area, lightweight, flexible optoelectronicdevices through low-cost solution-processable techniques. In thisdissertation, major work is focused on the design and synthesis of newconjugated polymers for the application in light-emitting diodes, solarcells and field-effect transistors.1. A series of novel branched zinc tetraphenylporphyrin-fluorenecopolymers, with different porphyrin content, were designed andsynthesized by Suzuki polycondensation reaction. With increasingcontent of porphyrins, the emission color of the copolymers changedfrom nearly white to red. The OLED device using P12as emitter showedpure red emission with a maximum luminance of740cd/m², which isamong the highest value for pure red light-emission OLEDs based onporphyrin containing polymers.2. A novel alternating D-A copolymer, PPor-BT, based on dioctylporphyrin (Por) and5,6-bis(octyloxy)benzo-2,1,3-thiadiazole (BT),was designed and synthesized by Sonogashira-coupling reaction.PPor-BT exhibited a broad absorption band from350to950nm with twopeaks centered at456and818nm corresponding to the Soret band andQ-bands absorption of porphyrin segments, respectively. The employmentof electron deficient BT unit to construct donor-acceptor structureobservably broadened the absorption spectrum and enhanced the Q-bandabsorption of the porphyrin-based polymer. Field-effect mobility of thepolymer reached4.3×10^-5cm²V^-1s^-1with an on/off current ratio of10⁴.3. Porphyrin ring was first introduced to D-A conjuated polymer as anedge-fused manner. Combining the high extinction coefficient ofporphyrins and broad absorption of D-A conjuated polymer, the polymerdemonstrated high photovoltaic performance. Power conversionefficiency of bulk heterojunction solar cells based on the polymer reached2.53%, which is the highest value for that of porphyrin-based conjugatedpolymers.4. A series of conjugated D-Ï€-A copolymers, based on benzodithiophene(BDT) donor unit and benzothiadiazole (BT) acceptor unit with differentÏ€-bridges were designed and synthesized via a Stille-coupling method. Itwas found that the Ï€-bridges significantly affect the moleculararchitecture and optoelectronic properties of the copolymers. Bulkheterojunction solar cells with the polymers as donor and PC₇₁BM as acceptor demonstrated power conversion efficiency varied from2.81%to3.72%and to4.93%. Compared to furan and thiophene,thieno[3,2-b]thiophene Ï€-bridge in the copolymers shows superiorphotovoltaic performance.5. A series of thieno[3,2-b]thiophene bridged conjugated D-Ï€-Acopolymers were designed and synthesized. Removing ofelectron-donating alkoxy-substituted or introducing higherelectronegativity oxygen atom or fluorine atom can lower HOMO levelsof the conjugated copolymers and thus increase the open-circuit voltageof corresponding BHJ solar cells. As a result, open-circuit voltage of thesolar cells increased from0.69V to0.74V,0.82V and0.79V,corresponding power conversion efficiency was4.37%,3.30%and6.26%。6. A series of conjugated polymers were designed and synthesized,wherein a single atom in the benzothiadiazole unit or thiophene rings wasvaried from sulfur to oxygen atom, which allows us to study the effect ofatomistic substitution in D-A copolymers. Introducing of higherelectronegativity oxygen atom in different position of the polymerdisturbed the original intramolecular charge transfer behavior and thuscrucially affected the properties of the polymer. Power conversionefficiency of corresponding BHJ solar cells varied from3.25%to0.02%or to4.00%. 7. A series of D-A copolymers of tetradodecyl-substitutedindacenodithiophene (IDT) donor unit with different acceptor units weresynthesized for the application as active materials in polymer solar cellsand field-effect transistors. The FET hole mobility of PIDT-DPP reached0.065cm2V^-1s^-1with an on/off ratio of4.6×10⁵. The power conversionefficiency of PIDT-DPP based solar cell was1.76%with a high opencircuit voltage of0.88V. The PSC based on PIDTDTBT exhibited a highPCE of6.17%.8. α, β-Dicyanostilbene was firstly introduced into polymer photovoltaicmaterials. The power conversion efficiency of PIDT-DCS based solarcell was1.03%with a high open circuit voltage of0.90V.9. A series of novel poly(thienylene vinylene) derivatives (PTVs), withimide substituent were designed and synthesized by Stille-couplingpolymerization. Adjusting the frontier orbitals of the polymers bycontrolling the electron-withdrawing imide substituent denisty, PCE ofsolar cells based on the PTVs can be increased to four times.