Synthesis And Application Of D-A Type Molecular Materials In Organic Solar Cells

Organic solar cells have attracted extensive attention due to the potentialadvantages, including simple preparation, low-cost and large-area production. In thisthesis, the exploration of the materials and devices based on polymer solar cells andorganic small molecule solar cells were sumarized systematically. In IDT, the rigidring unit could enhance both the degree of conjugation and the coplanarity of themolecular backbones as one of the good donor. Benzothiadiazole (BT) also beenrecognized as one of the most effective electron acceptor.In this thesis, two copolymers of indacenodithiophene (IDT) donor unit withdifferent building blocks including terthiophene (3T) as the other donor anddi-2-thienyl-2’,1’,3’-benzothiadiaole (DTBT) as acceptor unit were synthesized forapplication in polymer solar cells, respectively, PIDT3T for D-D structure andPIDTDTBT for D-A structure. And then, using thermal gravimetric analysis(TGA),UV-visible absorption spectroscopy (UV-vis) and cyclic voltammetry (CV),these two different type polymer are studied in thermal stability, photophysical,electrochemical and photovoltaic performance, respectively. At the meanwhile, thenew indacenodithiophene (IDT)-based molecules with differing solubilizing sidechains have been designed and synthesized for small molecule organic solar cells,BTIDT-C6and BTIDT-OC12for A-D-A structure. The IDT framework was used tostudy the alkyl/alkoxy side-chain effect in photophysical, electrochemical andphotovoltaic performance by preparing IDT-C6and IDT-OC12, where the side chainsin the cyclopentadienyl ring are4-hexylphenyl groups and4-dodeoxyphenyl groups,respectively. The main conclusions obtained in this paper by experiments are asfollows:1. Two indacenodithiophene-based copolymers PIDT3T and PIDTDTBT exhibitgood stability with decomposition temperature (Td) greater than400℃. Comparedwith PIDT3T, PIDTDTBT exhibits a more broad absorption. On the other hand, theenergy levels of the HOMO and LUMO, which are-5.30eV and-3.70eV forPIDTDTBT, and-5.35eV and-3.55eV for PIDT3T. The electrochemical band gap,1.6eV for PIDTDTBT, compared with that of PIDT3T (1.80eV). Under the sameillumination at100mWcm-2AM1.5G irradiation, the power conversion efficiency (PCE) of the polymer PIDTDTBT is much higher than the polymer PIDT3T, for4.52%and3.26%, respectively.2. Two indacenodithiophene-based small molecules with different side chains,BTIDT-C6and BTIDT-OC12，play a negligible role in the electrochemical and opticalproperties. The energy levels of the HOMO and LUMO, which are-5.37eV and-3.71eV for BTIDT-C6, and-5.34eV and-3.73eV for BTIDT-OC12. The electrochemicalband gap,1.66eV for BTIDT-C6, compared with that of BTIDT-OC12(1.61eV).However, they exhibit different melting point for110.2℃and69.4℃, respectively.What’s more, under the same illumination at100mWcm-2AM1.5G irradiation, thepower conversion efficiency (PCE) of the BTIDT-OC12is near20%higher than theBTIDT-C6, for4.83%and4.06%, respectively. The organic field-effect transistors(OFETs) device of BTIDT-C6showed a higher hole mobility of5.4×10-4cm2/Vs thanthat of BTIDT-OC12with hole mobility of1.1×10-4cm2/Vs.