The Design, Synthesis And Optoelectronic Properties Of D-A Polymers Based On Benzodiazole With Chalcogen Hetero Atoms

Nowadays,energy crisis the world facing is especially serious. New materials science and technology have been the basis and guide of the new technological revolution and play an increasingly important role on energy conservation and utilization of new energy, especially embodied in the development and utilization of solar energy. Polymer solar cells(PSCs) have gained much attention due to their low cost and compatibility with large-scale processing. Though power conversion efficiency(PCE) of PSCs haved already exceeded 10%, there is still a long way to reach threshold of the commercial application. Efficiency and stability still are two major problems of PSCs and related to the materials of active layer thus the design and synthesis of polymers with a proper level, strong ability to absorb sunlight and high mobility to improve PCE, currently is a priority of the research.First, polymer donors were summarized and the relationship between structure and properties of the polymers were discussed. On this basis, four benzodiazole heterocyles with chalcogen hetero atoms including 5,6-difluorobenzo- thiadiazole(FBT), 5,6-difluorobenzoselenadiazole(FBS), 5,6-bis(dodecyloxy)benzothiadiazole(12BT) and 5,6-bis(octyloxy)benzooxadiazole(8BX) were synthesized and constructed a serie of donor-acceptor(D-A) conjugated polymers together with thiophene derivatives. High hole mobilities and efficiencies were demonstrated in OFETs and PSCs for some of them, respectively.In chapter 3, we focused on the development of new D-A polymers with high hole mobility and the exploration of their utilization in thick-film PSCs where typical efficient donor materials didn’t perform well mainly due to low hole transport ability. D-A conjugated polymer FBT-Th4(1,4) based on FBT as the A-unit and alkylated quarterthiophene as the D-unit was synthesized, which absorption spectra indicate strong interchain aggregation ability with the dependence on molecular weight(MW) and temperature. The influences of MW on OFET and PSCs were studied. The increased MW recieved improved performances. FBT-Th4(1,4) got excellent performances of both OFET and PSCs. High hole mobilities up to 1.92 cm2/(Vs) were demonstrated in OFETs via annealing at 100 °C. The conventional PSCs showed PCE of 6.63%, while the inverted devices with active layer thickness from 100 to 440 nm displayed PCEs all over 6.5% with the highest efficiency of 7.64% at 230 nm. And a PCE of 9.27% could be obtained after optimization of the donor material and morphology.In chapter 4, thiophene and thieno[3,2-b]thiophene were used to replaced 2,2’-bithiophe, resulting in D-A polymers FBT-DT24-1T and FBT-DT24-TT with deeper HOMO level thus an increase of open-circuit voltage( Voc) of the PSCs devices. But the former showed weak interchain aggregation and light absorption. It only got a FET hole mobility of 2.6×10-3 cm2/(Vs) and a PCE of ~1% for inverted PSCs. FBT-DT24-TT showed very strong interchain aggregation and light absorption. Its FET hole mobility reached 0.1 cm2/(Vs) level. MW impacts PSCs performance greatly. Inverted PSCs based on FBT-DT24-TT with low MW, only got a PCE of 3.74%. It could reach 7.34% when FBT-DT24-TT with high MW was adopted. If chloronaphthalene was used as the solvent additive, the PCE could further increase to 7.78% and demonstrate PCEs all over 6.5% with active layer thickness from 100 to 355 nm. And a PCE of 8.81% could be obtained after optimization of the morphology.In chapter 5, D-A polymer family based on FBT and thiophene derivatives were developed and 2,2’-bithiophe was replaced with(E)-1,2-di(thiophen-2-yl)ethane and 2,2’-biselenophene, resulting in polymer FBT-DT24-TVT FBT-DT24-Bi Se, respectively, possessing higher HOMO level than FBT-Th4(1,4). When the devices was prepared from polymer:PC71BM(1:1.5) solution in cholrobenzene with 3% chloronaphthalene, PSCs devices got high short-circuit current(Jsc) and fill factor(FF), giving PCEs of 5.73% and 6.08%, respectively, even though Voc of ~0.69 V was relatively lower.In chapter 6, FBS, an analogue of FBT was synthesized and its first three D-A polymers incorporating thiophene derivatives. Compared with the former efficient FBT-based polymers, the FBS analogues showed much weaker interchain aggregation obtained from their absorption spectra and obvious bathochromic shift in solid state. But the introduction of Se made HOMO level increased and thus a decrease of Voc of the PSCs devices. Their optoelectronic devices displayed much poorer performances than their analogues.In chapter 7, two polymers based on 12 BT and 8BX were designed and synthesized, repectively. Phenanthrene was introduced to lower the HOMO level of the target polymers, thus a high Voc of ~0.86 V was got. Though PPA-DTBT and PPA-DTBX gave low efficiencies of 3.03% and 1.77%, respectively, our results suggest that the phenanthrene is a valuable electron-donating unit in the constructions of D-A polymers for PSCs with high Voc.