Synthesis And Properties Of The Organic Photovoltaic Materials Based On Diketopyrrolopyrrole And Thieno[3,4-c]pyrrole-4,6-dione

In recent years, organic photovoltaic materials have attracted great attentions. the power conversion efficiency(PCE) of the single junction organic solar cells have reached 10.1%, respectively, tandem devices have reached 11.3%. Diketopyrrolopyrrole(DPP) and thieno[3,4-c]pyrrole-4,6-dione(TPD) have been receiving considerable attentions as the excellent electron-accepting unit for constructing donor-acceptor structured semiconducting conjugated polymers(SCPs). Currently, PCE of up to 8.0% and 8.5% have been achieved for OPVs using DPP-based and TPD-based polymers. Developing such materials with novel structures and desired performance is of great scientific and practical significance in the field of organic electronics for commercial motives. In this thesis, we designed and prepared donor-acceptor structured organic photovoltaic materials based on diketopyrrolopyrrole and thieno[3,4-c]pyrrole-4,6-dione, and systematically studied the effect of energy levels and micro-morphology on photovoltaic performance. In detail, the dissertation is divided into two chapters:First of all, we optimized the molecular structure of DPP. With two strong electron withdrawing lactam which better for co-planar, Diketopyrrolopyrrole(DPP) is a kind of high efficient electron-accepting materials, which has been receiving considerable attention for a variety of applications, particularly for organic thin film transistors(OTFTs) and organic photovoltaics(OPVs). Particularly, SCPs based on DPP exhibited high carrier mobility up to 1 cm2 V-1 s-1 in OTFTs. However, open circuit voltage(Voc) had poor values(0.5~0.8 V). So, increasing Voc is the first problem we must to solve if we want to further improve the PCE of DPP-based materials. According to the relevant literature, the expansion of the molecular conjugate plane is an effective way to increase the device’s Voc values. So, we designed to introduce a benzene ring between the two pyrrolone of DPP to extend conjugate plane and to construct a new molecule of benzodipyrrolinone(BDP).We also synthesized a series of D-A copolymers of benzodipyrrolinone(BDP), by introducing electron-rich monomer, such as thiophene, naphthalene, benzene and benzo[1,2-b:4,5-b’]dithiophene(BDT), to tune the HOMO and LUMO levels, respectively. With respect to DPP-based photovoltaic materials, Preliminary photoelectric tests indicated that BDP-based photovoltaic materials had worse light absorption properties but better energy level structure. BDP-based photovoltaic materials had narrow spectral absorption and significant blue shift of absorbance, but the highest occupied molecular orbital(HOMO) energy level have reduced 0.05 e V, demonstrating its unique value in the OPVs.Then, we made a thorough inquiry with the backbone structure of the polymers. we introduced acetylenic bond to enhance conjugation effect, lower the HOMO energy level, improve open circuit voltage and the charge mobility. Preliminary tests found that the introduction of ethynylene linkages into the D-A systems could resulted in planar conformations, significant blue shift of absorbance, and a deeper HOMO value(~0.3 e V).With respect to PBDTDPP:PC71BM solar cells, EDPP:PC71BM devices gave a significant(~0.2 V) improvement of Voc. However, the Short-circuit current(Jsc) and fill factor(FF) had poor values. Resonant soft X-ray diffraction(RSo XS) suggested that the EDPP:PC71BM blends formed the large phase separation domains around 100 nm, which is the major reason for the low Jsc. With the optimized weight ratio of EDPP:PC71BM at 1:1, a best but moderate PCE of 1.98% was achieved, and Jsc=5.67 m A?cm-2, FF=0.39, Voc=0.88 V.