Narrow Band Gap Conjugated Materials: Synthesis And Their Application In Organic Electronics

With the continuous consumption of energy during the 21 th Centrury,energy problem and the environmental pollution are becoming more and more serious.It is important to find a clean energy to replace fossil fuels,so scientists focus on clean solar energy.Since then,solar cells have become the focus of research in various fields.Organic solar cells have important application due to their advantages of low cost,flexibility and printability.As a new kind of functional materials,organic conjugated materials have been widely studied in the field of organic solar cells(OSCs)and organic field-effect transistors(FETs)due to their tunable optical and electrical properties.However,enhancing the power conversion efficiencies(PCEs)of the organic solar cells,so as to improve the utilization rate of solar energy is still the direction of our efforts.The main way to improve the efficiency of solar cells is to design and synthesize organic conjugated materials with narrow band gap and low HOMO level.This dissertation focuses on the design,synthesis,and the study of the relationship between chemical structure and organic electronic properties of narrow band gap conjugated materials,and the contents are as follows:1.An asymmetric diketopyrrolopyrrole(DPP)polymer flanked with thienyl and thiazol linkers was explored.The asymmetric polymer has an ultra-small band gap,deep LUMO level at-4.03 eV,HOMO level at-5.48 e V and high hole mobility of 3.05 cm2 V-1 s-1 in field-effect transistors(FETs).The asymmetric polymers provide a high efficiency of 5.9% in polymer solar cells(PSCs)with a high fill factor(FF)of 0.66 and a low short circuit current density(Jsc)of 12.0 mA cm-2.Morphology investigation demonstrates that the asymmetric polymer performs large crystal domain in blended thin films,explain the relatively low photocurrent.The results indicate that our design by incorporating different aromatic linkers into the polymer backbone is an efficient method to adjust the energy levels and provide interesting properties in devices.2.A PBI derivative SdiCNPBI with a deep LUMO level of-4.56 eV was designed and synthesized by introducing two cyano groups into a molecule.The molecule was applied as an electron acceptor in non-fullerene solar cells.Absorption spectra of SdiCNPBI in CHCl3 solution and thin films are similar.PCEs from 0.1% to 1.4% can be achieved,indicating the efficient charge transfer,which was further confirmed by highly quenching photoluminescence(PL)spectra in blended thin films.The results demonstrate that bis-PBI structures are able to effectively prevent the molecular aggregation in blended thin flim.It is a design strategy to introduce electron-deficient building blocks in order to realize deep LUMO levels,which was beneficial for air-stable electron mobilities and high performance OSCs.