Synthesis Of Diketopyrrolopyrrole Derivatives And Applications In Photodetectors

Diketopyrrolopyrrole（DPP）and its derivatives are widely used in polymer solar cells,organic light-emitting diodes,organic semiconductors,organic photodetectors,etc.because of their characteristics of broad absorption spectrum,good thermal stability,strong designability.DPP small molecules also have many applications in the field of high-performance dyes due to their bright color,strong tinting strength,good photothermal stability,and strong fluorescence.Conventional DPP-based dyes exhibit bright red,and their absorption spectrum is mainly concentrated in the visible light region.In view of their highly conjugated chromophore structure and designability,it is expected to be modified on this basis,and the absorption spectrum is concentrated in the near-infrared region.In the field of organic optoelectronics,the application of DPP derivatives is often limited by their poor solubility.Introducing flexible or branched chain onto their structures has become an effective method to improve solubility.By selecting appropriate substituents,the solubility of DPP derivatives can be easily regulated,which is an vital way to expand the application of such structures in the field of organic optoelectronics.In this paper,the synthesis method of modified small molecule derivatives based on DPP with strong absorption in near-infrared light and weak absorption in visible light region was studied.Then,donor-acceptor type conjugated polymer with removable side flexible chain was designed and prepared and the applications of the polymer in different functional layer of photodetectors were explored.The main contents and conclusions are as follows:（1）Small molecules（PPCy）with planar conjugated structures were synthesized by introducing strong electron-donating groups on both sides and coordination with boron reagents,and the absorption spectrum of the molecule extends to the near-infrared region with a peak at784 nm.The yield was efficiently increased from 5%to 69%by a multi-step synthesis route.（2）The solubility of DPP derivatives is effectively improved by introducing tert-butoxycarbonyl（Boc）on the N atom,and the molecule was used as acceptor unit to copolymerize with thiophene to obtain conjugated polymer P1.The tert-butoxycarbonyl group of P1 can be removed at a temperature of 160°C to obtain an insoluble polymer P2.Both P1and P2 film have a broad absorption at 600-1000 nm.（3）P1 and P2 were used as active material and hole transport material to prepare photodetectors（PPD-1 and PPD-2）,respectively.The maximum specific detectivities of the devices PPD-1 and PPD-2 are 8.20×10¹¹ Jones and 3.96×10¹² Jones,respectively,and the dark current density of the device PPD-2 is 3.84×10^-9 A/cm².The performance of PPD-2 is than the device with PEDOT:PSS as hole transport layer material.