Synthesis And Photovoltaic Properties Of Small Molecule Donor Materials Based On Pyrrolopyrrole And Diphenylpyranylidene

The rapid consumption of petrochemical energy and the serious environment pollution caused by development of the energy,has triggered an increasing demand for renewable clean energy.As the most abundant,widely distributed,and environment-friendly power source,solar energy has become the primary candidate for the development of new energy technologies.In recent decades,organic solar cells that convert solar energy into electrical energy have been rapidly developed.Among them,small-molecule organic solar cells have received extensive attention from researchers for their many advantages that other solar cells cannot replace.Not only the electron donor materials in small molecule organic solar cells need to have broad and strong light absorption,but also the excitons generated by sun light can easily form effective dissociation at the donor and acceptor interface,and thus can quickly complete the charge transmission process.The current problem that needs to be solved is how to design and synthesize small molecular donor materials with narrow band gaps while considering the requirements of light absorption and solubility,as well as the morphology of the active layer and the modification of the device interface.In this thesis,a series of small molecule donor materials were designed and synthesized by combining highly electron-donating pyrrolopyrrole of goodabsorption of ultraviolet-visible light and the excellent planar electron-accepting diphenylpyranylidene units.Their photophysical and electrochemical properties were studied and their organic solar cells based on fullerene derivative PC₆₁BM acceptor were fabricated and characterized.In the first part,in order to broaden the overall light absorption range of the donor material,the pyrrolopyrrole group is used as the donor unit,Diphenylpyranylidene as an electron withdrawing unit,and phenyl or thiophene ring are used asπbridges to design electron push-pull type of small molecule X1-1,X1-2,X1-3,X2-1,X2-2 and X2-3.The structures of these molecules were charactized by ¹H-NMR、¹³ C-NMR and HRMS.In order to study the geometric structure,the distribution of electron clouds and the planarity of these molecules,density functional theory is used for calculation.The ultraviolet-visible light absorption and cyclic voltammetry test were carried out to study the optical and electrochemical properties.The results show that when theπbridge is changed from a phenyl ring to a thiophene ring,the light absorption range increases and the red shift occurs gradually.At the same time,it has good thermal stability as thermal weight loss test showed.The six small molecules with a good conjugated system have a good energy level match with classical electron-acceptor PC₆₁BM.Their organic solar cells based on fullerene derivative PC₆₁BM showed that the highest photoelectric conversion efficiency of X2-3 small molecules was0.79%.The acceptor-donor-acceptor structure of small molecule donor materials can lead to good intramolecular charge transfer and strengthens the adjustment of the material’s light absorption in the visible light range.Therefore,in the second part of this thesis,symmetrical structure of acceptor-donor-acceptor small molecules H1,H2 and H3 based on pyrrolopyrrole and Diphenylpyranylidene were designed and synthesized.The structures of these molecules were charactized by ¹H-NMR、¹³C-NMR and HRMS.In order to study the geometric structure,the distribution of electron clouds and the planarity of these molecules,density functional theory is used for calculation.The ultraviolet-visible light absorption and cyclic voltammetry test were carried out to study the optical and electrochemical properties.The results show that the three small molecules all exhibit extensive light absorption and good thermal stability.The three small molecules all form a good conjugated system,while satisfying the narrow band gap condition,which is consistent with the theoretical calculation results.Finally,these molecules were blended with the acceptor material PC₆₁BM as the active layer material and used in small molecule organic solar cells.Photovoltaic characteristics show that the highest photoelectric conversion efficiency exhibited by H3 small molecules is2.44%.Based on the above research,it is shown that when designing and synthesizing small molecule donor materials,it is necessary to consider the synthesis of high performance from the aspects of light absorption,energy level matching,band gap,solubility,and different conjugatedπbridges or increasing the length of conjugatedπbridges,materials to obtain high-efficiency photovoltaic devices.