Theoretical Research On The Photoelectric Performances Of The Donor/Acceptor Materials For Organic Solar Cells

Organic solar cell is an important research field of solar energy development and utilization.On the premise of understanding the history,device configuration,components of photovoltaic materials and working principle of of organic solar cells,to research and design high performance donor and acceptor materials for organic solar cells,and explain the relationship between the molecular structure and photoelectric properties theoretically is the main purpose of our research.By means of Density Functional Theory(DFT),Marcus Charge Transfer Theory,Combined with a variety of software such as GaussView,Chemdraw,HyperChem,Multiwfn,ADF,The photoelectric properties of a series of organic small molecules for donor/acceptor materials were studied Under Gauss 09 proceduce.The calculation results show that by adjusting the donor or acceptor ability of electron or other suitable methods can improve the molecular energy levels,optical properties,at the same time facilitate the charge transfer rate and carrier mobility.Theoretically explain and guide how to design and get efficient organic solar cell devices in experiments.The main contents of this paper are as follows:The preface mainly introduces the development of organic solar cells,the research status at home and abroad,device structure and working principle of the organic solar cells and the components of photovoltaic materials in organic solar cell.The second section mainly elaborates some theoretical and computational methods and characterization methods used in the calculation of this paper.For example,the theory of density functional theory and time density functional theory,Marcus theory,etc.Introduced the basic principle,meaning,and some formulas and reasoning process that need to be used in each theory.And the theoretical characteristics of photoelectric conversion efficiency of organic solar cells.The third section is a theoretical study on the effect of the structure modification of non-fullerene small molecule receptor materials based on diketopyrrolopyrrole.The A-D-A type experimental small molecule acceptors(SMa)of phthalimide end-capped diketopyrrolopyrrole,two structure modification strategies on central donor unit of replacing thiophene with thiazole ring and fusing diketopyrrolopyrrole(DPP)with side thiophene or thiazole ring are used to design three molecules(SMb,SMa1,SMb1).By comparing the influence of structure changes that DPP unit connection among thiophene ring or thiazole ring and directly remove the single bond between the DPP unit and thiophene rings or thiazole ring to fused with the DPP.The calculated results show the replaced thiazole ring can weaken the electron-donor ability while the fused DPP can enhance the electron-donor of the central unit.Enhanced A-D-A type of SMa1,SMb1 has an adjustable energy levels,better absorption efficiency and a higher electron mobility distinctly.So fusing DPP with side thiophene ring is a valuable strategy to enhance A-D-A type molecule thus improves the properties of small molecule acceptor materials.In the fourth section,we studied a series of A-D-A type small molecular donor materials T-ph-T,TphT,2T-ph-2T and 2Tph2 T which were composed of diketopyrrolopyrrole(DPP),thiophene,and phenyl unit.In this section,On the basis of the experimental molecule T-ph-T,we have changed the structure of the intermediate donor unit to regulate the effect of its electronic donor capacity.The single bond connected with benzene and thiophene ring was removed to blend the three ring into benzodithiophene(BDT)unit.Secondly we connect two thiophene ring on both sides of the benzene ring.Through the theoretical calculation,it is concluded that benzodithiophene can obviously improve the planarity of the material,reduce its HOMO energy and the enenrgy gap value,make the absorption spectra red shift,But it is inevitable that the reorganization energy will be increased.Two thiophene ring adjacent to benzene can raise the HOMO energy level,and increase the length of the conjugate chain,so the oscillator strength of the maximum absorption peak will be significantly enhanced,and the reorganization energy can be significantly reduced to improve the and hole mobility.The last section is the research of A-D-A type small molecular donor materials.On the based of experimental molecule D-TPD which compose of electron donor unit dithiophenepyrrole(DTP)and electron acceptor unit Thieno-pyrrole-dione(TPD)and thiophene bridge,four molecules D-TPD,D-TPD-T,D-DPP,D-DPP-T were designed and researched.DPP and TPD unit have some common characteristics like similar structure and electron-withdrawing ability.In the same A-D-A skeleton structure with DTP as the donor core,the effect of two different receptor units(DPP and TPD unit)interact with the DTP donor cell worth to explore.Meanwhile,What will be happen by adding an aromatic thiophene group to the tail end of the molecules in the A-D-A skeleton? Through theoretical calculation,we find the changes and laws of structural modification.D-TPD-T,D-DPP,D-DPP-T have better planar,optical absorption and hole transmission rate than D-TPD.Because the conjugate backbone of the DPP unit can extend the conjugate chain of the A-D-A skeleton,it can increase the conjugation,reduce the optical energy gap,and make the maximum absorption wavelength redshift.Adding thiophene group at the end can further increase the conjugate chain of A-D-A skeleton molecules to promote other photoelectric performance and hole transmission performance.Thus replacing TPD unit with DPP unit or add a conjugated thiophene group at both ends of the A-D-A framework can well regulate the photoelectric properties of the donor material.