Study On Donor Molecular Design And Photovoltaic Performance Of Organic Solar Cells

Organic solar cells have the advantages of low-cost,high-yield roll-to-roll production process to manufacture lightweight and flexible devices.In the past 30 years,extensive research work has been devoted to understanding and improving the performance of organic solar cells,including: organic material design,devic e process optimization and theoretical calculation of device efficiency.At present,the efficiency of organic solar cells has made a huge breakthrough.With the development of non-fullerene organic acceptor,the power conversion efficiency of binary polym er solar cells has exceeded 18%,and all-small molecule organic solar cells have also reached More than 15%,showing that organic solar cells have broad application prospects.This article focuses on the design of donor molecules for organic solar cells,synthesizes polymer donors and small molecule donors,and prepares non-fullerene organic solar cell devices with different structures according to the characteristics of the molecules and makes reasonable optimizations.The main research contents are as follows:1.In this work,three types of polymer donors with dithieno[2,3-d;2’,3’-d’]-benzo[1,2-b;4,5-b’]dithiophene(DTBDT)as the donor unit and bisthiophen imide(BTI)as the acceptor unit were designed,2-Octylthiophene is a π bridge,named as PDTBDT,PDTBDT-T,PDTBDT-T-Cl.All these polymers form a high-efficiency non-fullerene organic solar cell with Y6.The main feature of this system is the use of BTI as an acceptor unit to significantly reduce steric hindrance,thereby expanding the conjugated framework.Subsequently,in order to further optimize the structural properties of the polymer,a conjugated π bridge was used to expand the light absorption range and control the energy level of the polymer through chlorine atoms.After being mixed with the ac ceptor,PDTBDT-T-Cl:Y6 shows excellent charge separation effect due to the balance of crystallinity and compatibility,highly ordered face-on molecular orientation,which greatly enhances the charge transport ability and reduce the probability of charge re combination.Therefore,the power conversion efficiency of organic solar cells based on PDTBDT-T-Cl:Y6 reaches15.63%.This work aims to emphasize that BTI units can be effectively copolymerized with donor units to achieve extended conjugation,thereby imp roving the optical and electrochemical properties of the polymer.This work also provides some effective strategies for the future design of high-performance polymer donors.2.In this work,study the small molecule donors 2DTBDT and 2DTBDT-2T with A-D-A and A-π-D-π-A structures respectively.When the donor is blended with small molecules,the all small molecule organic solar cell is constructed.Electron-rich dithieno[2,3-d;2’,3’-d’]-benzo[1,2-b;4,5-b’]dithiophene(DTBDT)is used as the central core unit to expand the conjugation plane and enhance the rigidity of the molecule.And through the dimerization method,another DTBDT is inserted into the main skeleton,that is,2DTBDT is obtained by using double DTBDT as the core and rhodanine as the end group.After choosing dithiophene as the π bridge and deepening the HOMO energy level,2DTBDT-2T is obtained.In this system,the active layer of all small molecules is mixed with small molecules Y6 and IDIC-4F.Among them,the device based on 2DTBDT-2T: Y6 showed the highest efficiency,up to 12.31%,and the device based on 2DTBDT: Y6 had an efficiency of only 1.59%.When IDIC-4F is used as the acceptor,the result is completely opposite.The efficiency of 2DTBDT:IDIC-4F reaches 7.18%,while the efficiency of 2D TBDT-2T:IDIC-4F is only 5.71%.This result shows that when double DTBDT is used as the core unit and thiophene is added as a π bridge,the energy level of the molecule is changed,so the choice of acceptor is also changed.It further proves that in order t o obtain better device efficiency,it is not only necessary to achieve The energy level of the acceptor is matched,and the phase separation of the blend film is required to be reasonably optimized to achieve the purpose of improving the charge mobility an d inhibiting the charge recombination,and correspondingly improve the efficiency of the organic solar cell.