The Molecular Design And Device Characterization Of Donor Materials Of The Organic Solar Cells

Nowadays,energy plays an increasingly important role in human society on earth.The development of our society cannot inseparate from energy.Petrochemical and coal chemical industries which are all among the non-renewable types still are the widely used energy in our daily life.Renewable energy research has become the key to solve energy issues in many countries.Among them,solar energy and wind energy have already been used in the industry.Solar cells are one of the most promising and efficient technologies for obtaining solar energy.Organic solar cells(OSCs)which have the advantages of light weight,low cost,flexibility potential,and potential for preparing large-area devices have received widespread attention and have been rapidly developed in recent years.The donor material in the active layer is very important for scientific research.In this thesis,a variety of organic solar cell donor materials were designed and synthesized.The physical properties of the materials were tested and assembled,and battery devices were assembled for the study of photoelectric properties.This article mainly includes the following contents:(1)Two polymers,named PBDT-T-BD and PBDT-T-BQ,based on benzodithiophene were synthesized.The two polymers were respectively using pyridine and pyridin as acceptor units.The effects of different acceptors and nitrogen atom were carefully studyed.PBDT-T-BQ has a broad absorption and a narrow band gap compared to PBDT-T-BD,demonstrating that the nitrogen atom can reduce the band gap.The devices based on PC71BM showed relatively close PCE.The device based on PBDT-T-BD:ITIC showed the PCE of 2.76%,while the PBDT-T-BQ:ITIC active layer showed a poor morphology.The difference in light absorption ability and electrochemical performance is obvious,but the difference in photoelectric performance cannot be well compared because the device efficiency is about 3%.(2)Two small molecule donors,named 6TBT and 4T2BT were synthesized.6TBT and 4T2BT showed obvious wide band gap characteristics from the absorption spectrum and energy level.The absorption capacity of 4T2BT is wider than that of 6TBT.However,it was found that the two small molecules have strong crystallinity using DSC,which has a bad influence on the morphology of the active layer.AFM and TEM test results showed that the active layer had a large phase region,which exceeds 100 nm,which is very unfavorable for the transmission of photoexcitons.The devices based on 6TBT:PC71BM and 4T2BT:PC7iBM showed a best PCE of 3.10%and 2.02%,respectively.(3)The polymer PSBDT-TT-IID was synthesized by using benzodithiophene as donor unit and isoindigo as acceptor unit.Sulfur atom was introduced to the two-dimensional alkyl chain of BDT unit and 3-octylthieno[3,2-b]thiophene units was introduced to the system as ?-bridge.The effect of introducing electron-donating elements on the properties of materials and devices was investigated.The optical,electrochemical,thermal stability and other properties of the material were carefully measured.The conventional PSBDT-TT-IID:PC71BM-based devices were fabricated to characterize photovoltaic performances.The test results show that the PSBDT-TT-IID has a suitable levels to the PC71BM.The simulation proves that the polymer has a relatively flat structure.The PCE of the conventional devices based on PSBDT-TT-IID:PC71BM is 7.12%,which is a high value in this system.It is proved that the device performance has a certain tolerance to thickness,indicating that the system has a certain potential for large-area processing.Compared with the polymer reported by our group that does not contain sulfur in the side chain,the carrier mobility of PSBDT-TT-IID is lower,resulting in a slightly lower PCE.