Study Of The Electronic Effect Of Oxygen Atoms On The Photoelectric Properties Of Organic Semiconductors

Organic solar cells（OSCs）have received widespread attention in recent years due to their advantages such as simple fabrication processes,low cost,light weight,and the ability to fabricate flexible large area devices.By synthesizing new materials,optimizing device structures,and exploring new device fabrication processes,the power conversion efficiency（PCE）of OSCs has increased to over 20%.Designing and synthesizing more efficient photocatalytic active layer materials has always been a core issue in improving device performance.Oxygen atoms exist in a variety of functional groups.It has both the conjugation effect of electron giving and the induction effect of electron absorption,and can regulate the photoelectric properties of organic semiconductors in the design of molecular structures.Benzo[1,2-b:4,5-b’]dithiophene（BDT）units have excellent planar conjugate structures and strong intermolecularπ-πstacking,making them the most widely used donor units.Therefore,this project is mainly based on the theoretical basis of the electronic effects of oxygen atoms,designing semiconductor polymers containing BDT conjugated skeletons,and studying their optical and electrical properties.The specific research content is as follows:（1）Ester and carbonyl groups are common functional groups in chemical structures.The electronegativity of ester groups can well regulate the charge transfer absorption of organic semiconductors,which has unique advantages in improving the electrochemical performance of polymers.At the same time,ester groups are easy to synthesize and can be directly connected to alkyl chains to regulate molecular solubility.Similar to ester groups,ketone carbonyls also have a positively charged carbon atom.However,due to the lack of the p-πelectron conjugation effect of oxygen atoms,carbonyl groups have a stronger electron absorption ability than ester groups,which is crucial for regulating the energy level of polymer donors.However,reporting based on carbonyl groups is relatively rare.Therefore,this paper designed and synthesized two polymer donors,PTO and PTC,which contain ester and carbonyl groups,respectively.By blending the donor with the acceptor IT-4F,PTC:IT-4F-based OSCs obtained the highest PCE,at 11.83%.The V_OC obtained by PTC:IT-4F-based OSCs is the highest,at 0.95 V.The relationship between the molecular structure and device performance of the two polymer donors was deeply analyzed by means of structural characterization and device testing.（2）Based on the first work,ester based polymers have a wider band gap(E_g^opt),stronger molecular aggregation,and better device performance than carbonyl based polymers.Therefore,this study designed and synthesized three polymer donors containing terephthalic acid esters,P-n（2+6）,P-n8,and P-n10.Through the comparison of physical and chemical properties,the ester monomer in the better P-n（2+6）was selected and added to PM6 to prepare a ternary copolymer to regulate the photoelectric properties of PM6.It was found that the polymer donor P-0.9BDD-0.1（2+6）doped with 10%isooctyl side chain terephthalate monomer had the best performance,and when blended with the acceptor L8BO,the optimal device performance was obtained,with its PCE increased to 15.40%.P-0.9BDD-0.1（2+6）:Y6-based OSCs achieved the highest V_OC of 0.91 V.Further verified the regulatory effect of ester groups on the photophysical and electrochemical properties of semiconductor polymers,and even the impact of the photoelectric properties of OSCs.（3）By introducing an oxygen containing functional group ether bond into BDT monomer and inserting a methylene group between the oxygen atom and thiophene,the electron donor p-πconjugation effect of the oxygen atom is isolated,and the advantage of the high electronegativity of the oxygen atom is fully reflected,thereby regulating the frontier molecular orbital energy levels of the polymer.Four PM6derivatives PBDB-T-2H-（2+6）,PBDB-T-2H-（4+8）,PBDB-T-2Cl-（2+6）,and PBDB-T-2Cl-（4+8）were designed and synthesized.Through the characterization and analysis of their photophysical and electrochemical properties,it was found that the four polymers all have a deep HOMO level and a wide E_g^opt.The deepest HOMO level is-5.64 e V of PBDB-T-2Cl-（2+6）,and the widest E_g^opt is 1.84 e V of PBDB-T-2Cl-（4+8）.This provides an important theoretical and experimental basis for obtaining high V_OC.In this paper,through the study of polymer donor materials containing oxygen atoms,the influence of electronic effects of oxygen atoms on the photoelectric performance of OSCs was explored.The resulting devices all have a wider E_g^opt and lower HOMO energy levels,providing some reference significance for the further development of more efficient broadband gap polymer donor materials.