Syntheses And Photovoltaic Performance Of Perylene Diimides Polyploids

In recent years,the efficiency of bulk heterojunction(BHJ)organic solar cells(OSCs)based on narrow band gap polymer donors and non-fullerene small molecule acceptors have been rapidly improved,which indicates that the development of new organic semiconductor materials has become the dominant breakthrough for OSCs.A large number of narrow band gap conjugated polymers as novel electron donors have been developed,but the researches on electron acceptors are relatively lagging.Therefore,the current focus is being directed toward the development and application of novel electron acceptor materials with novel structures and excellent properties.Perylene diimides(PDI)derivatives as a class of non-fullerene electron acceptor materials have potential in research and application.In this research,six kinds of PDI diploids with different connecting positions,connecting methods and monomer structures were designed and synthesized to explore their photovoltaic performance.Aryl-bisalkynyl bridged and oxygen-ether bridged PDI diploids exhibit strong crystallinity and unbalanced carrier transporting properties,which limit the improvement of the photovoltaic performance for these materials.The PDI diploids with different postions connecting two PDI monomers show good absorption properties of visible light,suitable energy levels and weak crystallinity.And the best power conversion efficiency(PCE)of orthe-ortho PDI diploid is up to 8%.Three other kinds of PDI diploids with different side chains on PDI monomers were also designed.It was found that long alkyl side chains affect the carrier transporting porperties of the blended films and thus influence on the PCE in OSCs.Since the directly connected PDI diploids exhibit excellent photovoltaic performance,and the PDI polyploids show higher electron mobilities and more excellent phase separation morphology,nextly,three larger conjugated PDI polyploids were developed to explore the effect of the different ploidy numbers to the photovoltaic performance.Compared with bay-ortho PDI diploid,ortho-bay-ortho PDI triploid has an extended conjugate skeleton and distorted molecular structure,which is favorable for adjusting the morphology of the blended films to improve photovoltaic performance.The blended films for bay-bay-bay PDI triploid exhibit excellent phase separation morphology and the balance of carrier transporting properties,so the optimized PCE is up to 7.12%.By establishing a symmetric conjugate framework containing a thiophene unit,the charge separation efficiency and carrier transporting properties of the blended films can be effectively improved.The best PCE based on the linear-conjugated and ladder-conjugated PDI tetraploids were 7.17%and 8.13%,respectively.Two ladder-conjugated PDI tetraploids were designed and synthesized by two intramolecular ring-closure reactions between PDI monomers and a thiophene unit.Two ladder-conjugated PDI tetraploids have larger conjugation systems and stronger intermolecular interactions,and thus exhibit better electron transporting properties.In conclusion,we design and synthesize novel larger conjugated PDI polyploids,which are used as electron acceptor materials in OSCs with effectively improved PCEs.