Synthesis Of Perylene Diimide Derivatives And Their Application In Organic Solar Cells

Recently,with the exploration of various non-fullerene electron acceptor materials?NFAMs?,fullerene-free organic solar cells?OSCs?have gained rapid development,which have been boosted to over 11%.This is comparative to or even better than that of fullerene-based OSCs.In various NFAMs,perylene diimide?PDI?derivative is one of the mostly focused basic units and promising alternatives to fullerene derivatives due to its facile modified structure,appropriate low-lying energy levels,high molar extinction coefficient,complementary absorptions with narrow band gap polymer donors,and high electron mobility.In order to suppress the interactions and aggregations of planar molecules,PDI-based acceptors usually adopt a twisted molecular geometry to facilitate nanoscale phase domain formation for high OSCs performance.Although evolving twisted dimer or 3D non-planar structures seems to be a efficient way for PDI derivatives,the reduced?-?stacking of PDI molecules weaken their electron-transporting capability to some extent.Therefore,the larger conjugated molecules with fused-ring structures are favorable for?-?stacking in the design of PDI acceptors,which would promote the charge transfer in OSCs device.Consequently,ideal PDI molecules should possess enhanced conjugation and molecular packing order for improving charge mobility,while maintaining nonplanar structure to suppress the formation of large aggregates.In the paper,based on molecule design strategy,a series of derivatives of PDI derivatives were synthesized.Their opical properties,electrochemical properties,photovoltaic properties were studied.1.We synthesized and characterized three simple PDI derivatives named EH-PDI,Ph-PDI and Ph-PDI-C as the research model to further study the influence of bay-benzo fused PDI on optical spectrum,electrochemistry,film morphology,crystallinity and photovoltaic properties.When used a benzo[1,2-b:4,5-b?]dithiophene?BDT?cored small molecule as donor,the bay-position functional modification of PDIs from EH-PDI to Ph-PDI further to Ph-PDI-C showed improved photovoltaic performances.This study mainly focused on the extended conjugation systems on the bay-mono-position of the PDI molecule.2.Four molecules 4-PP-PDI-C,4-HP-PDI-C,4-NP-PDI-C and 4-i PP-PDI-C with different alkyl chains were successfully synthesized.Their opical properties,electrochemical properties,photovoltaic properties were studied compared with Ph-PDI-C.Alkyl-chain length exhibited slightly effects on the optical and electrochemical properties.Meanwhile,we found that the molecule 4-i PP-PDI-C with the shortest isopropyl chain showed the best photovoltaic performance with a power conversion efficiency?PCE?of 1.25%.These results indicated that tuning the alkyl chain is an important way to influence on the thin-film morphology and molecular packing,and thus the photovoltaic performance.3.A three-dimensional molecules C8C8-TP-PDI₃-C based on bay-benzo fused PDI as peripheric units and benzene as core was synthesized and characterized.Their opical properties,electrochemical properties,photovoltaic properties were studied comparison with C8C8-TP-PDI₃.Fused C8C8-TP-PDI₃-C showed a stronger absorption band at 250-380 nm,which could be contributed to the fused phenyl units.In addition,it displayed much higher LUMO level.More importantly,it enhanced conjugation and molecular?-?packing order and successfully improved charge-transporting properties.The devices based on C8C8-TP-PDI₃-C and PTB7-Th showed a PCE of 3.93%after without any treatment,while the devices based on PBDB-T as donor showed an outstanding PCE of 4.89%.4.Besides the fused molecules,two dendritic oligothiophene cored PDI molecules 3T-PDI₂ and 6T-PDI₄ were synthesized and characterized.Their opical properties,electrochemical properties,photovoltaic properties were studied with compared with EH-PDI.Both 3T-PDI₂ and 6T-PDI₄ showed higher solubility in common organic solvents,and reduced the intermolecular packing in solid film.Organic solar cells using these 3D non-planar PDI molecules as the electron acceptor and a low-bandgap polymer PTB7-Th as the donor were fabricated and tested.A PCE of 4.12%was obtained for the 6T-PDI₄ based device,which is higher than that of 3T-PDI₂ based device?3.41%?.