Asymmetric Small Molecule Acceptors:Syntheses And Photovoltaic Properties

There are a variety of organic photovoltaic material synthesis methods.Therefore,it is considered as a promising candidate for next-generation photovoltaic technology.But at present,its low efficiency,high cost,poor stability,and inability to put it into commercial use are still the key research issues in the field of organic photovoltaic materials.Solution-processed organic solar cells have shown great potentials as new energy sources due to their low cost,large area,and lightweight manufacturing.In the past few decades,p-type conjugated polymers and n-type fullerene derivatives have been the most commonly used electron donors and electron acceptors,respectively.Although the device performance mostly comes from the design of new polymer donors,the electron acceptors in organic photovoltaics are dominated by fullerene acceptors.However,the fullerene derivatives suffering from the drawbacks of difficult synthesis high cost and narrow absorption has greatly limited the further improvement of organic solar cells.In recent years,non-fullerene acceptor materials(NFAs),especially organic small molecules and oligomers have become promising alternatives to fullerene counterparts.At present,most of the studies of ITIC-like small molecule acceptors are focus on the symmetrical configuration,and corresponding PCE is generally lower than 15%.In order to further improve the PCE,asymmetric NFA is a good choice.Asymmetric NFA can not only be distinguished from symmetric NFA in structure,but also can increase the molecular dipole moment and dielectric constant,reduce the exciton binding energy,and optimize the energy level distribution and morphology,which is very beneficial for the exciton dissociation and charge transmission.At the same time,perylene diimides(PDIs)have attracted much attention due to their strong electron affinity,high electron mobility,excellent chemical and photothermal stability in optoelectronic fields.Among diverse structural functionalizations,heteroannulation at bay is a fascinating strategy to fine-tuning their electronic structures and energy levels.Heteroatom-decorated PDIs,especially chalcogen-annulated PDI derivatives exhibited synthetic accessibility and fascinating properties.We modified it by inserting three S atoms in one step at the bay position of the parent PDIs,and synthesized a variety of such materials to improve the electron mobility.Based on the above considerations,our main work is as follows:(1)Three asymmetric small molecule receptors with dithienopyrrole as the core.and dicyanoindanones with different chlorine atoms as terminal groups were designed and synthesized.Namely,TPIC,TPIC-2Cl and TPIC-4Cl contain 0,2 and 4 chlorine atoms,respectively.We have studied in detail the effects of heteroatoms on the photophysical,electrochemical,active layer morphology,charge transport,and photovoltaic properties of such materials.As the chlorine atoms gradually increase(0,2 to 4),these asymmetric acceptors show a gradually red-shifted absorption spectrum.Due to the gradual increase ofchlorine atoms,HOMO and LUMO move down little by little,and crystallinity gradually increases.Blended with polymer donor PM7 to prepare organic solar cells(OSC),PM7: TPIC-4Cl achieved a PCE of up to 15.31%,which is the highest PCE based on asymmetric SMA.(2)A one-step preparation of trisulfide-condensed PDIs using mononitrated PDIs and sulfur powder was designed and synthesized.The structural characterization and performance of organic field effect transistors(OFETs)were studied in detail.