Synthesis And Photovoltaic Properties Of Organic Small Molecular Acceptors Consisting Of Perylene Diimide

In recent years,with the continuous development of non-fullerene materials,the efficiency of non-fullerene organic solar cells has exceeded that of fullerene organic solar cells.Non-fullerene electron acceptors can be classified as polymer acceptors and small molecule acceptors.Compared with polymers,small molecules have the advantages of definite molecular weight,accurate structure and easy purification.Perylene diimide?PDI?,as one of the earliest electron acceptor materials for non-fullerene solar cells,has attracted much attention due to its unique molecular structure,easy chemical modification,adjustable energy levels and spectral complementarity with narrow bandgap polymers.However,PDI has a strong rigid conjugate planar structure,which is easy to aggregate and crystallize in the fabrication of bulk heterojunction devices,which limits the improvement of device efficiency.Many researchers have designed and synthesized of highly distorted molecular structures to reduce the aggregation,however,weakened the charge transfer ability.Therefore,the design of highly efficiency PDI small molecule acceptor should not only maintain a certain distorted configuration to reduce aggregation,but also ensure that its conjugated system enhances the charge transfer ability.In this study,the latest research progress of non-fullerene acceptors in bulk heterojunction solar cells is reviewed.We are analyzed the properties of these materials from the molecular structure and discussed the design strategies of the active layers.Four PDI small molecule acceptors were designed and synthesized by considering of absorption spectra,molecular energy levels,solubility,electron/hole mobility and phase morphology.The synthesized intermediates and target molecules were characterized by NMR,MALDI-TOF-MS and elemental analysis,respectively.The main contents of this paper are as follows:?1?Three non-fullerene small molecule acceptors?T-PDI,S-PDI and R-PDI?were designed and synthesized by three bridging modes?carbon-carbon triple bond,carbon-carbon single bond,ring fusion?based on truxene as core and perylene diimide as arms.The effects of the three modes on the photophysical,electrochemical and photovoltaic properties of acceptors were studied fully.The results show that the bridge between the central core and the electron-deficient unit plays an important role in the photovoltaic performance of non-fullerene small molecule acceptors.The cyclized R-PDI has the best photovoltaic performance,suitable microphase separation and high electron mobility.After adding 1%chloronaphthalene additive,the organic solar cell devices based on PTB7-Th:R-PDI exhibit 4.19%optimal power conversion efficiency?PCE?and 1.0 V high open-circuit voltage?VOC?.?2?A strong rigid conjugated star-shaped small molecule B-4TPDI with pyrene as the central core was developed.The effects of acetylene bridge on photophysical,electrochemical and photovoltaic properties of perylene diimide acceptors were systematically studied.The results show that the three small molecules have strong absorption in the range of 300-700 nm,which is conducive to the formation of complementary absorption with narrow bandgap polymer donors,thereby improving the short circuit current density(J_SC).When blended with donor polymer PTB7-Th,organic solar cell devices exhibit 7.71%optimal PCE and 18.13 mA cm^-2 high J_SC.Subsequently,we added B-4TPDI as the third component to PTB7-Th:ITIC and PBDB-T:ITIC binary system to fabricate ternary organic solar cells,obtained 8.76%and 10.93%PCE respectively,which significantly increased the short-circuit current density of the original binary cells.