Synthesis Of Non-fused Ring A-D-A Small Molecules And Photovoltaic Performance In Ternary Devices

The growing demand for renewable energy has promoted the rapid development of photovoltaic technology in the current era.Organic solar cells（OSCs）have attracted the attention of many researchers due to their clean energy characteristic.At present,the power conversion efficiency（PCE）of single-junction OSCs has exceeded19%,and it is still the research focus to improve PCE values of the OSCs.Among the many reported optimization strategies,ternary blending devices,introducing a third component to enhance the light absorption ability of the active layers,adjustment the energy level arrangement and optimize the microphase separation morphology of the active layers,are proved to be a simple and efficient strategy to improve photovoltaic performance of OSCs.Accordingly,serial small molecular donor and acceptors with non-fused structure have been designed and synthesized by brief synthesis process,which have been introduced to the classic binary blend（PM6:Y6）to fabricate high-performance ternary organic solar cells.The main research contents are shown as follows:1)Two A-D-π-D-A type small molecule acceptors DBD-4F and DBD-IC have been designed and synthesized with di（alkoxyl）benzene as the core,dithieno[3,2-b:2’,3’-d]pyrrole（DTP）as the conjugatedπbridges,2-（5,6-difluoro-3-oxo-2,3-dihydro-1H-inden-1-ylidene）malononitrileand3-（dicyanomethylidene）indan-1-one as the terminal groups,respectively.The noncovalent conformational lock between di（alkoxyl）benzene derivative and two DTP units would help two small molecules to form coplanar conformation as fuse structure.A series of binary and ternary OSCs have been fabricated by introducing DBD-4F as the third component to the PM6:Y6 blend films and adjusting the proportion of DBD-4F in the acceptor materials.Compared with the binary OSCs,the ternary OSC with 10 wt%DBD-4F（PM6:DBD-4F:Y6=1:0.1:0.9）shows a larger open-circuit voltage(V_oc)of 0.856 V because of the high-lying LUMO energy level of DBD-4F,and it also presents a larger fill factor（FF）of 73.11%because DBD-4F results in a optimized morphology,more efficient exciton dissociation,higher charge mobilities and less charge recombination.Therefore,the ternary OSC show a higher PCE of16.99%.2)An asymmetric small molecule donor TTBT-R,incorporating4,5-di（2-ethylhexyl）oxybenzo[2,1-b:3,4-b’]dithiopheneasthecore,undecylthieno[3,2-b]thiophene and hexylthiophene asπ-conjugated units and ethylrhodanine as the terminal groups,was designed and synthesized,which was used to fabricate high-performance ternary OSCs and study the effects of the asymmetric donor on performance of TOSCs.TTBT-R possesses complementary absorption band and cascaded energy levels with PM6 and Y6.The ternary blend film（PM6:TTBT-R:Y6=0.9:0.1:1）attains the most optimized morphology with nanofiber-like structure and small domain size as well as strong face-on molecular packing,which leads to the most balanced charge transport,highest charge mobilities and least charge recombination in its device.In addition,TTBT-R possesses lower-lying HOMO energy level than PM6,which brings about higher V_oc in ternary OSCs.Accordingly,the ternary OSC with 10 wt%TTBT-R achieved a PCE of 18.07%due to comprehensively improved V_oc（0.863 V）,J_sc(27.38 m A cm^-2),and FF（76.46%）values compared with the PM6:Y6 binary OSC.This work provides not only a small molecule with 4,5-dialkyloxybenzo[2,1-b:3,4-b’]dithiophene as the core but also an asymmetric strategy with non-fused structure to tune molecular packing,energy levels and absorption spectrum of small molecule for constructing high-performance ternary OSCs in first time.