Design,Synthesis And Photovoltaic Properties Of Small Molecular Donors Based On Benzothiadiazole Units

Organic solar cells(OSCs)are an important part of the organic photovoltaic field,they are made of Tin Oxide(ITO)conductive glass,anode buffer layer,active layer,cathode interface modification layer,and metal electrode.Recent years,because of OSCs have the advantages of being prepared by solution method,wide sources of materials,good processing performance,low preparation cost,and large-area device by printing method,have attracted more and more researchers'attention,and power conversion efficiency(PCE)continues to improve.Now,PCE(12.08%)based on all small molecule organic solar cells(SM-OSCs)still behind OSCs based on polymer donors and small molecule acceptors,there are still further work to improve PCE.In this paper,we designed and synthesized a series of wide bandgap small molecule donors with a benzothiadiazole-containing?bridge,and SM-OSCS were prepared to study theirs photovoltaic performance.The main works of this paper are follow:1.Eight small molecule OSCs donor materials(D1?D2?D3?D4?D5?D6?D7?D8)were synthesized by Rhodamine acetate 2-ethylhexyl ester,rhodamine acetate n-octyl ester,2-ethylhexyl cyanoacetate and n-octyl cyanoacetate as end group,benzo[1,2-b:4,5-b']dithiophene substituted with alkyl-thiophene as the core,benzothiadiazole with two oxyalkyl chains(2-ethylhexyl and n-octyl)coupled two thiophenes as?bridge.The optical properties were analyzed by UV-Vis spectroscopy.The thermal stability and crystallinity of eight small molecule donors were studied by thermogravimetric analysis and differential scanning calorimetry.Cyclic voltammetry curves of eight small molecule donors were tested by cyclic voltammetry to calculate the corresponding highest occupied molecular orbital(HOMO)and lowest unoccupied molecular orbital(LUMO).2.SM-OSCs devices based on eight small molecule donors were prepared by solution method and vacuum deposition technique.The photovoltaic performance,semiconductor performance and film morphology of SM-OSCs with different donors were characterized,the corresponding circuit density-voltage curves and external quantum efficiency curves were tested to calculate the photovoltaic parameters of the corresponding SM-OSCs devices.The correlation results show that after the introduction of benzothiadiazole,the small molecule donors have a wide band gap,and their absorption spectrums can form a good light absorption complementary with the non-fullerene acceptor IDIC-4F.SM-OSCs based on small molecule donor D8 and acceptor IDIC-4F,the mass ratio is 1:1,and carbon dioxide disulfide solvent annealing treatment for 30s,got best device efficiency with PCE 6.87%,and the open circuit voltage is 0.85V,the short circuit density is 15.16 mA/cm~2,the fill factor is 0.54.