| Organic solar cells(OSCs)as a new type photovoltaic technology have attracted wide attention due to their advantages of lightweight,flexibility,colour-tunable and compatibility with large-area printing fabrication.Improving the energy conversion efficiency(PCE)is the primary goal for OSCs and also the key to its commercialisation.To deeply investgate the relationship between molecular structure and device performance,and then to design novel high-performance active layer materials are effective ways to enhance PCE.In this study,we focused on the design of small molecule donors and polymer donors,using side chain optimization and terpolymerization strategies respectively to adjust their absorption spectra,molecular energy levels and aggregation characteristics.Besides,the relationship between molecular structure and photovoltaic performance was systematically investigated.The key research results are as follows.(1)A novel small molecule donor,BTR-SC1,with alkylthio and chlorine substitutions on the side-chains was designed and synthesized.BTR-SC1 exhibits strong absorption in the wavelength range of 400～700 nm with a low-lying highest occupied molecular orbital(HOMO)energy level of-5.51 eV.The molecule also exhibits ordered molecular stacking and strong crystalline properties.The PCE of BTR-SC1:Y6-based devices reached 14.6%,which was further increased to 15.8%after 4 wt%PM7 was introduced into the BTR-SC1:Y6 system as a morphology modulator.(2)PM7-Tz20 and PM7-Tz50 were synthesized via ternary polymerization strategy by incorporating different content of thiophene-bithiazole(BTz)unit as a third component into the PM7 backbone.Due to the presence of C=N double bonds and N…S non-covalent interactions,BTz exhibits better planarity and is able to inhibit the damage to the main chain by random ternary polymerized to a certain extent.When the BTz content is 20%,the π-πstacking and the ordering of molecular packing of the blend film are improved,forming an ideal continuous interpenetrating network morphology.As a result,a high PCE of 18.0%was obtained from PM7-Tz20:Y6 solar cells with a Voc of 0.84 V,a Jsc of 27.2 mA cm-2,and an FF of 78.6%.Notably,polymer PM7-Tz20 also displays excellent batch-to-batch reproducibility. |
