Synthesis And Device Performance Of Imide-based Non-fused Small Molecule Acceptors

For the past few years,organic solar cells（OSCs）have attracted widespread attention because of their many advantages,such as light weight,flexibility,translucency,and solution processability.With the successful introduction of non-fullerene acceptors with fused ring structures,OSCs have achieved remarkable results with power conversion efficiencies（PCE）of over 19%.However,the complex synthesis steps and high production costs of fused ring non-fullerene acceptors limited the development of OSCs.In this thesis,we prepared a series of highly efficient non-fused ring small molecule acceptors（NFRAs）with imide as the core,and systematically investigated the relationship between molecular structures and device performance,which provides new ideas for the construction of highly efficient organic solar cells.Details of the research results are as follows:1.By central core engineering,non-fused ring small molecule acceptor LA1 with a maleimide A’core and a thiophene as a separateπ-bridge to the cyclopentadienyl dithiophene（DTS）conjugated D-π-A’-π-D unit,and malononitrile as the end groups,and LA2 with a non-fused ring small molecule acceptor with the fused benzothiophene phthalimide as the A’core was synthesized.The experimental results show that LA1,the acceptor molecule with an unfused central core,has the lower highest occupied molecular orbital（HOMO）energy level and a higher lowest unoccupied molecular orbital（LUMO）energy level.When PM6 was selected as the polymeric donor material,the PM6:LA2-based device exhibited more balancedμ_h/μ_e value and suppressed bimolecular recombination,resulting in a short-circuit current density(J_SC)of 18.02m A cm^-2 and a fill factor（FF）of 0.584.Consequently,an impressive PCE of 9.62%was achieved,much higher than that of 4.99%for PM6:LA1 based devices.In addition,LA2 has higher intermolecular interaction parameters with PM6,allowing for a better active layer morphology.The results suggest that the design and development of novel central nuclear groups is important for the construction of non-fused ring small molecule acceptors.2.A long conjugated backbone non-fused ring small molecule receptor LA3 was designed and synthesized with a benzothiophene phthalimide core,tetrahexyl-indacaprobamate dithiophene（IDT-C6）as the electron donating units and chlorine-atom-substituted malononitrile as the electron-absorbing end groups.IDT-C6 exhibited appropriate energy level and absorption spectrum with PM6,the OSC device based on PM6:LA3 achieved 10.54%PCE and a high short-circuit current density of 16.49 m A cm^-2.This is mainly attributed to the effective inter-chainπ-πstacking of IDT unit and the strong intramolecular O…S interactions that give LA3 a better coplanar structure,which facilitates the ordered molecular stacking and efficient electron transport in the PM6:LA3 devices.It is shown that extending the molecular conjugate skeleton can effectively improve the charge transport capacity to obtain a high power conversion efficiency.