Molecular Engineering And Photovoltaic Properties Of Three Kinds Of Fused-Ring Electron Acceptors

Solar energy may be the most ideal,safe and renewable clean energy for future human beings.The application of solar energy is one of the optimal ways for future human society to solve energy and environmental problems.Solar cells directly convert light energy into electric energy through photoelectric effect.They are the most common and effective form of converting solar energy into electric energy in current time.At present,commercial solar cells are mainly inorganic semiconductor solar cells that rely on silicon panels to realize photoelectric conversion.However,their disadvantages such as high production cost,complex preparation process and serious pollution hinder the development and popularization of solar cells.Organic solar cells can make up for the disadvantages of inorganic solar cells due to their advantages of light texture,low processing cost,large area preparation and good mechanical processing performance.In recent years,organic solar cells（OSCs）have achieved rapid development due to the development of a large number of new donor and receptor materials and the research on device physics.In this paper,several series of aromatic polycyclic non-fullerenes small molecular acceptor materials were designed and synthesized,and their optical and electrochemical properties,charge transfer and photovoltaic properties were systematically studied.The main contents can be summarized as follows:In Chapter 2,two novel dithieno[3,2-b:2,3-d]pyrrol fused-ring electron acceptors（FREAs）with branched alkyl side-chains have been developed.With 2-ethylhexyl and 2-butyloctyl introduced on N-position of pyrrol unit,the side-chain engineered acceptors（INPIC-EH and INPIC-BO）were evaluated for OSCs by comparing with our reference INPIC-4F featuring a linear octyl side chain.The results show that the absorption width and intensity of the three receptors and the energy levels are basically unaffected.Noteworthy,side-chain engineering has a large impact on the film morphology of active layers which influence the processes of exciton dissociation,charge collection and recombination thus result in the change of photovoltaic performance.In Chapter 3,two novel nonfullerene acceptors（NFAs）featuring 5,5,12,12-tetra-（4-hexylphenyl）-inducing bis-（dithieno[3,2-b:2’,3’-d]pyrrole）（INP）core with meta-or para-alkoxyphenyl sidechains are designed and denoted as m-INPOIC or p-INPOIC,respectively.The impact of alkoxyl group positioning on molecular orientation and photovoltaic performance of NFAs is revealed through a comparison study with the counterparts bearing para-alkylphenyl（INPIC-4F）sidechains.The OSCs by blending m-INPOIC and PBDB-T as active layers exhibit a power conversion efficiency（PCE）of 12.1%without any processing additive or post-device treatment.By introducing PC₇₁BM as the solid processing-aid,the binary OSCs was further optimized to deliver an impressive PCE of 14.0%,which is among the highest PCEs for as-cast single-junction OSCs reported in literature to date.More attractively,PBDB-T/m-INPOIC/PC₇₁BM based OSCs exhibit over 11%PCEs even with active layer thicker than 300 nm.And the devices can retain over 95%PCE after a storage for 20 days.In Chapter 4,a conjugated small molecule electron acceptor material FBDT-IC has designed and synthesized,with a hepta-fused ring unit of benzo[1,2-b:5,4-b’]dithiophene（aBDT）as the core,and the electron-withdrawing unit 2-（3-oxo-2,3-dihydro-1H-inden-1-ylidene）malononitrile（IC）as the end-group.The organic solar cell with FBDT-IC as the acceptor material exhibits high power conversion efficiency（8.63%）.It is worth mentioning that the V_OC of the device reaches 0.98 V.It indicates that the new designed electron donating unit which based on benzo[1,2-b:5,4-b’]dithiophene is a better electron donor for non-fullerene small molecule acceptor materials.