Synthesis And Photovoltaic Properties Of Organic Photovoltaic Materials Based On Spiro (Cyclopentadithiophenefluorene) And Thiophene-annulated Azepine

In recent years,organic solar cells(OSCs)have been developed rapidly,and their energy conversion efficiencies(PCEs)have been improved steadily.Among them,organic small molecule/polymer donor materials and non-fullerene small molecule acceptor materials have been received more and more attention due to their excellent photovoltaic performance.In this dissertation,we designed and synthesized organic small molecules/polymer donor materials and non-fullerene small molecule electron acceptor materials.The thermal stability,photophysical,electrochemical and photovoltaic properties of these small molecules and polymers were inverstigated in detail.The main research work is as follows:1.We have designed and synthesized two A-π-D-π-A type small molecular donor materials(SFThYT and SFTh RDN),where spiro[cyclopenta[1,2-b:5,4-b′]-dithiophene-4,9′-fluorene](SF)and alkylthiophene were used as the central don or unit and the π-conjugated bridge,indenedione and 3-ethylrhodanine were em ployed as the terminal acceptor unit,resepectively.The effects of the monothio phene π-conjugated bridge and different acceptors on the molecular configuratio n,absorption properties,electronic energy levels,carrier transport properties,the morphology of active layers,and photovoltaic properties are investigated in de tail.Solution-processing organic solar cells(OSCs)based on the two small mol ecules and PC70 BM have been fabricated.After optimization,power conversion efficiencies(PCEs)of 6.17% and 2.33% were obtained for SFThYT and SFT hRDN,respectively.Moreover,both of OSCs based on two small molecular m aterials showed rather high VOC up to 1 V.2.We designed and synthesized a non-fullerene small molecular acceptor material SFIC,in which spiral SF and dicyanon indanone were used as the centeral donor unit and the terminal acceptor unit,respectively.The thermal stability,photophysical and electrochemical properties of SFIC were studied,and the primary photovoltaic properties of the bulk heterojunction OSCs were investigated with SFIC as acceptor material and low-bandgap PTB7-Th as donor material.The results showed that the SFIC had a broad absorption spectrum(300-800 nm)and a low-lying bandgap(1.38 eV),which is complementary to the absorption of PTB7-Th in the longwavelength band.At the same time,SFIC has a relatively high LUMO level,indicating a high VOC should be achieved in non-fullerene OSCs.A primary PCE of1.08% has been obtained based on non-fullerene OSCs with SFIC/PTB7-Th as the active layer.3.We designed and synthesized five conjugated polymers based on thiophene-annulated azepine unit,which can be assgined as D-D type(PAPTh,PAPDTh and PAPBDT)and D-A type(PAPBT and PAPDPP).The thermal stability,photophysical and electrochemical properties of these two polymers were studied comparatively.All the polyemers showed excellent thermal stability and solubility.The absorption spectra and molecular energy levels can be fune tuned by copolymerization with various the electron-donating and electron-withdrawing units.The results showed that D-A copolymers had broader absorption spectra than that of D-D conjugated polymers.The as-synthesized D-A polymers could be used as the donor materials in fullerene-based OSCs,whereas the D-D polymers could be expected to empolye as non-fullerene-based OSCs due to their relatively narrow absorption ability.OSCs based on PAPDPP showed a primary PCE of 0.51%.