Organic Solar Cell Device Optimization For Ladder Typed Polymer Donors And Small Molecule Acceptors

Solar energy is a promising clean and renewable energy due to the low cost,inexhaustible,environmental friendly etc.Organic solar cells(OSCs)offer great opportunities asrenewable energy sources due to their attractive features,including low-cost large area fabrication,lightweight,and goodmechanical flexibility when compared with the traditional silicon based solar cells.Recently,ladder typed building blocks,in which aromatic rings and/or heteropoly rings are bonded with a carbon-carbon double bond into a "ladder" shape,have been widely utilized in organic solar cells.Such structure bearing extended conjugation length,which could facilitate the delocalization of electrons,reduce the intramolecular degree and improve the charge transport performance.So,in this thesis,ladder typed polymer donors and small molecules are designed and detailed optimization for organic solar cell devices have been processed as following: Part I.The Study of Photovoltaic Properties of New Conjugated Polymers Based on the Indacenodithiophene(IDT)Firstly,two novel conjugated polymers PIDT-TPD and PDMIDT-TPD based on ladder type building blocks were designed and synthesized.Compared with IDT,DMIDT possessestwo ethylene bridges at the side direction between the main chain and the aryl side chain,which can effectively reduce the molecular recombination energy and improve the charge carrier properties.Such rigid structure also helps to improve the crystallinity of the material and produce the preferred topography of the active layer.In this section,PC71 BM and ITIC were selected as the electron acceptor in the active layer and the device performances were optimized by changing the ratios of the donors and acceptors,additives type and concentration,annealing processing and interface modification etc.Finally,the best efficiency of up to 8.26% was achieved based on the polymer PDMIDT-TPD.Part?.The Study of Photovoltaic Properties of Novel Conjugated Polymers Based on the "Ladder" Structure Containing Two Pyran Units(BDTP)Secondly,a novel "ladder" structure containing two pyran units(BDTP)were designed and compared to the other two pyran-based units i.e.dithienopyranopyran(DTP)and dibenzopyran(DBP).The new building block BDTP could effectively increased the conjugate length and broadens the UV absorption for thefinal materials in the visible region,and its planar structure facilitates the stacking of molecules and improves the charge transport performances.By utilization of the BDTP building block,four novel conjugated polymers PBDTP-BT,PBDTP-DTBT,PBDTP-DTFBT and PBDTP-DTDFBT were synthesized;the effects of thiophene bridges and the introduction of the F atom on the polymers properties studied.When the F atom is introduced,it can effectively adjust the energy level of the material and improve the open circuit voltage of the device;it can alsoform F···H and F···S supramolecular interactions in the molecule to improve the planar backbone formation.PC71 BM was selected as the acceptor material for the photovoltaic properties investigation and similarly,they were optimized by changing the ratios of the donors and acceptors,additives type and concentration,annealing processing and interface modification etc.Finally,the polymers PBDTP-DTFBT and PBDTP-DTDFBT show good photoelectric properties and the best PCE reached 7.26%.Part?.The Study of Photovoltaic Properties of Novel Small Molecule acceptors Based on the "Ladder" Structure FTICFinally,three new ladder typed small molecules(FTIC-C8C6,FTIC-C6C6 and FTIC-C6C8)were designed,synthesized and the different chain lengths of the side chains was changed to analyze the regulation on the phtotovoltaic performance.The polymer PBDB-T was chosen as the donor material and the photovoltaic properties were studied in inverted devices.The device performance was were optimized by changing the ratios of the donors and acceptors,additives type and concentration,annealing processing and interface modification etc.When adding 0.5% DIO,the efficiency of FTIC-C6C8 reached 10%.When the interface layer PFN-Br was used on the Zn O interlayer,the efficiency of the device can be further increased to 11.12%.