Synthesis And Properties Of Diketopyrrolopyrrole And Benzotriazole Based Small Molecular Photovoltaic Donors

It is very important to develop novel organic small molecular photovoltaic materials for exploring the relationship between the structure and the property and improving the power conversion efficiency(PCE)of the devices.Herein,fifteen novel organic-small-molecule(OSM)-based donors were designed and synthesized successfully,which all contained diketopyrrolopyrrole(DPP)and benzotriazole(BTz)as central acceptor unit.In addition,different end-capping units and various 7r-linkages were used to investigate their between structure and photovoltaic performance.The contents are as follows:Firstly,to nvestigate the influence of triple bond and end-cappping groups on photovoltaic properties,four DPP based OSMs were designed and synthesized successfully,consisting of carbazole and fluorene as terminal electron-donating groups,respectively,single or triple bond as ?-linkage,respectively.In contrast,the triple-bond-linkage structural design could not only lower the highest occupied molecular orbital(HOMO)levels and enhance the planarity,but also delicately balance the relationship between the deep-lying HOMO and narrow band gap(Eg),thus improving the photovoltaic performance.In addition,materials with fluorine as end-capped groups presented a decerease of HOMO levels,resulting in an increased open-circuit voltage(VOC)caused by the relatively weak electron-donating ablity of fluorine unit.Secondly,to systematically investigate the linkage effect of compounds,four novel OSMs have been synthesized successfully,consisting of DPP as electron-withdrawing group,and triphenylamine(TPA)as electron-donating unit.In addition,four ?-linkage units,single bond,double bond,triple bond and acrylonitrile were introduced in these synthesized compounds.Among them,with double bond as ?-linkage could not only increase the HOMO levels and deepen the LUMO levels,leading to a narrow Eg,but also enhance the molecule coplanarity and broaden the absorption ranges,facilitating the intramolecular charge transfer(ICT)interaction,and thus increasing the short current intensity(JSC).With triple bond as ?-linkage could not only lower the HOMO and lowest unoccupied molecular orbital(LUMO)levels,but also balance the relationship between the low-lying HOMO and narrow Eg,thus increasing the VOC and the Jsc.With acrylonitrile as ?-linkage could also lower the energy levels and Eg,while the cyano groups on double bond decreased the coplanarity which hindered the ICT transition,thereby affecting the improvement of photovoltaic performance.Thirdly,three OSMs were designed and synthesized successfully,consisting of monofluorinated BTz as electron-withdrawing group,and TPA as electron-donating unit.In addition,the synergistic effect between fluorine atom and ?-linkage was investigated to obtain devices with high VOC.Among them,the fluorine atom and double-bond exhibited a synergistic effect on increasing the coplanarity and absorption ability,and decreaing the Eg,which improving the Jsc;the fluorine atom and triple-bond exhibited a synergistic effect on decreaing the HOMO level efficiently,resulting in an increased VOC,and thus achiving the design purpose of high VOV.Finally,three novel A'-A-A' type DPP-based molecular donors with deep-lying energy levels and narrow Eg were successfully designed and synthesized.in addition,a new D-A-D type donor was also synsthsized as a reference molecule.The relationship between molecular structure and property was deeply investigated by theoretical and experimental studies.As a result,A'-A-A' type materials could not only lower the HOMO and LUMO levels,but also improve the charge transfer properties,giving rise to improving the photovoltaic display of OSM solar cells.