Synthesis And Photovoltaic Performance Study Based On Indoline Types Sensitized Dyes

Because of the low cost,flexible modification and high photo-electricity conversion efficiency,dye-sensitized solar cells?DSSCs?have attracted considerable attention and it has been considered as the powerful competitor to the silicon cell.Sensitizing dye that absorbs sunlight to excite a photoelectron is an indispensable component in order to achieve high photo-electricity conversion efficiency in DSSCs.Nine novel indoline-type dyes were synthesized with indoline and its derivatives as donor,double bond,phenyl,furan,thiophene or 4-phenyl-2-thiophen-thiazole as ?bridge and cyanoacetic acid as acceptor.Their structures were characterized with NMR and LC-MS.Their spectral properties,electrochemical properties and photovoltaic performance were measured and investigated systematically and the structure-property relationship was analyzed.Firstly,four novel indoline-type sensitizing dyes WB-1^WB-4 were synthesized with N-fluorenyl-indoline donor,? bridge containing double bonds,phenyl,furan or thiophene and cyanoacetic acid acceptor.Phenylhydrazine reacted with cyclonpentanone by Fisher indole synthesis to produce indole;After Pd-C catalytic hydrogenation,indoline derivative was obtained and reacted with 2-bromofluoene by nucleophilic substitution to synthesize N-fluorenyl-indoline.An aldehyde group was introduced on the benzene ring of N-fluorenyl-indoline via Vilsmeier reation,then WB-1 was synthesized through Knoevenagel condensation between the aldehyde andV cyanoacetic acid.On the other hand,N-fluorenyl-indoline was brominated by NBS to get the bromide.The bromide was coupled with 4-formyl phenylboronic acid,5-formyl-thiophene-2-boronic acid and 5-carboxaldehyde-2-boronic acid,respectively,to get aldehydes.Then aldehydes reacted with cyanoacetic acid by the Knoevenagel condensation to give WB-2^WB-4.Amongst dyes WB-1^WB-4,WB-4 with N-fluorenyl-indoline as donor,thiophene as ? bridge and cyanoacetic acid as acceptor showed the best photoelectric conversion efficiency 5.89%(JSC=13.88 mA�cm^-2,VOC=0.65 V,ff=0.66).Secondly,four novel indoline-type sensitizing dyes WB-5^WB-8 were synthesized with indoline or its derivatives as donor,4-phenyl-2-thiophen-thiazole as? bridge and cyanoacetic acid as acceptor.N-phenyl-indoline was synthesized by the nucleophilic substitution reaction between indoline derivative and bromobenzene and then brominated and converted to boronate ester.Then the boronate ester reacted with4-phenyl-2-thiophen-thiazole by Suzuki coupling to introduce ? bridge.The aldehyde was obtained by Vilsmeier reaction and WB-5 was synthesized through the Knoevenagel condensation reaction between the aldehyde and cyanoacetic acid.On the other hand,indoline derivative reacted with 4-phenyl-2-thiophen-thiazole by nucleophilic substitution on N atom in order to introduce ? bridge.After Vilsmeier reation,the intermediates with one aldehyde group and double aldehydes were obtained.WB-6 was synthesized by the Knoevenagel condensation between the intermediate with one aldehyde group and cyanoacetic acid.The intermediates with double aldehydes reacted with cyanoacetic acid by the Knoevenagel condensation to give WB-7 with one carboxylic acid and WB-8 with two carboxylic acids,respectively.Among these compounds,WB-7 with indoline derivative containing aldehyde group as donor,4-phenyl-2-thiophen-thiazole as ? bridge and cyanoacetic acid as acceptor exhibited the highest photoelectric conversion efficiency 4.29%(VOC= 0.66 V,JSC = 8.12 mA�cm^-2,ff = 0.81).Thirdly,WB-9 was synthesized with N-phenyl-indoline donor,an additional coumarin donor,thiophene bridge and cyanoacetic acid acceptor.N-phenyl-indoline was brominated and then converted to boronate ester.Then the boronate ester reactedwith 6-bromo-3-thiophene coumarin by Suzuki coupling to introduce the additional coumarin donor and thiophene bridge.After Vilsmeier reaction to introduce the aldehyde group,WB-9 was synthesized between the aldehyde intermediate and cyanoacetic acid through the Knoevenagel condensation.Compared with ZX which has the similar structure with coumarin donor linked on the N atom of indoline,WB-9shows better photoelectric conversion efficiency 5.47%(VOC = 0.72 V,JSC = 11.09mA�cm^-2,ff = 0.68).