Application Of Novel Redox Couples And Phenoxazinc Dyes In Dye Sensitized Solar Cells

The subject of this dissertation is the redox couple and sensitizers in dye-sensitized solar cells（DSSCs）.In order to reduce the large loss-in-potential in the process of dye regeneration,the redox couples of[copper（6,6’-dimethyl-2,2’-bipyridine）₂]2+/1+（[Cu（dmbp）₂]2+/1+）and 2-Phenyl-4,4,5,5-tetramethylimidazoline-l-oxyl-3-oxide（PTIO）,which possess high redox potentials and one electron transfer for regeneration of the dye,have been developed as redox mediators in DSSCs.Aimed at broadening the absorption spectra of dye,phenoxazine dyes which yield light-harvesting ranging from the entire visible region to part of the NIR region have been designed and developed for DSSCs:A series of metal-free organic dyes LJJ101-LJJ103 with phenoxazine unit as electron donor and indolinum carboxyl acid as electron acceptor have been synthesized and applied in DSSCs.LJJ series dyes exhibited strong light-harvesting abilities,ranging from the entire visible region to part of the NIR region.Compared to LJJ101,a slight red-shift could be found in the maximum absorption of LJJ102 with the introduction of thiophene unit,while a distinct red-shift was obtained in the maximum absorption of LJJ103 with squaraine unit employed into the molecule structure.When applied in DSSCs,in contrast to LJJ101,the devices based on LJJ102 and LJJ103 exhibited broader IPCE spectra responses from 400 nm to about 850 nm,and accordingly,showed a higher Jsc.The DSSCs sensitized by LJJ103 yielded the best conversion efficiency（PCE）of 5.1%under AM 1.5 illumination.The[Cu（dmbp）₂]2+/1+ redox couple,which possesses a distorted tetragonal geometry,has been developed as a redox mediator and applied in DSSCs.In combination of an organic sensitizer Y123,the device based on[Cu（dmbp）₂]2+/1+ system achieved a high VOC of 1048 mV,which was 324 mV and 204 mV higher than that of I3-/I-and[Co（bpy）3]3+/2+ that could be ascribed to the higher redox potential of[Cu（dmbp）₂]2+/1+.The[Cu（dmbp）₂]2+/1+ system showed an extremely low driving force of only 0.11 eV,however,a rapid dye regeneration was observed.The dye regeneration process of the[Cu（dmbp）₂]2+/1+ system was similar to the I3-/I-,which was twice faster than that of the[Co（bpy）3]3+/2+ system.Therefore,the loss-in-potential for dye regeneration has been reduced and an overall efficiency of 10.3%at AM 1.5G 100 mW cm-2 was yielded.The exploration of catalytic performance of Pt and PEDOT counter electrodes for[Cu（dmbp）₂]2+/1+ redox system was further conducted.The Tafel and EIS measurements indicated that PEDOT counter electrode exhibited better compatibility with[Cu（dmbp）₂]2+/1+.While applied in DSSCs,an enhancement of fill factor was obtained and a power conversion efficiency of 11.9%was yielded with PEDOT counter electrode.Organic free radical PTIO was investigated and introduced as an alterative redox mediator in DSSCs and was compared to the efficient TEMPO/TEMPO+ system.A sensitizer CZ-1 with high HOMO level containing carbazole electron donor group and pyridinium cation electron acceptor group was designed and synthesized in combination with the redox system.While applied in DSSCs,a high VOC of 902 mV was achieved because of the high redox potential of PTIO/PTIO+.Despite the slightly higher VOC,PTIO/PTIO+ displayed a distinct lower Jsc thus a lower PCE of 4.3%compared to that of TEMPO/TEMPO+,which could mainly be ascribed to the relatively less efficient regeneration for CZ-1+ and the inefficient catalytic activity between the platinum counter electrode and PTIO/PTIO+.