Application Of Organic Dye-sensitizers With Maleic Anhydride,Quinoxaline And Pyridine-N-oxide As Anchor Group In DSSCs

As an important component in the dye-sensitized solar cells (DSSCs), designing new types of dye-sensitizers is always important for improving the performance of DSSCs. Compared with metal complex sensitizers, organic sensitizers have their unique advantages like good photoelectrical properties, easy synthesis, etc. Now organic dyes often base on donor-linker-acceptor structure, also known as D-π-A. However, unlike various kinds of donor groups, the main choice for the anchor part is focused on acidic groups such as carboxylic acid, cyanoacrylic acid, etc, this limitation is not good for further structure modification.In the first part of this paper, two organic dyes WA-1and WA-2were designed and synthesized with maleic anhydride as the anchor group. Owing to the strong electron withdrawing property, the UV-Vis spectra were extended to700nm for the dye series. But the ring opening adsorption of anhydride brought about150nm blue-shifts, WA-2only obtained an efficiency of3.60%eventually.Type II dye-sensitizers often employ catechol or its derivatives as anchor groups, which can inject electrons directly by the dye-to-TiO2charge-transfer bands. To further broaden UV-Vis absorption, WQ-1and WQ-2with quinoxaline-2,3-diol were synthesized and applied into DSSCs. The dye structures and adsorption states were determined by FTIR spectra and reference dyes. Overall WQ dyes showed comparatively good performance given their simple structures, and WQ-2got an efficiency of2.25%co-sensitized with CDCA.The published literature showed the introduction of heteroatom, especially pyridinium cation was beneficial for the modification of organic dye-sensitizers. Three organic dyes (WL101-WL103) were synthesized with pyridine-N-oxide as the anchor group, WL102got an efficiency of3.72%and the IPCE peak value reached95%. FTIR spectra showed a good coordination between pyridine-N-oxide and the Br(?)nsted acid sites on the TiO2films. After initial modification, four more dyes (WL201-WL204) were synthesized, and WL202increased the efficiency to3.86%.To further improve the performance, benzodiazosulfide was introduced as an auxiliary electron withdrawing moiety and five D-A-A pyridine-N-oxide dyes WL301-WL305were synthesized and applied in the DSSCs. WL305with2-ethylhexyloxy chains on the donor side obtained an efficiency of6.08%. The dye series also performed well in the stable test, FTIR test confirmed that the introduction of benzodiazosulfide didn’t affected the adsorption state.