Molecular Engineering Of Organic Sensitizers Based On Dithieno[3,2-b:2’,3’-d]Pyrrole For Dye Sensitized Solar Cells

Since the discovery by Gr tzel and co-workers in1991, dye sensitized solar cells(DSSCs) have attracted extensive attention in the last two decades because of theirease of fabrication, high efficiency and cost–effectiveness.Chapter one: we briefly described the research background of DSSCs, andintroduced their schematic structure, working principle, evaluation parameters,working electrode and the electrolytes. Besides, the latest development of newsensitizers were also reviewed. Bearing these in mind, the molecular design andresearch contents of this thesis were outlined.Chapter two: we reported a series of tirphenylamine dyes bearinghexyloexyphenyl substituted dithieno[3,2-b:2′,3′-d] pyrrole (HOP-DTP) asπ-linker coded as XS54-XS56. For comparison, dye XS57featuring thedihexylcyclopentadithiophene (DH-CPDT) bridge was prepared as a reference.The photophysical, electrochemical and photovoltaic properties of these dyes havebeen systematically investigated. Device performance characteristics demonstratethe superiority of employing4-HOP-DTP (XS54) relative to DH-CPDT (XS57) asthe conjugated spacer in triphenylamine organic dyes. As a consequence, DSSCssensitized by XS54in combination with cobalt electrolyte achieves a short-circuitphotocurrent density (Jsc) of13.5mA cm–2, and power conversion efficiency (PCE)of8.14%under the standard AM1.5G illumination (100mW cm–2).Chapter three: three new sensitizers containing N-heterocycle-substituted DTPspacer were designed and synthesized, and the influence of different substitutedgroups of the DTP spacer on dye performance was further investigated. It is foundthat the incorporation of dihexylaniline or hexylcarbazole unit into DTP birgde cannotably retard the charge recombination at the titania/electrolyte interface, thusimproving the cell photocurrent and photovoltag. In addition, we check the effect ofthe dye absorption time on the performance of DSSCs. When the absorption time wasperformed for36h, DSSCs based on dye XS59displayed the highest PCE of8.20%.Chapter four: we developed two new sensitizers (coded as M28and M29)featuring hexahexyltruxene-substituted triphenylamine segment as donor groups forfurther improving the cells performance. It can be found that incorporating truxene unit into donor part of the sensitizer can efficiently broaden the light absorption,enhance the maximum molar absorption coefficient as well as supress chargerecombination and prolong the electron life time, in comparison with the referencedye C241. As a result, DSSCs sensitized by M29contributes a Voc of953mv and aPCE of8.5%.Chapter five: Indoline photosensitizers exhibit impressive short-circuitphotocurrent but show generally low open-circuit voltage which limit theirimprovement in PCE. Here, we reported three indoline dyes (i.e XW69, XW70andXW71) featuring DTP linker for iodine-free dye-sensitized solar cells in thin-filmfor the first time. Under the standard AM1.5G illumination, DSSCs based onXW70employing Co-phen electrolyte displays a promising conversion efficiencyas high as8.78%and a impressive Vocvalue of943mV.