Synthesis And Photovoltaic Performance Of Organic Sensitizers Based On The π-bridge With Dithieno[3,2-b:2’,3’-d] Pyrrole

Dye-sensitized solar cells（DSSCs）have attracted considerable attention because of their relatively high solar energy conversion efficiency,low fabrication cost,and eco-friendly specialty.In a typical DSC,a photosensitizer plays a crucial role in photogeneration of charge carrriers.Elaborate engineering of some ruthenium polypyridine and zinc porphyrin complexes as well as metal-free organic dyes has greatly impelled the efficiency progress of this cutting-edge photovoltaic technology.In this regard,of particular interest is the design of organic D-π-A dyes primarily owing to both raw materials abundance and high solar energy conversion efficiency.Key developments on D-π-A dyes have involved（i）reducing molecular energy gap（DE）to enhance an overlap between the electronic absorption spectrum of a dye and the standard solar emission spectrum for a high photocurrent and（ii）tuning steric and/or electronic structures of a dye to modulate the physicochemical characteristics of the titania/dye/electrolyte interface for a reasonable open-circuit photovoltage.Amongst the various strategies to narrow down DE of a DSC,one common tactic is the π-conjugation extension.Besides,adding build blocks and alkyl chain are efficient to modulate the electron transfered kinetics of the titania/dye/electrolyte interface.Hence,M47-49 are designed and synthesized.Five new dithieno[3,2-b:2′,3′-d]pyrrole units（DTPA1-3,PDTP and CZDTP）based on the truxene core,phenothiazine and carbazole have been designed and synthesized for a potential application in photovoltaic cells.One of these units（DTPA1）has been employed as π-linker to construct a new organic dye（M47）,with bis（4-（hexyloxy）phenyl）amine as donor and cyanoacrylic acid as acceptor.For comparison,dye M48 and M49 bearing the hexyl-substituted DTP（HDTP）and 2,2’-bithiophene spacer under the same conditions was prepared as a reference.Absorption spectra,electrochemical cyclic voltammetry,theoretical calculations,current voltage curves and controlled intensity modulated photovoltage spectroscopy have been investigated to explain the phenomenons about three dye sensitized solar cells.The new organic dye（M47）exhibited a higher solarto-electrical energy conversion efficiency when compared to reference dyes（M48 and M49）under the same conditions.M47 sensitized solar cells employing a cobalt electrolyte afford a short circuit photocurrent of 12.1 mA cm^-2,an open circuit voltage of 758 mV,and a fill factor of 0.56,corresponding to an overall power conversion efficiency of 5.1% under standard AM 1.5 sunlight.In addition,there is not merely extended the π-conjugation length of the bridge,which is beneficial to red-shift the absorption spectrum,but also improved reaction yield form 19.8% to 87.0%,affording a new optimized way about the dye of designed and synthesized,by replacing the donor form bis（4-（hexyloxy）phenyl）amine to 4-（hexyloxy）-N-（4-（hexyloxy）phenyl）-N-phenylaniline.