Abstract
A series of phenothiazine based dyes (OMS1–3), comprising different conjugation lengths and numbers of electron deficient (cyanovinyl) moieties with cyanoacrylic acid as an anchor, have been synthesized. The dyes display broad UV-visible absorption, from 389 nm to 484 nm. The higher molar extinction coefficient and longer absorption peak are achieved as the conjugation length and numbers of electron deficient units increase. The cell performance based on these dyes exhibits efficiencies ranging from 0.68–4.00%, compared to a standard N719-based device (PCE = 7.49%) fabricated under similar conditions. Although the OMS3 dye has two electron deficient units between phenothiazine units, an insignificant electron trapping effect is observed. From the results, the OMS3 based cell exhibits the highest short circuit current (JSC) at 8.72 mA cm−2 and the highest open-circuit voltage (VOC) at 0.66 V, together with the best cell performance at 4.00%.
Highlights
A p-conjugated linker incorporates several lowband gap units to form a D–A–p–A con guration due to redshi ed absorption and air stability.[7]
We report the synthesis and characterization of three organic dyes with different conjugation lengths and numbers of electron de cient units at C3 and C7 positions of the phenothiazine core
The intermediates, compounds 1,16 3, 4,17 and 6 with aldehyde functional groups were obtained by Vilsmeier–Haak reaction in the presence of POCl3 and dimethylformamide (DMF)
Summary
A p-conjugated linker incorporates several lowband gap units to form a D–A–p–A con guration due to redshi ed absorption and air stability.[7]. Introduction of a cyanovinyl unit is attractive for DSSC application due to the electron withdrawing nature which would increase intramolecular charge transfer and reduce the optical band gap.[9] In addition, the incorporation of a cyanovinyl unit into the dipolar structure can effectively stabilize the LUMO level.[10] the cyanovinyl unit possesses electron withdrawing characteristics, it shows less charge trapping a er appropriate modi cation of the conjugated spacer via quantum chemistry computations with Mulliken charge in the S1 electronic transition state.[11]. Paper derivatives substituted on C3, C7, N-10 and multi-anchor sensitizers show great potential in tuning the optical properties and solar efficiency.[12] To the best of our knowledge, phenothiazine-based sensitizers have never been explored by adopting different numbers and positions of electron de cient cyanovinyl units. The photophysical properties of the compounds and the performance of the DSSCs fabricated with these dyes are discussed
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