Synthesis And Properties Of D-π-A Type Of Organic Photosensitizers

As the demand for energy source is expanding increasingly and the traditional fossil fuel will be exhausted in the near future, solar energy, as a clean, huge and wide distributed energy source, has attracted considerable attentions. For the application of solar-to-power conversion, the rising technology of dye sensitized solar cell (DSSC) is a good candidate for commercial application due to several characteristic advantages such as easy fabrication, environmental friendness and low cost.Photosensitizer is one of the critical components in the device of DSSC and has been studied intensively. Recent research topics have been transferred from rare metal complexes (mainly Ru complexes) to a great variety of organic dyes, which have been significantly developed during the past decade and the conversion efficiency has been promoted by almost one magnitude, which is comparable to that of Ru complexes. Among various organic dyes, triarylamine dyes possessed the highest photovoltaic efficiency with long term stability.Among the reported donor-π-acceptor (D-π-A) type of organic dyes, triarylamine has been proved to be a good donor, while cyanoacrylic acid or rhodanine acetic acid is the most favorite acceptor. The design of new organic dye is mainly focused on the replacement of different π bridge. Organic photosensiziters exhibiting good performance normally contain thiophene and its derivatives as π linkers. Benzothiophene has been widely applied in the field of polymer science; however, it has never been used as a π bridge in photosensitizers in DSSC.Herein we designed and synthesized a series of new dyes bridged with benzothiophene and its derivatives, using hexyloxy substituted triphenylamine (TPA) or fluorene substituted aniline (FA) as donor and cyanoacrylic acid as an acceptor. Their spectrscopic and electrochemical properties have been investigated, and the performances on DSSC devices were also tested. The relationship between structure and performance were analyzed through quantum chemistry calculation. Besides, some D-π-A type of BDP dyes have been synthesized and investigated.The results are summarized as follows:1.4,7-dihydro-4,7-ethanobenzo[c]thiophene (BCOD thiophene), benzo[c]thiophene were introduced for the first time into D-π-A type of organic dyes as π bridges.11new dyes containing TPA or FA as donor and cyanoacrylic acid as an acceptor were synthesized.2. The spectroscopic and electrochemical properties of these photosensitizers, and their photovoltaic performance in dye sensitized solar cells have been evaluated. Among the TPA substituted dyes, LQ3which contains one benzo[c]thiophene as a π bridge achieved the highest power conversion efficiency of5.03%, which is higher than that of the reference compound C217(3.69%) measured under the same condition, suggesting the appropriate expanding conjugation in n bridge resulted in the expansion of the spectrum response and subsequently increased short-circuit photocurrent density (Jsc). Further extending the π-conjugation significantly stabilized the LUMO energy level and resulted in the decreasing of the dye stability, enhancing the possibility of dye aggregation and causing the excited state of the dye mismatch the conducting band of TiO2. In FA dye series, BCOD-fused thiophene bridged photosensitizers showed better performance than those of the benzo-fused thiophene linked dyes.3. Synthesized two D-π-A type of dyes based on BDP derivatives. Quantum chemical calculation indicated that charge separation between ground state and excited state can be well formed. Extending π conjugation at a position of the BDP caused its absorption spectrum red shift for120nm into the red-visible region and the band width expand for about150nm.