Design Of New Dye Molecules And Their Application In P-type Dye Sensitized Solar Cells And Detection

Since the seminal paper of O’Regan B. and Gr?tzel M. in 1991, dye-sensitized solar cells(DSSCs) have attracted a great deal of interest in the solar energy community due to their comparatively low manufacturing costs and high energy conversion efficiencies. DSSCs consist of photoactive anode n-type dye-sensitized solar cells(n-DSSCs) and photoactive cathode p-type dye-sensitized solar cells(p-DSSCs). The majority of studies in this field are n-DSSCs, but there has been relatively less attention focused on p-DSSCs. The development of p-DSSCs can provide an entry to the preparation of tandem solar cells(pn-DSSCs). The tandem structure design with a theoretical efficiency limitation well beyond that of single-junction DSSCs, provides an effective way for the next breakthrough in improving the photoconversion efficiency of dye-sensitized solar cells. The future performance improvements of pn-DSSCs are mainly dependent on the key breakthrough of p-DSSCs, therefore, it’s of urgent significance to study p-DSSCs and to enhance the performance. The photosensitizers play a key role in determining DSSCs’ performance, intelligent dye design could help to increase the charge separation on light absorption, reduce the charge recombination and increase the light-harvesting efficiency. In this thesis, we have designed and synthesized a series of novel dyes, and investigated their photophysical and electrochemical properties. In addition, the photovoltaic performances of the as-assembled p-DSSCs based on these new dyes were measured. On the other hand, taking into account the intramolecular charge transfer in the dye molecules and the characteristics of dicyanovinyl groups, we have studied the application of the dye molecule for cyanide anion detection. The main contents and results are as follows:1. Four push-pull type triphenylamine-based dyes with dicyanovinyl as the acceptor units(T3 and T4) and 1,3-diethyl-2-thiobarbituric acid as the acceptor units(T3H and T4H), have been designed and synthesized, respectively. The effect of the length of thiophene units and different acceptor units on the photophysical, electrochemical and photovoltaic properties has been investigated. Results indicate that the increased oligothiophene units in T4 between triphenylamine and carboxylate anchoring group could enhance the light harvesting efficiency. Moreover, the 1,3-diethyl-2-thiobarbituric acid incorporated as the acceptor moiety offers much stronger and broader absorption reaching the near-infrared region(NIR), thus leading to higher power conversion efficiency. The power conversion efficiencies(PCE) based on the four dyes are 0.180%(T3), 0.207%(T4), 0.226%(T3H) and 0.317%(T4H), respectively. Excitingly, T4 H shows the highest efficiency, with a high photocurrent(J =6.735 mA/cm2), which is close to the top value(7.57 mA/cm2) reported to date for p-DSSCs.2. On the basis of our previous work, two push-pull type dyes T5 and T6 with five and six thiophene units as π-spacers have been designed and synthesized. When the new dyes are applied as p-type sensitizers, the distance between the donor and the semiconductor surface is elongated. The effect of the increased π-spacer on the photophysical, electrochemical and photovoltaic properties of the two dyes together with T3 and T4 synthesized in our previous work has been investigated by UV-visible absorption spectroscopy and cyclic voltammetry. The results indicate that the power conversion efficiencies of the four dyes displayed in the order 0.184%(T3) < 0.208%(T4) > 0.186%(T5) > 0.178%(T6). It turned out that four thiophene units could offer T4 with the highest performance under the same donor and acceptor. Further increased length instead, results in decreased efficiencies. We estimate that the longer spacer could effectively prevent charge recombination on the NiO-dye surface, however, the increased thiophene units also could decrease the conductance of the oligothiophene spacer, which is unfavorable for hole injection from dye molecule to the valence band of NiO. The results demonstrate that the distance between donor and the semiconductor should be optimized. The appropriate length is required to balance charge recombination and charge transporting efficiency. 3. P1 is the first push-pull type triphenylamine-based dye molecule for p-DSSCs with a typical D-π-A structure which devoted to NIR fluorescent emitting. Considering the influences of the carboxylate group, we synthesized an analogue of P1 without the carboxyl group(P2) and developed P2 as a NIR fluorescent sensor to detect cyanide anions. In P2, dicyanovinyl as the electron acceptor can react with cyanide anion(CN-) by nucleophilic addition reaction, which may break the acceptor structure and influence the electronic structure and optical properties of the sensor molecule, and thus realize specific response for the cyanide anions. The anion sensing properties of the NIR probe P2 was investigated using UV-vis, fluorescence, 1H NMR titration, 13 C NMR titration and theoretical simulations. The results indicate that the fading of the solution color and a rapid quenchable NIR fluorescent response to cyanide anions could be clearly observed upon adding CN- into P2 solution. Furthermore, the detection limit was calculated to be 0.46 nM. Therefore, Probe P2 is demonstrated to be of high sensitivity and selectivity for cyanide anions. 4. In this work, monolayer sensor molecules are firstly developed for the detection of trace amounts of cyanide anions in aqueous solution, which was inspired by the fact that in dye-sensitized solar cells, dye molecules adsorb onto the semiconductor surface by forming a monolayer. Compound P1 with a carboxyl group on the triphenylamine could be adsorbed onto a metal oxide(such as NiO and TiO2) surface to form a monolayer M-P1. The detection behavior could be easily observed from a visual color change of the metal oxide films, which was also in agreement with their UV-vis absorption spectral changes. The results indicate that M-P1 could be applied to detect trace amounts of CN- in aqueous solution with high sensitivity, selectivity and anti-interference ability. The detection limit of the monolayer sensor is determined to be 2.99 nM. Therefore, the monolayer sensor is very efficient for detecting trace amounts of analytes in dilute solution and the detection could be easily observed by the naked eye, which provides a new idea for constructing probes in the future.