Triphenylamine And Acridine Based D-π-A Organic Sensitizers:Synthesis And Photovoltaic Characteristics

To develop high-efficiency, stable and low-cost Dye-sensitized Solar Cells (DSSC), we take the core element of DSSC--Dye as the subject of our research. We have synthesized several kinds of new D-π-A small molecule organic dyes and polymer dyes, and then we systematically analysed the relationship and coresponding rules between structure and properties. The primary content and conclusions are drawn as following:(1) Three efficient dyes (POZ-3, POZ-4, POZ-5) with different arylamine electron donors (10-phenyl-10H-phenothiazine,10-phenyl-10H-phenoxazine and triphenylamine) attached to the7-position of model dye (POZ-2) have been designed and synthesized. Then the performance of the DSSCs based on these different dyes were tested and analyzed, and among which the POZ-3cell shows the highest η of7.8%. According to the optimized geometries of POZ-3and POZ-4, near90°dihedral angle between PTZ/POZ and benzene which caused by steric effects leads to the inhibition of electron transition from the bottom PTZ/POZ group to cyanoacrylic acid acceptors. The transient photovoltage decay and charge extraction experiments shows that the lower conduction-band edge of POZ-5outreaches the beneficial effect of its longer charge recombination lifetime (τn) at a given dn, that explaining its fall of Voc, which result in the lowest power conversion efficiency. It can be seen that the structure variation of electron donor has some degree of influence not only on charge combination, but also on conduction-band edge. This work should enlighten the further design of photosensitizers.(2) The properties of two POZ-based dyes which have different conjugated directions, extra phenyl ring and alkyl chain have been comparatively studied. The result shows that dye POZ-2exhibits higher power conversion efficiency (η=6.5%) than dye POZ-1(η=2.4%) under standard illumination (Global Air Mass1.5). The optimized geometries and charge extraction measurements have suggested that the conjugative and delocalization ability of POZ-2were better than POZ-1when the phenyl ring was added in POZ-1and the conjugated direction has been changed from along with’N’atom to along with2-position of POZ unit. Nearly90°of the dihedral angle between POZ and phenyl ring unit in POZ-1leads to the intramolecular charge transfer transition (HOMO-LUMO) being prohibited from the POZ donor to thiophen-conjugated unit and cyanoacrylic acid acceptors. Also, the interfacial charge recombination is a crucial influential factor of Voc.(3)2-hexylthiophene moiety has been introduced to the triphenylamine donor unit of dye L1for L101. The results showed that the solubility and light-harvesting capacity of L101have been enhanced which led to a higher Jsc. Moreover, introducing hexylthiophene moietie could improve the conduction band edge of TiO2, so the Voc of L101was higher than L1, and the overall power conversion efficiency(η) of L101has increased to5.1%from4.7%of L1. This slight improvement shows that the function of introducing2-hexylthiophene moieties to the TPA units could help to achieve better performance for small molecular organic sensitizer, but this improvement is not so distinct as in the Ru-complex (C101). Our work will shed light on the future design of organic small molecular dyes.(4) Three conjugated polymers (PPTZF, PPTZCZ and PTPACZ) which have a number average molecular weight of2300-3000(DP-4) have been synthesized, and the influence of polymer molecules’energy level and photovoltaic characteristic with different donor units in the backbone have been investigated. The PTPACZ cell which had TPA and CZ as back bone display a power conversion efficiency of4.4%. Up to now, it’s the highest efficiency of polymer dyes applied in DSSCs as sensitizers. Our work demonstrated that the engineering of small organic molecules are also suitable for polymer dye’s design...