The Design, Synthesis And Application Of New Triphenylamine Based P-type Organic Dyes For NiO Solar Cells

Dye-sensitized solar cells(DSSCs) as a new type of solar cells have been widely regarded as the promising alternative to conventional Si-based solar cells due to its low cost, simple fabrication and good thermal stability. Currently, most of research efforts have been put into studying the n-type dye-sensitized(n-DSSCs) and the power conversion efficiency(PCE) has reached 13%, but still below its theoretical efficiency of 30%. On the other hand, the pn-tandem DSSCs have theoretical efficiency as high as 43%, which is potential to be alternation for the Si-based solar cells. However, at present, the PCE of pn-tandem DSSCs is only 2.42%, due to the low performance of p-type dye-sensitized solar cells(p-DSSCs). Therefore, it is in urgent need to investigate p-DSSCs and to improve its efficiencies. In this paper, a series of new p-type sensitizers based on triphenylamine were designed and synthesized, the structure-property relationship and NiO based solar cells performance were discussed. The research contents are as follows:(1) Three new triphenylamine based “D-A-A” type organic dyes were designed and synthesized. The electron-withdrawing 2,1,3-benzothiadiazole(BT) was first inserted between the donor and the acceptor in p-type sensitizers. Moreover, different acceptors were introduced to further tune the bandgap of the dye molecules. Their photophysical and electrochemical properties were investigated. Among these dyes, the best performance was achieved by the dye W2 with octyl 2-cyanoacrylate acceptor. It shows power conversion efficiency of 0.166 %, with short circuit current of 4.16 mA/cm2, and open circuit voltage of 0.121 V.(2) Three new near-infrared(NIR) organic dyes were designed and synthesized with triphenylamine as the donor, the strong electron-withdrawing units diketopyrrolopyrrole(DPP), isoindigo(ID) and DPP derivatives were used as the acceptor respectively. The absorption spectra, electrochemical performance and J-V curves were studied. The results showed that the photosensitizers contain DPP units have wider absorption range and higher molar extinction coefficient. Among three dyes, 1 achieved the best performance with overall conversion efficiency 0.085%, short circuit current of 2.25 mA/cm2, and open circuit voltage of 0.117 V.(3) In order to enhanced the utilization of sunlight with longer wavelengths, four triphenylamine based “D-A-A” type NIR sensitizers are designed and synthesized. The absorption spectra, electrochemical performance and J-V curves were studied respectively. It turned out that all these dyes showed broad absorption spectra and high molar extinction. However, their larger planar architectures resulted in poor molecule solubility and the HOMO level was not low enough to afford a high Voc, all the sensitizers exhibited the low photoelectric conversion efficiency. Among the four sensitizers, dye L1 presented the highest power conversion efficiency of 0.050 %, with short circuit current density(Jsc) of 1.38 m A/cm2, and the open circuit potential(Voc) of 115 m V.