Design and Synthesis of Novel Benzene-Bridged Double D-π-A Materials for Dye-Sensitized Solar Cells

As compared to the rod-shape of the single D-π-A analogue dye (D21L6), the twisted shape of the double D-π-A branched dye is favorable for reducing intermolecular interaction and retarding dark current. The relationship among the chemical structures, optoelectronic properties and device performance has been systematically investigated. In this work, novel benzene-bridged organic dyes (designated p-BTTAand m-BTTA) have been designed and synthesized for dye-sensitized solar cells (DSCs). The structural difference between the two sensitizers is the position of bridge. Double D-π-A dye of p-BTTA and m-BTTA result in a broader and more intense charge transfer band in comparison to those of D21L6 because of extending π-conjugated framework. p-BTTA yields higher molar extinction coefficient than m-BTTA due to better planarity in conjugated reginon. m-BTTA and p-BTTA yield higher molar extinction coefficient than that of D21L6 which can improve light-harvesting capacity and demonstrate better solar cell performance than D21L6. The monochromatic incident photon-to-current conversion efficienc of m-BTTA-based DSCs exceeds 80% in abroad spectral region covering from 350 to 630 nm and reaches its maximum of 90% at 500 nm. Consequently, a high power conversion efficiency of 7.48% is achieved for a DSCs based on sensitizer m-BTTA using a liquid electrolyte, which reaches approximately 98.6% of the N719-based device (PCE=7.59%) under same condition. The lower conversion efficiency of p-BTTA (PCE=6.06%) is primarily attributed to its poor solubility. In chapter 3, OHexDPTP-BTBA dye which incorporates electron-deficient pyrimidine as the π-spacer has been designed and synthesized. In comparison with the model compound M-TP-BTBA, which adopts phenylene as the π-spacer, OHexDPTP-BTBA demonstrates better planarity in conjugated reginon which is favorable for effective intramolecular charge transfer. OHexDPTP-BTBA exhibits high power conversion efficiency up to 7.45%, with Voc of 0.70 V, Jsc of 16.13 mA/cm2.