New tetrazole based dyes as efficient co-sensitizers for dsscs: Structure-properties relationship

Abstract Two new compounds based on the phenyltetrazole system, 5-(4-decyloxyphenyl)tetrazole (LTz-4) and N,N-diethyl-4-{[(2′-nitro-4′-tetrazoyl)phenyl]diazenyl}aniline (SD - 6), were synthesized and characterized as co-adsorbents in Dye-Sensitized Solar Cells (DSSCs). The effects of hydrophobic chain length and anchoring group on the properties of DSSCs containing the previously reported dye HD-14 and compared with the benchmark deoxycholic acid (DCA) are described. The charge-transfer resistance of dye/TiO2 interface followed the order HD-14 – SD - 6 > HD-14 – LTz-4 > HD-14 –DCA. However, the VOC for the dye HD-14 with co-adsorbent DCA was 0.71 V, for the and the dye HD-14 with co-adsorbent LTz-4 was 0.70 V and for the dye HD-14 with co-adsorbent SD - 6 was 0.67 V. Co-adsorbents LTz-4 and SD - 6 achieved mean solar-to-power conversion efficiencies (%η), for three devices, of 9.20 and 7.48, respectively, compared to 9.14 for DCA under the same experimental device conditions. For LTz-4 co-adsorbent, the results can be attributed to the repellent effect of the long alkyl chain that prevents the charge recombination on the semiconductor surface. For SD - 6, the molecular volume of the co-adsorbent and the presence of the nitro group in a lateral position should make it difficult to form a more compact layer with the dye. The sum of these contributions would allow the electrolyte to approach, reducing the efficiency of electron injection into TiO2.