A novel trigeminal zinc porphyrin and corresponding porphyrin monomers for dye-sensitized solar cells

Abstract

A novel trigeminal zinc porphyrin sensitizer (T) and two zinc porphyrin monomers (M1 and M2) were successfully designed and synthesized. The spectral, electrochemical, and photovoltaic properties of the porphyrin dyes were investigated. Compared with M1, the molecule of M2 has an additional aliphatic n-hexyloxyl chain at the meso-position of the porphyrin framework, and such a structure is favorable for the formation of a compact hydrophobic layer at the TiO₂ surface and the retardation of the diffusion of I₃⁻ ions into the nanoporous TiO₂ electrode, resulting in more effective suppression of the charge recombination process and a higher V_oc. Meanwhile, M2 has larger IPCE values than those of M1, leading to the higher J_sc value. Thus, the DSSC devices based on M2 demonstrated a relatively high power conversion efficiency of 5.77%, with the J_sc, V_oc and ff values of 13.93 mA cm⁻², 732 mV, and 0.566, respectively. Even though dye T has the highest molar absorption coefficients and multiple binding moieties, the corresponding power conversion efficiency is 2.30%, which is lower than those for M1 and M2. These observations may be ascribed to the low efficiency of the electron injection process caused by the isolation of the LUMOs from the anchoring carboxyl groups in addition to the lowest adsorption amount.