Enhanced Charge Separation Efficiency in Pyridine‐Anchored Phthalocyanine‐Sensitized Solar Cells by Linker Elongation

Abstract

A series of zinc phthalocyanine sensitizers (PcS22-24) having a pyridine anchoring group are designed and synthesized to investigate the structural dependence on performance in dye-sensitized solar cells. The pyridine-anchor zinc phthalocyanine sensitizer PcS23 shows 79 % incident-photon to current-conversion efficiency (IPCE) and 6.1 % energy conversion efficiency, which are comparable with similar phthalocyanine dyes having a carboxylic acid anchoring group. Based on DFT calculations, the high IPCE is attributed with the mixture of an excited-state molecular orbital of the sensitizer and the orbitals of TiO2 . Between pyridine and carboxylic acid anchor dyes, opposite trends are observed in the linker-length dependence of the IPCE. The red-absorbing PcS23 is applied for co-sensitization with a carboxyl-anchor organic dye D131 that has a complementary spectral response. The site-selective adsorption of PcS23 and D131 on the TiO2 surface results in a panchromatic photocurrent response for the whole visible-light region of sun light.

New Insight into an Old Problem: Analysis, Interpretation, and Theoretical Modeling of the Absorption and Magnetic Circular Dichroism Spectra of Monomeric and Dimeric Zinc Phthalocyanine Cation Radical

“…Such a transition can be observed both in solution and in the solid state. Formation and understanding of the spectroscopic signatures of the phthalocyanine-centered cation radicals are also important when electron transfer, and specifically formation of the charge-separated states, in the phthalocyanine-containing supramolecular systems are needed for solar cell applications. − Typically, upon oxidation of main group and transition-metal phthalocyanines to their respective cation radical forms, both the monomeric cation radical [MPc] +• and the dimeric [MPc] 2 2+ species (M is a divalent metal) can be formed in solution . The monomeric cation radical is paramagnetic and can be easily identified by electron paramagnetic resonance (EPR) spectroscopy (classic signal observed at g ≈ 2, which is characteristic for delocalized organic radical cations) .…”

Increased Light-Harvesting in Dye-Sensitized Solar Cells through Förster Resonance Energy Transfer within Supramolecular Dyad Systems

“…The spectral shape of the dye-stained film was almost similar to that of the mixed solution, and the molar ratio between PcS18 and 1 was about 3:1 estimated from the absorbance at two Q bands and their molar extinction coefficients. Although several dyes having pyridine units have been used as sensitizers for DSSCs through the formation of coordination bonds with the TiO 2 surface, − the TiO 2 electrodes stained by only 1 and 2 showed a very light purple. This suggests that the binding of pyridine unit in 1 and 2 with the TiO 2 surface pyridine is unstable.…”

Pyridyl‐ and Picolinic Acid Substituted Zinc(II) Phthalocyanines for Dye‐Sensitized Solar Cells

“…In this case, coordinate bonds form between the pyridyl ring and the Lewis acid sites of TiO 2 surface, rather than the ester linkages with the Brønsted acid sites of TiO 2 surface typically observed for carboxylic acid sensitizers. Later on, this concept was applied to Pors and more recently to Pcs . Despite their great potential, very few examples of systems combining N‐heterocycles and carboxylic acid moieties have been described .…”