Preparation and Spectral, Electrochemical, and Photovoltaic Properties of Acene-Modified Zinc Porphyrins

Abstract

A series of acene-modified zinc porphyrins (benzene to pentacene, denoted as LAC-1 to LAC-5) were prepared to study their absorption spectra, electrochemical properties, and photovoltaic properties. For the absorption spectral changes in THF, porphyrin B bands are red-shifted and broadened from 449 to 501 nm for LAC-1 to LAC-3, showing the effect of additional π-conjugation. In contrast, the B bands of LAC-4 and LAC-5 are blue-shifted. In addition, the tetracenyl group of LAC-4 gives rise to absorption bands in between B and Q bands. On the other hand, the Q bands of LAC-1 to LAC-5 are systematically broadened and red-shifted from 629 to 751 nm. By comparison, the absorption bands of LAC porphyrins on TiO2 films are broadened and slightly shifted. Fluorescence emission maxima of LAC porphyrins in THF are also systematically red-shifted from LAC-1 to LAC-5. Cyclic voltammetry experiments in THF/TBAP show that the first reductions are systematically positive-shifted from −1.16 to −0.85 V vs SCE for LAC-1 to LAC-5, indicating the effect of increasing π-conjugation. As for the performance of DSSCs using LAC porphyrins, the overall efficiencies are LAC-1 (2.95%), LAC-2 (3.31%), LAC-3 (5.44%), LAC-4 (2.82%), and LAC-5 (0.10%). Overall efficiency of a LAC-3-sensitized solar cell is nearly twice of that of a LAC-1-sensitized solar cell and is about 81% overall efficiency of N719-sensitized solar cells under the same experimental conditions. The conversion efficiency of incident photons to current (IPCE) experiments shows that the broadened absorption bands of LAC-3 effectively minimizes the gap between B and Q bands, contributing to the improved DSSC performance. The very poor performance of LAC-5 is suggested to be caused by rapid nonradiative relaxation of the molecule in the singlet excited state.

Acene‐Modified Triphenylamine Dyes for Dye‐Sensitized Solar Cells: A Computational Study

“…Similar to our findings, the HOMO and LUMO patterns of their acene-modified zinc porphyrin dyes demonstrate increasing localization on the tetracenyl and pentacenyl groups for LAC4 and LAC5. [23] The increasing localization of p orbitals at tetracenyl and pentacenyl units might also affect the fluorescence emission of TPA-AC4 and TPA-AC5, since electronic localization in the tetracenyl and pentacenyl moieties may enable intersystem crossing and internal conversion to become the main channels of deactivation, [23] as discussed later.…”

“…Acenes are polycyclic aromatic hydrocarbons consisting of linearly fused benzene rings with big p conjugations, and acene compounds such as anthracene are expected to be beneficial to red-shift the absorption spectra. [23][24][25] Lin et al have reported a series of acene-modified zinc porphyrins (benzene to pentacene) and investigated their absorption spectra, electrochemical properties, and photovoltaic properties. For the performance of the DSSCs, the overall efficiencies first increase then decrease, and the introduction of anthracene shows the highest efficiency.…”

“…For the performance of the DSSCs, the overall efficiencies first increase then decrease, and the introduction of anthracene shows the highest efficiency. [23] Recently, Lin and co-workers reported some zinc porphyrin sensitizers modified by a series of cyclic aromatic hydrocarbon substituents as photosensitizers for DSSCs. They found that the incorporation of the pyrenylethynyl unit broadened and red-shifted the spectral feature and made the incident photon-to-current efficiency spectrum cover broadly across the entire visible region of 400-800 nm.…”

Zinc–Porphyrin Dyes with Different meso‐Aryl Substituents for Dye‐Sensitized Solar Cells: Experimental and Theoretical Studies

“…[9] So far, a large number of porphyrins have been developed as sensitizers for DSSCs such as carboxyphenyl metalloporphyrins (h = 0.2-3.6 %); [10] thiophene-, olefin-, and acetylene-linked porphyrins (h = 3.6-5.1 %); [11] quinoxaline-fused porphyrins (h = 5.2-6.5 %); [12] zinc-zinc porphyrin dimers (h = 2.1-5.5 %); [13] bacteriochlorin (h = 1.1-6.6 %); [14] 2,4-pentadienoic acid bpyrrolic-functionalized porphyrins (h = 3.03-7.47 %); [15] phenylethynyl-substituted porphyrins (h = 0.25-6.12 %); [16] meso-(diarylamino)-substituted porphyrins (h = 3.8-13 %); [7,17] 4-ethynylstyryl b-pyrrolic-functionalized porphyrins (h = 4.3-7.1 %); [18] and acene-modified porphyrins (h = 0.10-5.44 %). [19] The performances of these porphyrins varied depending on the chemical structure. Hence, a further structural modification and improvement of the porphyrinbased dye is still a challenge and needs to be carried out.…”

Signature of the Dirac cone in the properties of linear oligoacenes

“…On the theory side, oligoacenes have been subject of an intensive debate due to pronounced correlation effects 3,4 . Much of the interest in this class of molecules is driven by organic electronics 5 and photovoltaics 6,7 , where oligoacenes and their derivatives find frequent applications [8][9][10][11][12] . From a broader perspective, a study of systems with linearly fused rings, 'nanographenes', offers means to learn how properties of a molecular wire converge to the one-dimensional limit.…”