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Issue 6, 2015
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The effects of heavy atoms on the exciton diffusion properties in photoactive thin films of tetrakis(4-carbomethoxyphenyl)porphyrins

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Abstract

The singlet exciton diffusion properties of solution-cast thin films prepared from mixed substituent monoiodophenyl or monobromophenyl derivatives of 5,10,15,20-tetrakis(4-carbomethoxyphenyl)porphyrin (TCM4PP) were investigated for use in solar energy conversion applications. The photoluminescent singlet decay lifetime PL(t) of pristine porphyrin films and films lightly doped (0.1–0.6% wt) with [6,6]-phenyl-C61-butryic acid methyl ester (PCBM) were used to obtain relative quenching efficiencies (Q). The exciton diffusion coefficient (D) and exciton diffusion length (LD) for each derivative were obtained by modeling the quenching efficiency and PL lifetime decay data using a 3D exciton Monte Carlo diffusion simulation. Although the three TCMPP derivatives showed nearly identical absorbances and electrochemical properties, the monobromophenyl or monoiodophenyl substituted porphyrins exhibited significantly lower steady-state emission intensities and fluorescent lifetimes in solution. Amorphous thin films of the halogenated derivatives also exhibited a decrease in the PL decay lifetimes, relative quenching efficiencies, and reduced singlet exciton diffusion lengths. The singlet exciton diffusion length for TCM4PP was calculated to be 15 nm and decreased by 71% to 4.4 nm for TCM3IPP with the addition of a single iodo substituent. Photocurrent–voltage measurements of the derivatives in a PCBM bulk heterojunction device suggest that lowered exciton diffusion and enhanced singlet to triplet exciton conversion, due to the heavy atom effect, decreases photoconversion efficiency.

Graphical abstract: The effects of heavy atoms on the exciton diffusion properties in photoactive thin films of tetrakis(4-carbomethoxyphenyl)porphyrins

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Publication details

The article was received on 06 Oct 2014, accepted on 30 Nov 2014 and first published on 03 Dec 2014


Article type: Paper
DOI: 10.1039/C4TC02232G
Author version available: Download Author version (PDF)
Citation: J. Mater. Chem. C, 2015,3, 1243-1249
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    The effects of heavy atoms on the exciton diffusion properties in photoactive thin films of tetrakis(4-carbomethoxyphenyl)porphyrins

    A. L. Ortiz, G. S. Collier, D. M. Marin, J. A. Kassel, R. J. Ivins, N. G. Grubich and M. G. Walter, J. Mater. Chem. C, 2015, 3, 1243
    DOI: 10.1039/C4TC02232G

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