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Porphyrin dimers as donors for solution-processed bulk heterojunction organic solar cells

Hsu, Fang-Chi, Hsieh, Ming-Kuang, Kashi, Chiranjeevulu, Yeh, Chen-Yu, Lin, Tai-Yuan, Chen, Yang-Fang
RSC advances 2016 v.6 no.65 pp. 60626-60632
butyric acid, chemical bonding, guidelines, porphyrins, solar cells, solvents, spectral analysis
We synthesize a novel class of porphyrin dimers consisting of two zinc-metalated porphyrin units covalently linked through ethynyl (KC1) or butadiyne (KC2) group as electron donors blended with [6,6]-phenyl C₇₀ butyric acid methyl ester (PC₇₀BM) as electron acceptor for the fabrication of organic bulk heterojunction (BHJ) solar cells. The solution processed BHJ solar cells with porphyrin dimers:PC₇₀BM show superior performance than those based on their parent monomer due to much broader light absorption spectra. It is found that devices with KC2 : PC₇₀BM blend in the weight ratio of 1 : 4 exhibit higher power conversion efficiency (PCE) over those with KC1:PC₇₀BM blend. When the KC2:PC₇₀BM blend is processed from solvent containing 3% v/v 1-chloronaphathalene (CN), the PCE of the solar cell is improved to 2.03% from 1.73%. The superior performance and the performance improvement of the solar cells with KC2:PC₇₀BM are due to the high short circuit current density (Jₛc) resulting from a higher effective device mobility and a lower series resistance. The study provides a useful guideline for designing porphyrin based donor materials for optoelectronic device application.