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Issue 34, 2015
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Phthalimide-based π-conjugated small molecules with tailored electronic energy levels for use as acceptors in organic solar cells

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Abstract

The design, synthesis, and characterization of seven phthalimide-based organic π-conjugated small molecules are reported. The new materials are based on a phthalimide–thiophene–CORE–thiophene–phthalimide architecture. The CORE units utilized were phthalimide (M2), diketopyrrolopyrrole (M3), isoindigo (M4), naphthalene diimide (M5), perylene diimide (M6), and difluorobenzothiadiazole (M7); they were specifically selected to progressively increase the electron affinity of the resulting compound. A small molecule with no core (M1) was synthesized for comparison. Each material was synthesized through optimized direct heteroarylation cross-coupling procedures using bench top solvents in air. Combinations of UV-visible spectroscopy (UV-vis), cyclic voltammetry (CV), differential scanning calorimetry (DSC), ultraviolet photoelectron spectroscopy (UPS) and density functional theory (DFT) were used to characterize each material. The use of various core acceptor building blocks with differing electron affinities resulted in the series M1–M7 having a range of energetically deep LUMO levels and a range of HOMO–LUMO gap energies. Meanwhile, the melting and crystallization temperatures of the molecules M1–M7 were also found to vary according to the change in central acceptor unit. Compounds M1–M7 were employed as acceptors in combination with either the polymeric donor P3HT or small molecule donor DTS(FBTTh2)2 to understand how the LUMO levels of each acceptor influences the open circuit voltage (Voc). It was found that, in general, Voc was only weakly related to the offset between the HOMO energy level of the donor and LUMO level of the acceptor used, with a Voc of up to 1.2 V being achieved for M1.

Graphical abstract: Phthalimide-based π-conjugated small molecules with tailored electronic energy levels for use as acceptors in organic solar cells

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Supplementary files

Article information


Submitted
24 Jun 2015
Accepted
28 Jul 2015
First published
29 Jul 2015

This article is Open Access

J. Mater. Chem. C, 2015,3, 8904-8915
Article type
Paper
Author version available

Phthalimide-based π-conjugated small molecules with tailored electronic energy levels for use as acceptors in organic solar cells

A. D. Hendsbee, S. M. McAfee, J. Sun, T. M. McCormick, I. G. Hill and G. C. Welch, J. Mater. Chem. C, 2015, 3, 8904
DOI: 10.1039/C5TC01877C

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