Abstract
Poly[(5,5’-(2,3-bis(2-ethylhexyloxy)naphthalene-1,4-diyl)bis(thiophene-2,2′-diyl))-alt-(2,1,3-benzothiadiazole-4,7-diyl)] (PEHONDTBT) was synthesized for the first time and through direct arylation polymerization (DAP) for use as p-donor material in organic solar cells. Optimized reaction protocol leads to a donor-acceptor conjugated polymer in good yield, with less structural defects than its analog obtained from Suzuki polycondensation, and with similar or even higher molecular weight than other previously reported polymers based on the 2,3-dialkoxynaphthalene monomer. The batch-to-batch repeatability of the optimized DAP conditions for the synthesis of PEHONDTBT was proved, showing the robustness of the synthetic strategy. The structure of PEHONDTBT was corroborated by NMR, exhibiting good solubility in common organic solvents, good film-forming ability, and thermal stability. PEHONDTBT film presented an absorption band centered at 498 nm, a band gap of 2.15 eV, and HOMO and LUMO energy levels of −5.31 eV and −3.17 eV, respectively. Theoretical calculations were performed to understand the regioselectivity in the synthesis of PEHONDTBT and to rationalize its optoelectronic properties. Bilayer heterojunction organic photovoltaic devices with PEHONDTBT as the donor layer were fabricated to test their photovoltaic performance, affording low power-conversion efficiency in the preliminary studies.
Highlights
Conjugated polymers with alternating electron-donor and electron-acceptor units along their backbones (D−A CPs) have been investigated during the last decades for a variety of applications in organic electronics, such as organic photovoltaic (OPV) devices [1,2,3], organic light-emitting diodes (OLEDs) [4,5], organic field-effect transistors (OFETs) [6,7], polymer-based organic batteries [8,9], and chemical sensors [10,11]
Synthesis of EHON derivatives are given in electronic supplementary information (ESI)
In pathway A, the thiophene spacers are flanking the EHON unit, while in pathway B, the thiophenes are coupled to the 2,1,3-benzothiadiazole moiety
Summary
Conjugated polymers with alternating electron-donor and electron-acceptor units along their backbones (D−A CPs) have been investigated during the last decades for a variety of applications in organic electronics, such as organic photovoltaic (OPV) devices [1,2,3], organic light-emitting diodes (OLEDs) [4,5], organic field-effect transistors (OFETs) [6,7], polymer-based organic batteries [8,9], and chemical sensors [10,11]. CPs are typically prepared by versatile and reliable cross-coupling reactions, such as Suzuki–Miyaura, Migita–Stille, and Kumada–Corriu, among others, which tend to give high reactivity, high molecular-weight, and well-defined polymers They require multiple synthetic steps, using expensive and toxic organometallic precursors. The 2,3-dialkoxynaphthalene unit has been the least studied of the series, producing polymers with reduced yield and low molecular weight, which limits its field of applications [38,39] These phenylene and naphthalene polymers are prepared by Suzuki or Stille couplings, but there are some recent examples of dialkoxyphenylene-based polymers successfully synthesized by DAP with high molecular weight [40,41,42,43]. The batch-to-batch repeatability of the optimized DAP reaction was tested and demonstrated
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