New Benzotriazole and Benzodithiophene-Based Conjugated Terpolymer Bearing a Fluorescein Derivative as Side-Group: In-Ternal Förster Resonance Energy Transfer to Improve Organic Solar Cells

Abstract

A new benzodithiophene and benzotriazole-based terpolymer bearing a fluorescein derivative as a side group was synthesized and studied for organic solar cell (OSC) applications. This side group was covalently bounded to the backbone through an n-hexyl chain to induce the intramolecular Förster Resonance Energy Transfer (FRET) process and thus improve the photovoltaic performance of the polymeric material. The polymer exhibited good solubility in common organic chlorinated solvents as well as thermal stability (TDT10% > 360 °C). Photophysical measurements demonstrated the occurrence of the FRET phenomenon between the lateral group and the terpolymer. The terpolymer exhibited an absorption band centered at 501 nm, an optical bandgap of 2.02 eV, and HOMO and LUMO energy levels of −5.30 eV and −3.28 eV, respectively. A preliminary study on terpolymer-based OSC devices showed a low power-conversion efficiency (PCE) but a higher performance than devices based on an analogous polymer without the fluorescein derivative. These results mean that the design presented here is a promising strategy to improve the performance of polymers used in OSCs.

Computational prediction of the properties of bis(ethynylthienyl)dialcoxynaphthalene‐based conjugated polymers for organic solar cell applications

“…Regarding the increase in PCEs, new CPs are constantly being designed to produce materials with suitable frontier molecular orbitals (FMO) and bandgap ( E g ) energy levels, broad absorption in the visible region, good charge carrier mobility, and proper solution processability, to name a few properties [14–16]. The most successful strategy to fine‐tune those properties has been alternating electron‐donor (D) monomers, such as carbazole (CBz), cyclopenta[2,1‐ b ;3,4‐ b ′]dithiophene (CPDT), thieno[3,2‐ b ]thiophene (TT), benzo[1,2‐ b :4,5‐ b ′]dithiophene (BDT), and so forth, with electron‐acceptor (A) building blocks, such as thieno[3,4‐ c ]pyrrole‐4,6‐dione (TPD), benzo[1,2‐ c :4,5‐ c ′] dithiophene‐4,8‐dione (BDD), 3,6‐di(thien‐2‐yl) pyrrolo[3,4‐ c ] pyrrole‐1,4‐dione (DPP), isoindigo (iI), benzo[ d ][1,2,3] triazole (BTz), [1,2,5]thiadiazolo[3,4‐ f ] benzotriazole (TDzBTz), benzo[ c ]‐1,2,5‐thiadiazole (BTDz), among others, along the backbone [17–23].…”