Green-Solvent-Processed Conjugated Polymers for Organic Solar Cells: The Impact of Oligoethylene Glycol Side Chains

Abstract

Organic photovoltaics (OPVs) possess the advantageous trait of solution processability, yet OPV blends typically use hazardous chlorinated solvents for processing. In order to realize the full advantages of OPVs, as well as growing to an industrial scale, the use of environmentally friendly solvents for processing OPVs needs to be pursued. In this study, we utilized the well-studied polymer PBnDT-FTAZ system as the model conjugated polymer, and synthesized a series of structurally similar conjugated polymers with oligo­(ethylene glycol) (OEG) side-chains, aiming to understand the structural requirements to convert conventional conjugated polymers into green-processable alternatives. We elucidated the impact of these OEG chains on the properties of modified polymers when compared with the original PBnDT-FTAZ, including solubility and optoelectronic properties. Finally, aiming to understand the impact of changing side chains to the device performance, we fabricated solar cells with a nonfullerene acceptor (IT-M), achieving decent device efficiencies (over 7%). Additionally, using renewable and green solvent, 2-methyltetrahydrofuran (2-MeTHF), we were able to achieve device efficiencies of over 2%.

Designing Simple Conjugated Polymers for Scalable and Efficient Organic Solar Cells

“…Additionally, the S N 2 chemistry to attach the side chain will require additional synthetic steps if switching to oligo(ethylene glycol) side chains, which are commonly used to add solubility in green processing solvents. [33][34][35][36] For these reasons, we wanted to systematically explore and modify the reaction scheme to realize both low SC and low cost, making PTQ10 a great candidate for scaling-up of organic solar cells.…”

“…[34,35] One common approach to add green solvent processability to a conjugated polymer is to replace the alkyl side chains with OEG variants. [33][34][35][36] Many OEG side chain variants are commercially available, but most have end groups as alcohols (RÀ OH) instead of bromines (RÀ Br). In fact, the cost of RÀ OH side chain is significantly less than RÀ Br in the case of OEG variants.…”

A Donor Polymer with a Good Compromise between Efficiency and Sustainability for Organic Solar Cells

“…In view of large‐scale applications, along with the sustainability of the synthetic approach, further efforts are needed to improve polymer processing, that is, by lowering its molecular weight or introducing longer alkyl chains, thus helping the deposition of the active layer from a nonhalogenated, more environmental‐friendly solvent, such as o ‐xylene. [ 28 ]…”

PAMAM‐containing semiconducting polymers: Effect of dendritic side chains on optoelectronic and solid‐state properties

“…In addition of being an efficient strategy to module the optoelectronic, thermomechanical, and solid-state properties of π-conjugated polymer, side-chain engineering is especially efficient to fine-tune the solubility properties. 18,21,55 By incorporating charge or neutral polar moieties to π-conjugated polymers, solubility can be significantly altered, thus enabling new avenues for the processing of these materials in greener and/or printing-F I G U R E 3 2D GIWAXS pattern (left) and 1d sectoraveraged profiles out-of-plane and in-plane (right) of (a) P2 (10 mol% of PAMAM side chains), (b) P3 (20 mol% of PAMAM side chains), (c) P4 (30 mol% of PAMAM side chains) thin films after thermal annealing at 150 C for an hour compatible solvents. Given that dendritic side chains possess a high concentration of peripheral functional moieties, this design is attractive to access greener semiconducting polymers.…”