Approaching highly stable optoelectronic device operation at elevated temperature by locking backbone torsion of conjugated polymers

The ability of organic electronics to maintain stability during prolonged operation at elevated temperatures is crucial for the durability and longevity of optoelectronic devices, thereby ensuring their commercial success. However, achieving stable optoelectronic properties for conjugated polymers at high temperatures remains fundamentally challenging, and understanding the causes of their instability is even more complex. Here, we identify backbone twisting motion as the primary reason for the unstable electrical and optical properties of donor-acceptor (D-A) conjugated polymers, using diketopyrrolopyrrole (DPP)-based polymers as a model system. The backbone thiophene-ring twist transition is responsible for shifts in the bandgap and alterations in charge transport properties. Above this transition temperature, the twisting motion of the thiophene induces localization of the intrachain electrons, resulting in reduced charge carrier mobility, and a significant blue shift in optical absorption. Additionally, we demonstrated that intramolecular hydrogen bonding interaction within a newly synthesized DPP polymer can induce co-planarity in the backbone and suppress backbone twisting.