Unlocking the Full Potential of Polymer-Based Solid-State Photon Upconversion

To harvest the full potential of polymer-based solid-state photon upconversion (UC) devices, we examined the effect of the molecular weight of a fluorescent polymer on the UC efficiency. With a high-molecular-weight polymer, a long triplet lifetime of 11.2 ms was achieved, which led to a characteristic threshold intensity of 67 mW cm⁻², considerably lower than those of previously reported polymer-based UC devices. Furthermore, the external quantum efficiency of our UC device was as high as ∼0.35%. Consequently, fluorescent conjugated polymers with long triplet lifetimes can serve as attractive candidates for efficient solid-state UC devices.