(Invited) Ternary-Cascaded Triplet Energy Landscape for Solid-State Photon Upconversion

Here, we introduce a new strategy for improving the efficiency of solid-state photon upconversion based on triplet–triplet exciton annihilation (TTA-UC). We designed a ternary blend system consisting of a triplet sensitizer (TS), an exciton-transporting host polymer, and a small amount of an annihilator. The key idea underpinning this concept involves sequential triplet energy transfer from the TS to host and then to the annihilator, driven by the cascaded triplet energy landscape. Because of the small annihilator blend ratio, the local density of triplet excitons in the annihilator domain is higher than the overall density, leading to faster TTA. Based on the excitation-intensity and blend-ratio dependences of TTA-UC efficiency, we found that our concept has a positive impact on accelerating TTA.