Triplet–triplet
annihilation upconversion (TTA-UC) is a
process by which a lower energy photon can be upconverted to a higher
energy state. The incorporation of TTA-UC materials into solid-state
hosts has enabled advances in solar energy and many other applications.
The choice of host system is, however, far from trivial and often
calls for a careful compromise between characteristics such as high
molecular mobility, low oxygen diffusion, and high material stability,
factors that often contradict one another. Here, we evaluate these
challenges in the context of the state-of-the-art of primarily polymer
hosts and the advantages they hold in terms of material selection
and tunability of their diffusion or mechanical or thermal properties.
We encourage more collaborative research between polymer scientists
and photophysicists in order to further optimize the current systems
and outline our thoughts for the future direction of the field.