Efficient Solid-State Photon Upconversion Enabled by Spin Inversion at Organic Semiconductor Interface

We realized solid-state UC with 100 times higher efficiency than a conventional system by discovering a novel UC mechanism in bilayer organic semiconductor heterojunctions. The UC occurred through spin inversion during the charge separation and recombination at the interface. The key to the success was the triplet formation at the interface, as this could avoid the loss process during triplet diffusion, which is a problematic issue in conventional systems. As a result of this finding, efficient UC from near-infrared to visible light on flexible thin films under LED light excitation was made possible.