Near-Infrared to Visible Photon Upconversion by Palladium(II) Octabutoxyphthalocyanine and Rubrene in the Solid State

In this study, we observe near-infrared-to-visible photon upconversion via sensitized triplet–triplet annihilation in a solid-state film based on neat palladium(II) 1,4,8,11,15,18,22,25-octa-n-butoxyphthalocyanine [PdPc(OBu)8] and 5,6,11,12-tetraphenylnapthacene (rubrene). By continuous excitation at 730 nm, the system reaches a maximum upconversion quantum yield of 3.6 × 10–2% at power densities below 0.2 W cm–2. Although the observed upconversion quantum yield is most likely negatively affected by efficient singlet exciton fission in the films, a quantum yield of upconverted states of 1.3% confirms the potential for this system if the upconverted state is harvested via electron or energy transfer. By doping the films with a dibenzotetraphenylperiflanthene emitter, the energy transfer strategy shows to effectively raise the upconversion quantum yield by three times, which is promising for the use of this solid-state upconverter for power conversion efficiency enhancement of emerging high-energy band gap solar cells.