Photon Upconversion-Driven Charge Injection in CsPbI ₃ -Rubrene-TiO ₂ Films

Maximizing photoconversion efficiency in light-harvesting assemblies necessitates the effective capture of both visible and near-infrared photons. We integrated a CsPbI 3 -rubrene photon upconversion system to extend the spectral response of a dye-sensitization process. Excitation of the CsPbI 3 film facilitates triplet energy transfer to rubrene, which subsequently generates excited singlet through triplet–triplet annihilation. Notably, charge injection into TiO 2 is observed exclusively from the rubrene singlet excited state ( E S = 2.23 eV), and not from the triplet state ( E T = 1.14 eV) as it lacks sufficient energy to drive the injection process. In this architecture, rubrene serves a dual purpose: it acts as an annihilator for upconverting low-energy photons and participates directly in the dye-sensitization of TiO 2 . Mechanistic insights into the energy transfer steps and the kinetics of charge injection are elucidated using photoluminescence and transient absorption measurements. The ability to harvest low-energy photons is useful for enhancing the performance of solar cells and other light-energy conversion devices.