Quantum-Cutting Ytterbium-Doped CsPb(Cl_1–xBr_x)₃ Perovskite Thin Films with Photoluminescence Quantum Yields over 190%

A two-step solution-deposition method for preparing ytterbium-doped (Yb³⁺) CsPb­(Cl_1–xBr_x)₃ perovskite thin films is described. Yb³⁺-doped CsPb­(Cl_1–xBr_x)₃ films are made that exhibit intense near-infrared photoluminescence with extremely high quantum yields reaching over 190%, stemming from efficient quantum cutting that generates two emitted near-infrared photons for each absorbed visible photon. The near-infrared Yb³⁺ f–f photoluminescence is largely independent of the anion content (x) in CsPb­(Cl_1–xBr_x)₃ films with energy gaps above the quantum-cutting threshold of twice the Yb³⁺ f–f transition energy, but it decreases abruptly when the perovskite energy gap becomes too small to generate two Yb³⁺ excitations. Excitation power dependence measurements show facile saturation of the Yb³⁺ luminescence intensity, identifying a major challenge for future solar applications of these materials.