A two-step solution-deposition method for preparing ytterbium-doped (Yb3+) CsPb­(Cl1–x Br x )3 perovskite thin films is described. Yb3+-doped CsPb­(Cl1–x Br 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(Cl1–x Br 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.

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Metal-halide semiconductors exhibit attractive properties for a host of applications including photovoltaics, solid-state lighting, and photodetection. Among the remarkable recent developments is the discovery of extraordinarily high photoluminescence quantum yields in Yb3+-doped inorganic lead-halide perovskites. Although all previous research and development of such quantum-cutting materials has involved solution-phase preparation, particularly as colloidal nanocrystals, such methods can introduce both processing and technical challenges that limit the scope of accessible compositions, morphologies, and scaled-up applications. Here, we demonstrate a scalable single-source vapor deposition (SSVD) method for depositing high-quality conformal thin films of complex metal-halide perovskites, including doped perovskites, over large areas at high deposition rates. Focusing on quantum-cutting Yb3+:CsPb­(Cl1–x Br x )3, we demonstrate large-area deposition of films with photoluminescence quantum yields as high as 183%, starting from single-source powders prepared mechanochemically from solid ionic precursors. We also prepare thin films of the solar absorber material (FA0.81MA0.14Cs0.05)­Pb­(Cl0.02Br0.14I0.84)3 to illustrate the generality of this SSVD method. These results demonstrate a promising approach to high-throughput vapor processing of metal-halide coatings for photonic and optoelectronic applications.

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CsPb(Cl 1−x Br x ) 3 (0 ≤ x ≤ 1) nanocrystals and thin films doped with a series of trivalent rare-earth ions (RE 3+ = Y 3+ , La 3+ , Ce 3+ , Gd 3+ , Er 3+ , Lu 3+ ) have been prepared and studied using variable-temperature and time-resolved photoluminescence spectroscopies. We demonstrate that aliovalent (trivalent) doping of this type universally generates a new and oftenemissive defect state ca. 50 meV inside the perovskite band gap, independent of the specific RE 3+ dopant identity or of the perovskite form (nanocrystals vs thin films). Chloride-to-bromide anion exchange is used to demonstrate that this near-band-edge photoluminescence shifts with changing band-gap energy to remain just below the excitonic luminescence for all compositions of CsPb(Cl 1−x Br x ) 3 (0 ≤ x ≤ 1). Computations show that this shift stems from the effect of the changing lattice dielectric constants on a shallow defect-bound exciton. Microscopic descriptions of this dopant-induced near-band-edge state and its relation to quantum cutting in Yb 3+ -doped CsPb(Cl 1−x Br x ) 3 are discussed.