Publication date: 21st July 2025
Quantum cutting represents a transformative strategy to mitigate thermalization losses that typically occur when high-energy photons are absorbed by semiconductors.[1,2] Recent advances have extended this concept from rare-earth doped crystals to semiconductor–rare-earth hybrid systems, particularly those utilizing halide perovskite absorbers,[2] thereby exploiting their exceptional optoelectronic properties.
In this study, we focus on Ytterbium (Yb)-doped CsPb(Cl1-xBrx)3, a metal halide perovskite that absorbs in the visible and exhibits intense near-infrared (NIR) photoluminescence (PL) — a clear signature of quantum cutting. We first optimized the composition of Yb-doped CsPb(Cl1-xBrx)3 by tuning both the Br content (x = 0.2 - 0.65) and [Yb:Cs] ratio (0.4 - 1.2). We observe a gradual blue shift of the absorption peak as the Br content decreases, and a red shift as the Yb concentration increases. Upon absorption of photons with wavelength < 500 nm, the doped perovskite converts the absorbed energy into NIR photons. The NIR PL signal appears at ~985 nm (1.26 eV), characteristic of Yb³⁺ ²F₅/₂ → ²F₇/₂ f-f transitions, confirming the occurrence of quantum cutting. The highest PL intensity is observed for (Cl0.6Br0.4) and a [Yb:Cs] ratio of 0.6. The NIR emission energy is slightly higher than the energy gap of Sn–Pb based perovskites (MA(Pb1-ySny)I3), which exhibit an optical bandgap around 1.21 eV when y = 0.65 - 0.85. This spectral alignment would be critical for enabling efficient energy transfer between the quantum cutting layer and the absorber layer.
Both doped and undoped perovskite films are synthesized following a double-step deposition from solution.[2] We use a suite of advanced spectroscopic techniques, including Rutherford backscattering spectrometry (RBS), X-ray photoelectron spectroscopy (XPS), PL, ultraviolet photoelectron and inverse photoemission spectroscopies (UPS/IPES), to systematically investigate the elemental composition and electronic structure of Yb-doped CsPb(Cl0.6Br0.4)3. RBS and XPS depth profiling provides insights into the composition and elemental distribution of the films. Both techniques reveal an Yb enrichment near the surface of the film, corroborated by PL measurements, which show a stronger NIR 985 nm emission when the film is illuminated from the surface side than from the bottom side. We discuss the potential integration of Yb-doped CsPb(Cl0.6Br0.4)3 with Sn–Pb based perovskite absorbers, offering a pathway to surpass conventional efficiency limits while providing a cost-effective strategy for enhanced energy conversion.
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