Proceedings of International Conference on Hybrid and Organic Photovoltaics (HOPV19)
Publication date: 6th February 2020
Hybrid organic-inorganic and all-inorganic lead halide perovskites have emerged as promising materials for different technological applications, such as photovoltaic devices, LEDs, and lasers. These semiconductors have been studied in the bulk and in the form of nanoparticles with different quantum confinement geometries (1D to 3D). However, most studies reported in the literature regarding 3D quantum confined perovskite or quantum dots (QDs) were carried out in a weak confinement regime, with particle sizes equal or larger than the exciton Bohr radius. Here, we explore the non-linear properties of perovskites in a strong quantum confinement regime. We synthesized colloidal dispersions of CsPbBr3 perovskite QDs with nanoparticle radius of the order of 2-4 nm. The QDs were characterized by transmission electron microscopy, while their optical properties were studied by steady-state and time-resolved photoluminescence spectroscopy and ultrafast transient absorption spectroscopy. The photoluminescence maximum and first excitonic absorption peak are observed at wavelengths l = 450-460 nm, and 420-450 nm, respectively. Based on Poisson statistics for exciton population in QDs, we obtain an absorption cross-section of the material at 3.2 eV varying between 2.8×10–15 cm–2 and 5.0×10–15 cm–2, depending on the size of the QDs. The formation of biexcitons is evidenced by the non-linear optical response of QDs submitted to increasing photoexcitation energy fluences. The biexciton lifetime is found to be extremely short, only 5-8 ps. The biexciton binding energy is derived as being 99 meV. This value is significantly larger than the typical binding energy reported in the literature. The difference is clearly attributed to the strong quantum confinement regime.
We gratefully acknowledge NCCR-MUST, Swiss National Science Foundation, and Swiss Confederation for their financial support
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