Experimental Determination of the Molar Absorption Coefficient of Cesium Lead Halide Perovskite Quantum Dots

Lead halide perovskite (CsPbX₃, where X = Cl, Br, or I) quantum dots (QDs), with tunable optical and electronic properties, have attracted attention because of their promising applications in solar cells and next-generation optoelectronic devices. Hence, it is crucial to investigate in detail the fundamental size-dependent properties of these perovskite QDs to obtain high-quality nanocrystals for practical use. We propose a direct method for determining the concentration of solution-processed CsPbX₃ QDs by means of spectrophotometry, in which the molar absorption coefficient (ε) is obtained using absorption and the Beer-Lambert law. By tuning the size of CsPbX₃ QDs, we obtain their corresponding ε leading to a calibration curve for calculating the nanocrystal concentrations. The ε at the band edge for CsPbX₃ (X = Cl, Br, or I) nanocrystals was found to be strongly dependent on the bandgap of the nanocrystals. We also obtained a reliable size dependence of the bandgap calibration curves to estimate the size of QDs from the absorption spectra.