Abstract
Solution-processed organo-lead halide perovskites are produced with sharp, color-pure electroluminescence that can be tuned from blue to green region of visible spectrum (425–570 nm). This was accomplished by controlling the halide composition of CH3NH3Pb(BrxCl1–x)3 [0 ≤ x ≤ 1] perovskites. The bandgap and lattice parameters change monotonically with composition. The films possess remarkably sharp band edges and a clean bandgap, with a single optically active phase. These chloride–bromide perovskites can potentially be used in optoelectronic devices like solar cells and light emitting diodes (LEDs). Here we demonstrate high color-purity, tunable LEDs with narrow emission full width at half maxima (FWHM) and low turn on voltages using thin-films of these perovskite materials, including a blue CH3NH3PbCl3 perovskite LED with a narrow emission FWHM of 5 nm.
Highlights
The field of solution processed organic−inorganic halide perovskite based optoelectronics has emerged in the last couple of years.[1−6] This was initially driven by solar cells based on organo-lead halide perovskite that demonstrate power conversion efficiencies of above 20%.7 Thin films based on the mixed-halide CH3NH3Pb(IxCl1−x)[3] version of these perovskite materials feature high photoluminescence quantum yield (PLQE).[8]
We demonstrate high color-purity, tunable light emitting diodes (LEDs) with narrow emission full width at half maxima (FWHM) and low turn on voltages using thin-films of these perovskite materials, including a blue CH3NH3PbCl3 perovskite LED with a narrow emission FWHM of 5 nm
There are recent reports that the optical bandgap of lead halide perovskites can be tuned in the visible range of ∼550−780 nm through the use of solid solutions of bromide-iodide mixed halides.[10−12] These solid solution based thin films can be prepared by varying the ratio of the two individual pure trihalide perovskite solutions mixed together
Summary
LEDs to be realized, which have proven to be a difficult task with gallium nitride (GaN) being the only widely used option for commercial application. Urbach energy “EU” is an empirical parameter that gives an indication of the energetic disorder for a given semiconductor.[23,24] The Urbach energy is derived from the PDS absorption data by using the following expression: A = A0 exp((E − Eg)/EU), where A is the absorbance, A0 is a constant, and Eg is the bandgap of the material.[12,24,25] Figure 2d shows the correlation between the extracted Urbach energies and the full width at half maxima (FWHM) of the PL spectra and the (200) XRD reflection of the 5:1 organic to inorganic molar starting ratio CH3NH3Pb(BrxCl1−x)3 [0 ≤ x ≤ 1] perovskite films with various chloride content. Additional figures, including EDX, PDS absorption spectra, XRD spectra, and SEM images (PDF)
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