2 research outputs found
Tunable Near-Infrared Luminescence in Tin Halide Perovskite Devices
Infrared
emitters are reasonably rare in solution-processed materials.
Recently, research into hybrid organo-lead halide perovskite, originally
popular in photovoltaics,− has gained traction in light-emitting
diodes (LED) due to their low-cost solution processing and good performance.− The lead-based electroluminescent materials show strong colorful
emission in the visible region, but lack emissive variants further
in the infrared. The concerns with the toxicity of lead may, additionally,
limit their wide-scale applications. Here, we demonstrate tunable
near-infrared electroluminescence from a lead-free organo-tin halide
perovskite, using an ITO/PEDOT:PSS/CH<sub>3</sub>NH<sub>3</sub>SnÂ(Br<sub>1–<i>x</i></sub>I<sub><i>x</i></sub>)<sub>3</sub>/F8/Ca/Ag device architecture. In our tin iodide (CH<sub>3</sub>NH<sub>3</sub>SnI<sub>3</sub>) LEDs, we achieved a 945 nm near-infrared
emission with a radiance of 3.4 W sr<sup>–1</sup> m<sup>–2</sup> and a maximum external quantum efficiency of 0.72%, comparable with
earlier lead-based devices. Increasing the bromide content in these
tin perovskite devices widens the semiconductor bandgap and leads
to shorter wavelength emissions, tunable down to 667 nm. These near-infrared
LEDs could find useful applications in a range of optical communication,
sensing and medical device applications
Preparation of Single-Phase Films of CH<sub>3</sub>NH<sub>3</sub>Pb(I<sub>1–<i>x</i></sub>Br<sub><i>x</i></sub>)<sub>3</sub> with Sharp Optical Band Edges
Organometallic lead-halide perovskite-based
solar cells now approach
18% efficiency. Introducing a mixture of bromide and iodide in the
halide composition allows tuning of the optical bandgap. We prepare
mixed bromide–iodide lead perovskite films CH<sub>3</sub>NH<sub>3</sub>PbÂ(I<sub>1–<i>x</i></sub>Br<sub><i>x</i></sub>)<sub>3</sub> (0 ≤ <i>x</i> ≤ 1) by
spin-coating from solution and obtain films with monotonically varying
bandgaps across the full composition range. Photothermal deflection
spectroscopy, photoluminescence, and X-ray diffraction show that following
suitable fabrication protocols these mixed lead-halide perovskite
films form a single phase. The optical absorption edge of the pure
triiodide and tribromide perovskites is sharp with Urbach energies
of 15 and 23 meV, respectively, and reaches a maximum of 90 meV for
CH<sub>3</sub>NH<sub>3</sub>PbI<sub>1.2</sub>Br<sub>1.8</sub>. We
demonstrate a bromide–iodide lead perovskite film (CH<sub>3</sub>NH<sub>3</sub>PbI<sub>1.2</sub>Br<sub>1.8</sub>) with an optical
bandgap of 1.94 eV, which is optimal for tandem cells of these materials
with crystalline silicon devices