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/CH₃NH₃Sn­(Br_1–<i>x</i>I_<i>x</i>)₃/F8/Ca/Ag device architecture. In our tin iodide (CH₃NH₃SnI₃) LEDs, we achieved a 945 nm near-infrared emission with a radiance of 3.4 W sr^–1 m^–2 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 CH₃NH₃Pb(I_1–<i>x</i>Br_<i>x</i>)₃ 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 CH₃NH₃Pb­(I_1–<i>x</i>Br_<i>x</i>)₃ (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 CH₃NH₃PbI_1.2Br_1.8. We demonstrate a bromide–iodide lead perovskite film (CH₃NH₃PbI_1.2Br_1.8) with an optical bandgap of 1.94 eV, which is optimal for tandem cells of these materials with crystalline silicon devices