Abstract
Metal halide perovskites have been investigated for the next-generation light-emitting materials because of their advantages such as high photoluminescence quantum yield (PLQY), excellent color purity, and facile color tunability. Recently, red- and green-emissive perovskite light-emitting diodes (PeLEDs) have shown an external quantum efficiency (EQE) of over 20%, whereas there is still room for improvement for blue emissive PeLEDs. By controlling the halide compositions of chloride (Cl−) and bromide (Br−), the bandgap of perovskites can be easily tuned for blue emission. However, halide segregation easily occurrs in the mixed-halide perovskite under light irradiation and LED operation because of poor phase stability. Here, we explore the effect of A-site cation engineering on the phase stability of the mixed-halide perovskites and find that a judicious selection of low dipole moment A cation (formamidinium or cesium) suppresses the halide segregation. This enables efficient bandgap tuning and electroluminescence stability for sky blue emissive PeLEDs over the current density of 15 mA/cm2.
Highlights
Metal halide perovskites (MHPs) are composed of three elements with ABX3 structures, where theA-site is typically occupied by an organic cation such as methylammonium (MA+ ), formamidinium (FA+ ) or an inorganic cation cesium (Cs+ ); the B-site is occupied by a lead (Pb2+ ) or tin (Sn2+ ) ion; and the X-site is occupied by a halide anion such as chloride (Cl− ), bromide (Br− ), iodide (I− ) or a mix of the three
The sky-blue emissive perovskite light-emitting diodes (PeLEDs) were constructed with the following structures: indium tin oxide (ITO) as anodes; PEDOT:PSS as hole transporting layers; quasi-2D mixed-halide perovskite films as the emissive layer; TPBi as the electron transporting layer; lithium fluoride (LiF)/Al as the cathode (Figure 1a)
We studied the effect of A-site cations on the color tunability and EL spectrum stability of
Summary
Metal halide perovskites (MHPs) are composed of three elements with ABX3 structures, where theA-site is typically occupied by an organic cation such as methylammonium (MA+ ), formamidinium (FA+ ) or an inorganic cation cesium (Cs+ ); the B-site is occupied by a lead (Pb2+ ) or tin (Sn2+ ) ion; and the X-site is occupied by a halide anion such as chloride (Cl− ), bromide (Br− ), iodide (I− ) or a mix of the three. Metal halide perovskites (MHPs) are composed of three elements with ABX3 structures, where the. In terms of light emitting devices, the most attractive property of perovskite is the tunable nature of the bandgap, and the emission wavelength, by adjusting the halide composition; wavelengths across the electromagnetic spectrum from deep-blue to infrared range have been reported. MHPs have excellent luminescence properties including high color purity (full width at half-maximum (FWHM) ≤ 20 nm) and a high photoluminescence quantum yield (PLQY). Red- and green-emissive PeLEDs achieved high external quantum efficiencies (EQEs) of over 20% and showed great potential for display applications [7,9,10], whereas blue-emissive PeLEDs have shown much lower EQEs of ~12% [11,12,13]; this poor performance of blue-emissive PeLEDs is still considered to be one of the most challenging barriers to their device applications.
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