Enhanced brightness of red light-emitting diodes based on CsPbBr_xI_3-x–PEOXA composite films

The ionic crystals of perovskites have been widely studied for light-emitting diodes (LEDs) applications because their optical bandgap can be adjusted by changing the composition of the halide anions. However, the small ion size of Cs⁺ in inorganic perovskite causes poor crystallinity and a low exciton binding energy owing to the inherent defects in the bulk perovskite, which hinder the luminescence efficiency of perovskite LEDs (PeLEDs). Moreover, cesium lead iodide (CsPbI₃), which is studied as an emitter of red PeLEDs, is not only required to be heat-treated at a high temperature of 300 °C for phase stabilization but also vulnerable to O₂ and moisture in the air. To solve these problems, high performance red PeLED based on CsPbBr_0.6I_2.4 perovskites were fabricated by using poly(2-ethyl-2-oxazoline) (PEOXA) as a hydrophilic polymer. This method reduced the transition temperature of CsPbBr_0.6I_2.4 from the δ–phase (tilted octahedral) to the α–phase (cubic) and stabilized the perovskite phase. Thus, an exceptionally efficient and stable PeLED based on a CsPbBr_0.6I_2.4–45% PEOXA film with a maximum external quantum efficiency (EQE) of 5.4%, luminance of 201.2 cd/m², and current efficiency (CE) of 3.2 cd/A was fabricated. Moreover, the PeLED exhibited a low turn-on voltage (1.5 V) and CIE coordinates of (0.726, 0.274), with pure-red emission.