Enhanced brightness of red light-emitting diodes based on CsPbBrxI3-x–PEOXA composite films

Abstract

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 CsPbBr0.6I2.4 perovskites were fabricated by using poly(2-ethyl-2-oxazoline) (PEOXA) as a hydrophilic polymer. This method reduced the transition temperature of CsPbBr0.6I2.4 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 CsPbBr0.6I2.4–45% 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.