Effect of nematic liquid crystal on light extraction in perovskite light-emitting diodes

Perovskite materials have been widely applied as the active emitter in light-emitting diodes for display and illumination. The key evaluation index of the perovskite light-emitting device (PeLED) is external quantum efficiency (EQE) determined by the efficiencies of radiative recombination and light extraction simultaneously. In this work, the effects of nematic liquid crystal (NLC) on light extraction of bulk perovskite are firstly and systematically studied, and the performance improved PeLEDs are further fabricated. The luminance as large as 5033 cd/m2 and EQE of 0.32% are obtained, both having an order of magnitude improvement over the reference device. Results demonstrate that the presence of rod-shaped nematic liquid crystals reduces the large refractive index contrast between the bulk perovskite layer and charge transportation layers and induces light to propagate in an out-of-plane direction instead of non-directional scattering. Moreover, this PeLED shows great device stability since the passivation effect of amino groups of nematic liquid crystals. This work suggests that the utilisation of nematic liquid crystal can be a cost-effective strategy for achieving a high-performance perovskite-based optoelectronic device.