Controlling the formation energy of perovskite phase via surface polarity of substrate for efficient pure-blue light-emitting diodes

Quasi-two-dimensional (quasi-2D) perovskites are composed of self-organized multiple-quantum-well structures. Imbalanced crystallization during the solution-processed deposition results in the formation of different 2D phases, which are affected by the surface polarity of substrates. Herein, we investigate the influence of the surface polarity of the underlying hole injection layer (HIL) on the crystallization dynamics of each 2D phase and the luminescence properties of resulting quasi-2D perovskite films. Incorporating L-dopa involving hydroxyl groups into the HIL gives the substrate a higher surface polarity, allowing the decrease in the critical free energy of nucleation. This HIL ensures the formation of dense nuclei involving a small-sized nucleus, which enables the quasi-2D perovskite film to entail a lower-n-dominated phase distribution. The modulated phase distribution eventually induces a hypsochromically shifted luminescence spectrum. Furthermore, by controlling the ratio of L-phenylalanine and L-dopa, efficient perovskite light-emitting diodes (PeLEDs) having well-matched electronic structure and pure-blue perovskite emitter are realized with a maximum external quantum efficiency of 5.57% at 472 nm. This work provides a facile approach to achieving efficient pure-blue PeLEDs.