Regulating the phase distribution of quasi-2D perovskites using a three-dimensional cyclic molecule toward improved light-emitting performance

In this study, a molecule with a three-dimensional (3D) cyclic structure, a cryptand, is demonstrated as an effective additive for the quasi-two-dimensional (quasi-2D) PEA₂Cs_n-1Pb_nBr_3n+1 (n = 3, herein) to improve its light-emitting performance. The cryptand can effectively regulate the phase distribution of the quasi-2D perovskite through its intense interaction with PbBr₂, benefitting from its cage-like structure that can better capture the Pb²⁺ ions. Due to the inhibited growth of the low-n phases, a much-concentrated phase distribution is achieved for the cryptand-containing films. Moreover, its constituent O/N atoms can passivate the uncoordinated Pb²⁺ ions to improve the film quality. Such a synergistic effect thereby facilitates the charge/energy transfer among the multiple phases and reduces the non-radiative recombination. As a result, the quasi-2D perovskite light-emitting diode (PeLED) with the optimized cryptand doping ratio is shown to deliver the highest luminance (L_max) of 15 532 cd m^-2 with a highest external quantum efficiency (EQE) of 4.02%. Compared to the pristine device, L_max is enhanced by ∼5 times and EQE is enhanced by ∼10 times.