Symmetry-Engineered Multifunctional Hemicyanine Hole Transport Material for High Performance Blue Perovskite Light-Emitting Diodes

As an essential component in blue perovskite light-emitting diodes (PeLEDs), functionally tailored hole transport materials (HTMs) play a decisive role in reducing the hole injection barrier, mitigating interfacial defects, and thus enhancing device performance. Herein, we report two solution-processable D-π-A hemicyanine dyes, which exhibit asymmetric/symmetric configurations and contain electron-withdrawing groups and Lewis base donors. As multifunctional HTMs, two dyes not only present high hole mobilities with improved energy level alignment in PeLEDs, but also enable the perovskite defects passivation and n phases manipulation. Interestingly, the symmetric dye achieves dual-channel hole injection and multisite anchoring for the quasi-2D perovskite (PEACsPbBr_2.1Cl_0.9). The passivated perovskite film forms an augmented distribution of large n phases and suppressed small n phases, thereby promoting radiative exciton recombination. Consequently, symmetric dye-treated PeLED exhibits an impressive blue electroluminescence (EL) with a maximum luminance reaching 5842 cd m^-2, a peak external quantum efficiency (EQE) of 13.71% and an improved operational half lifetime (T₅₀) of 6.7 min at 100 cd m^-2, demonstrating its performance advantages over the reported PEACsPb(Br_xCl_1-x)₃ PeLEDs. This work provides an innovative perspective for designing multifunctional HTMs by conformation engineering and gains insight into the interfacial contact for high performance perovskite optoelectronics.