Enhanced Brightness Through Rational Design of Hole Transport Layer for Blue Perovskite Light-Emitting Diodes

State-of-the-art blue lead-halide perovskite light-emitting diodes (PeLEDs) suffer from low brightness and short lifetime, which constitutes a critical bottleneck for the development of full-color perovskite displays. A major performance bottleneck originates from the considerable hole injection barrier at the interface of hole-transporting layers (HTLs) and blue perovskite emissive layers. To address this, we propose a non-protic interfacial modification strategy, by designing and synthesizing two novel organic small molecules - 9,9-dibutyl-N²,N²,N⁷,N⁷-tetrakis(4-methoxyphenyl)-9H-fluorene-2,7-diamine (MPFO) and 9,9-bis(3-(dimethylamino)propyl)-N²,N²,N⁷,N⁷-tetrakis(4-methoxyphenyl)-9H-fluorene-2,7-diamine (MPFO-MAP)-to modify the poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) HTL. MPFO-MAP, with terminal dimethylamino groups, concurrently reduces the hole-injection barrier, accelerates hole transport, thereby balancing electron and hole current, while passivates PEDOT:PSS/perovskite interfacial defects to enhance radiative recombination. The MPFO-MAP modified blue PeLED achieves a maximum luminance of 8272 cd/m² and a champion external quantum efficiency of 12.6%, representing 2.9-fold and 3.7-fold improvements over the pristine PEDOT:PSS device, respectively. This dual-function non-protic interfacial engineering strategy provides a versatile molecular design blueprint for high-brightness blue PeLEDs and can be extended to other perovskite-based optoelectronic devices, facilitating their practical application.