Harnessing Conformational Disorder of Organic Cations for Efficient Blue Quasi‐2D Perovskite LEDs

Despite quasi‐2D perovskite offering great control over the optoelectronic properties, disordered organic cations are often perceived as detrimental to device performance, primarily affecting charge carrier mobility. However, it is proposed that such disordered organic cations‐enabled excellent excitonic properties can be beneficial for fabricating high‐efficiency perovskite light‐emitting diodes (PeLEDs) facilitated by reduced dielectric screening effect. Here, by incorporating acetamidinium bromide additives, the conformational disorder of organic cation is precisely manipulated and meticulously probed using sum frequency generation vibrational spectroscopy. Finally, a distinctive inverse relationship is elucidated between the degree of conformational order, characterized as relative structure ordering , and key performance metrics such as photoluminescence quantum yield and external quantum efficiency (EQE). By optimizing the configurational disorder, sky‐blue (485 nm) PeLEDs achieve a noteworthy EQE of 14.42% and exhibit significantly prolonged operational stability in open‐air conditions. This finding underscores the potential advantages of disordered organic cations in enhancing exciton properties and radiative recombination efficiency.