Self-Organized Carbazole Phosphonic Acid Additives at Buried Interface Enhance Efficiency of Blue Perovskite LEDs

Carbazole phosphonic acids (CPAs) that are used in self-assembled monolayers (SAMs) are well-reported. Yet, an understanding of their broader application still needs to be fully established. In this work, we demonstrate that incorporating CPAs into blue quasi-2D perovskite precursors as additives is an effective strategy for fine-tuning phase distribution and enhancing the radiative characteristics of the resultant films. 2-(9H-Carbazol-9-yl)ethylphosphonic acid (2PACz) emerges as the most effective molecule for improving device performance. Significantly, when the perovskite film is deposited onto a hole injection structure of ITO/Mg0.1Ni0.9Ox/SAM/poly(9-vinylcarbazole) (PVK), 2PACz preferentially migrates to the PVK/perovskite interface. This phenomenon is driven by the strong interaction between the carbazole components of both PVK and 2PACz, leading to a stabilized interface. Coupled with the controlled phase distribution of the perovskite, this approach results in a marked increase in external quantum efficiency for blue perovskite LEDs, advancing from 11% to beyond 15%. These insights underscore the versatility of CPAs in the development of high-efficiency optoelectronic devices.