Efficient Dion-Jacobson perovskite light-emitting diodes via mixed cation engineering.

Quasi-two-dimensional (quasi-2D) perovskites with high exciton binding energy (Eb) can confine carriers to form an energy funnel cascade, accelerate carrier localization to the emitting domain, and decrease nonradiative recombination loss. Herein, it is shown that partially alloying Cs+ cations into formamidinium (FA)-based Dion-Jacobson (DJ) perovskites and adjusting the stoichiometric ratio can simultaneously modify the tolerance factor, decrease the phase formation enthalpy, improve the morphology, modulate the phase distribution, and boost the current efficiency. By incorporating CsBr to substitute for some of the FABr, perovskite films with narrower phase distributions and fewer defects are obtained, and the current efficiency is boosted from 18.2 to 25.3 cd/A. A high current efficiency of 42.1 cd/A, a record (as far as we are aware) external quantum efficiency (EQE) of 10.5%, and a maximum luminance of 18600 cd/m2 with an emission peak at 529 nm are obtained when the Lewis base passivation agent TPBi is dissolved in the antisolvent. This is the first time, to the best of the authors' knowledge, that efficient 1,4-phenyldimethylammonium dibromide (PHDMADBr)-based green-light DJ perovskite light emitting diodes (PeLEDs) based on mixed Cs+ and FA+ cations have been fabricated.

Enhancing the Luminance Efficiency of Formamidinium-Based Dion-Jacobson Perovskite Light-Emitting Diodes via Compositional Engineering.

In this paper, the phase formation mechanism of formamidinium (FA)-based Dion-Jacobson (DJ) perovskites is uncovered for the first time, which includes the formation of the n1 domain (n = 1 perovskite phase) and a trace amount of the large n domain in the spin-coating process and the growth of the n2 domain and the large n domain during the thermal annealing stage. The phase formation mechanism clearly reveals the different phase distributions between FA-based Ruddlesden-Popper (RP) and FA-based DJ perovskite films at different stages of film preparation due to the larger formation energy of the DJ perovskites. According to this phase formation mechanism, we put forward an effective strategy of the small A-site cation compositional engineering. Then, excess perovskitizer cations (FA+) are introduced to increase the crystallinity, modulate the phase distribution and passivate defects without disturbing the structure of DJ perovskites simultaneously. The final green-light DJ PeLED devices show a maximum luminance of 41 520 cd/m2 and a maximum current efficiency of 31.1 cd/A (EQE: 8.5%), which are the record values so far. The final DJ PeLEDs show an improved operational lifetime of ca. 15 min at an initial luminance of ca. 800 cd/m2. Our results suggest that DJ perovskites can be promising for light-emitting applications.