Quasi-two-dimensional perovskite light-emitting diodes (quasi-2D PeLEDs) are emerging as high-potential candidates for new generation of wide-color gamut displays due to their simple, low-cost solution process, and high color purity. However, the luminescence performance of quasi-2D perovskite films is severely limited by dispersed phase distribution and excessive defect density, which are caused by excessive diffusion of nucleation sites during the perovskite growth stage. Here, the benzylphosphonic acid (BPA) molecule, owing to its strong P–O–Pb bond energy sites and strong electronegativity to PEA⁺, can aggregate lead-halide octahedron to grow high-dimensional phases, avoiding scattered low-dimensional phases (n = 1). The continuous gradient phase distribution will be beneficial to smooth carrier injection and effectively suppress the leakage current in PeLEDs. Meanwhile, the introduction of phosphonic acid groups will fill the vacancies of Pb ions and reduce non-radiative recombination. As a result, the maximum external quantum efficiency (EQE) of PeLEDs can be increased from 8% to 20.6% with a 514 nm light emission and a 21 nm full-width half maximum, and the device lifetime (T₅₀) is nearly 6-fold of the pristine sample. In addition, this strategy is also suitable for other wavelength. For example, in blue light, performance improvement is also realized that the maximum EQE of 8% and the luminance increased from 1045 to 5264 cd/m². These results provide a feasible strategy to regulate the phase distribution and passivate the defects of quasi-2D perovskites.

Developing light-emitting diodes (LEDs) with the merits of low driving and high brightness has always been attractive. Considering the carrier dynamic process under electroexcitation, the built-in potential (V_bi) represents the moment that the photons start to be produced in a LED. However, it has not been carefully studied and discussed. Here, we observed that by employing an interface regulation strategy to enhance hole concentration, the V_bi of quantum dot LEDs (QLEDs) can be reduced. Combined with the characterization methods of Mott–Schottky (MS) and scanning Kelvin probe microscopy (SKPM), the key indicator of V_bi on driving voltage for QLEDs is confirmed. Profiting from the reduction of V_bi, a record-breaking ultra-low turn-on voltage of 2.2 V (@1 cd/m²) is achieved in a blue QLED. The blue QLED shows an advantage of high brightness under low driving voltages, i.e., 1000 cd/m²@3.10 V and 5000 cd/m²@3.88 V. This work proposes a reference strategy to predict and analyze the driving voltage issue, which is beneficial to facilitating the development of low-driving QLEDs in the future.