The successful implementation of perovskite light-emitting diodes (PeLEDs) in advanced displays and lighting has proven to be challenging because of the inferior performance of blue devices. Here, we point out that a strained system would lead to the quasi-degenerate energy state to enhance the excited-state transition due to the formation of double-polarized transition channel. The tensile strained structure also brings about a synergetic control of the carrier dynamics in virtue of lattice structure deformation and reduced dimensional phase regulation to promote carrier population in large bandgap domains and to realize near-unit energy transfer from the large bandgap phases to the emitter phases. Accordingly, high external quantum efficiencies of 14.71 and 10.11% are achieved for the 488- and 483-nanometer PeLEDs. This work represents a versatile strategy using a strained system to achieve enhanced radiative emission for the development of efficient PeLEDs.

The efficiency of blue perovskite light-emitting diodes (PeLEDs) is lagging far behind their green and red counterparts. Here, we demonstrate high-efficiency sky-blue PeLEDs by employing pseudohalide thiocyanates, which are ammonium thiocyanate (NH4SCN), methylammonium thiocyanate (MASCN), and guanidine thiocyanate (GASCN), as additives in a quasi-two-dimensional cesium lead halide perovskite emission layer. Although the thiocyanate incorporation can modify the formation energy to induce more n = 1 phases that are undesirable for light emission due to their strong electron–phonon coupling, the pseudohalide additive is able to passivate the nonradiative trap defects and stabilize the perovskite structure by filling the halide vacancy, coordinating to Pb with the Pb–S bond, and enhancing the bonding of the perovskite lattice. It is found that the passivation effect outperforms the electron–phonon coupling loss, yielding a higher photoluminescence quantum yield. As a result, the external quantum efficiencies of the sky-blue PeLEDs are improved from 5.75 to 11.93%. The thiocyanate-modulated devices also exhibit good spectral and operational stability. This work revealed the important roles of the pseudohalide thiocyanates in the improvement of sky-blue PeLEDs.

Halide perovskite light‐emitting diodes (PLEDs) have raised considerable attention due to their high color purity and rapid development performance. Although high‐efficiency PLEDs have been continuously and repeatedly reported, the lack of a highly reproducible manufacturing process for PLEDs hinders their future development and commercialization. Here, a generic protocol for rational control of the nucleation and crystallization process of the perovskite emission layer is reported. Through the monitoring of the photoluminescence during spin‐coating, the antisolvent dripping time can be precisely determined. Therefore, it is possible to repeatedly produce a perovskite emission layer with high PLQY, smooth surface/interface, and good homogeneity. As a result, high‐performance PLEDs are easily obtained. Moreover, the standard deviation of the fabricated PLEDs performance is smaller than 0.8%, showing high reproducibility independent of the process conditions such as the process temperature, solvent atmosphere, and spin‐coating parameters, which highlights the statement of the importance of rationally control of the antisolvent process. The methodology provides important progress towards highly reproducible manufacturing of PLEDs for practical applications.