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.

Information visualization plays a prominent role in the development of wearable health monitoring devices. The use of multicolor electroluminescent (EL) devices for signal indicators has attracted considerable attention due to their simplicity, low cost, and easy observation. Here, we demonstrated a visual electrocardiogram (ECG) synchronization monitor using perovskite-based multicolor light-emitting diodes (PMCLEDs). The PMCLED can emit colorful light according to the change of the ECG signal. Through the addition of polyethylene glycol (PEG) in the charge transport layer (CTL) to modulate the carrier injection, color switching from deep red to green in a wide color range is obtained. The fabricated flexible PMCLEDs exhibit good color-tunable stability and high bending resistance, which can be conformally integrated on human skin for wearable application. By converting the small ECG signal to a voltage scheme to drive the PMCLEDs with dynamic sequential color change, we realized the function of real-time visualization of ECG information through a facile and low-cost way. The ECG visualization design may provide opportunities for the development of healthcare products with real-time biosignal monitoring.

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In recent years, impressive progress has been made in developing high‐performance perovskite light‐emitting diodes (PeLEDs) with efficiencies comparable to those of traditional organic light‐emitting diodes (OLEDs). It is convinced that the position of exciton recombination zone is crucial for the performance of the LEDs, however, the dynamics of the exciton recombination zone in PeLEDs and its influence on the performance of PeLEDs remain unclear. Herein, luminescent quantum‐dots (QDs) sensing layers with different energy band landscape and electric properties are introduced into PeLEDs as probers to investigate the position of recombination zone. Consequently, it is found that the band offset between the perovskite layer and the adjacent layer is vital to the position of recombination zone. Modulating the recombination zone towards the bulk of the emission layer helps to improve the device performance as well as the operational stability.