Regulation of Optoelectronic Properties for Sky-Blue Perovskite Light-Emitting Diodes Using Small Amine Molecule Ligands

Perovskite light-emitting diodes (PeLEDs) have significant potential for applications such as full-color displays and energy-efficient lighting. However, the development of blue PeLEDs lags far behind that of red and green devices, which has seriously impeded the further development of PeLEDs. Here, we achieve sky-blue PeLEDs by using a method of substituting the large cationic ligand phenethylamine (PEA) with the doping of small amine molecules. We systematically analyze the working mechanism of 8 small amine molecules (i.e., large-size monoamine, small-size monoamine, and diamine molecules) during the formation of perovskite films, together with their effects on the optoelectronic properties of films and the performance of PeLEDs. Finally, 2-aminoacetamidine dihydrobromide (2-AD) based sky-blue PeLEDs are developed with a maximum external quantum efficiency (EQE) of 3.63%, which is 3.7-fold higher than that of pristine devices. In addition, the maximum luminance is enhanced with a factor of 10.3-fold (3192 cd/m<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><roman>2</roman></sup>), and the operational voltages are largely reduced (e.g., the turn-on voltage is decreased from 4 to 2.9 V compared to pristine devices). The findings not only give an insightful understanding of the effect of ligand engineering on PeLEDs, but also provide an alternative approach to achieve high-performance blue PeLEDs.