Metal halide perovskites are promising materials for light-emitting diodes (LEDs) due to their high photoluminescence quantum yields, narrow emission linewidths and defect tolerance. Low-dimensional analogs of 3D perovskites are obtained by inserting large organic ligands that divide the lattice into a finite number (n) of inorganic monolayers. Increasing the organic ligand content decreases the average n value and increases the bandgap. Extra ligands (e.g. IPABr or PEABr) have been applied to achieve blue emission, but limited control over the distribution of quantum well (QW) widths results in sky-blue emission (longer than 490 nm) and low device performance (EQE below 1.5%). Other strategies in controlling QW thickness also lead to wide n distributions: these films exhibit either redshift of the TA signal wavelength or asymmetric emission peaks. There is, as a result, significant interest in controlling the QW distribution while keeping photoluminescence quantum yield high. The dynamic nature of QW formation produces a distribution of differently-sized QWs with various bandgaps. The thin (low-n) QWs funnel high-energy excitons to the lowest-bandgap (high-n) perovskite QWs, shifting the emission profile to green, even when the concentration of larger-n QWs is low. It is thus critical to suppress n > 3 QW formation to ensure the emission remains blue.
Recently, the research group of Prof. Liang-sheng Liao, collaborated with Prof. Edward H. Sargent (University of Toronto), reported a quasi-two-dimensional CsPbBr3 blue emitter by using chelating effect of amino-acid analogs. They demonstrated that adding amino-acid in perovskite precursors helps to control quantum-well thickness distribution and passivate traps. Transient absorption and density functional calculations confirm the validity of this strategy. Benefit from the controlled size distribution and well passivation, they achieve blue LEDs with an external quantum efficiency of over 6% and CIE coordinates of (0.12, 0.14).
The first author, Dr. Ya-Kun Wang, is from FUNSOM, Soochow University.
Link to Paper: https://doi.org/10.1038/s41467-020-17482-0
Link to Prof. Liao’s Group: http://funsom.suda.edu.cn/funsomen/c4/00/c3002a50176/page.htm
Editor: Danting Xiang