Highly Efficient Blue Light-Emitting Diodes Based on Perovskite Film with Vertically Graded Bandgap and Organic Grain Boundary Passivation Shells

["Metal halide perovskite materials have emerged as a promising class of semiconductors for high-performance optoelectronic applications, particularly for light-emitting diodes (LEDs), due to their high quantum efficiency, facile color tunability, narrow emission line widths, as well as cost-effectiveness. Despite the great successes on green and red perovskite LEDs (PeLEDs), the external quantum efficiency (EQE) of blue PeLEDs still lags far behind that of green and red counterparts. Here, wavelength tunable pure and deep blue PeLEDs with high EQE are presented, achieving 17.5% and 10.8% for emission wavelengths of 472 and 461 nm, respectively. The wavelength tenability and high EQE are attributed to the unique vertically graded bandgaps and grain boundary organic shells in the perovskite films. The results demonstrate a significant performance improvement in blue PeLEDs, provide a novel route to fabricate high-performance pure and deep blue PeLEDs that can match the performance of the green and red PeLEDs for future lighting and display applications.","The wavelength tunable pure and deep blue perovskite light-emitting diodes with high external quantum efficiency (EQE) of 17.5% and 10.8% for emission wavelengths of 472 and 461 nm, respectively are presented. The wavelength tenability and high EQE are attributed to the unique vertically graded bandgaps and grain boundary organic shells in the perovskite films after PbCl2 doping.image"]