Surface Treatment Engineering Enables Highly Efficient Perovskite Light-Emitting Diodes with Significantly Enhanced Modulation Speed

Perovskite light-emitting diodes (PeLEDs) have emerged as promising candidates for high-speed data-driven illumination sources in optical communication, but the mechanisms influencing the modulation speed of PeLEDs are rarely discussed. Although it has been reported to increase the modulation bandwidth by reducing the device area, this is often geometrically limited and reduces the luminous efficiency. Here, with the surface treatment of 3-trifluoromethyl-benzylammonium iodide (3-TFBzAI) in different solvents, we can create a passivation/insulating layer on perovskites to promote/decrease the efficiency and modulation speed of PeLEDs. Based on devices with different surface treatments, an equivalent circuit model to affect the modulation speed of a PeLED is constructed using impedance analysis. The optimal post-treatment with chlorobenzene/isopropanol (CB/IPA) mixed solvent not only facilitates the luminous efficiency through efficient recrystallization and surface passivation but also, more importantly, boosts the modulation speed through favored charge injection and reduced parasitic capacitance. In particular, this improvement is more pronounced in small-area devices; up to a 77.6% increment of 3 dB bandwidth is realized in below 0.25 mm2 near-infrared PeLEDs with the resulting average external quantum efficiency of 11.67% and a 3 dB bandwidth of 1.9 MHz when the modulation speed is not affected by the active size.