Surface Treatment\nEngineering Enables Highly Efficient\nPerovskite Light-Emitting Diodes with Significantly Enhanced Modulation\nSpeed

Perovskite light-emitting diodes (PeLEDs) have emerged\nas promising\ncandidates for high-speed data-driven illumination sources in optical\ncommunication, but the mechanisms influencing the modulation speed\nof PeLEDs are rarely discussed. Although it has been reported to increase\nthe modulation bandwidth by reducing the device area, this is often\ngeometrically limited and reduces the luminous efficiency. Here, with\nthe surface treatment of 3-trifluoromethyl-benzylammonium iodide (3-TFBzAI)\nin different solvents, we can create a passivation/insulating layer\non perovskites to promote/decrease the efficiency and modulation speed\nof PeLEDs. Based on devices with different surface treatments, an\nequivalent circuit model to affect the modulation speed of a PeLED\nis constructed using impedance analysis. The optimal post-treatment\nwith chlorobenzene/isopropanol (CB/IPA) mixed solvent not only facilitates\nthe luminous efficiency through efficient recrystallization and surface\npassivation but also, more importantly, boosts the modulation speed\nthrough favored charge injection and reduced parasitic capacitance.\nIn particular, this improvement is more pronounced in small-area devices;\nup to a 77.6% increment of 3 dB bandwidth is realized in below 0.25\nmm<sup>2</sup> near-infrared PeLEDs with the resulting average external\nquantum efficiency of 11.67% and a 3 dB bandwidth of 1.9 MHz when\nthe modulation speed is not affected by the active size.