Band Alignment with Self‐Assembled 2D Layer of Carbon Derived from Waste to Balance Charge Injection in Perovskite Crystals Based Rigid and Flexible Light Emitting Diodes

Abstract The halide perovskite nanocrystals (P‐NCs) can address a plethora of issues of the light‐emission technologies, due to its low temperature processing. To successfully employ P‐NCs for light‐emitting diodes (LEDs), one needs to resolve the issues of stability of the LEDs. The stability of device can be achieved by charge balance of electrons and holes recombination in active material. To investigate this herein, a self‐assembled carbon dots (CDs) layer is fabricated from waste small strands of human hair. The self‐assembled CDs layer is used beneath P‐NCs layer to reduce the band‐off set for hole transport, thus balancing the electron and holes carrier in active layer. The layer is used as an active light‐emitting layer to fabricate a LED device that exhibits green luminescence of 4800 cd m⁻² at a current efficiency of 10.7 cd A⁻¹ and external quantum efficiency of 4.8%. The LED exhibits operational stability of nearly 200 h. The same film is used to demonstrate a flexible device with maximum luminescence of 2259 cd m⁻², with a high current density of 474 mA cm⁻², current efficiency of 1.37 cd A⁻¹ and a low turn‐on voltage of 3.5 V. All the display devices are measured in air without encapsulation.