Modulating carrier injection through rational control of hole transport layer for perovskite light-emitting diodes

Charge balance in the emissive layer through well-matched energy levels and reduced barrier of the transport layers can help to attain maximum radiative recombination. In this work, four hole transporting layers (HTLs) have been used to regulate the hole injection in the emissive layer. The HTLs have varying HOMO levels aligning with the work function of FTO and HOMO of the emissive layer. Among the four HTLs, NPD-based perovskite LED device demonstrated the best performance with the highest brightness of 24,343 cd m⁻², current efficiency of 16.2 cd A⁻¹, and turn-on voltage of 4.7 V. The main reason for such improved results was the well-matched HOMO of NPD with both the anode and emissive layer supporting enhanced hole injection. Both the photoluminescence and electroluminescence studies confirm pure green emission with CIE coordinates (0.22, 0.75). The best quality film morphology for NPD-based perovskite film supported efficient transport of the charges. The crystallinity of the NPD-based perovskite film was also found to be optimum. Finally, stability of the working PLEDs is tested and superior stability with 79% of the retention of initial brightness is observed for NPD-based device.