Porphyrin-nitrogen carbon dot composites for high-performance organic light-emitting diodes

Fluorescent organic light-emitting diodes (OLEDs) still face major obstacles to combining high efficiency with solution processability and energy-sustainable operation. In this work, a tetra-carboxyphenyl porphyrin–nitrogen carbon dots (TCPP-NCDots) derivative is introduced as a solution-processable electron transport layer (ETL) in OLEDs based on a green–yellow emissive polymer. The structural, optical, and electronic properties of the TCPP-NCDots ETL are comprehensively characterised by ultraviolet–visible absorption spectroscopy, steady-state photoluminescence, Fourier-transform infrared spectroscopy, atomic force microscopy, and cyclic voltammetry. These studies reveal a synergistic effect of porphyrin functionalisation on the carbon dots, which improves electron injection and transport toward the emissive layer. At an optimum concentration of 1 mg mL−1, the TCPP-NCDots ETL yields a 21.6% enhancement in external quantum efficiency compared with the reference device without an ETL, while simultaneously suppressing efficiency roll-off. The optimised devices also maintain stable operation under ambient conditions, highlighting TCPP-NCDots as a promising, sustainable ETL platform for next-generation fluorescent OLEDs.