Quenching‐Resistant Solid‐State Photoluminescence of Graphene Quantum Dots: Reduction of π−π Stacking by Surface Functionalization with POSS, PEG, and HDA

Abstract Graphene quantum dots (GQDs) have attracted great attention as next‐generation luminescent nanomaterials due to the advantages of a low‐cost process, low toxicity, and unique photoluminescence (PL). However, in the solid‐state, the strong π−π stacking interactions between the basal planes of GQDs lead to aggregation‐caused PL quenching (ACQ), which impedes practical application to light‐emitting devices. Here, surface functionalized GQDs (F‐GQDs) by polyhedral oligomeric silsesquioxane (POSS), poly(ethylene glycol) (PEG), and hexadecylamine (HDA) to reduce π−π stacking‐induced ACQ is presented. The POSS‐, PEG‐, and HDA‐functionalized GQDs show a significant enhancement in PL intensity compared to bare GQDs by 9.5‐, 9.0‐, and 5.6‐fold in spin‐coated film form and by 8.3‐, 7.2‐, and 3.4‐fold in drop‐casted film form, respectively. Experimental results and molecular dynamics simulations indicate that steric hindrance of the functionalization agent contributes to reducing the π−π stacking between adjacent GQDs and thereby enabling quenching‐resistant PL in the solid‐state. Moreover, the GQD‐based white light‐emitting diodes fabricated by mounting HDA‐GQDs on a UV‐LED chip exhibits efficient down‐conversion for white light emission with a high color rendering index of 86.2 and a correlated‐color temperature of 5612 K at Commission Internationale de l'Éclairage coordinates of (0.333, 0.359).