Nonlinear N,Cl-GQDs as Efficient Energy Transfer Antenna Materials for FRET-Enhanced Solar Energy Conversion

Abstract

Hybrid solar cells (HSCs) require advanced photoelectrodes to efficiently harvest light across a broad spectrum while minimizing charge recombination. Despite their complementary properties, the synergistic integration of nonlinear graphene quantum dots (GQDs) and dye sensitizers remains underexplored. In this study, an efficient hybrid photoelectrode is deposited by sensitizing fluorescent nonlinear GQDs with N3 dye on a plasmonic Au@TiO₂ substrate. The hydrothermal method is used to systematically engineer blue, brownish, and bluish-green, fluorescent N-doped, Cl-doped, and N,Cl-codoped GQDs. The N,Cl-GQDs exhibit self-defocusing behavior, indicating a negative nonlinear refractive index and distinct nonlinear optical properties. Nonlinear GQDs serve as light-harvesting antenna to optimize charge separation dynamics, with N3 dye molecules acting as energy acceptors in the coupled system. The spectral overlap between N,Cl-codoped GQDs and N3 dye maximizes fluorescence resonance energy transfer (FRET) efficiency and electron injection while suppressing recombination. Under AM1.5G illumination, the optimized photoelectrode achieves a V_oc of 0.705 V, a J_sc of 7.9 mA/cm², a fill factor of 70%, and a power conversion efficiency (η) of 3.9%, demonstrating improvements over reference N3-based solar cells. This study highlights the potential of nonlinear N,Cl-GQDs as effective energy transfer antenna materials for FRET-based solar energy conversion systems.