Nonradiative electron-hole recombination dynamics in edge-selective phosphorus-doped graphene quantum dots for energy conversion applications

Abstract

Doping with heteroatoms is an effective way to modify the electronic structures and photophysical properties of graphene quantum dots (GQDs). However, there are few studies on phosphorus-doped GQDs (P-GQDs), especially with respect to the dynamics of electron-hole recombination, which plays a crucial role in the energy conversion performance of P-GQDs. In the current study, we investigate the effect of phosphorus-containing groups (i.e., phosphine oxide, phosphonic acid, phosphate, and phosphinic acid) on the electronic structures, optical properties, and dynamics of nonradiative recombination of P-GQDs with different edge coverages and structural symmetries. Our results show that P-doping disrupts the integrity of the conjugated π-skeleton of carbon system, leading to the localization of electrons in P-GQDs. The phosphine oxide has a stronger effect on the sp2 bonding environment of the carbon skeleton, leading to a greater impact on the geometrical and electronic structures of the P-GQDs than in the other P-functionalized systems. The increase in the passivation density of phosphinic acid leads to localization of electron and hole densities at the periphery of the GQDs. In addition, the PC bond in phosphonic acid dramatically increases the electronic coupling, leading to the fastest non-radiative decay rate. The overall photovoltaic performance of phosphate- and phosphine oxide-functionalized GQDs are better than the other P-functionalized GQDs. Our calculations provide guidance for the rational design of P-doping configurations in P-GQDs to improve their energy conversion efficiency.