Effect of boron and nitrogen doping on carrier relaxation dynamics of graphene quantum dots

In the present work, we perform ab initio nonadiabatic molecular dynamics to investigate the charge carrier relaxation dynamics in pristine, boron doped and nitrogen doped graphene quantum dots, respectively. Heteroatom doping changes the local bonding environment of carbon atoms, and induces the charge trapping states into the band gaps of boron doped graphene quantum dot (BGQD) and nitrogen doped graphene quantum dot (NGQD), respectively. Elastic electron-phonon energy exchange destroys the electronic coherence of charge trapping states resulting in a slower electron trapping in BGQDs and a slower hole trapping in NGQDs, respectively, which indicate the high electron mobility of BGQD and high hole mobility of NGQD. In addition, our calculation results suggest the slow and asymmetric electron and hole relaxations of BGQDs are beneficial for both oxidation and reduction reactions for water splitting, while the slower electron relaxation than hole relaxation promises NGQDs the oxidation activity for catalyzing the water splitting. Our work can be used to guide the chemical modification of electronic structures of graphene based QD materials. (paper)