Tailoring the defect ionization energy to activate the near-infrared photocatalytic activity of poly(heptazine imide)

The role of defects in photocatalysis is rarely investigated more intuitively from the perspective of defect ionization energy (DIE), although it is the most important parameter for evaluating the depth of defect traps. Here, the crystalline poly(heptazine imide) (PHI) is adopted as an illustrative example to optimize the DIE and charge separation by regulating the carbon doping contents, ultimately activating the near-infrared photocatalytic activity. Shallow defect traps induced by doping (DIE < 25meV) facilitate charge separation by releasing shallowly trapped carriers. In contrast, deep defect traps (DIE > 25meV) act as non-radiative recombination centers, causing carrier quenching. More importantly, the non-radiative recombination rate in PHI is 1-2 orders of magnitude faster than the radiative recombination rate, so suppressing non-radiative recombination is more important for improving charge separation efficiency. Our work elucidates the role of defects in photocatalysis more intuitively from the perspective of DIE, and establishes a discernible relationship between DIE and photocatalytic activity.