Suppressing Non-Radiative Recombination via Shallow-Level Defect Capture-Release Mechanism in Calcium Poly(heptazine imide) for Enhanced Photocatalytic Activity

Non-radiative recombination is a key factor restricting photocatalytic efficiency, which leads to the rapid annihilation of photogenerated carriers through deep-level defect centers. Shallow-level defects can suppress non-radiative recombination through a unique carrier capture-release mechanism. Herein, calcium poly(heptazine imide) (CaPHI) is used as a model photocatalyst to investigate the suppressing effect of shallow-level defects on non-radiative recombination. By regulating the concentration of shallow-level defects, the probability of carriers being captured by deep-level defects is reduced. As a result, the non-radiative recombination rate decreased from 0.6361 to 0.3737 ns −1 , representing a reduction of 41.3%. The optimal CaPHI exhibits an apparent quantum efficiency of 60.57% at 420 nm for hydrogen evolution, surpassing most previously reported poly(heptazine imide) materials. This study elucidates the role of shallow-level defects from the perspective of suppressing non-radiative recombination, providing a new insight for addressing this issue in semiconductor photocatalysts.