Our results show that the 3D CsPbBr3 NCs exhibit enhanced dye degradation activity compared to 0D Cs4PbBr6 NCs. However, correlating the results of EPR measurements with the photocatalytic activity suggests that CsPbBr3 NCs undergo decomposition during the photocatalytic process. This phenomenon indicates that CsPbBr3 NCs act as sacrificial agents, thereby enhancing the photocatalytic activity. Our study demonstrates the effectiveness of EPR spectroscopy in probing the decomposition of CsPbBr₃ and Cs₄PbBr₆ NCs, revealing that lightinduced radical formation accelerates their decomposition. This research uncovers radical-driven decomposition pathways, providing new insights into the decomposition mechanisms of HP-NCs. These findings are pivotal for enhancing the stability and efficiency of HP-NCs in both optoelectronic and photocatalytic applications and provide essential guidance for developing more robust materials.