Unshaded Regions Contribute 4–12× Higher Module‐Level Reverse‐Bias Current Density than Shaded Regions in Partially Shaded Solar Cells Revealed by a Physically Interpretable Model

Partial shading forces the affected cell in a photovoltaic module to operate under reverse bias,resulting in a module‐level reverse‐bias current. This reverse‐bias is widely recognized as the direct physical origin of hotspots formation in photovoltaic (PV) modules, and severe hotspots can lead to irreversible degradation of PV modules. Existing breakdown‐extended models typically treat a partially shaded cell as a homogeneous unit, obscuring the respective contributions of shaded and unshaded regions within the same cell. In this study, a physically interpretable dual‐region equivalent‐circuit model for a shaded cell was constructed based on the mechanism of the avalanche multiplication effect. In the model, avalanche multiplication in the shaded region is driven primarily by leakage current, whereas in the unshaded region it is driven by both leakage current and photogenerated current. Based on the measured I–V characteristic data under different shading ratios, the model parameters are determined via numerical fitting with clear physical meaning. The results show that the unshaded region contributes approximately 4–12 times higher module‐level reverse‐bias current density than the shaded region. This study provides a mechanistic framework for analyzing module operation under partial shading and interpreting reverse‐bias behavior in terms of region‐resolved contributions.