Despite the existence of accurate mathematical models facilitating the analysis of photovoltaic (PV) sources’ behaviour under diverse conditions, including normal operation and situations involving mismatch phenomena such as partial shadowing and various faults (i.e., PV cells operating in forward bias and reverse bias quadrants), an important issue still persists. Crucial parameters essential for adjusting these models, particularly those related to reverse-biased characteristics such as breakdown voltage, are often absent in manufacturers’ datasheets. This omission presents a substantial challenge, as it restricts the ability to acquire comprehensive and accurate information required for a thorough analysis of devices in the second quadrant. To address this issue, our research introduces a novel method for measuring the reverse-biased I–V characteristics of individual PV cells within a module without having to dissociate them from the PV module encapsulants. The process involves measuring the forward-bias I–V curves of both the fully illuminated PV module and a partially shaded PV module with only one completely shaded cell. This can be achieved outdoors and by utilising commercially available I–V tracers. Thus, the reverse I–V curve can easily be derived from these forward bias I–V curves. Finally, the proposed method serves as a nondestructive technique for characterising solar cells in the second quadrant. This innovative approach offers a promising solution for assessing the performance and health of PV modules without causing damage and may result in significant cost savings.