Shade Performance of a Back-contact Module Assembled with Cells Featuring Soft Breakdown Characteristic

We investigate the shade performance of modules assembled with interdigitated-back-contact (IBC) cells that consist of abutted p+n+ regions on the rear side. Because of the soft breakdown characteristic of these cells, the shade performance of such modules is different from the standard front-contact modules that exhibit high breakdown voltage. We fabricated IBC cells that feature early and relatively homogeneous breakdown characteristic, and then these cells were assembled into 60-cell modules. The module power was measured under illuminated and several shaded conditions, and the expected enhancement of module power under partial shading was verified. Further, a SPICE model was built to simulate the shade performance of cells with different breakdown voltages. We found that when the shaded area in the module exceeds a certain value, the dissipated power from the shaded cells is higher than the power generated by the non-shaded cells and hence the activation of bypass diodes is beneficial. Due to this reason bypass diodes are still necessary for such modules.