Approaches to an Improved IV and QE Characterization of Bifacial Silicon Solar Cells and the Prediction of their Module Performance

Being interested in bifacial and not fully covered rear contact (e. g. back contact) silicon solar cells and their rear side importance, we have studied how the sample holders add an external current mainly due to the reflectance properties of their surface and we have found that this influence can be higher than one percent in JSC. In a second approach, an innovative measurement setup configuration is presented, which includes a simultaneous front-rear illumination. For this configuration we have measured two types of bifacial solar cells which can be distinguished by their ratio of front to rear performance and we have found differences in power output of about thirty percent if the rear illumination is applied or not. Modules with different back sheets were further manufactured using these types of bifacial solar cells. Outdoor measurements for modules with transparent back sheets demonstrated an average gain in power output of up to twenty percent if the module was placed on a highly reflecting surface and scattered light penetrated the module from the rear side. A set of mini modules was also tested indoors to show how the back sheet influences the reflection as well as the spectral resolved response of the devices.