Circuit modeling of the emitter-wrap-through solar cell

Back-contact solar cells have the potential to reduce module assembly costs and give a higher conversion efficiency. Such a device must be simple to fabricate on an industrial scale and be tolerant of low minority-carrier diffusion lengths. The emitter-wrap-through (EWT) cell is a device design that can meet these goals. In this device, the diffused junction is present on both sides and is connected by laser-drilled holes through the silicon. EWT cells were frequently found to have poor fill factors (FF's) due to shunt-like behavior. The holes were found to possess no defects that adversely affect device performance. However, detailed equivalent circuit modeling of the EWT cell was able to explain the shunt-like behavior. Experiments were performed to confirm the physical mechanisms described by the equivalent circuit model. Device optimization guided by the equivalent circuit model has led to the demonstration of a large area EWT cell with a FF of 77.6% and efficiency of 18.2%.