Design, Optimization, and In-Depth Understanding of Front and Rear Junction Screen-Printed Double-Side Passivated Contacts Solar Cells

In this work, detailed numerical modeling is performed for front junction (FJ) and rear junction (RJ) n-type Si solar cells with screen-printed double-side poly-Si based tunnel oxide passivated contacts (TOPCon). A roadmap for efficiency projections of commercial-type RJ and FJ topologies reaching ~24% and >22.5% efficiencies, respectively, has been developed to quantify and explain the impact of various technological innovations on the performance of each design. By investigating several key parameters such as front poly sheet resistance and thickness, bulk material properties, and current transport in our simulation model, we determine and explain why RJ cells outperform FJ cells. Our findings reveal that FJ suffers from present technological limitations of p-poly based passivated contacts, namely, i) large recombination observed in textured p-TOPCon layers and ii) low boron solid solubility and hole mobility in p-poly Si which results in very high sheet resistance of the front p-poly emitter that contributes to FF degradation, especially when using thin poly layer to reduce absorption loss. RJ, on the other hand, desensitizes the cell efficiency to front sheet resistance allowing application of ultra-thin front n-poly layers and is therefore ideally suited for double-side TOPCon cells.