Experimental and simulated analysis of p a-Si:H defects on silicon heterojunction solar cells: trade-offs between VOC and FF

We investigate the effects of p a-Si:H emitter layer defects on n-type silicon heterojunction solar cells (SHJ) by experimental and simulated device analysis. Simulation of interdigitated back contact heterojunction (IBC-SHJ) solar cells shows that reducing the p-layer dangling bond density (Ddb) > 5×1018 cm-3eV-1 is an effective way to simultaneously increase VOC and FF. We use front and rear heterojunction test structures to diagnose the trade-offs between VOC and FF. Analysis of the dark current-voltage (JV) characteristics and suns-VOC curves of IBC-SHJ cells with different emitter p-layers shows the benefits of a low-high doping stack emitter structure where the lowly doped layer has less defects, providing low surface recombination, while the high doped layer enhances carrier transport and contacting. By utilizing the stack emitter structure we achieved IBC-SHJ solar cell with 20.2% efficiency.