Heterojunction solar cell efficiency improvement on various c-Si substrates by interface recombination modelling

High efficiency Si heterojunction (HJ) solar cells must exhibit low interface recombination, as it limits the cell open circuit voltage (VOC). The study of the interface recombination of various a-Si:H/c-Si lifetime test samples gives insight into the recombination mechanisms, which are found compatible with an amphoteric recombination model [1]. We find that there is a trade-off between reduced interface defect density, yielding high-VOC cells (713mV), and increased field effect passivation resulting in higher efficient cells (19.1%) on flat wafers. Predicted VOCs of 725mV are reached for optimally textured n- and p-type c- Si wafers passivated by intrinsic a-Si:H, but the VOCs of the cells are lower. The injection-level dependence of the surface recombination identifies the efficiency limiting factors of HJ solar cells. Such measurements are thus a powerful indicator to achieve highly efficient devices.