Homo-heterojunction concept: From simulations to high efficiency solar cell demonstration

The novel solar cell architecture called silicon homo-heterojunction (HHJ) cell is investigated combining experimental and simulation approaches. This structure intends to overcome the limitations of the silicon heterojunction technology regarding the amorphous/ crystalline silicon interface (p) a-Si:H/(i) a-Si:H /(n) c-Si) by the addition of a (p+) c-Si layer at the hetero-interface. First, the added (p+) c-Si layer is experimentally investigated using boron implantation through the realization and characterization of symmetric solar cell precursors. An adapted process flow taking into account the (p+) c-Si profile optimization, the annealing effects on substrate degradation, and the impact on surface passivation, is deeply explored. Then, large area solar cells are processed and the solar cell performance are discussed in view of the data obtained on precursors and with the help of realistic numerical simulations. Overall, we observe that the HHJ solar cells exhibit a small performance improvement compared to reference heterojunction cells. In particular, a gain in the fill factor is observed, which is shown to be originated from both an improvement in field effect and a decrease of the vertical series resistance from the a-Si:H layers. The experimental data obtained on the processed homo-heterojunction solar cells confirm that this technology can lead to improved conversion efficiencies compared to the high quality reference heterojunction solar cells.