Microdoping of Layers for High Efficiency Silicon Heterojunction Solar Cells

Within this paper two approaches have been attempted to improve the interfaces of silicon heterojunction devices, either intrinsic amorphous silicon a-Si:H(i) to doped layer a-Si:H(n) or a-Si:H(i) layer to silicon oxide and nanocrystalline layer nc-Si:H (n or p). For the conventional a-Si:H based device, microdoping was implemented in the i2 layer of the a-Si:H(i) layer stack, aiming to increase the fill factor. An improvement in fill factor of up to 0.5%abs. was shown by introducing microdoping into a fraction of the i2 layer, resulting in an improved efficiency reaching 23.4% compared to the undoped reference at 23.2%. For "next generation" SHJ devices based on nc-Si:H, microdoping was implemented in the interfacial silicon oxide layer. For nc-Si:H(n) the fill factor showed a gain of up to 0.3%abs. compared with the undoped group, with the best cell reaching 22.9% efficiency. When introducing microdoping in the silicon oxide layer for nc-Si:H(p), a similar trend is observed as an increase in FF of ~0.3%abs. compared with undoped group drives the efficiency for the best cell at 23%. The two microdoping approaches decreased the series resistance, positively affecting the fill factor.