Interdigitated back-contacted crystalline silicon solar cells with low-temperature dopant-free selective contacts

Abstract

In the field of crystalline silicon solar cells, great efforts are being devoted to the development of selective contacts in search of a fully low-temperature and dopant-free fabrication process compatible with high photovoltaic conversion efficiencies. For high-efficiency devices, selective contacts have to simultaneously combine high conductivity with excellent passivating properties. With this objective, a thin passivating extra layer of a-Si:H or SiO₂ is usually introduced between the conducting layer and the silicon substrate. In this work, we present an interdigitated back-contacted (IBC) silicon based solar cell that avoids the use of either thermal SiO₂ or a-Si:H interlayers achieving a dopant-free, ITO-free and very low thermal budget fabrication process. In this work, we propose a new electron transport layer using ultrathin Al₂O₃/TiO₂ stacks deposited by atomic layer deposition at 100 °C covered with a thermally evaporated Mg capping film. A specific contact resistance of 2.5 mΩ cm² has been measured together with surface recombination velocities below 40 cm s⁻¹. This electron-selective contact is combined with a thermally evaporated V₂O_x-based hole selective contact to form the rear scheme of an IBC structure with a 3 × 3 cm² active area as a proof-of-concept resulting in efficiencies beyond 19%. This approach sheds light on potential technological simplification and cost reduction in crystalline silicon solar cells.