Electron contact interlayers for low-temperature-processedcrystalline silicon solar cells

This study focuses on electron-selective passivating contacts for crystalline silicon (c-Si) solar cells where an interlayer is used to provide a low contact resistivity betweenthe c-Si substrate and the metal electrode. These electron contact interlayers areused in combination with other passivating interlayers (e.g., a-Si:H, TiOx, and Nb2O5)to improve surface passivation whilst still permitting contact resistivities suitable forhigh-efficiency solar cells. We show that a wide variety of thermally evaporatedmaterials, most of which have ionic character, enable an Ohmic contact betweenn-type c-Si and Al. From this pool of compounds, we observed that CsBr has espe-cially promising behavior because of its excellent performance and thermal stabilitywhen combined with thin passivating layers. With different test structures, we wereable to demonstrate low contact resistance using TiOx/CsBr, Nb2O5/CsBr, and a-Si:H/CsBr stacks on n-type c-Si. The quality of the provided surface passivationdepended on the stack but we achieved the best overall passivation stability withTiOx/CsBr. Finally, we were able to demonstrate an efficiency >20% on a laboratory-scale solar cell that implements the TiOx/CsBr/Al stack as full-area rear-side electronselective contact.