Electron contact interlayers for low-temperature-processed crystalline
silicon solar cells
Abstract
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 between the c-Si substrate and the
metal electrode. These electron contact interlayers are used in
combination with other passivating interlayers (e.g., a-Si:H,
TiO2, and Nb2O5) to
improve surface passivation whilst still permitting contact
resistivities suitable for high efficiency solar cells. We show that a
wide variety of thermally evaporated materials, most of which have ionic
character, enable an Ohmic contact between n-type c-Si and Al. From this
pool of compounds, we observed that CsBr has especially promising
behavior because of its excellent performance and thermal stability when
combined with thin passivating layers. With different test structures,
we were able to demonstrate low contact resistance using
TiO2/CsBr, Nb2O5/CsBr
and a-Si:H/CsBr stacks on n-type c-Si. The quality of the provided
surface passivation depended on the stack but we achieved the best
overall passivation stability with TiO2/CsBr. Finally,
we were able to demonstrate an efficiency >20% on a
laboratory-scale solar cell that implements the
TiO2/CsBr/Al stack as full-area rear side electron
selective contact.
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