Stable Dopant-Free Electron-Selective Contact for Silicon Solar Cells

Commercialized passivated emitter rear cell (PERC) silicon solar cells feature direct contact of metal with silicon, which leads to severe recombination loss and low open-circuit voltage (V-oc). To overcome the loss, the authors demonstrated a highly stable and thickness-tolerant dopant-free electron-selective contact consisting of a strontium fluoride/aluminum (SrF2/Al) stack. The insertion of a dielectric SrF2 layer can mitigate the Fermi-level pinning effect that typically occurs between the silicon substrate and the Al electrode. A comparatively small Ohmic contact resistivity of 2 m Omegacm(2) on lightly doped n-type c-Si can be achieved when using 4 nm of SrF2. Furthermore, the thermally evaporated SrF2 exhibits high stability with lifetimes exceeding 10,000 h in ambient air without encapsulation. The prototype solar cell with contact on the local rear opening shows 21.56% efficiency without further passivation processes. Our findings show a simple, efficient, and stable solution for various optoelectronic devices.