Aluminum Halide-Based Electron-Selective Passivating Contacts for Crystalline Silicon Solar Cells.

Area of Science:

• Materials Science
• Photovoltaics
• Semiconductor Devices

Background:

• Conventional doped-silicon-layer passivating contacts in crystalline silicon (c-Si) solar cells suffer from parasitic absorption losses.
• Wide-bandgap metal compound-based passivating contacts are being explored as alternatives to mitigate these losses.

Purpose of the Study:

• To investigate thermally-evaporated aluminum halides (AlX) as electron-selective passivating contacts for c-Si solar cells.
• To evaluate the performance and stability of AlX-based contacts in solar cell applications.

Main Methods:

• Fabrication of aluminum halide (AlX) layers via thermal evaporation.
• Characterization of AlX/n-type c-Si (n-Si) heterocontacts, including contact resistivity measurements.
• Fabrication and testing of n-Si solar cells incorporating AlX-based passivating contacts, with and without SiO₂ interlayers and pre-annealing.

Main Results:

• Achieved low contact resistivities of 60.5 mΩ cm² (AlCl_x/n-Si) and 38.4 mΩ cm² (AlF_x/n-Si).
• Demonstrated power conversion efficiencies (PCEs) of 19.1% (AlCl_x/Al) and 19.6% (AlF_x/Al) in proof-of-concept solar cells.
• A remarkable PCE of 21% was achieved with a SiO₂/AlF_x/Al rear contact, showing enhanced electron selectivity and passivation.
• AlF_x-based contacts exhibited good thermal stability (up to ≈400 °C) and improved long-term environmental stability.

Conclusions:

• Aluminum halides (AlX), particularly AlF_x, are effective electron-selective passivating contacts for c-Si solar cells.
• The implementation of SiO₂ interlayers and pre-annealing significantly enhances the performance of AlX passivating contacts.
• AlF_x-based passivating contacts show great potential for future high-efficiency and stable solar cell applications.