Optimization of BBr₃-Based Co-Diffusion Processes for Bifacial N-Type Solar Cells

Area of Science:

• Materials Science
• Semiconductor Physics
• Photovoltaics

Background:

• N-type silicon wafers are crucial for advanced solar cell designs.
• Bifacial solar cells offer enhanced energy generation potential.
• Efficient doping techniques are essential for high-performance solar cells.

Purpose of the Study:

• To develop and optimize co-diffusion processes for bifacial N-type solar cells.
• To investigate the effects of spin on doping (SOD) and atmospheric pressure chemical vapor deposition (APCVD) parameters on cell efficiency.
• To achieve high conversion efficiency and open-circuit voltage in bifacial N-type solar cells.

Main Methods:

• Fabrication of bifacial N-type solar cells using phosphorous source via SOD and boron tribromide (BBr₃) via APCVD.
• Controlled co-diffusion by adjusting nitrogen (N₂) carrier gas flowrate and drive-in temperatures.
• Systematic variation of H₃PO₄ concentration in the SOD process.

Main Results:

• The highest conversion efficiency reached 15.8% with an open-circuit voltage of 593 mV.
• Optimal conditions included 2% H₃PO₄ doping, 15 slm N₂ flowrate, and a 930°C drive-in temperature.
• Lower H₃PO₄ concentrations resulted in higher sheet resistance and a thinner N+ emitter layer, improving V(oc), shunt resistance, fill factor, and efficiency.

Conclusions:

• Co-diffusion is an effective method for fabricating high-efficiency bifacial N-type solar cells.
• Optimizing SOD parameters, particularly H₃PO₄ concentration, is critical for enhancing solar cell performance.
• The study demonstrates a viable pathway for improving bifacial solar cell technology through precise process control.