Enhanced Electron Transport at the n+ Poly-Si/LiF/Al Interface in n-TOPCon Silicon Solar Cells

lithium fluoride (LiF) film has been employed as an electron-selective contact in optoelectronic devices. In this study, the effect of rapid thermal processing (RTP) on n-type tunnel oxide passivated contact (n-TOPCon) silicon solar cells using LiF/Al as the electrodes was investigated. Enhanced electron transport at the n
⁺
poly-Si/LiF/Al interface of n-TOPCon solar cells after RTP was observed. X-ray photoelectron spectroscopy studies revealed that Li nanoscale metal and Al-F chemical bonds had been formed after RTP, indicating that chemical reaction between LiF and Al had occurred. Nanometer-sized Li metal accumulating at the n
⁺
poly-Si/LiF/Al interface resulted in a decreased work function, which would enhance the surface band bending of n
⁺
poly-Si. The synergistic effect of the enhanced band bending and Al-F bonds enhanced electron transfer. After RTP at 400 °C, the solar cell fill factor (FF) was increased from 77.1% to 80.9% and the cell efficiency was increased from 20.3% to 21.5%. The increased FF and cell efficiency were ascribed to the decreased series resistance, which was dramatically decreased from 1.33 Ω·cm
²
to 0.86 Ω·cm
²
.