Effects of LPCVD-deposited thin intrinsic silicon films on the performance of boron-doped polycrystalline silicon passivating contacts

Highly efficient n-type tunnelling oxide passivated contact solar cells can be realized by integrating p-type polycrystalline silicon (p+ poly-Si) boron (B) diffusion technology. In this study, the intrinsic silicon (i-Si) film was prepared with varying crystalline states, by precisely controlling the deposition temperature using low-pressure chemical vapor deposition (LPCVD). The i-Si films transitioned from amorphous to polycrystalline when the deposition temperature was increased from 560 °C to 590 °C, with the crystallization rate increasing from 0 % to 81.5 %. An inverse correlation was observed between the electrical properties of B-diffused p+ poly-Si and the crystallization rate of i-Si thin films. The crystal structure of p+ poly-Si contained an amorphous phase, even after high-temperature B diffusion (>900 °C).The defect density and grain boundary potential barriers within the crystal were increased, which resulted in enhanced carrier scattering probability and deteriorated material performance. Amorphous silicon film deposited at lower temperatures can achieve low contact resistivity (ρc = 0.81 mΩ·cm2) and improved passivation performance (Δi-Voc > 10 mV) after B diffusion. These results have significant implications for the development of highly efficient passivated contact solar cells with excellent passivation performance and low contact resistance hole-selective contacts.