多晶硅定向凝固硼分凝行为的协同调控机制研究

Nowadays, the solar cell industry is developing at high speed. P-type casting polycrystalline silicon accounts for more than 60% of the installed solar cells. Boron doping is an important way to modify the electronic properties of P-type silicon. However, boron shows obvious segregation effect in directional solidification process of polycrystalline silicon, which significantly reduces the yield of ingot and the conversion efficiency of solar cells. Therefore, effective control of the distribution of boron in polycrystalline silicon ingot has become a key issue for the development of photovoltaic industry. In this project, a pulsive crystal growth technology for polycrystalline silicon ingot is proposed, and the segregation behavior of boron is collaboratively controlled by instantaneous moving speed of the liquid-solid interface and atomic diffusion migration distance. It is also in the object to study the segregation behavior of doping boron in the ingot at different solidification rates, and connect with the liquid-solid interface moving speed. Derive the relationship of diffusion distance for boron atoms in the metastable region with the interface instantaneous moving speed by using Scheil equation. Meanwhile, based on molecular dynamics simulation, the states, diffusion and migration mechanism of boron atoms at the metastable region ahead of the interface are studied. A “dopant-interface” interaction model between the liquid-solid interface and doping atoms in directional solidification process is to be constructed, which can guide the design of pulsive crystal growth process.

目前，世界太阳能电池产业高速发展，在已安装的太阳能电池中，P型铸造多晶硅占比超过60%。硼掺杂是调整P型多晶硅电学性能的重要手段，然而，硼在多晶硅定向凝固过程中会表现出明显的分凝效应，大幅降低了铸锭的良率及电池片的转换效率。有效控制多晶硅铸锭内硼的分布已成为光伏产业发展的关键问题。本项目提出一种多晶硅铸锭的波动式长晶技术，通过液固界面瞬时推移速度和原子扩散迁移距离协同调控硼的分凝行为。拟研究不同的凝固速度下掺杂原子硼在铸锭内的分凝行为，并与凝固过程中液固界面推移速度建立联系，结合Scheil方程推导界面前沿亚稳区中硼原子的扩散距离随界面瞬时推移速度的变化规律。同时，基于分子动力学模拟研究硼原子在界面前沿亚稳区中的赋存状态及扩散迁移机制，构建定向凝固过程中液固界面与掺杂原子间的“界质”作用模型，指导波动式长晶工艺的制定。

硼掺杂是调整P型多晶硅电学性能的重要手段，然而，硼在多晶硅定向凝固过程中会表现出分凝效应，大幅降低了铸锭的良率及电池片的转换效率。有效控制多晶硅铸锭内硼的分布已成为光伏产业发展的关键问题。本项目提出了一种多晶硅铸锭的波动式长晶技术，通过液固界面瞬时推移速度和原子扩散迁移距离协同调控硼的分凝行为。研究了不同的凝固速度下掺杂原子在铸锭内的分凝行为，并与凝固过程中液固界面推移速度建立联系，结合Scheil方程推导界面前沿亚稳区中硼原子的扩散距离随界面瞬时推移速度的变化规律，构建定向凝固过程中液固界面与掺杂原子间的“界质”作用模型，指导波动式长晶工艺的制定。同时，基于定向凝固过程中杂质分凝的有效调控，通过平衬底形核和凹角形核方式诱导实现晶体生长控制，获得了纯度高、晶粒尺寸均一、位错含量低的铸锭组织，其中(100)晶面占比超过30%，孪晶占比超过10%。将该铸锭成功应用于制备冶金法多晶硅电池（光电转换效率为18.65 %）和高纯多晶硅溅射靶材。