熔盐电化学法生长径向p-n结硅纳米线机制

With unique functions of absorbing light and efficient carrier separation performance, radial p-n junction silicon nanowires (SiNWs) are regarded as the most efficient ones in the field of new solar cells. The methods of p-n junction SiNWs preparation have many problems, such as complicated processes, high cost and difficultly manipulation. In the study, a simple, low cost, industrial method is developed for p-n junction SiNWs preparation, which is electrochemical methods using metallurgical grade silicon as anode and p-type silicon as cathode in molten salt. The mechanisms of the method and p-n junction formation are studied by electrode reactions of Si, B, and P. The size, structural defects and the effective doping of p-n junction SiNWs are investigated for revealing its principle of growth control. Nucleation and growth mechanism of SiNWs are also discussed in the molten salt. The above studies, which reveals the internal mechanism of the growing method of radial p-n junction SiNWs, provide the theory and technical support to use this method efficiently.

径向p-n结硅纳米线由于具有优异的光吸收性能以及高效的载流子分离性能，在新一代太阳电池方面具有广阔的应用前景。目前，径向p-n结硅纳米线的制备存在工艺复杂，成本高和控制困难等问题。本课题从熔盐电化学理论出发，提出以冶金级硅为阳极，p型硅片为阴极，在氟化物熔盐体系中制备径向p-n结硅纳米线的新思路。该方法具有成本低，工艺灵活，易于控制，很容易由实验室向工业现场转变等优点。课题拟研究Si、B、P的电极反应过程，弄清其反应机理和p-n结构形成机理；研究p-n结硅纳米线纳米尺寸、结构缺陷和有效掺杂的控制条件，揭示其生长控制机制；研究硅纳米线生长过程，确定其形核与生长机理。通过上述研究揭示该径向p-n结硅纳米线生长方法的内在机制，为该法的有效应用提供理论支持。

径向异质结构硅纳米线由于具有独特的量子性质，在电致发光、三维光波导及新一代太阳电池方面具有广阔的应用前景。径向异质结构硅纳米线精确设计是一个相当复杂的问题，对其目前和潜在的应用有着极其重要的意义。本课题从熔盐电化学理论出发，以冶金级硅为阳极，p型硅片为阴极，在氟化物熔盐体系中制备径向异质结构硅纳米线。分别研究Si、B、P和SiO2的电极反应过程，在NaF-KF共晶熔盐体系中，Si和B电极循环伏安曲线分别都只有一个还原峰，交流阻抗谱中也只有一个响应半圆与之对应， Si、B阴极的电极过程都为一步电荷转移过程；SiO2电极循环伏安图上出现两个还原峰，表明SiO2的电脱氧反应是分两步进行。调控电解工艺参数，获得不同位置掺杂B的异质结构硅纳米线，并研究其生长过程，获得了异质结构硅纳米线形核与生长机理。NaF-KF熔盐中电解得到的硅线经体积分数分别为5% HNO3与5% HF组成的混合酸酸浸4h后，纯度达到99.999% (5N)。