【摘要】：多晶硅太陽能電池因生產(chǎn)成本低和光電轉(zhuǎn)換效率較高而成為光伏市場(chǎng)主流。但多晶硅太陽能電池因位錯(cuò)等晶體缺陷的存在,比單晶硅太陽能電池光電轉(zhuǎn)換效率要低。降低定向凝固多晶硅中位錯(cuò)等缺陷密度成為業(yè)界努力的目標(biāo)之一,然而實(shí)驗(yàn)上尚難以在硅晶體生長(zhǎng)過程之中觀測(cè)分析缺陷的形成,對(duì)缺陷形成機(jī)理缺乏深入的認(rèn)識(shí)。本文運(yùn)用分子動(dòng)力學(xué)模擬方法,硅原子間相互作用采用Tersoff勢(shì)函數(shù)進(jìn)行計(jì)算,就多晶硅中位錯(cuò)和孿晶這兩類最重要的晶體缺陷開展了模擬研究,結(jié)果表明:(1)硅生長(zhǎng)孿晶形成于{111}密排面上,是一個(gè)在密排面上HCP結(jié)構(gòu)和FCC結(jié)構(gòu)競(jìng)爭(zhēng)生長(zhǎng),且HCP結(jié)構(gòu)逐漸占優(yōu)直至占據(jù)整個(gè)區(qū)域的過程。能量分析發(fā)現(xiàn),硅原子在{111}密排面上的錯(cuò)排能非常低,生長(zhǎng)過程兩種結(jié)構(gòu)同時(shí)出現(xiàn)的概率非常高。當(dāng)硅晶體沿{111}面生長(zhǎng)時(shí),固液界面保持穩(wěn)定并為密排面,形成孿晶概率最高;沿(110)和(112)面生長(zhǎng)時(shí),固液界面均會(huì)轉(zhuǎn)化成被{111}小面包圍的之字型界面,孿晶在{111}小面上形成,形成概率比沿{111}面生長(zhǎng)時(shí)低;沿(100)面生長(zhǎng)時(shí),固液界面穩(wěn)定,未能形成{111}小面,整個(gè)生長(zhǎng)過程中也沒有形成孿晶。(2)硅晶體生長(zhǎng)過程中位錯(cuò)的形核是伴隨在孿晶的形成過程之中,在{111}小面上競(jìng)爭(zhēng)生長(zhǎng)的HCP結(jié)構(gòu)和FCC結(jié)構(gòu)之間容易形成位錯(cuò)。不同面位錯(cuò)形核的難易程度由大到小的順序?yàn)?(100)面(110)面(112)面(111)面。硅晶體沿相同晶面生長(zhǎng)時(shí),生長(zhǎng)溫度越高,位錯(cuò)越難形成。(3)硅晶體生長(zhǎng)過程中易形成三種位錯(cuò),它們是伯氏矢量為1/6112、1/12111的不全位錯(cuò)和1/6110梯桿位錯(cuò)。這些位錯(cuò)在晶體生長(zhǎng)過程中伴隨著分解和合成復(fù)雜變化,如伯氏矢量為1/2110的全位錯(cuò)會(huì)分解為兩個(gè)伯氏矢量為1/6112的不全位錯(cuò);伯氏矢量1/6112的不全位錯(cuò)仍會(huì)分解為亞穩(wěn)態(tài)的1/12111的不全位錯(cuò);而兩個(gè)伯氏矢量為1/6112的不全位錯(cuò)會(huì)合成一個(gè)伯氏矢量為1/6110的梯桿位錯(cuò)。(4)位錯(cuò)形成后會(huì)反作用于硅晶體的生長(zhǎng)過程。當(dāng)硅晶體沿(110)面生長(zhǎng)時(shí),與生長(zhǎng)面垂直的刃位錯(cuò)對(duì)硅晶體生長(zhǎng)速率影響不大,而螺位錯(cuò)和60°位錯(cuò)則因?qū)ιL(zhǎng)面的小面化有影響,而降低了硅晶體生長(zhǎng)速率。
[Abstract]:Polysilicon solar cells have become the mainstream of photovoltaic market because of their low production cost and high photoelectric conversion efficiency. However, the photoelectric conversion efficiency of polysilicon solar cells is lower than that of single silicon solar cells due to dislocation and other crystal defects. Reducing the density of defects such as dislocation in directionally solidified polysilicon has become one of the goals of the industry. However, it is difficult to observe and analyze the formation of defects in the process of silicon crystal growth, and there is a lack of in-depth understanding of the mechanism of defect formation. In this paper, the molecular dynamics simulation method is used to calculate the interaction between silicon atoms by Tersoff potential function. The two most important crystal defects, dislocation and twinning in polysilicon, are simulated. The results show that: (1) the silicon growth twin is formed on the {111} dense row surface, which is a competitive growth process between HCP structure and FCC structure on the dense arrangement surface, and the HCP structure gradually dominates until it occupies the whole region. Energy analysis shows that the misarrangement energy of silicon atoms on {111} dense arrangement surface is very low, and the probability of simultaneous appearance of the two structures in the growth process is very high. When the silicon crystal grows along the {111} plane, the solid-liquid interface is stable and dense, and the probability of twinning is the highest, and when the solid-liquid interface grows along (110) and (112) planes, the solid-liquid interface is transformed into a zigzag interface surrounded by {111} facets, and the twins are formed on the {111} facet, which is lower than that along the {111} plane. When the solid-liquid interface grows along the plane, the solid-liquid interface is stable and the {111} facet is not formed, and no twins are formed during the whole growth process. (2) the nucleation of dislocation in the process of silicon crystal growth is accompanied by the formation of twins, and it is easy to form dislocations between the competitive growth of HCP structure and FCC structure on {111} facets. The order of difficulty of dislocation nucleation in different planes is (100) face (110) surface (112) surface (111) surface. When silicon crystals grow along the same crystal plane, the higher the growth temperature is, the more difficult it is to form dislocations. (3) three kinds of dislocations are easy to form during the growth of silicon crystals, which are incomplete dislocations of 1: 6112, 1: 12111 and 1: 6110 ladder dislocations. These dislocations are accompanied by complex changes in decomposition and synthesis during crystal growth, such as the total dislocation of 1 鈮，

本文編號(hào)：2506469