MoS2/SnS异质结太阳能电池的模拟研究

硫化亚锡(SnS)是一种Ⅳ-Ⅵ族层状化合物半导体材料,其禁带宽度与太阳能电池最佳带隙1.5 eV非常接近,并且在可见光范围内光的吸收系数很大(α>10⁴ cm^-1),因此SnS是一种很有应用前景的材料。本文利用太阳能电池模拟软件wxAMPS模拟了MoS₂/SnS异质结太阳能电池,主要研究SnS吸收层的厚度、掺杂浓度和缺陷态等因素对太阳能电池性能的影响。研究发现:SnS吸收层最佳厚度为2 μm,最佳掺杂浓度为1.0×10¹⁵ cm^-3;同时高斯缺陷态浓度超过1.0×10¹⁵ cm^-3时,电池各项性能参数随着浓度的增加而减小,而带尾缺陷态超过1.0×10¹⁹ cm^-3·eV^-1时,电池性能才开始下降;其中界面缺陷态对太阳能电池影响比较严重,界面缺陷态浓度超过1.0×10¹² cm^-2时,开路电压、短路电流、填充因子和转换效率迅速下降。另外,通过模拟获得的转换效率高达24.87%,开路电压为0.88 V,短路电流为33.4 mA/cm²。由此可知,MoS₂/SnS异质结太阳能电池是一种很有发展潜力的光伏器件结构。     

InGaN/GaN多量子阱LED载流子泄漏与温度关系研究

通过测量光电流,直接观察了InGaN/GaN量子阱中载流子的泄漏程度随温度升高的变化关系。当LED温度从300K升高到360K时,在相同的光照强度下,LED的光电流增大,说明在温度上升之后,载流子从量子阱中逃逸的数目更多,即载流子泄漏比例增大。同时,光电流的增大在激发密度较低的时候更为明显,而且光电流随温度的增加幅度与激发光子的能量有关。用量子阱-量子点复合模型能很好地解释所观察到的实验现象。实验结果直接证明,随着温度的升高,InGaN/GaN量子阱中的载流子泄漏将显著增加,而且在低激发密度下这一效应更为明显。温度升高导致的载流子泄漏增多是InGaN多量子阱LED发光效率随温度升高而降低的重要原因。     

热丝CVD法在单晶硅衬底上低温外延生长Si和Ge薄膜的研究

采用热丝CVD法在单晶Si衬底上进行了Si和Ge 薄膜的低温外延生长,用XRD和Raman谱对其结构性能进行了分析.结果表明:在衬底温度200 ℃时,Si(111)单晶衬底上外延生长出了Raman峰位置为521.0 cm-1;X射线半峰宽(FWHM)为5.04 cm-1.结晶质量非常接近于体单晶的(111)取向的本征Si薄膜;在衬底温度为300 ℃时,在Si(100)单晶衬底上异质外延,得到了Raman峰位置为300.3 cm-1的Ge薄膜,Ge薄膜的晶体取向为Ge(220).研究表明热丝CVD是一种很好的低温外延薄膜的方法.     

Simulation and experimental study of a novel bifacial structure of silicon heterojunction solar cell for high efficiency and low cost

A novel structure of Ag grid/SiN_x/n~+-c-Si/n-c-Si/i-a-Si:H/p~+-a-Si:H/TCO/Ag grid was designed to increase the efficiency of bifacial amorphous/crystalline silicon-based solar cells and reduce the rear material consumption and production cost. The simulation results show that the new structure obtains higher efficiency compared with the typical bifacial amorphous/crystalline silicon-based solar cell because of an increase in the short-circuit current(J_(sc)), while retaining the advantages of a high open-circuit voltage, low temperature coefficient, and good weak-light performance. Moreover,real cells composed of the novel structure with dimensions of 75 mm × 75 mm were fabricated by a special fabrication recipe based on industrial processes. Without parameter optimization, the cell efficiency reached 21.1% with the J_(sc) of 41.7 mA/cm~2. In addition, the novel structure attained 28.55% potential conversion efficiency under an illumination of AM 1.5 G, 100 mW/cm~2. We conclude that the configuration of the Ag grid/SiN_x/n~+-c-Si/n-c-Si/i-a-Si:H/p~+-a-Si:H/TCO/Ag grid is a promising structure for high efficiency and low cost.     

变温退火制备铝诱导大晶粒多晶硅薄膜的机理研究

为了缩短铝诱导法制备大晶粒多晶硅薄膜的退火时间,用射频磁控溅射法在玻璃衬底上沉积了a-Si/SiO2/Al叠层膜,并用两种方法进行变温退火.分析了变温退火工艺对铝诱导晶化过程的影响,着重讨论了退火过程中温度由低温升到高温时不形成小晶粒的机理和条件.研究表明,当退火温度升高时,是否形成小晶粒取决于晶粒半径、耗尽层厚度和相邻晶粒间距三者之间的关系.     

Enhanced near-infrared responsivity of silicon photodetector by the impurity photovoltaic effect

The near-infrared responsivity of a silicon photodetector employing the impurity photovoltaic(IPV) effect is investigated with a numerical method. The improvement of the responsivity can reach 0.358 A/W at a wavelength of about1200 nm, and its corresponding quantum efficiency is 41.1%. The origin of the enhanced responsivity is attributed to the absorption of sub-bandgap photons, which results in the carrier transition from the impurity energy level to the conduction band. The results indicate that the IPV effect may provide a general approach to enhancing the responsivity of photodetectors.     

铅基卤化物钙钛矿太阳电池的模拟研究

多元硫化物Cd_0.5Zn_0.5S和氧化亚铜Cu₂O载流子迁移率较大,且其制作工艺相对于传统的电子传输层和空穴传输层更为简单,因此这两种材料在钙钛矿太阳电池中具有很好的应用潜力。本文利用SCAPS-1D软件对以Cu₂O和Cd_0.5Zn_0.5S为传输层、以铅基卤化物钙钛矿为吸收层的太阳电池进行模拟,主要研究了该器件的材料厚度、掺杂浓度、禁带宽度等因素对太阳电池性能的影响。结果表明:当光吸收层(CH₃NH₃PbI₃)厚度开始增大时电池性能逐渐提高,但是增大到一定厚度时,电池性能下降,光吸收层的最佳厚度为400 nm;当光吸收层的缺陷态密度小于1.0×10¹⁴ cm^-3时,缺陷态密度对电池性能的影响比较小;此外,铅基卤化物钙钛矿的禁带宽度对电池性能有重要影响,最佳禁带宽度为1.5 eV左右。通过模拟,得到了优化后的性能参数为:开路电压为1.010 V,短路电流密度为31.30 mA/cm²,填充因子为80.01%,电池转换效率为25.20%。因此,Cu₂O/CH₃ NH₃PbI₃/Cd_0.5Zn_0.5S钙钛矿太阳电池是一种很有发展潜力的光伏器件。     

β-FeSi2 as the bottom absorber of triple-junction thin-film solar cells: A numerical study

Using β-FeSi2 as the bottom absorber of triple-junction thin-film solar cells is investigated by a numerical method for widening the long-wave spectral response. The presented results show that the β-FeSi2 subcell can contribute 0.273 V of open-circuit voltage to the a-Si/μc-Si/β-FeSi2 triple-junction thin-film solar cell. The optimized absorber thicknesses for a- Si, μ-Si, and/3-FeSi2 subcells are 260 nm, 900 nm, and 40 nm, respectively. In addition, the temperature coefficient of the conversion efficiency of the a-Si/μc-Si//3-FeSi2 cell is -0.308 %/K, whose absolute value is only greater than that of the a-Si subcell. This result indicates that the a-Si/μc-Si/β-FeSi2 triple-junction solar cell has a good temperature coefficient. As a result, using β-FeSi2 as the bottom absorber can improve the thin-film solar cell performance, and the a-Si/μc-Si/β-FeSi2 triple-junction solar cell is a promising structure configuration for improving the solar cell efficiency.     

Photoemission cross section:A critical parameter in the impurity photovoltaic effect

A numerical study has been conducted to explore the role of photoemission cross sections in the impurity photovoltaic(IPV) effect for silicon solar cells doped with indium. The photovoltaic parameters(short-circuit current density, opencircuit voltage, and conversion efficiency) of the IPV solar cell were calculated as functions of variable electron and hole photoemission cross sections. The presented results show that the electron and hole photoemission cross sections play critical roles in the IPV effect. When the electron photoemission cross section is 10-20cm~2, the conversion efficiencyη of the IPV cell always has a negative gain(?η 0) if the IPV impurity is introduced. A large hole photoemission cross section can adversely impact IPV solar cell performance. The combination of a small hole photoemission cross section and a large electron photoemission cross section can achieve higher conversion efficiency for the IPV solar cell since a large electron photoemission cross section can enhance the necessary electron transition from the impurity level to the conduction band and a small hole photoemission cross section can reduce the needless sub-bandgap absorption. It is concluded that those impurities with small(large) hole photoemission cross section and large(small) electron photoemission cross section,whose energy levels are near the valence(or conduction) band edge, may be suitable for use in IPV solar cells. These results may help in judging whether or not an impurity is appropriate for use in IPV solar cells according to its electron and hole photoemission cross sections.     

热丝CVD法沉积固态扩散源制备晶硅太阳电池p+/n+发射极研究

为进一步提高晶硅太阳能电池发射极的性能,本文提出了一种新的发射极制备技术-低温CVD法沉积固态薄膜扩散源并进行高温扩散.采用热丝化学气相沉积法(HWCVD)在单晶硅片上沉积重掺杂硅基薄膜作为固态扩散源,然后在空气氛围下的管式炉中进行高温扩散,最后用稀HF溶液去除表面的BSG/PSG.通过掺磷薄膜扩散在P型单晶硅片上制备了方阻在50～250 Ω/□范围内可控的n+型发射极;通过掺硼薄膜扩散在N型硅片上制备了方阻在150 ～600Ω/□□范围内可控的p+型发射极.并且通过在源气体中加入CO2作为氧源,实现了扩散后硅片表面残留扩散源层的彻底去除.