基于沉积温度优化和后退火工艺改善a-Si∶H/c-Si界面钝化质量的研究

a-Si∶H薄膜作为钝化层,在提高硅异质结太阳能电池效率方面发挥关键作用,工业化生产中通常采用PECVD法制备制备a-Si∶H薄膜.在本文中,首先对关键工艺参数如沉积温度进行了优化,并在160℃下获得了最佳的钝化效果.接着,通过傅里叶变换红外光谱法对a-Si∶H薄膜的微结构进行表征,以探索其钝化机理:低温下制备的a-Si∶H薄膜氢浓度高并有微空洞,从而影响钝化效果;高温下制备的a-Si∶H薄膜消除了微空洞而明显改善钝化质量.但是,过高的沉积温度又会导致a-Si∶H薄膜中微空位的产生从而影响钝化效果.此外,对比了两种典型后退火工艺对钝化效果的影响:一种是基于200℃退火10 min,一种是基于450℃退火30 s,并对相关钝化机理进行了研究.结果表明,第二种退火方式明显改善样品的钝化效果,主要原因是该退火消除了低温沉积样品中的微空洞和高温沉积样品中的微空位.最后,通过透射电镜研究了退火后的a-Si∶ H/c-Si界面微结构,并未观察到影响钝化效果的外延生长.     

N型TOPCon晶硅太阳能电池光注入退火增效的研究

N型隧穿氧化层钝化接触(Tunnel Oxide Passivating Contacts,TOPCon)太阳能电池完成印刷烧结后,再经过光注入,效率有明显提升,主要表现在Voc(开路电压)及FF(填充因子)的提升.其机理在于通过温度和光照强度调节费米能级变化,控制H总量及价态来提高钝化性能.钝化膜层的质量、硅基体掺杂...     

基于氢等离子体处理改善氢化非晶硅/晶体硅界面钝化效果的工艺研究

薄层a-Si∶H钝化技术对于提高硅异质结太阳能电池的效率至关重要,通常有三类工艺可显著改善a-Si∶H薄膜的钝化效果:晶硅表面湿化学处理(薄膜沉积前);氢等离子体处理(薄膜沉积过程中);后退火处理(薄膜沉积后).该论文基于等离子增强型化学气相沉积系统,采用氢等离子处理和后退火处理改善a-Si∶ H/c-Si界面的钝化效果,样品的有效少数载流子寿命最高达到1 ms,并研究了射频功率密度、腔体压力、氢气流量等工艺参数对钝化效果的影响;采用光发射谱、台阶仪等对氢等离子体处理所涉及的物理过程进行研究,得出该工艺对a-Si∶H薄膜具有刻蚀作用;根据钝化效果和刻蚀速率的关系,得出低刻蚀速率由于给予薄膜充足的时间进行结构弛豫或重构,显著改善钝化效果;基于快速热退火方法进一步改善钝化效果,采用傅里叶变换红外光谱对a-Si∶H薄膜的钝化机理进行研究,并基于化学退火模型进行讨论;采用透射电镜研究了a-Si∶ H/c-Si界面的微结构,并没有观测到影响钝化效果的外延生长.     

LPCVD法制备TOPCon太阳能电池工艺研究

本文主要对低压化学气相沉积(LPCVD)法制备N型高效晶硅隧穿氧化层钝化接触(TOPCon)电池工艺进行研究。分析LPCVD法制备隧穿氧化层及多晶硅层的影响因素,研究了不同氧化层厚度、多晶硅厚度及多晶硅层中P掺杂量对太阳能电池转换效率的影响。结果表明：当隧穿氧化层厚度在1.55 nm时,钝化效果最佳;多晶硅层厚度120 nm时V_oc达到最高值;多晶硅层厚度在90 nm时E_ff最高。当P掺杂量为3.0×10¹⁵ cm^-2时可获得较高的V_oc,原因是随着P掺杂量的增加,多晶硅层场钝化效果提高。     

透明导电薄膜与p-Si:H膜接触特性的研究

本实验采用PECVD方法在不同透明导电薄膜上沉积了p型掺杂(p-Si:H)膜.用拉曼(Raman)光谱测试了p-Si:H膜的晶化率,并用扫描电子显微镜(SEM)观察了其形貌.结果表明:在SnO2上沉积的p-Si:H膜的晶化率较其它两种衬底高,相应的SEM形貌显示颗粒尺寸也较大.通过I-V测试仪测试了ZnO:Al/p-Si:H、SnO2/p-Si:H和SnO2/ZnO:Al/p-Si:H的接触特性,结果显示ZnO:Al/p-Si:H的接触特性并不比SnO2/p-Si:H差.     

全TOPCon电池正面多晶硅层硼掺杂工艺

为提升隧穿氧化层钝化接触(TOPCon)电池光电转换效率,本文通过高温扩散在n型TOPCon电池正面制作p型隧穿氧化层钝化接触结构,提升发射极钝化性能,减少正面金属复合。本文研究了不同沉积时间、推进温度、推进时间等工艺参数对实验样品钝化性能及掺杂曲线的影响。实验结果表明,当沉积时间为1 500 s,推进温度为920℃,推进时间为20 min时,掺硼多晶硅层可获得较优的钝化性能及掺杂浓度,其中样品多晶硅层硼掺杂浓度达到1.40×10²⁰ cm^-3,隐开路电压(iV_oc)大于720.0 mV。依据该参数制备的TOPCon电池光电转换效率可达23.89%,对应的短路电流密度为39.36 mA/cm²,开路电压(V_oc)达到726.4 mV,填充因子(FF)为83.54%。     

MWECR CVD法高速沉积α-Si:H薄膜的红外光谱研究

应用微波电子回旋共振化学气相沉积(MWECR CVD)方法,在较高速度下沉积了α-Si:H薄膜,用FTIR红外谱仪研究了α-Si:H薄膜的结构特性随H2/SiH4、沉积温度和沉积速率变化关系,并对2000cm-1附近的特征吸收峰用高斯函数进行了拟合分析,获得了沉积高质量α-Si:H薄膜的最佳工艺条件.     

多晶硅绕镀层的去除工艺研究

本文旨在针对TOPCon(Tunnel Oxide Passivated Contact背面隧穿氧化钝化接触)晶硅电池制备过程中,背面钝化多晶硅层沉积引起的硅片正面边缘沉积多晶硅绕镀层的去除进行工艺研究,进一步解决了电池外观不良和该多晶硅层对电池正面光的吸收影响.文中分别尝试采用HF-HNO3混酸溶液和KOH碱溶液两种方式进行腐蚀处理,然后通过对处理后硅片正面的工艺控制点监控和电池EL检测等手段评估去除效果.其中HF 1wt;、HNO350wt;混合溶液时腐蚀4 min以上可去除该绕镀层,但是大于6 min后硅片正面的方块电阻提升、硼掺杂浓度等变化幅度很大.KOH质量分数0.1wt;、添加剂体积分数5vol;混合溶液60℃时,腐蚀2.5 min以上可去除该绕镀层且方块电阻等测试相对变化幅度较小.故前者对电池后期电极的制备工艺要求更高否则容易引起欧姆接触不良,后者则对电池电极的制备工艺控制窗口更大.所以认为在多晶硅绕镀层的去除方面KOH腐蚀更适合工业批量化生产工艺选择.     

超薄多晶硅的掺杂、钝化及光伏特性研究

本文对70 nm超薄多晶硅的掺杂工艺、钝化性能及光伏特性进行了研究。确定了70 nm超薄多晶硅的掺杂工艺,研究表明当离子注入剂量为3.2×10¹⁵ cm^-3,在855 ℃退火20 min时,70 nm超薄多晶硅的钝化性能可以达到与常规120 nm多晶硅相当的水平,且70 nm多晶硅的表面掺杂浓度达到5.6×10²⁰ atoms/cm³,远高于120 nm掺杂多晶硅的表面掺杂浓度(2.5×10²⁰ atoms/cm³)。基于70 nm超薄多晶硅厚度减薄和高表面浓度掺杂的特点,较低的寄生吸收和强场钝化效应使得在大尺寸(6英寸)直拉单晶硅片上加工的N型TOPCon太阳能电池的光电转换效率得到明显提升,主要电性能参数表现为:电流I_sc升高20 mA,串联电阻R_s降低,填充因子FF增加0.3%,光电转换效率升高0.13%。     

铝诱导纳米硅制备大晶粒多晶硅薄膜的研究

本文以超白玻璃为衬底,利用热丝化学气相沉积和磁控溅射法制备了Glass/nc-Si/Al的叠层结构,然后置于管式退火炉中在H2气氛下进行5h诱导晶化,用XRD、光学显微镜、扫描电镜和拉曼光谱对样品进行了表征.结果表明所有样品都是有(111)择优取向的多晶硅薄膜,在425℃诱导时,多晶硅晶粒尺寸最大达400 μm,但薄膜不连续;随着诱导温度升高到450℃,样品表面已形成了连续的多晶硅薄膜,但晶粒尺寸有所减小;475℃下诱导获得的最大晶粒尺寸约为200μm,此时多晶硅薄膜的结晶质量更好.还从动力学的角度分析了铝诱导纳米硅的晶化机理.     

热丝辅助MW ECR CVD技术高速沉积高质量氢化非晶硅薄膜

氢化非晶硅薄膜具有优异的光电特性,在制备薄膜太阳能电池中有重要的应用.本文采用热丝辅助MWECR CVD技术,通过调整各种工艺参数,制备了高沉积速率(DR＞2.5nm/s)及高光敏性(σph/σD＞105)的氢化非晶硅薄膜.实验表明,在衬底表面温度的分布中,热丝辐射和离子轰击引起的温度对薄膜的光敏性影响较大;在薄膜沉积的最后几分钟适当加大H2稀释率,有利于薄膜光电特性的改善.     

Characterization of thin‐film a‐Si:H/µc‐Si:H tandem solar cells on glass substrates

Techniques, such as photoluminescence (PL) and electron‐beam‐induced current (EBIC), have already proven their effectiveness and applicability for solar materials. Although, the methods are standard techniques for multicrystalline Si PV, their application to thin films is challenging and requires special adjustment and a careful selection of the measuring parameters. Here we report on the investigation of thin‐film tandem solar cells consisting of hydrogenated amorphous (a‐Si:H) and microcrystalline silicon (µc‐Si:H) on glass substrates. We observe a homogeneous spatial distribution of the PL signals caused by the dominance of the surface recombination. A typical PL spectrum exhibits sub‐band gap features of a‐Si:H. We relate the sub‐band‐gap spectral features mainly to transitions of carriers trapped in deep states. Observations on partially processed stacks support this supposition. PL is only detectable on the a‐Si:H layer, while EBIC signal is generated mainly in the µc‐Si:H layer. It is found out that the luminescence features of the thin a‐Si:H layer resemble those on bulk a‐Si:H.     

Effect of hot-wire passivation on the properties of hydrogenated microcrystalline silicon films to reduce post-deposition oxidation

Hydrogenated microcrystalline silicon (μc-Si:H) films have a large number of grain boundaries that oxidize after deposition, leading to deterioration of device performance. In this study, post-treatment of μc-Si:H thin films was carried out with methane-related radicals generated by a hot wire. The effect of the hot-wire passivation on the properties of the μc-Si:H thin films was investigated using Fourier-transform infrared (FT-IR) transmission spectroscopy. Through post-treatment, hydrogen on the silicon-crystallite surface was substituted with hydrocarbon. Further, an increase in filament temperature (T_ft) was found to enhance passivation. For films treated at T_ft above 1700 °C, post-oxidation and nitridation hardly occurred, whereas films treated at T_ft below 1400 °C were oxidized and nitrided even after post-treatment.     

Influence of sputtering conditions on H content and SiH bonding in aSi: H alloys

The influence of sputtering conditions on H concentration and SiH bonding has been determined for the case of diode reactive sputtering of Si in ArH mixtures, and a simple model for SiH reaction kinetics has been developed. H content and SiH bonding can be varied and controlled over wide ranges by appropriate selection of sputtering conditions. SiH reaction kinetics are found to be governed primarily by deposition rate (reaction time), H partial pressure (H availability) and possibiy substrate temperature (mobility of Si and H on the surface of the growing film). H concentration increases with decreasing deposition rate and increasing H partial pressure. SiH bonding increases with increasing deposition rate and decreasing H partial pressure. Polymerization of H and Si (SiH₂, SiH₃) occurs for lowest deposition rates and highest H partial pressures. Polymerization reactions are enhanced in films deposited at very high target power densities. The high power density causes substrate temperature to be higher than expected, and the enhanced polymerization may be due to increased Si and H surface mobility at the elevated temperatures.     

Complex study of mechanical properties of a-Si:H and a-SiC:H boron doped films

The aim of the present work is to provide the complex study of the mechanical properties of p-doped a-Si:H and a-SiC:H thin films prepared under different plasma conditions. For the investigation of the samples we used mainly the continuous depth sensing indentation technique (DSI), pin-on-disc test and internal stress measurement. The morphology of the thin film surface and the indentation prints are studied using optical microscopy, scanning electron microscopy (SEM) and topography mode of atomic force microscopy (AFM). The dependence of the mechanical parameters upon the deposition conditions were compared with the optoelectronic properties of studied films.     

Optical and structural proprieties of nc-Si:H prepared by argon diluted silane PECVD

Using argon as a diluent of Silane, hydrogenated amorphous and nanorocrystalline silicon films Si:H were prepared by radio-frequency (13.56 MHz) plasma enhanced chemical vapor deposition (rf-PECVD). The deposition rate and crystallinity varying with the deposition pressure and rf power, were systematically studied. Structural analysis (Raman scattering spectroscopy and X-ray diffraction), combined with optical measurements spectroscopy were used to characterize the films. The argon dilution of silane for all samples studied was 95% by volume, and the substrate temperature was 200 °C. The deposition pressure was varied from 400 mTorr to 1400 mTorr and varying rf power from 50 to 250 W. The structural evolution studies, shows that beyond 200 W of rf power, an amorphous-nanocrystalline transition was observed, with an increase in crystalline fraction by increasing rf power and working pressure. The films were grown at high deposition rates. The deposition rates of the films near the amorphous-nanocrystalline phase transition region were found in the range 6–10 Å/s. A correlation between structural and optical properties has been found and discussed.     

Abnormal frequency dispersion of the admittance associated with a chromium/plasma deposited a-SiNx:H/p-Si structure

Admittance (Y_m) versus applied gate bias (V_G) on MIS structure (Cr/a-SiNx:H/p-Si) was measured as a function of frequency (mHz-MHz)/temperature (77-400 K) as parameters to investigate minority carrier behavior. Strong frequency dispersion in measured capacitance at inverting gate bias (positive biases for p-type silicon substrate) and low frequency behavior in capacitance-voltage (C-V) curves under high measuring frequencies (above kHz) at 300-400 K temperature interval are reported. This phenomenon is interpreted via lateral hopping conductivity of self-inversion charges beyond the gate inside a-SiNx:H film near interface as generation mechanism of minorities with a lower activation energy (0.11 eV) rather than prevailing mechanisms of much higher activation energies (namely, generation-recombination and diffusion).     

p/i界面掺碳缓冲层沉积时间对非晶硅太阳电池性能的影响

本文研究了pin型非晶硅(a-Si)太阳电池p/i界面掺碳缓冲层(C-buffer layer)沉积时间对电池效率和稳定性的影响.研究发现,随着掺碳缓冲层沉积时间的增加,太阳电池的初始效率有所增加,当沉积时间增加到约60s时,电池的初始效率达最大值,而后随着沉积时间的继续增加,电池效率下降.而在太阳电池的稳定性方面,当缓冲层沉积时间小于50s时,随着沉积时间的增加,电池衰退率增大;大于50s后,电池的衰退率又随沉积时间的增大而减小.     

Optical properties and chemical bonding characteristics of amorphous SiNX:H thin films grown by the plasma enhanced chemical vapor deposition method

Amorphous silicon nitride (SiN_X:H) thin films grown by the plasma enhanced chemical vapor deposition (PECVD) method are presently the most important antireflection coatings for crystalline silicon solar cells. In this work, we investigated the optical properties and chemical bonding characteristics of the amorphous SiN_X:H thin films deposited by PECVD. Silane (SiH₄) and ammonia (NH₃) were used as the reactive precursors. The dependence of the growth rate and refractive index of the SiN_X:H thin films on the SiH₄/NH₃ gas flow ratio was studied. The chemical bonding characteristics and the surface morphologies of the SiN_X:H thin films were studied using the Fourier transform infrared spectroscopy and atomic force microscopy, respectively. We also investigated the effect of rapid thermal processing on the optical properties and surface morphologies of the SiN_X:H thin films. It was found that the rapid thermal processing resulted in a decrease in the thickness, increase in the refractive index, and coarser surfaces for the SiN_X:H thin films.