气压对VHF-PECVD制备的μc-Si∶H薄膜特性影响的研究

本文主要研究了用VHF PECVD方法制备的不同工作气压的微晶硅薄膜样品。结果表明 :沉积速率随反应气压的增大而逐渐增大 ;光敏性 (光电导 /暗电导 )和激活能测试结果给出了相同的变化规律 ;傅立叶红外测试、X射线衍射和室温微区喇曼谱的结果都表明了样品的晶化特性 ;

功率密度对VHF-PECVD制备μc-Si:H的影响

在不同功率密度下用甚高频化学气相沉积(VHF-PECVD)法制备了一系列微晶硅(μc-Si:H)薄膜,并对薄膜的微观结构进行了研究.重点研究了在较低的功率密度下,功率密度的改变对薄膜沉积速率和结晶状况的影响.结果表明,随着功率密度的提高,沉积速率逐渐加大,进一步提高功率密度时,沉积速率趋于饱和;与此同时,薄膜的孵化层厚度和形核密度随功率密度而变化.

μc-Si∶H/a-Si∶H多层膜的周期性结构和量子尺寸效应

利用射频辉光放电法 ,通过周期性交替切换两种耦合电极的方式 ,制备了 μc- Si∶ H/a- Si∶ H多层膜 .低角度X射线衍射 (L AXRD)测试表明 ,这种多层膜具有良好的周期性结构 .观察了上述多层膜的光学性质及电导率与温度的关系 ,发现其吸收边随着 a- Si∶ H层的减薄而蓝移 ,低温下的电导激活能 Ea 随着 a- Si∶ H层的减薄而减小 .

纳米硅(nc-Si∶H)/晶体硅(c-Si)异质结太阳电池计算机模拟

文章运用美国宾州大学发展的 AMPS程序模拟计算了 n-型纳米硅 ( n+ -nc-Si∶ H) /p-型晶体硅 ( p-c-Si)异质结太阳电池的光伏特性。结果显示 ,界面缺陷态是决定电池性能的关键因素 ,显著影响电池的开路电压 ( VOC和填充因子 ( F F)。计算得到了这种电池理想情况下 (无界面态、有背面场、正背面反射率分别为 0和 1 )的理论极限效率 ηmax=3 1 .1 7% ( AM1 .5 1 0 0 MW/cm2 0 .40～ 1 .1 0 μm波段 )。

嵌入a-Si∶H薄层的μc-Si/c-Sipn异质结太阳能电池热平衡态特性的数值模拟分析

应用计算机数值模拟方法计算ｐ＋ （μｃ－Ｓｉ∶Ｈ） ／ｎ （ｃ－Ｓｉ） 及ｐ＋ （μｃ－Ｓｉ∶Ｈ） ／ｉ （ａ－Ｓｉ∶Ｈ） ／ｎ （ｃ－Ｓｉ） 异质结太阳能电池中的电场强度分布， 说明μｃ－Ｓｉ／ｃ－Ｓｉ异质结电池制造中μｃ－Ｓｉ∶Ｈ 膜厚选择，进而对嵌入ａ－Ｓｉ∶Ｈ 薄层的μｃ－Ｓｉ／ｃ－Ｓｉ异质结太阳能电池设计进行分析， 包括ａ－Ｓｉ∶Ｈ 薄层ｐ 型掺杂效应及本底单晶硅的电阻率选择，

温度对a-Si:H/c-Si异质结太阳能电池光伏特性的影响

运用开路电压解析模型和AMPS模拟分析温度对a-Si:H/c-Si异质结太阳能电池性能的影响及其机理。随着温度T的升高,热电压增大,开路电压V_(OC)减小。当T<270 K时,填充因子FF迅速增加;当T≥270 K时,FF保持不变,a-Si:H/c-Si异质结太阳能电池的转化效率在T=270 K取得最佳值。低温工作时,空穴输运受到价带补偿界面势垒的限制,J-V曲线出现S-Shape现象,填充因子FF显著降低。

The study of a new n/p tunnel recombination junction and its application in a-Si:H/μc-Si:H tandem solar cells

This paper reports that a double N layer （a-Si：H/μc-Si：H） is used to substitute the single microcrystalline silicon n layer （n-μc-Si：H） in n/p tunnel recombination junction between subcells in a-Si：H/μc-Si：H tandem solar cells. The electrical transport and optical properties of these tunnel recombination junctions are investigated by current voltage measurement and transmission measurement. The new n/p tunnel recombination junction shows a better ohmic contact. In addition, the n/p interface is exposed to the air to examine the effect of oxidation on the tunnel recombination junction performance. The open circuit voltage and FF of a-Si：H/μc-Si：H tandem solar cell are all improved and the current leakage of the subcells can be effectively prevented efficiently when the new n/p junction is implemented as tunnel recombination junction.

An analytical model to explore open-circuit voltage of a-Si:H/c-Si heterojunction solar cells

The effect of the parameters on the open-circuit voltage, V_(OC) of a-Si:H/c-Si heterojunction solar cells was explored by an analytical model. The analytical results show that V_(OC) increases linearly with the logarithm of illumination intensity under usual illumination. There are two critical values of the interface state density(D_(it)) for the open-circuit voltage(V_(OC)), D_(it)^(crit,1) and D_(it)crit,2(a few 1010 cm^(-2)·e V^(-1)). V_(OC) decreases remarkably when D_(it) is higher than D_(it)^(crit,1). To achieve high V_(OC), the interface states should reduce down to a few 1010 cm^(-2)·e V^(-1). Due to the difference between the effective density of states in the conduction and valence band edges of c-Si, the open-circuit voltage of a-Si:H/c-Si heterojunction cells fabricated on n-type c-Si wafers is about 22 mV higher than that fabricated on p-type c-Si wafers at the same case. V_(OC) decreases with decreasing the a-Si:H doping concentration at low doping level since the electric field over the c-Si depletion region is reduced at low doping level. Therefore, the a-Si:H layer should be doped higher than a critical value of 5×10^(18) cm^(-3) to achieve high V_(OC).

The influence of SiNx substrate on crystallinity of μc-Si film used in thin film transistors

This paper found that the crystalline volume ratio （Xc） of μc-Si deposited on SiNx substrate is higher than that on 7059 glass. At the same silane concentration （SC） （for example, at SC=2%）, the Xc of μc-Si deposited on SiNx is more than 64%, but just 44% if deposited on Conning 7059. It considered that the ‘hills＇ on SiNx substrate would promote the crystalline growth of μc-Si thin film, which has been confirmed by atomic force microscope （AFM） observation. Comparing several thin film transistor （TFT） samples whose active-layer were deposited under various SC, this paper found that the appropriate SC for the μc-Si thin film used in TFT as active layer should be more than 2%, and Xc should be around 50%. Additionally, the stability comparison of μc-Si TFT and a-Si TFT is shown in this paper.

Structural Un-uniformity and Electrical Anisotropy of μc-Si:H Films

Structural un-uniformity and electrical anisotropy of μc-Si∶H film are investigated in this paper. It is found that the structure of μc-Si∶H film along the direction perpendicular to the substrate is not uniform, which is modulated by film thickness. In addition, there is a dark conductivity anisotropy along the direction parallel(σ∥) and perpendicular(σ⊥)to the substrate in μc-Si∶H film. The reasons for such an property of μc-Si∶H film and the effect of oxygen contamination are analyzed.

Simulation of a-Si:H/c-Si heterojunction solar cells: From planar junction to local junction

In order to obtain higher conversion efficiency and to reduce production cost for hydrogenated amorphous silicon/crystalline silicon(a-Si:H/c-Si) based heterojunction solar cells, an a-Si:H/c-Si heterojunction with localized p–n structure(HACL) is designed. A numerical simulation is performed with the ATLAS program. The effect of the a-Si:H layer on the performance of the HIT(heterojunction with intrinsic thin film) solar cell is investigated. The performance improvement mechanism for the HACL cell is explored. The potential performance of the HACL solar cell is compared with those of the HIT and HACD(heterojunction of amorphous silicon and crystalline silicon with diffused junction) solar cells.The simulated results indicate that the a-Si:H layer can bring about much absorption loss. The conversion efficiency and the short-circuit current density of the HACL cell can reach 28.18% and 43.06 m A/cm^2, respectively, and are higher than those of the HIT and HACD solar cells. The great improvement are attributed to(1) decrease of optical absorption loss of a-Si:H and(2) decrease of photocarrier recombination for the HACL cell. The double-side local junction is very suitable for the bifacial solar cells. For an HACL cell with n-type or p-type c-Si base, all n-type or p-type c-Si passivating layers are feasible for convenience of the double-side diffusion process. Moreover, the HACL structure can reduce the consumption of rare materials since the transparent conductive oxide(TCO) can be free in this structure. It is concluded that the HACL solar cell is a promising structure for high efficiency and low cost.

Influence of substrate temperature on the deposition and structural properties of μc-Si:H thin films fabricated with VHF-PECVD

With in situ optical emission spectroscopy （OES） diagnosis on VHF-generated H2 ＋ SiH4 plasmas,and with the measurements of deposition rate and structure of μc-Si. H thin films fabricated with VHFPECVD technique at different substracte temperature, influence of substrate temperature on the deposition of μc-Si.H thin film and on its structural properties have been investigated. The results show that with the increase of substrate temperature,the crystalline volume fraction Xc and average grain size d are enhanced monotonously, but the deposition rate increases firstly and then decreases. The optimized substrate temperature for μc-Si：H thin films deposition under our current growth system is about 210 ℃ ,at which deposition rate O. 8 nm/s of pc-Si;H thin film with Xc-60% and d-9 nm can be obtained.

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10min,一种是基于450℃退火30s,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。

微晶硅/晶体硅HIT结构异质结太阳电池的模拟计算与分析

运用AFORS-HET程序模拟分析μc-Si(p)/μc-Si(i)/c-Si(n)HIT结构异质结太阳电池的光伏特性,并研究发射层厚度、本征层厚度、本征层能隙宽度、界面态密度以及能带失配等参数对太阳能电池光伏特性的影响.计算结果表明:插入5 nm较薄微晶硅本征层,电池的转换效率最佳;随着微晶硅本征层厚度增加,电池性能降低,电池的界面缺陷态显著影响电池的开路电压和填充因子.对能带补偿情况进行模拟分析,结果显示,随着价带补偿(ΔEV)的增大,由界面态所带来的电池性能的降低逐渐被消除,当ΔEV=0.25eV时,界面态带来的影响几乎完全消除.通过优化各参数,获得微晶硅/晶体硅HIT结构异质结太阳能电池的最佳转换效率为19.86%.

Growth Mechanism of Microcrystalline Silicon Films by Scaling Theory and Monte Carlo Simulation

Hydrogenated microcrystalline silicon （~c-Si：H） films with a high deposition rate of 1.2nm/s were prepared by hot-wire chemical vapor deposition （HWCVD）. The growth-front roughening processes of the μc-Si..H films were investi- gated by atomic force microscopy. According to the scaling theory, the growth exponent β≈0.67, the roughness exponent α≈0.80,and the dynamic exponent 1/z = 0.40 are obtained. These scaling exponents cannot be explained well by the known growth models. An attempt at Monte Carlo simulation has been made to describe the growth process of μc-Si： H film using a particle reemission model where the incident flux distribution,the type and concentration of growth radical, and sticking,reemission,shadowing mechanisms all contributed to the growing morphology.

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 gridlSiN_(x)/n+-c-Si/n-c-Si/i-a-Si:H/p^(+)-a-Si:HlTCO/Ag grid was designed to increase the ef-ficiency 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 bifa-cial 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.

Effect of substrate temperature on the growth and properties of boron-doped microcrystalline silicon films

Highly conductive boron-doped hydrogenated mieroerystalline silicon （μc-Si：H） films are prepared by very high frequency plasma enhanced chemical vapour deposition （VHF PECVD） at the substrate temperatures （Ts） ranging from 90℃ to 270℃. The effects of Ts on the growth and properties of the films are investigated. Results indicate that the growth rate, the electrical （dark conductivity, carrier concentration and Hall mobility） and structural （crystallinity and grain size） properties are all strongly dependent on Ts. As Ts increases, it is observed that 1） the growth rate initially increases and then arrives at a maximum value of 13.3 nm/min at Ts=210℃, 2） the crystalline volume fraction （Xc） and the grain size increase initially, then reach their maximum values at TS=140℃, and finally decrease, 3） the dark conductivity （σd）, carrier concentration and Hall mobility have a similar dependence on Ts and arrive at their maximum values at Ts-190℃. In addition, it is also observed that at a lower substrate temperature Ts, a higher dopant concentration is required in order to obtain a maximum σd.

Effect of H treatment on performance of HIT solar cells

Hydrogen is a ubiquitous element in semiconductor processing and particularly in amorphous and microcrystalline silicon where it plays a crucial role in the growth processes as well as in the material properties. Because of its low mass it can easily diffuse through the silicon network and leads to the passivation of dangling bonds but it may also play a role in the stabilization of metastable defects. Thus a lot of work has been devoted to the study of hydrogen diffusion, bonding and structure in disordered semiconductors. The sequence, deposition-exposure to H plasma-deposition was used to fabricate the microcrystalline emitter. A proper atomic H pretreatment of c-Si surface before depositions i layer was expected to clean the surface and passivatates the surface states, as a result improing the device parameters. In this study, H2 pretreatment of c-si surface was used at different time, power and temperature. It is found that a proper H pretreatment improves passivation of c-si surface and improves the device parameters by AFM and testing I-V.

Preparation of hydrogenated microcrystalline silicon films with hot-wire-assisted MWECR-CVD system

Intrinsic hydrogenated microcrystalline silicon （μc-Si：H） films have been prepared by hot-wire-assisted microwave electron-cyclotron-resonance chemical vapour deposition （HW-MWECR-CVD） under different deposition conditions, Fourier-transform infrared spectra and Raman spectra were measured. Optical band gap was determined by Tauc plots, and experiments of photo-induced degradation were performed. It was observed that hydrogen dilution plays a more essential role than substrate temperature in microcrystalline transformation at low temperatures. Crystalline volume fraction and mean grain size in the films increase with the dilution ratio （R=H2/（H2＋SiH4））. With the rise of crystallinity in the films, the optical band gap tends to become narrower while the hydrogen content and photo-induced degradation decrease dramatically. The samples, were identified as μc-Si：H films, by calculating the optical band gap. It is considered that hydrogen dilution has an effect on reducing the crystallization activation energy of the material, which promotes the heterogeneous solid-state phase transition characterized by the Johnson-Mehl-Avrami （JMA） equation. The films with the needed structure can be prepared by balancing deposition and crystallization through controlling process parameters.

Effects of deposition pressure and plasma power on the growth and properties of boron-doped microcrystalline silicon films

Using diborane as doping gas, p-doped μc-Si：H layers are deposited by using the plasma enhanced chemical vapour deposition （PECVD） technology. The effects of deposition pressure and plasma power on the growth and the properties of μc-Si：H layers are investigated. The results show that the deposition rate, the electrical and the structural properties are all strongly dependent on deposition pressure and plasma power. Boron-doped μc-Si：H films with a dark conductivity as high as 1.42 Ω^-1·cm^-1 and a crystallinity of above 50% are obtained. With this p-layer, μc-Si：H solar cells are fabricated. In addition, the mechanism for the effects of deposition pressure and plasma power on the growth and the properties of boron-doped μc-Si：H layers is discussed.