Quantum efficiency and temperature coefficients of GaInP/GaAs dual-junction solar cell

GaInP/GaAs dual-junction solar cell with a conversion efficiency of 25.2% has been fabricated using metalorganic chemical vapor deposition (MOCVD) technique. Quantum efficiencies of the solar cell were measured within a temperature range from 25 to 160A degrees C. The results indicate that the quantum efficiencies of the subcells increase slightly with the increasing temperature. And red-shift phenomena of absorption limit for all subcells are observed by increasing the cell's work temperature, which are consistent with the viewpoint of energy gap narrowing effect. The short-circuit current density temperature coefficients dJ (sc)/dT of GaInP subcell and GaAs subcell are determined to be 8.9 and 7.4 mu A/cm(2)/A degrees C from the quantum efficiency data, respectively. And the open-circuit cell voltage temperature coefficients dV (oc)/dT calculated based on a theoretical equation are -2.4 mV/A degrees C and -2.1 mV/A degrees C for GaInP subcell and GaAs subcell.

Transition films from amporphous to microcrystalline silicon and solar cells

A series of hydrogenated silicon films near the threshold of crystallinity was prepared by very high frequency plasmaenhanced chemical vapor deposition (VHF-PECVD)from a mixture of SiH4 diluted in H-2. The effect of hydrogen dilution ratios R = [H-2]/[SiH4] on the microstructure of the films was investigated. The photoelectronic properties and stability of the films were studied as a function of crystalline fraction. The results show that the diphasic films gain both the fine photoelectric properties like a-Si: H and high stability like mu w-Si:H. By using the diphasic silicon films as the intrinsic layer, p-i-n junction solar cells were prepared. Current-voltage (J-V) characteristics and stability of the solar cells were measured under an AM1.5 solar simulator. We observed a light-induced increase of 5.2% in the open-circuit voltage (V-oc) and a light-induced degradation of similar to 2.9% inefficiency.

Impact of hydrogen dilution on microstructure and optoelectronic properties of silicon films deposited using tirisilane

We explored the deposition of hydrogenated amorphous silicon (a-Si: H) using trisilane (Si3H8) as a gas precursor in a radiofrequency plasma enhanced chemical vapour deposition process and studied the suitability of this material for photovoltaic applications. The impact of hydrogen dilution on the deposition rate and microstructure of the films is systematically examined. Materials deposited using trisilane are compared with that using disilane (Si2H6). It is found that when using Si3H8 as the gas precursor the deposition rate increases by a factor of similar to 1.5 for the same hydrogen dilution (R = [H-2]/[Si3H8] or [H-2]/[Si2H6])- Moreover, the structural transition from amorphous to nanocrystalline occurs at a higher hydrogen dilution level for Si3H8 and the transition is more gradual as compared with Si2H6 deposited films. Single-junction n-i-p a-Si: H solar cells were prepared with intrinsic layers deposited using Si3H8 or Si2H6. The dependence of open circuit voltage (V-oc) on hydrogen dilution was investigated. V-oc greater than 1 V can be obtained when the i-layers are deposited at a hydrogen dilution of 180 and 100 using Si3H8 and Si2H6, respectively.

Deposition of p-type nc-SiC : H thin films with subtle carbon incorporation for applications in p-i-n solar cells

This paper presents a detailed study on the effects of carbon incorporation and substrate temperature on structural, optical, and electrical properties of p-type nanocrystalline amorphous silicon films. A p-nc-SiC: H thin film with optical gap of 1.92 eV and activation energy of 0.06 eV is obtained through optimizing the plasma parameters. By using this p-type window layer, single junction diphasic nc-SiC : H/a-Si : H solar cells have been successfully prepared with a V-oc of 0.94 eV.

mc-Si : H/c-Si solar cell prepared by PECVD

Hetero-junction solar cells with an me-Si: H window layer were achieved. The open voltage is increased while short current is decreased with increasing the mc-Si:H layer's thickness of emitter layer. The highest of V-oc of 597 mV has obtained. When fixed the thickness of 30 nm, changing the N type from amorphous silicon layer to micro-crystalline layer, the efficiency of the hetero-junction solar cells is increased. Although the hydrogen etching before deposition enables the c-Si substrates to become rough by AFM images, it enhances the formation of epitaxial-like micro-crystalline silicon and better parameters of solar cell can be obtained by implying this process. The best result of efficiency is 13.86% with the V-oc of 549.8 mV, J(sc) of 32.19 mA center dot cm(-2) and the cell's area of 1 cm(2).

Nanocrystalline silicon films with high conductivity and the application for PIN solar cells

Intrinsic nanocrystalline silicon films (nc-Si:H) were prepared by plasma enhanced chemical vapor deposition (PECVD) method. Films' microstructures and characteristics were studied with Raman spectroscopy and Atom Force Microscope (AFM). The electronic conductivity of nc-Si:H films was found to be 4.9 x 10(0)Omega(-1) cm(-1), which was one order of magnitude higher than the reported 10(-3)-10(-1)Omega(-1)cm(-1). And PIN solar cells with nc-Si:H film as intrinsic thin-layer (ITO/n(+)-nc-Si:H/i-nc-Si:H/p-c-Si/Ag) were researched. The cell's performances were measured, the open-circuit voltage V-oc was 534.7 mV, short-circuit current I-sc was 49.24 mA (3 cm(2)) and fill factor FF was 0.4228. (c) 2006 Elsevier Ltd. All rights reserved.

Nanostructure in the p-layer and its impacts on amorphous silicon solar cells

The open circuit voltage (V-oc) of n-i-p type hydrogenated amorphous silicon (a-Si:H) solar cells has been examined by means of experimental and numerical modeling. The i- and p-layer limitations on V-oc are separated and the emphasis is to identify the impact of different kinds of p-layers. Hydrogenated protocrystalline, nanocrystalline and microcrystalline silicon p-layers were prepared and characterized using Raman spectroscopy, high resolution transmission electron microscopy (HRTEM), optical transmittance and activation energy of dark-conductivity. The n-i-p a-Si:H solar cells incorporated with these p-layers were comparatively investigated, which demonstrated a wide variation of V-oc from 1.042 V to 0.369 V, under identical i- and n-layer conditions. It is found that the nanocrystalline silicon (nc-Si:H) p-layer with a certain nanocrystalline volume fraction leads to a higher V-oc. The optimum p-layer material for n-i-p type a-Si:H solar cells is not found at the onset of the transition between the amorphous to mixed phases, nor is it associated with a microcrystalline material with a large grain size and a high volume fraction of crystalline phase. (c) 2006 Elsevier B.V. All rights reserved.

Light-induced changes in diphasic nanocrystalline silicon films and solar cells

A series of diphasic nanocrystalline silicon films and solar cells was prepared using different hydrogen dilution ratios of silane by very high frequency plasma enhanced chemical vapor deposition (VHF-PECVD). It was observed that after light soaking the open circuit voltage (V-oc) of the diphasic solar cells increased, while that of amorphous silicon solar cells decreased. Raman scattering spectroscopy was performed on the series of diphasic silicon films before and after light soaking. It was found that after light soaking the nanostruclures in the diphasic nanocrystalline silicon films were changed. Both the grain sizes and grain volume fraction reduced, while the grain boundary components increased. These results provide experimental evidence for the conjecture that the light-induced increase in V-oc of the diphasic nanocrystalline solar cells might be induced by the changes in the nanostructure of the intrinsic layer. (c) 2006 Elsevier B.V. All rights reserved.

Numerical simulation of nc-Si : H/c-Si heterojunction solar cells

AMPS simulator, which was developed by Pennsylvania State University, has been used to simulate photovoltaic performances of nc-Si:H/c-Si solar cells. It is shown that interface states are essential factors prominently influencing open circuit voltages (V-OC) and fill factors (FF) of these structured solar cells. Short circuit current density (J(SC)) or spectral response seems more sensitive to the thickness of intrinsic a-Si:H buffer layers inserted into n(+)-nc-Si:H layer and p-c-Si substrates. Impacts of bandgap offset on solar cell performances have also been analyzed. As DeltaE(C) increases, degradation of VOC and FF owing to interface states are dramatically recovered. This implies that the interface state cannot merely be regarded as carrier recombination centres, and impacts of interfacial layer on devices need further investigation. Theoretical maximum efficiency of up to 31.17% (AM1.5,100mW/cm(2), 0.40-1.1mum) has been obtained with BSF structure, idealized light-trapping effect(R-F=0, R-B=1) and no interface states.

Parallel optical communication subsystem based on VCSEL - art. no. 67833I

A parallel optical communication subsystem based on a 12 channels parallel optical transmitter module and a 12 channels parallel optical receiver module can be used as a 10Gbps STM-64 or an OC-192 optical transponder. The bit error rate of this parallel optical communication subsystem is about 0 under the test by SDH optical transport tester during three hours and eighteen minutes.

The application of parallel optical transmitter and receiver modules in communication subsystems

A new 12 channels parallel optical transmitter module in which a Vertical Cavity Surface Emitting Laser (VCSEL) has been selected as the optical source is capable of transmitting 37.5Gbps date over hundreds meters. A new 12 channels parallel optical receiver module in which a GaAs PIN (p-intrinsic-n-type) array has been selected as the optical receiver unit is capable of responding to 30Gbps date. A transmission system based on a 12 channels parallel optical transmitter module and a 12 channels parallel optical receiver module can be used as a 10Gbps STM-64 or an OC-192 optical transponder. The parallel optical modules and the parallel optical transmission system have passed the test in laboratory.

Nanostructure in the p-layer and its impacts on amorphous silicon solar cells

The open circuit voltage (V-oc) of n-i-p type hydrogenated amorphous silicon (a-Si:H) solar cells has been examined by means of experimental and numerical modeling. The i- and p-layer limitations on V-oc are separated and the emphasis is to identify the impact of different kinds of p-layers. Hydrogenated protocrystalline, nanocrystalline and microcrystalline silicon p-layers were prepared and characterized using Raman spectroscopy, high resolution transmission electron microscopy (HRTEM), optical transmittance and activation energy of dark-conductivity. The n-i-p a-Si:H solar cells incorporated with these p-layers were comparatively investigated, which demonstrated a wide variation of V-oc from 1.042 V to 0.369 V, under identical i- and n-layer conditions. It is found that the nanocrystalline silicon (nc-Si:H) p-layer with a certain nanocrystalline volume fraction leads to a higher V-oc. The optimum p-layer material for n-i-p type a-Si:H solar cells is not found at the onset of the transition between the amorphous to mixed phases, nor is it associated with a microcrystalline material with a large grain size and a high volume fraction of crystalline phase. (c) 2006 Elsevier B.V. All rights reserved.

Light-induced changes in diphasic nanocrystalline silicon films and solar cells

A series of diphasic nanocrystalline silicon films and solar cells was prepared using different hydrogen dilution ratios of silane by very high frequency plasma enhanced chemical vapor deposition (VHF-PECVD). It was observed that after light soaking the open circuit voltage (V-oc) of the diphasic solar cells increased, while that of amorphous silicon solar cells decreased. Raman scattering spectroscopy was performed on the series of diphasic silicon films before and after light soaking. It was found that after light soaking the nanostruclures in the diphasic nanocrystalline silicon films were changed. Both the grain sizes and grain volume fraction reduced, while the grain boundary components increased. These results provide experimental evidence for the conjecture that the light-induced increase in V-oc of the diphasic nanocrystalline solar cells might be induced by the changes in the nanostructure of the intrinsic layer. (c) 2006 Elsevier B.V. All rights reserved.

TCNQ电荷转移配合物薄膜的制备和表征

TCNQ电荷转移配合物作为一种新型有机材料具有很多特殊的物理、化学性质，由于它在材料研究方面的特殊贡献而成为研究热点。本论文在此领域的主要研究内容如下： 1. C18TCNQ和TMB电荷转移配合物LB膜的制备和表征 利用LB技术制备了TMB•C18TCNQ LB膜，与LB-Doping法相比省略了电子给体的液相掺杂步骤，简单、易行。研究结果表明，与TMB•C18TCNQ LB-Doping膜比较，LB膜的结构和表面形貌都发生了很大变化，LB膜中TMB和C18TCNQ的环面分别垂直于基底表面，脂肪烃链有向垂直于基底表面方向变化的趋势，5层LB膜的表面形貌是由许多堆积在一起的六边形片状微晶组成。所以，通过选择制备方法获得具有不同结构的配合物薄膜是可能的。 2. TMB•TCNQ和硬脂酸混合LB膜的制备和表征 利用LB技术组装了TMB•TCNQ和硬脂酸的混合LB膜。研究发现：本身没有两亲性的TMB•TCNQ可以通过硬脂酸的夹带作用转移到基底上。混合LB膜中硬脂酸与TMB•TCNQ是物理混合，很容易被除去，而且，可以根据实际应用需要来决定混合LB膜中硬脂酸的比例。 3. TMB•TCNQ和硬脂酸混合LB膜的热稳定性研究 利用变温红外光谱研究TMB•TCNQ和硬脂酸的混合LB膜的热稳定性。结果显示，混合LB膜中硬脂酸相变发生70-72 oC，TMB•TCNQ在142-144 oC发生反掺杂（分解）。 4. TCNQ和TMB电荷转移配合物自组装膜的制备和表征 利用layer-by-layer法制备了TMB•TCNQ自组装膜。结果表明，通过三氯锗丙酸的中介作用成功地将TMB和TCNQ组装到基底上并形成电荷转移配合物，电荷转移度约为0.48。 5. 利用红外光谱研究硬脂酸镉LB膜的亚晶胞堆积类型 利用红外光谱研究了沉积在CaF2基底上的1，3，5，7-层硬脂酸镉（CdSt）LB膜的亚晶胞堆积形式，以及交替沉积LB膜中氘代硬脂酸镉（d-CdSt）LB膜对1，2，3-层硬脂酸镉LB膜的亚晶胞堆积的影响。结果表明：1-层CdSt LB膜的亚晶胞是六方堆积，而厚度超过3层的CdSt LB膜的亚晶胞是正交堆积。只有相同种类的CdSt LB膜层与层之间的相互作用才会影响碳氢长链的堆积形式，而不同种类的CdSt LB膜和d-CdSt LB膜之间的相互作用不会影响碳氢长链的堆积形式，不论这种作用是亲水头基之间的还是疏水长链之间的。 6. 近红外光谱分辨率对定量分析的影响 利用近红外光谱分析方法建立了多组分混合物中对乙酰氨基苯酚和乙水杨胺的定量分析模型。研究发现，光谱分辨率对定量分析模型有重要影响，针对具体样品的特定组分，需要选择合适的光谱分辨率，进而获得最佳的定量分析结果。

双结晶性PEG-PCL两嵌段共聚物的合成，结晶行为和形态

聚乙二醇－聚ε-己内酯两嵌段共聚物（PEG-PCL）由于其在生物医用材料中的潜在应用而受到广泛的关注。然而，研究表明这类嵌段共聚物的许多性质，如药物渗透性，降解性能和机械性质等，都要受到它们的结晶行为与聚集态结构的显著影响。而在本课题开始之前，还没有关于PEG-PCL的结晶行为与形态的系统研究报道。因此，本文希望通过对PEG-PCL两嵌段共聚物结晶行为与形态的研究，能为这类生物降解高分子材料的工业应用提供一定的科学依据。本文使用辛酸亚锡为催化剂，甲氧基聚乙二醇（mPEG）为大分子引发剂，合成了一系列分子量分布比较窄，PCL质量百分含量为0.16-0.93的PEG-PCL两嵌段共聚物。两嵌段共聚物中的PEG段分子量固定为5000，共聚物的组成通过改变PCL链段的长度来调节。本文使用DSC，WAXD，常温或变温FTIR详细研究了PEG-PCL的结晶和熔融行为，使用偏光显微镜（POM）观察了PEG-PCL的结晶形态及结晶生长行为，利用SAXS研究了PEG-PCL的微观形态，得出了如下结果：（1）WAXD与FTIR的结果表明，两嵌段共聚物中的PEG与PCL形成微相分离的结晶微区，不存在两者的共晶或混晶。PCL含量为0.23-0.87的两嵌段共聚物中都能观察到的PEG与PCL的结晶。变温FTIR结果显示，当PCL含量低于或等于0.36，两嵌段共聚物中的PEG先从熔体中结晶；反之，当PCL含量等于或大于0.43，则熔体中PCL结晶先出现。（2）DSC结果表明，随着PEG-PCL中PCL段长度的增加，PCL段的结晶和熔融温度显著增加；相反，PEG段的结晶和熔融温度则显著降低。当PCL的质量分数由0增加至0.93，PEG的结晶度从79%降低至0，然而PCL的结晶度却不是单调变化，而是出现一个最大值。（3）在POM下观察PEG-PCL的36 oC等温熔体结晶过程，当PCL质量分数不超过0.36时，在偏光显微镜下只能观察到PEG球晶；而当PCL质量分数大于或等于0.56时，只能观察到PCL球晶；PCL含量为0.43和0.50的两种两嵌段共聚物中观察到了一种独特的同心球晶，同心球晶的中心部分形态类似于PCL球晶，而外部则类似于PEG球晶。PEG球晶与PCL球晶生长速率受PCL含量的影响显著：当PCL质量分数从0增加至0.50，PEG球晶的生长速率大大降低；然而，PCL球晶的生长速率却不是单调变化，而是在PCL质量分数为0.62时达到最大值。（4）SAXS结果表明，结晶后的PEG-PCL的微区结构是由交替的PEG与PCL的层状微区组成。共聚物的长周期在PCL质量分数为0.50时达到最大值。当PCL质量分数由0增加至0.50时，由于PCL层厚度的显著增加，共聚物的长周期显著增加；而当PCL含量由0.50继续增加至0.87，由于PEG层厚度的急剧降低，又使得共聚物的长周期迅速降低。（5）首次利用POM和微区红外光谱详细研究了PEG-PCL50/50(w/w)同心球晶的形成过程，发现同心球晶的形成是由于一种独特的结晶动力学造成的。另外，即使同心球晶的中心和外部的形态差别巨大，但是红外显微镜结果显示，两部分的组成却是相同的。