双光栅结构薄膜太阳能电池的优化

为了提高单晶硅薄膜太阳能电池短路电流密度和转换效率, 采用在单晶硅薄膜太阳能电池正背面分别集成硅介质光栅和铝金属光栅的方法, 并利用有限时域差分法软件仿真研究了两种光栅的周期、厚度、占空比对单晶硅薄膜太阳能电池短路电流密度和光转换效率的影响。结果表明, 通过优化可得当正背面光栅都处于最优值时(介质光栅占空比F=0.8、介质光栅周期P=0.632μm、介质光栅厚度h_g=0.42μm; 金属光栅占空比F₁=0.9、金属光栅周期P=0.632μm、金属光栅厚度h_m=0.005μm), 短路电流密度可达35.15mA/cm2, 转换效率为43.35%;将最优光栅单晶硅薄膜太阳能电池与传统单晶硅薄膜太阳能电池对比, 无论是光程路径还是吸收效率, 光栅单晶硅薄膜太阳能电池都有显著的提高。这为以后制备高性能薄膜太阳能电池提供了理论指导。     

RF power performance evaluation of surface channel diamond MESFETs

We experimentally investigate the large-signal radio frequency performances of surface-channel p-type diamond MESFETs fabricated on hydrogenated polycrystalline diamond. The devices under examination have a coplanar layout with two gate fingers, total gate periphery of 100 μm; in DC they exhibit a hole accumulation behavior with threshold voltage V_t ≈ 0-0.5 V and maximum drain current density of 120 mA/mm. The best small-signal radio frequency performances (maximum cutoff or transition frequency f_T and oscillation frequency f_max) were obtained close to the threshold and were of the order of 6 and 15 GHz, respectively. The power radio frequency response was characterized by driving the devices in class A at an operating frequency of 2 GHz and identifying through the active load-pull technique the optimum load for maximum power added efficiency. A power gain in linearity of 8 dB and an output power of approximately 0.2 W/mm with 22% power added efficiency were obtained on the optimum load impedance at a bias point V_DS = −14 V, V_GS = −1 V. To the best of our knowledge, these are the first large signal measurements ever reported for surface MESFET on polycrystalline diamond, and show the potential of such technology for the development of microwave power devices.     

Efficiency calculations for thin-film polycrystalline semiconductor p-n junction solar cells

Numerical calculations have been made of the effect of grain size on the short-circuit current and the AM1 efficiency of polycrystalline thin-film GaAs and InP (2 µm thick) and silicon (25 µm thick) p-n junction solar cells. Junction solar cells are seen to be more efficient than Schottky-barrier cells, due to the higher dark current associated with Schottky diodes. GaAs shows the highest efficiency and both GaAs and InP attain 90 percent of their maximum efficiencies at a grain size of 10 µm, while silicon requires grain sizes of 200 µm to attain 90 percent of maximum efficiency. However, the deleterious effect of poor lifetimes and mobilities is less for silicon polycrystalline cells than for the direct-bandgap devices.     

New interconnection technology for enhanced module efficiency

In order to enhance solar modular efficiency, an innovative interconnection method for solar cells has been developed. The solar cells are two-dimensionally interconnected to a large-area, shingle-roof patterned solar cell array. Test samples were fabricated using silicon solar cells with conventional cell structures. Packing densities over 96% and module efficiencies of 17.3% and 13.4% (AM 1.5, 100 mW/cm² ) were obtained for single-crystalline and polycrystalline silicon solar cells, respectively     

Survey of material options and issues for thin film silicon solar cells

The high production cost of thick high-efficiency crystalline silicon solar cells inhibits widespread application of photovoltaic devices whereas the most developed of thin film cell technologies, that based on amorphous silicon, suffers inherent instability and low efficiency. Crystalline thin-film silicon solar cells offer the potential for a long-term solution for low cost but high-efficiency modules for most applications. This paper reviews the progress in thin-film silicon solar cell development over the last two decades, including progress in thin-film crystal growth, device fabrication, novel cell design, new material development, light trapping and both bulk and surface passivation. Quite promising results have been obtained for both large-grain (>100 μm) polycrystalline silicon material and the recently developed microcrystalline silicon materials. A novel multijunction solar cell design provides a new approach to achieving high-efficiency solar cells from very modest quality and hence low-cost material. Light trapping is essential for high performance from thin-film silicon solar cells. This can be realized by incorporating an appropriate texture on the substrate surface. Both bulk and surface passivation is also important to ensure that the photogenerated carriers can be collected effectively within the thin-film device. © 1998 John Wiley & Sons, Ltd.     

用于高效太阳电池的硅基微纳结构及制备

介绍了用于高效太阳电池的几种硅基微纳结构的最新研究进展,重点介绍了几种硅基微纳结构的制备方法,如阳极腐蚀制备多孔硅、各向异性制绒以及气液固(VLS)生长纳米线等,并对各种方法的特点作了分析比较,指出了各种方法存在的问题。最后对今后研究的方向做了展望,由于太阳电池在性能提高以及产业应用方面的需求,未来用于高效太阳电池的硅基微纳结构仍是研究的热点之一。进一步提升其对太阳电池效率的优化能力将是研究的重要关注点,而其制备技术也将向着低成本、大规模及可控制的方向发展。     

Light‐trapping and back surface structures for polycrystalline silicon solar cells

Light‐trapping in polycrystalline silicon solar cells is usually considered to be more difficult to implement than that in single crystal silicon solar cells due to the random crystallographic orientations in various grains. Furthermore, if minority carrier diffusion length is on the order of or less than solar cell thickness, which is the case of most cost‐effective polycrystalline silicon, the translation of optical gain, achieved from light‐trapping, into electrical gain will be rather limited, even with a perfect back surface passivation. In this work, geometrical light‐trapping structures are demonstrated using a simplified isotropic etching at polycrystalline silicon surfaces. Combined with a back surface reflector (BSR), an enhanced absorption in the long wavelength region is measured with a low parasitic absorption. Different light‐trapping structures are experimentally compared. To further examine the electrical gain from light‐trapping, a three‐terminal solar cell structure is used. This structure allows three different back surface configurations to be realized in a single device: unpassivated, passivated with a floating junction, and enhanced with a collecting junction. Results indicate that even with a relatively short minority‐carrier diffusion length the current collection in the long wavelength region can be significantly improved and the light‐trapping effect is enhanced as well. Copyright © 1999 John Wiley & Sons, Ltd.     

硅微纳结构及其在新型太阳电池中的应用

综述了近年来各种硅微纳结构的特征和制备技术,介绍了其在新型太阳电池中的应用现状与前景.首先,阐述了硅微纳结构在传统p-n结、新型径向p-n结以及异质结太阳电池结构设计中的研究进展;其次,从光吸收增强、表面修饰及钝化的角度,分析了硅微纳结构太阳电池的增效措施;最后,提出了柔性硅微纳结构太阳电池开发的新思路.     

SiGe/Si quantum structures as a thermistor material for low cost IR microbolometer focal plane arrays

Uncooled microbolometer thermal infrared detector technology is presently revolutionizing the infrared technology field. Essential improvement of the cost/performance ratio would be achieved by microbolometer arrays with higher sensitivity, since this allows the use of simpler and less costly camera optics, which implies a lower cost of the complete IR camera. The sensitivity of the microbolometers depends critically on the signal-to-noise ratio of the integrated thermistor material, which is set by its temperature coefficient of resistance (TCR) and noise characteristics.In this work we have investigated the use of epitaxial silicon-germanium/silicon (SiGe/Si) quantum well (QW) structures as a thermistor material. Si_0.68Ge_0.32/Si QW structures typically give a TCR of 3.0%/K and low noise values. A calculation of the noise equivalent temperature NETD of a bolometer gives 25 mK using the following assumptions: f-number = 1, 30 Hz video frame rate for a 640 × 480 array, with a pixel size 25 × 25 μm.Higher TCR values are foreseen for SiGe/Si quantum dot structures, and the noise is expected to be similar to the QW based structures.     

High efficiency inversion layer solar cells on polycrystalline silicon by the application of silicon nitride

Plasma enhanced CVD silicon nitride is introduced for the fabrication of inversion layer solar cells on p-type polycrystalline silicon. The same high interface quality as obtained for Si-nitride on monocrystalline silicon could also be achieved for polycrystalline silicon. This includes high interface charge densities up to 6.6 × 10¹²cm^-2and high UV sensitivity of the cells. For 4-cm²polycrystalline metal-insulator-semiconductor inversion layer (MIS/IL) solar cells active area efficiencies up to 13.4 percent (12.3-percent total area efficiency) under AM1 illumination could be reached, the highest values yet reported for polycrystalline silicon inversion layer solar cells on a total area basis. For the coprocessed MIS/IL cells on monocrystalline 0.7-ω. cm p-Si     

多晶硅太阳电池背表面刻蚀提升其性能的产线工艺研究

对比研究了产线上多晶硅太阳电池背表面刻蚀对 其光电转换性能的影响。示范性实验结果表明:多晶硅太阳电池背表面刻蚀能够改善其短路 电流, 从而相应的光电转换效 率提升了约 0．1％。依据多晶硅太阳电池背表面刻蚀前后的扫描 电镜(SEM)形貌、背表面漫 反射光谱及完整电池片外量子效率的测试结果,改进的光电转换的原因可能源于背表面刻蚀 “镜面”化有利于太阳光子在背表面内反射和改进印刷Al浆与背表面覆盖接触。背表面刻蚀 与当前晶硅电池产线工艺兼容,能够提升电池片的光电转换效率,是一种可供选择的产线升 级工艺。     

Design of photovoltaic device and DC–DC converter on a single chip using 0.18 μm standard CMOS technology

In this paper, we propose a photovoltaic power supply for a stand-alone system that provides electrical generation and voltage boost functions on a single silicon chip. This power supply consists of solar cells, an oscillator, and a bootstrap charge pump, which are all designed in a 0.18 μm standard complementary metal-oxide semiconductor technology. Two types of solar cells are embedded in the system to improve its power efficiency. One type is used for the power supply and the other type is used to provide the voltage bias. Three different solar cells structures were designed. A pn structure and an np structure are used for the power supply cells and an npn series-connected structure is used for the oscillator circuit to operate the DC–DC converter The voltage-current characteristics of the solar cell under microscopic illumination have been measured and the performance of bootstrap charge pump circuits was confirmed. We remodeled our solar cell equivalent circuit to reflect these measurement results.     

Growth-direction-dependent characteristics of Ge-on-insulator by Si–Ge mixing triggered melting growth

The lateral liquid-phase epitaxy of Ge-on-insulator (GOI) using Si seeds has been investigated as a function of the Si-seed orientation and the growth direction. Giant single-crystalline GOI structures with ∼200 μm length are obtained using Si(1 0 0), (1 1 0), and (1 1 1) seeds. The very long growth is explained on the basis of the solidification temperature gradient due to Si-Ge mixing around the seeding area and the thermal gradient due to the latent heat around the solid/liquid interface at the growth front. In addition, growth with rotating crystal orientations is observed for samples with several growth directions. The rotating growth is explained on the basis of the bonding strength between lattice planes at the growth front. This rotating growth does not occur in any direction for (1 0 0) orientated seeds. Based on this finding the mesh-patterned GOI growth with a large area (250 μm × 500 μm) is demonstrated.     

Use of tin oxide as an inexpensive antireflection coating for p on n polycrystalline silicon solar cells

The potential of tin oxide as an inexpensive antireflection (AR) coating for polycrystalline silicon solar cells has been investigated. Undoped tin oxide films of a desired thickness were deposited over p on n polycrystalline silicon solar cells by spray pyrolysis of an alcoholic solution of hydrated stannic chloride at 500°C. Evaluation of cell performance before and after this AR coating showed that the AR coating is highly compatible with the polycrystalline silicon solar cells. About 40-50 percent improvement in the short-circuit current of p on n polycrystalline cells has been measured. The coating may be highly suited to large-scale production of low-cost polycrystalline silicon solar cells for terrestrial application.     

Highly transparent modulated surface textured front electrodes for high‐efficiency multijunction thin‐film silicon solar cells

To further increase the efficiency of multijunction thin‐film silicon (TF‐Si) solar cells, it is crucial for the front electrode to have a good transparency and conduction, to provide efficient light trapping for each subcell, and to ensure a suitable morphology for the growth of high‐quality silicon layers. Here, we present the implementation of highly transparent modulated surface textured (MST) front electrodes as light‐trapping structures in multijunction TF‐Si solar cells. The MST substrates comprise a micro‐textured glass, a thin layer of hydrogenated indium oxide (IOH), and a sub‐micron nano‐textured ZnO layer grown by low‐pressure chemical vapor deposition (LPCVD ZnO). The bilayer IOH/LPCVD ZnO stack guarantees efficient light in‐coupling and light trapping for the top amorphous silicon (a‐Si:H) solar cell while minimizing the parasitic absorption losses. The crater‐shaped micro‐textured glass provides both efficient light trapping in the red and infrared wavelength range and a suitable morphology for the growth of high‐quality nanocrystalline silicon (nc‐Si:H) layers. Thanks to the efficient light trapping for the individual subcells and suitable morphology for the growth of high‐quality silicon layers, multijunction solar cells deposited on MST substrates have a higher efficiency than those on single‐textured state‐of‐the‐art LPCVD ZnO substrates. Efficiencies of 14.8% (initial) and 12.5% (stable) have been achieved for a‐Si:H/nc‐Si:H tandem solar cells with the MST front electrode, surpassing efficiencies obtained on state‐of‐the‐art LPCVD ZnO, thereby highlighting the high potential of MST front electrodes for high‐efficiency multijunction solar cells. Copyright © 2015 John Wiley & Sons, Ltd.     

Design and optimization of high voltage LDMOS transistors on 0.18 μm SOI CMOS technology

In this paper, we have studied the effect of systematic downscaling of MOS channel length of the performance of the hybrid GaN MOS-HEMT with numerical simulations. The improvement in on-state conduction, together with concomitant short channel effects, including drain induced barrier lowering (DIBL) is quantitatively evaluated. A specific on-resistance of 2.1 mΩ cm² has been projected for a MOS channel length of 0.38 μm. We also have assessed the impact of high-k gate dielectrics, such as Al₂O₃. In addition, we have found that adding a thin GaN cap layer on top of AlGaN barrier can help reducing short channel effects.     

Nano‐cones on micro‐pyramids: modulated surface textures for maximal spectral response and high‐efficiency solar cells

The front‐side reflection represents a significant optical loss in solar cells. One way to minimize this optical loss is to nano‐texture the front surface. Although nano‐textured surfaces have shown a broad‐band anti‐reflective effect, their light scattering and surface passivation properties are found to be generally worse than those of standard micro‐textured surfaces. To overcome these setbacks in crystalline silicon solar cells, advanced texturing and passivation approaches are here presented. In the first approach, we propose a modulated surface texture by superimposing nano‐cones on micro‐pyramidal surface texture. This advanced texture applied at the front side of crystalline silicon wafers completely suppresses the reflection in a broad wavelength range from 300 nm up to 1000 nm and efficiently scatters light up to 1200 nm. In the second approach, we show a method to minimize recombination at nano‐textured surfaces by using defect‐removal etching followed by dry thermal oxidation. These two approaches are applied here in an interdigitated back‐contacted crystalline silicon solar cell and result in decoupling of the interplay between the mechanisms behind short‐circuit current density and open‐circuit voltage. The device exhibits a conversion efficiency equal to 19.8%, record external quantum efficiency (78%) at short wavelengths (300 nm), and electrical performance equal to the performance of the reference interdigitated back‐contacted device based on front‐side micro‐pyramids. Copyright © 2015 John Wiley & Sons, Ltd.     

背接触太阳电池的背面设计优化

利用quokka3仿真软件建立三维模型,对n型叉指背接触(IBC)单晶硅太阳电池的单元电池结构设计和栅线参数进行了仿真优化,并通过激光和丝网印刷进行了实验验证.实验结果表明,在不同IBC单元电池结构设计下,当p+发射区与n+背表面场区的宽度比值为4时,IBC太阳电池效率比宽度比值为2.3时的高0.11％.可通过减小单元...     

Structural modification of semiconductor optical amplifiers for wavelength division multiplexing systems

In this paper, the semiconductor optical amplifier is analyzed for in-line and pre-amplifier for wavelength division multiplexing (WDM) transmission having minimum crosstalk and power penalty with sufficient gain. It is evaluated that the cross gain saturation of the SOA can be reduced by settling crosstalk at lower level and also minimizing the power penalty by slight increase in the confinement factor. At an optimal confinement factor of 0.41069, high amplification is obtained up to saturation power of 20.804 mW. For this confinement factor, low crosstalk of −9.63 dB and amplified spontaneous emission noise power of 119.4 μW are obtained for −15 dBm input signal. It has been demonstrated for the first time that twenty channels at 10 Gb/s WDM can transmit up to 5600 km by use of this optimization. In this, cascading of in-line SOA is done at the span of 70 km for return zero differential phase shift keying modulation format with the channel spacing of 100 GHz. The optical power spectrum and clear eye are observed at the transmission distance of 4340 and 5600 km in RZ-DPSK system. The bit error rate for all channels increases more than 10⁻¹⁰ with the increase in launched input power.     

Study of metal assisted anisotropic chemical etching of silicon for high aspect ratio in crystalline silicon solar cells

Textured surface is commonly used to enhance the efficiency of silicon solar cells by reducing the overall reflectance and improving the light scattering. In this study, a comparison between isotropic and anisotropic etching methods was investigated. The deep funnel shaped structures with high aspect ratio are proposed for better light trapping with low reflectance in crystalline silicon solar cells. The anisotropic metal assisted chemical etching (MACE) was used to form the funnel shaped structures with various aspect ratios. The funnel shaped structures showed an average reflectance of 14.75% while it was 15.77% for the pillar shaped structures. The average reflectance was further reduced to 9.49% using deep funnel shaped structures with an aspect ratio of 1:1.18. The deep funnel shaped structures with high aspect ratios can be employed for high performance of crystalline silicon solar cells.