不同反射率双面太阳电池背面综合转换效率差异性研究

双面太阳电池是指硅片的正面和反面都可以接受光照并产生光生电压和电流的太阳电池,由于受到结构等各种因素的影响,目前还没有完善的测试方案用于双面太阳电池的完整测试。基于太阳能仿真环境PC1D,采用控制变量的方法来测定电池背面反射率对双面太阳电池综合转换效能的影响,研究了双面电池在不同背面受光条件下的测试结果,得出电池背面背景反射率增大时,双面太阳电池的综合转换效能的变化规律;确定了双面电池合理的测试条件,给出了双面电池科学的测试方案。结论对双面太阳电池的测试和应用具有重要意义。     

P型双面单晶硅太阳电池单元宽度的优化北大核心CSCD

在正面光照和背面光照两种条件下,利用半导体器件仿真软件分析了单元电池宽度对产业化P型双面单晶硅太阳电池电学性能的影响。为进一步提高双面太阳电池光电转换效率,对单元电池宽度进行了优化。仿真结果表明,在正、背面光照条件下,随着单元电池宽度的增大,双面电池短路电流密度均增大;当单元电池宽度较小时,正、背面短路电流密度增大较迅速。随着单元电池宽度的增大,正、背面开路电压均增大,而正、背面填充因子先增大后减小。当正、背面入射光强一定时,存在最优的单元电池宽度,使得双面太阳电池转换效率达到最大值。随着单元电池宽度的增大,正面和背面光电转换效率均先增大后减小,但正、背面光照条件下的最优单元宽度不同。当单元电池宽度一定时,存在最优的正、背面栅电极间距。     

硼扩散片弯曲度的控制技术研究

对硼扩散片弯曲度的控制技术进行了研究。结果发现单面扩散后硅片的弯曲度比双面扩散的弯曲度大,晶锭加工之前的热处理工艺有助于弯曲度的改善。在单面减薄后对硅片进行碱处理工艺,进一步改善了扩散片的弯曲度。通过对硅单晶进行热处理、以及对硅扩散片进行碱处理等一系列措施,使扩散片的弯曲度有了较大幅度的改善。     

管式炉扩散法制备20％效率的n型双面电池

采用一种管式扩散炉工艺制备了平均效率为20％的n型双面晶硅太阳电池.制得的n型双面晶硅电池峰值正面效率为20.30％、背面效率为17.59％.硼、磷扩散工艺分别在硼、磷高温管式扩散炉中实现,POCl3气氛的高温扩散工艺沉积PSG/SiOx层,BBr3气氛的高温扩散工艺沉积BSG/SiOx层.电化学电容-电压法测试显示正面硼发射极没有受到POCl3高温扩散的影响.采用电致发光测试方法研究了该n型双面电池的边缘漏电情况.该n型双面电池工艺制作流程采用常规的产线设备,适合大规模生产.     

表面多孔硅层对单晶硅太阳电池性能的影响（英文）

反射率对太阳电池的性能至关重要。采用电化学法在单晶硅衬底上制备多孔硅来降低器件的反射率,并采用快速热退火法对多孔硅层进行磷扩散处理,进而制备了单晶硅太阳电池。扫描电子显微镜(SEM)显示出单晶硅表面形成了孔径均匀的多孔硅层,且孔径随着刻蚀时间的增加而增大;紫外-可见光分光光度计表明,该多孔硅层的反射率在400～1 100 nm的光谱范围达到12%;磷扩散后薄层方块电阻达到42Ω/□,证明多孔硅层促进了磷扩散。最终在850℃、40 s快速热退火扩散条件下,成功制备出了效率为12.32%、短路电流密度为27.99 mA/cm~2、开路电压为0.49 V以及填充因子达到71%的太阳电池。     

高效率n型硅离子注入双面太阳电池

为进一步提升n型硅双面太阳电池的转化效率,采用了磷离子注入技术制备n型硅双面太阳电池的背场.基于离子注入技术准直性和均匀性好的特点,掺杂后硅片的表面复合电流密度降低到了1.4×10-13 A/cm2,隐性开路电压可达670 mV,且分布区间更紧凑.在电阻率为1～3 Ω·cm的n型硅片基底上,采用磷离子注入技术工业化生产的n型硅双面太阳电池的正面平均转化效率达到了20.64％,背面平均转化效率达到了19.52％.内量子效率的分析结果显示,离子注入太阳电池效率的增益主要来自长波段光谱响应的提升.     

聚焦离子束刻蚀性能的研究

对聚焦离子束 (FIB)的基本刻蚀性能进行了实验和研究 .通过扫描电镜对 FIB刻蚀坑的观测 ,给出了在不同材料上 (硅、铝和二氧化硅 ) FIB的刻蚀速率及刻蚀坑的形貌同离子束流大小的关系 .由于不同材料的原子结合能、原子量及晶体结构等因素对离子束溅射产额的影响 ,从而影响着离子束的刻蚀速率 ;随着离子束流的增大 ,刻蚀速率并非线性增加 ,且刻蚀坑的形貌越来越不均匀 ,对此也作了系统的分析和探讨     

GaAs通孔刻蚀微掩模形成机理研究

通孔刻蚀是GaAs制造工艺的重要环节,通过通孔刻蚀工艺实现GaAs背面和正面金属导通互连。在通孔刻蚀工艺中,微掩模的形成对器件性能及可靠性产生不利影响。微掩模将阻碍GaAs刻蚀,形成柱状堵孔以及侧壁聚合物等,造成后续背面金属接触不良、粘附不牢,进而影响通孔接触电阻、电感等关键参数,最终影响器件性能及可靠性。分析了GaAs微掩模形成的主要原因和形成机理,通过工艺优化解决了通孔刻蚀堵孔及侧壁聚合物等问题,从而提高了器件性能及可靠性。     

啁啾光纤光栅相位掩模槽形控制新方法研究

在啁啾光纤光栅相位掩模的制作中,针对光刻胶光栅槽形要求比较高的问题,提出离子束刻蚀和反应离子束刻蚀相结合的方法,来实现对相位掩模槽形占宽比的控制.运用高级线段运动算法模拟分析刻蚀中的图形演化,用Ar离子束刻蚀对光刻胶光栅掩模形貌进行修正,然后采用CHF3反应离子束刻蚀,实验和模拟均表明,Ar离子束刻蚀能很好的改善掩模与基片交界处的基片侧壁形貌,使得在CHF3反应离子束刻蚀下能得到较小的占宽比.对槽形控制提供了有意义的实验手段.     

光刻时保护背面氧化膜的作用

硅平面器件在工艺流程中,通过每次光刻时,背面氧化膜均被刻蚀,因此引起了两个严重问题:一,在扩散时硅片的背面与正面(抛光的一面)刻蚀后的图形区都等同的扩入了p、n型杂质,使背面也形成两个pn结.为了消除背面的pn结,不得不增设减薄工序加以磨除.二,在硅片高温扩散时各种有害的重金属杂质可以自由通过背面渗入硅片体内,造成结特性退化和不稳,严重的影响器件的成品率.     

20.7% efficient ion‐implanted large area n‐type front junction silicon solar cells with rear point contacts formed by laser opening and physical vapor deposition

In this work, we report on ion‐implanted, high‐efficiency n‐type silicon solar cells fabricated on large area pseudosquare Czochralski wafers. The sputtering of aluminum (Al) via physical vapor deposition (PVD) in combination with a laser‐patterned dielectric stack was used on the rear side to produce front junction cells with an implanted boron emitter and a phosphorus back surface field. Front and back surface passivation was achieved by thin thermally grown oxide during the implant anneal. Both front and back oxides were capped with SiN_x, followed by screen‐printed metal grid formation on the front side. An ultraviolet laser was used to selectively ablate the SiO₂/SiN_x passivation stack on the back to form the pattern for metal–Si contact. The laser pulse energy had to be optimized to fully open the SiO₂/SiN_x passivation layers, without inducing appreciable damage or defects on the surface of the n⁺ back surface field layer. It was also found that a low temperature annealing for less than 3 min after PVD Al provided an excellent charge collecting contact on the back. In order to obtain high fill factor of ~80%, an in situ plasma etching in an inert ambient prior to PVD was found to be essential for etching the native oxide formed in the rear vias during the front contact firing. Finally, through optimization of the size and pitch of the rear point contacts, an efficiency of 20.7% was achieved for the large area n‐type passivated emitter, rear totally diffused cell. Copyright © 2014 John Wiley & Sons, Ltd.     

Evaluation of advanced p‐PERL and n‐PERT large area silicon solar cells with 20.5% energy conversion efficiencies

In this paper, we evaluate p‐type passivated emitter and rear locally diffused (p‐PERL) and n‐type passivated emitter and rear totally diffused (n‐PERT) large area silicon solar cells featuring nickel/copper/silver (Ni/Cu/Ag) plated front side contacts. By using front emitter p‐PERL and rear emitter n‐PERT, both cell structures can be produced with only a few adaptations in the entire process sequence because both feature the same front side design: homogeneous n⁺ diffused region with low surface concentration, SiO₂/SiN_x:H passivation, Ni/Cu/Ag plated contacts. Energy conversion efficiencies up to 20.5% (externally confirmed at FhG‐ISE Callab) are presented for both cell structures on large area cells together with power‐loss analysis and potential efficiency improvements based on PC1D simulations. We demonstrate that the use of a rear emitter n‐PERT cell design with Ni/Cu/Ag plated front side contacts enables to reach open‐circuit voltage values up to 676 mV on 1–2 Ω cm n‐type CZ Si. We show that rear emitter n‐PERT cells present the potential for energy conversion efficiencies above 21.5% together with a strong tolerance to wafer thickness and bulk resistivity. Copyright © 2014 John Wiley & Sons, Ltd.     

Optimizing annealing steps for crystalline silicon solar cells with screen printed front side metallization and an oxide‐passivated rear surface with local contacts

Silicon solar cells that feature screen printed front contacts and a passivated rear surface with local contacts allow higher efficiencies compared to present industrial solar cells that exhibit a full area rear side metallization. If thermal oxidation is used for the rear surface passivation, the final annealing step in the processing sequence is crucial. On the one hand, this post‐metallization annealing (PMA) step is required for decreasing the surface recombination velocity (SRV) at the aluminum‐coated oxide‐passivated rear surface. On the other hand, PMA can negatively affect the screen printed front side metallization leading to a lower fill factor. This work separately analyzes the impact of PMA on both, the screen printed front metallization and the oxide‐passivated rear surface. Measuring dark and illuminated IV‐curves of standard industrial aluminum back surface field (Al‐BSF) silicon solar cells reveals the impact of PMA on the front metallization, while measuring the effective minority carrier lifetime of symmetric lifetime samples provides information about the rear side SRV. One‐dimensional simulations are used for predicting the cell performance according to the contributions from both, the front metallization and the rear oxide‐passivation for different PMA temperatures and durations. The simulation also includes recombination at the local rear contacts. An optimized PMA process is presented according to the simulations and is experimentally verified. The optimized process is applied to silicon solar cells with a screen printed front side metallization and an oxide‐passivated rear surface. Efficiencies up to 18.1% are achieved on 148.8 cm² Czochralski (Cz) silicon wafers. Copyright © 2009 John Wiley & Sons, Ltd.     

Optimization of the rear contact pattern of high-efficiency silicon solar cells with and without local back surface field

The influence of the point spacing and size on the cell efficiency is studied for different silicon solar cell structures with local rear contacts: the PERC (passivated emitter and rear cell) with its high recombination at the rear contacts and the LBSF (local back surface field) or PERL (passivated emitter and rear locally diffused) cell with reduced combination at the rear contacts due to a diffused high-low junction (or LBSF) beneath the contacts. Float zone materials of different resistivities have been investigated. The experimental results are explained by three-dimensional finite difference simulations for the open-circuit voltage, the short-circuit current and the fill factor.     

17.6% efficient tricrystalline silicon solar cells with spatially uniform texture

Up to now solar cells fabricated on tricrystalline Czochralski‐grown silicon (tri‐Si) have shown relatively low short‐circuit current densities of about 31–33 mA/cm² because the three {110}‐oriented grains cannot effectively be textured by commonly used anisotropic etching solutions. In this work, we have optimised a novel chemical texturing step for tri‐Si and integrated it successfully into our solar cell process. Metal/insulator/semiconductor‐contacted phosphorus‐diffused n⁺p junction silicon solar cells with a silicon‐dioxide‐passivated rear surface and evaporated aluminium contacts were manufactured, featuring a spatially uniform surface texture over all three grains on both cell sides. Despite the simple processing sequence and cell structure, an independently confirmed record efficiency of 17.6% has been achieved. This excellent efficiency is mainly due to an increased short‐circuit current density of 37 mA/cm² obtained by substantially reduced reflection and enhanced light trapping. Copyright © 2003 John Wiley & Sons, Ltd.     

Process development and comparison of various boron emitter technologies for high‐efficiency (~21%) n‐type silicon solar cells

This paper shows for the first time a comparison of commercial‐ready n‐type passivated emitter , rear totally diffused solar cells with boron (B) emitters formed by spin‐on coating, screen printing, ion implantation, and atmospheric pressure chemical vapor deposition. All the B emitter technologies show nearly same efficiency of ~20%. The optimum front grid design (5 busbars and 100 gridlines), calculated by an analytical modeling, raised the baseline cell efficiency up to 20.5% because of reduced series resistance. Along with the five busbars, rear point contacts formed by laser ablation of dielectric and physical vapor deposition Al metallization resulted in another 0.4% improvement in efficiency. As a result, 20.9% efficient n‐type passivated emitter, rear totally diffused cell was achieved in this paper. Copyright © 2016 John Wiley & Sons, Ltd.     

Theory and experiments on the back side reflectance of silicon wafer solar cells

New passivation layers for the back side of silicon solar cells have to show high performance in terms of electrical passivation as well as high internal reflectivity. This optical performance is often shown as values for the back side reflectance R_b which describes the rear internal reflection. In this paper, we investigate in detail the meaning of this single‐value parameter, its correct determination and the use in one‐dimensional simulations with PC1D. The free‐carrier‐absorption (FCA) as non‐carrier‐generating absorption channel is analyzed for solar cells with varying thickness. We apply the optical analysis to samples with different thickness, silicon oxide layer thickness, rear side topography as well as passivation layers (SiO₂, SiN_x, SiC and stack systems). Additionally, the optical influence of the laser‐fired contacts (LFC) process is experimentally investigated. Finally, we show that with correct parameters, the one‐dimensional simulation of very thin silicon solar cells can successfully be performed. Copyright © 2007 John Wiley & Sons, Ltd.     

A novel low-cost, high-efficiency micromachined silicon solar cell

This letter presents a new process for the fabrication of solar cells and modules from single crystal silicon wafers with substantially reduced silicon consumption and processing effort compared to conventional wafer-based cells. The technique of narrow trench etching in an alkaline solution is used to create a series of thin silicon strips extending vertically through the wafer. By turning the silicon strips on their side, a large increase in surface area is achieved. Individual cells fabricated using the new process have reached efficiencies up to 18.5% while a 575 cm/sup 2/ module incorporating a rear reflector and a cell surface coverage of 50% has displayed an efficiency of 12.3% under standard rating conditions. The technique has the potential to reduce silicon consumption by a factor of 10 compared to standard wafer-based silicon solar cells and, therefore, to dramatically reduce the dependence to the expensive silicon feedstock.     

Optimizing the diffused regions of interdigitated backside buried contact solar cells

Recombination and a number of other important factors must be considered in the optimization of the diffused regions of high‐efficiency silicon solar cells. In this paper, we examine issues related to the four types of diffusions used in rear‐junction, interdigitated backside buried contact solar cells made on n‐type silicon wafers: the phosphorus‐diffused front‐surface field (FSF), the boron‐diffused emitter, and the boron and the phosphorus diffused contact regions. Dark saturation current density, effective lifetime, implied open‐circuit voltage and sheet resistance are characterized for the optimization of the above‐mentioned diffused regions. Diffusion uniformity and the avoidance of the diffusion‐induced dislocations are also discussed for the heavily diffused, metal coated contact diffusions. It is found that the optimal sheet resistances of the FSF for planar and textured surfaces are 120 Ω/□ and 105 Ω/□ respectively, whereas the optimal post‐processing sheet resistance for the boron emitter is approximately 100 Ω/□. Moreover, sheet resistance as heavy as 10–20 Ω/□ for the boron groove diffusion and 5–10 Ω/□ for the phosphorus groove diffusion have been achieved without introducing the diffusion‐induced misfit dislocations. Careful consideration of the issues discussed here led to an absolute efficiency improvement on the planar n‐type IBBC solar cell of more than 0·6%. Copyright © 2006 John Wiley & Sons, Ltd.     

Beneficial and constraining effects of laser scribing in buried-contact solar cells

Residual deformations of the silicon lattice following laser scribing have been shown to be present in the grooved region of buried-contact silicon solar cells. A freshly cleaved surface perpendicular to the phosphorus-diffused laser-scribed grooves has been used in conjunction with an electron beam-induced current scan to identify the regions to which the phosphorus has diffused. The presence of residual deformations/dislocations/stress is shown to facilitate the diffusion of phosphorus to depths as large as 30 μm from the grooved wall surface. This is shown to have beneficial effects on device performance through substrate gettering for the top surface of buried-contact solar cells, but potentially detrimental effects regarding shunting of the rear floating junction where boron-diffused grooves are formed through a rear n-type layer. Solutions to the shunting of the floating junction are identified, with devices of high voltage and fill factor demonstrated. Further work is necessary to optimize the performance of these devices when used in conjunction with upright pyramids, although photolithographically defined inverted pyramids in conjunction with photolithographically defined metal contacts and a rear floating junction have been used to demonstrate an independently confirmed efficiency of approximately 22%.© 1997 John Wiley & Sons, Ltd.