基于Quokka优化叉指背接触太阳电池的效率

叉指背接触太阳电池因前表面无栅线所带来的高短路电流及栅线位于背面所获得的组件高密度封装的优势,吸引了众多光伏制造者的关注。然而,由于电池背面的p~+发射区和n~+背表面场(BSF)区呈交叉分布,在电池制备过程中需进行掩膜技术和激光烧蚀技术的隔离,显然增加了电池制备成本。因此,首先选用Quokka软件从钝化减反层及p~+发射区占比的角度探究了优化电池效率的方向,其次利用实验验证了结果的正确性。仿真及实验结果均表明在n~+背场区和p~+发射区分别沉积SiO_2/SiN_x/SiO_xN_y叠层和Al_2O_3/SiN_x/SiO_xN_y层的钝化效果均优于不含SiO_xN_y层,而p~+发射区与相邻的n~+背场区单元宽度越窄且p~+发射区占比越高则电池效率越高。     

背接触太阳电池发射区设计及可靠性研究

利用Silvaco-TCAD仿真软件全面系统地分析了不同发射区表面浓度和结深对n型插指背接触(IBC)太阳电池短路电流、开路电压、填充因子及转换效率的影响.借鉴双极半导体器件抗二次击穿技术,详细分析了不同发射区结深、发射区边缘刻蚀技术和发射区边缘选择性掺杂技术对IBC电池热击穿特性的影响.结果表明:发射区表面浓度越大、结深越深,IBC电池效率越高.当发射区表面浓度为5× 1020 cm-3、结深为1 μm时,转换效率高达23.35％.同时,深结发射区也有助于改善IBC电池的热击穿特性.发射区边缘刻蚀结构不具有改善IBC电池热击穿特性的作用,而发射区边缘选择性掺杂结构可有效改善IBC电池的热击穿特性,从而提高IBC太阳电池组件的可靠性.     

前结背接触晶硅太阳电池发射区研究

利用Silvaco-TCAD仿真软件全面系统地分析了发射区表面浓度(cE)、结深(xj)及发射区覆盖比率(EF)对P型前结背接触晶硅太阳电池输出特性的影响。结果表明:基于常规低成本P型晶硅衬底(利用直拉法生长,电阻率为1.5?·cm,少子寿命为10μs)的前结背接触太阳电池,其上表面发射区表面浓度及结深对太阳电池的输出特性产生显著影响。上表面发射区表面浓度和结深越大,短波入射光外量子效率越小。当上表面发射区表面浓度为1×1019 cm–3,结深为0.2μm时,电池效率高达20.72%。侧面和下表面发射区表面浓度及结深对太阳电池输出特性的影响较小。但侧面和下表面发射区覆盖比率对太阳电池的输出特性产生显著影响。侧面和下表面发射区覆盖比率越大,太阳电池外量子效率和转换效率越高。     

晶硅衬底参数对背接触太阳电池性能的影响

利用Silvaco-TCAD半导体器件仿真软件对n型插指背接触(IBC)晶硅太阳电池衬底参数进行了优化,全面系统地分析了晶硅衬底厚度、电阻率、少子寿命对IBC太阳电池量子效率、短路电流、开路电压、转换效率的影响.结果表明:晶硅衬底少子寿命是影响IBC太阳电池性能的最主要因素.少子寿命越高,电池转换效率越高.当晶硅衬底电阻率为2Ω·cm,少子寿命为500 μs时,最优的衬底厚度范围为60～65μm,IBC太阳电池转换效率约为22.5％.利用高质量晶硅材料制备IBC太阳电池时,可降低对衬底厚度的要求.当晶硅衬底厚度为150 μm、少子寿命为500μs时,最优衬底电阻率为0.3 Ω·cm,IBC太阳电池转换效率约为23.3％.少子寿命越低,IBC太阳电池最优的衬底电阻率越大.     

网版参数对单晶硅太阳电池栅线印刷的影响

常规太阳电池表面由于扩散浓度高,导致载流子复合严重,电池转换效率很难提高,目前高方阻密栅线工艺是提高产业化太阳电池转换效率的重要途径之一。通过扩散工艺很容易实现高方阻,难点在于优化电池正面网版参数,得到最优的栅线形貌及高宽比。针对该问题,基于丝网印刷网版参数,研究不同感光胶EOM膜厚、网版纱度、网版目数、下墨量对单晶硅太阳电池栅线印刷的影响,使用扫描电子显微镜(SEM)和激光共聚焦显微镜(LSM)观察了栅线的形貌、高宽比。结果表明感光胶并非越厚越好,当感光胶厚度达到20μm时栅线的高宽比达到最优,此时电池的转换效率最高;当网版目数、线径相同时纱厚较小的网版印刷出的栅线较均匀;当网版目数、线径均不同时,下墨量大的网版具有优势。     

N 型背接触晶硅太阳电池前表面场研究

利用 Silvaco 公司的 Athena 工艺仿真软件和 Atlas 器件仿真软件,对 N 型插指背结背接触(InterdigitatedBack Contact,IBC)晶硅太阳电池普遍采用的前表面场（FSF）结构进行研究,详细分析了 IBC 晶硅电池 FSF 表面掺杂浓度及扩散深度对电池性能的影响。结果表明：具有不同表面掺杂浓度和扩散深度的 FSF 对 IBC 晶硅太阳电池短路电流密度(Jsc)、开路电压(Voc)和填充因子(FF)产生显著影响,从而影响电池的转换效率(Eff)。具有较低表面浓度、深扩散 FSF 结构的 IBC 晶硅太阳电池可获得较高转换效率,当表面掺杂浓度为 5×1017cm–3时,电池转换效率Eff最高,且随 FSF 扩散深度增加略有增加,最高转换效率可达 22.3%。     

三结太阳电池栅线对激光辐照中的传热影响研究

为了研究三结太阳电池表面的栅线在1 070 nm连续激光辐照过程中的传热影响机制,文中通过激光辐照过程中三结太阳电池实时的电致发光现象分析三结太阳电池的损伤情况,并建立三维锗基太阳电池模型,借助有限元分析软件COMSOL对连续激光辐照锗基太阳电池的温度分布进行仿真。结果表明:在连续激光功率密度为72.5 W/cm2、辐照时间为41 s时,三结太阳电池的顶电池出现轻微损伤,损伤区域首先沿着栅线分布。在锗基太阳电池的仿真模型中,电池的温度升高至1 318 K,栅线引起了三结太阳电池热量传递方向的各项异性,沿着栅线具有更高的热传导速率。仿真结果能够对实验现象给予合理的解释。     

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。     

n型异质结背接触太阳电池前表面的场钝化

利用Silvaco-TCAD仿真软件建立二维模型,对n型异质结背接触(HBC)单晶硅太阳电池前表面场进行模拟研究。通过在n型单晶硅衬底正面分别引入一层较薄的本征非晶硅层和一层n+非晶硅层对电池前表面进行高质量的场钝化,分析了n+非晶硅层的厚度和掺杂浓度以及本征非晶硅层的厚度和带隙宽度对电池电学性能的影响。模拟结果表明:当n+非晶硅层厚度小于6 nm,掺杂浓度为1×1019 cm-3,本征非晶硅层的厚度为3 nm,带隙宽度大于1.5 eV时,电池前表面实现了良好的场钝化效果,HBC太阳电池获得了24.5%的转换效率。     

太阳电池栅线优化设计

优化设计太阳电池的电极图形可以获得高的光电转换效率。文中以实例介绍了晶体硅太阳电池上丝网印刷电极的优化设计,讨论了电池的功率损耗与扩散薄层电阻及细栅线宽度的关系,在原始设计的基础上设计出了理想尺寸的太阳电池栅线。经过优化改进的太阳电池可降低由电极设计引起的总功率损失,并且提高了电池片的光电转化效率。     

n型单晶硅片的电阻率和扩散方阻对IBC太阳电池电性能的影响

叉指背接触式(IBC)太阳电池因正面没有金属栅线遮挡,具有较高的短路电流,且组件外观更加美观。但由于IBC太阳电池正负电极在背面交叉式分布,在制备过程中需要采用光刻掩模技术进行隔离,难以实现大规模生产。采用Quokka软件仿真模拟了电阻率和扩散方阻对n型IBC太阳电池效率的影响,并对不同电阻率和扩散方阻的电池片进行了实验验证,从n型单晶硅片电阻率的选择和扩散工艺优化方面为IBC太阳电池的规模化生产提供了理论基础。实验结果表明,电阻率为3~5Ω·cm、扩散方阻为70Ω/时,小批量生产的IBC太阳电池平均光电转换效率可达23.73%,开路电压为693 mV,短路电流密度为42.44 mA/cm²,填充因子为80.69%。     

Opto‐electrical modelling and optimization study of a novel IBC c‐Si solar cell

Interdigitated back contact (IBC) crystalline silicon (c‐Si) solar cells are attracting a lot of attention because of their capability to reach world record conversion efficiency. Because of the relatively complex contact pattern, their design and optimization typically require advanced numerical simulation tools. In this work, a TCAD‐based simulation platform has been developed to account accurately and in detail the optical and passivation mechanisms of front texturization. Its validation has been carried out with respect to a novel homo‐junction IBC c‐Si solar cell based on ion implantation and epitaxial growth, comparing measured and simulated reflectance, transmittance, internal quantum efficiency, external quantum efficiency spectra, and current density–voltage characteristics. As a result of the calibration process, the opto‐electrical losses of the investigated device have been identified quantitatively and qualitatively. Then, an optimization study about the optimal front surface field (FSF) doping, front‐side texturing morphology, and rear side geometry has been performed. The proposed simulation platform can be potentially deployed to model other solar cell architectures than homo‐junction IBC devices (e.g., passivated emitter rear cell, passivated emitter rear locally diffused cell, hetero‐IBC cell). Simulation results show that a not‐smoothed pyramid‐textured front interface and an optimal FSF doping are mandatory to minimize both the optical and the recombination losses in the considered IBC cell and, consequently, to maximize the conversion efficiency. Similarly, it has been showed that recombination losses are affected more by the doping profile rather than the surface smoothing. Moreover, the performed investigation reveals that the optimal FSF doping is almost independent from the front texturing morphology and FSF passivation quality. According to this result, it has been demonstrated that an IBC cell featuring an optimal FSF doping does not exhibit a significant efficiency improvement when the FSF passivation quality strongly improves, proving that IBC cell designs based on low‐doped FSF require a very outstanding passivation quality to be competitive. Deploying an optimization algorithm, the adoption of an optimized rear side geometry can potentially lead to an efficiency improvement of about 1%_abs as compared with the reference IBC solar cell. Further, by improving both emitter and c‐Si bulk quality, a 22.84% efficient solar cell for 280‐μm thick c‐Si bulk was simulated. Copyright © 2017 John Wiley & Sons, Ltd.     

Study of Back Contacts for CdTe Solar Cells

ZnTe/ZnTe:Cu layer is used as a complex back contact.The parmeters of CdTe solar cells with and without the complex back contacts are compared.The effects of un-doped layer thickness,doped concentration and post-deposition annealing temperature of the complex layer on solar cells preformance are investigated.The results show that ZnTe/ZnTe:Cu layer can improve back contacts and largely increase the conversion efficiency of CdTe solar cells.Un-doped layer and post-deposition annealing of high temperature can increase open voltage.Using the complex back contact,a small CdTe cell with fill factor of 73.14% and conversion efficiency of 12.93% is obtained.     

金属网栅电磁屏蔽窗口薄膜的设计与制备

通过光刻掩膜技术、电阻热蒸发沉积技术制备电磁屏蔽窗口金属网栅薄膜,研究金属网栅的红外透射率和电磁屏蔽效能。为了能有效地屏蔽电磁波,使用CST Studio Suite电磁仿真软件设计不同周期、线宽的金属网栅,采用光刻掩膜技术、电阻热蒸发技术在双面抛光单晶硅基片上完成线宽为30μm,周期分别为350μm、450μm、550μm、650μm、750μm的金属网栅薄膜的制备。采用真空型傅立叶红外光谱仪和矢量网络分析仪分别对不同结构参数金属网栅薄膜的光谱特性和电磁屏蔽效能进行测试。结果:实现在双面抛光单晶硅基底上制备的网栅在12~18 GHz频段内,网栅的电磁屏蔽效能均达到12 dB以上。在3~5μm波段的透射率损失仅为8%。为了得到既具有高透光率,又具有强电磁屏蔽效能金属网栅薄膜需要合理设计金属网栅的线宽和周期。制备过程中网栅的光学-电学特性不仅受周期和线宽影响,掩膜板的加工精度、金属网栅的加工缺陷等也会造成不同程度的影响。     

Gapless point back surface field for the counter doping of large‐area interdigitated back contact solar cells using a blanket shadow mask implantation process

Gapless interdigitated back contact (IBC) solar cells were fabricated with phosphorous back surface field on a boron emitter, using an ion implantation process. Boron emitter (boron ion implantation) is counter doped by the phosphorus back surface field (BSF) (phosphorus ion implantation) without gap. The gapless process step between the emitter and BSF was compared to existing IBC solar cell with gaps between emitters and BSFs obtained using diffusion processes. We optimized the doping process in the phosphorous BSF and boron emitter region, and the implied V_oc and contact resistance relationship of the phosphorous and boron implantation dose in the counter doped region was analyzed. We confirmed the shunt resistance of the gapless IBC solar cells and the possibility of shunt behavior in gapless IBC solar cells. The highly doped counter doped BSF led to a controlled junction breakdown at high reverse bias voltages of around 7.5 V. After the doping region was optimized with the counter doped BSF and emitter, a large‐area (5 inch pseudo square) gapless IBC solar cell with a power conversion efficiency of 22.9% was made.     

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。     

Experimental and simulated analysis of front versus all‐back‐contact silicon heterojunction solar cells: effect of interface and doped a‐Si:H layer defects

Front silicon heterojunction and interdigitated all‐back‐contact silicon heterojunction (IBC‐SHJ) solar cells have the potential for high efficiency and low cost because of their good surface passivation, heterojunction contacts, and low temperature fabrication processes. The performance of both heterojunction device structures depends on the interface between the crystalline silicon (c‐Si) and intrinsic amorphous silicon [(i)a‐Si:H] layer, and the defects in doped a‐Si:H emitter or base contact layers. In this paper, effective minority carrier lifetimes of c‐Si using symmetric passivation structures were measured and analyzed using an extended Shockley–Read–Hall formalism to determine the input interface parameters needed for a successful 2D simulation of fabricated baseline solar cells. Subsequently, the performance of front silicon heterojunction and IBC‐SHJ devices was simulated to determine the influence of defects at the (i)a‐Si:H/c‐Si interface and in the doped a‐Si:H layers. For the baseline device parameters, the difference between the two device configurations is caused by the emitter/base contact gap recombination and the back surface geometry of IBC‐SHJ solar cell. This work provides a guide to the optimization of both types of SHJ device performance, predicting an IBC‐SHJ solar cell efficiency of 25% for realistic material parameters. Copyright © 2013 John Wiley & Sons, Ltd.     

Optimization of interdigitated back contact silicon heterojunction solar cells: tailoring hetero‐interface band structures while maintaining surface passivation

Interdigitated back contact silicon heterojunction (IBC‐SHJ) solar cells have the potential for high open circuit voltage (V_OC) due to the surface passivation and heterojunction contacts, and high short circuit current density (J_SC) due to all back contact design. Intrinsic amorphous silicon (a‐Si:H) buffer layer at the rear surface improve the surface passivation hence V_OC and J_SC, but degrade fill factor (FF) from an “S” shape J–V curve. Two‐dimensional (2D) simulation using “Sentaurus device” demonstrates that the low FF is related to the valence band offset (energy barrier) at the hetero‐interface. Three approaches to the buffer layer are suggested to improve the FF: (1) reduced thickness, (2) increased conductivity, and/or (3) reduced band gap. Experimental IBC‐SHJ solar cells with reduced buffer thickness (<5 nm) and increased conductivity with low boron doping significantly improves FF, consistent with simulation. However, this has only marginal effect on efficiency since J_SC and V_OC also decrease due to poor surface passivation. A narrow band gap a‐Si:H buffer layer improves cell efficiency to 13.5% with unoptimized passivation quality. These results demonstrate that tailoring the hetero‐interface band structure is critical for achieving high FF. Simulations predicts that efficiences >23% are possible on planar devices with optimized pitch dimensions and achievable surface passivation, and 26% with light trapping. This work provides criterion to design IBC‐SHJ solar cell structures and optimize cell performance. Copyright © 2010 John Wiley & Sons, Ltd.     

Two-dimensional analysis of the interdigited back-contact solar cell

Using two-dimensional computer analysis, the interdigited back contact silicon solar cell (IBC) was analyzed at high illumination levels and the results were compared with the conventional Front Junction cell. The change of effectiveness of Chockley-Read-Hall bulk and surface recombination centers at high currents as well as the induced internal electric field are argued to explain the improved efficiency predicted for IBC cells at high illumination levels. For a 100 μm cell thickness and lifetime τ_p0 = 10 μsec the efficiency is indicated to increase from 7.5% at 1 sun to 14.0% at 100 suns AMO, when a surface recombination velocity (s₀) equal to 1000 cm/sec is assumed. The substrate thickness to provide maximum efficiency was found to be approximately 50 μm. It is confirmed that the surface lifetime is a significant factor in determining the device conversion efficiency. Since surface recombination dominates the efficiency, a new IBC cell design with a front doping gradient has been introduced to suppress the surface recombination. The IBC cell with 10¹⁸/cm³ front surface n⁺-doping concentration is optimum for an impurity diffusion depth of 10 μm, s₀ = 1000 cm/sec, τ_p0 = 10 μsec, for which an efficiency of 12% is computed at 1 sum AMO. A useful efficiency of about 8% at 1 sun AMO, even with s₀ = 10⁵ cm/sec, is predicted with front doping.