非晶硅太阳电池结构模拟设计

为了从理论上分析提高非晶硅太阳能电池的转化效率,运用微电子和光子结构分析一维器件模拟程序模拟非晶硅太阳电池a-SiC∶H/a-Si∶H/a-Si∶H结构,分析比较了不同前端接触透明导电层的功函数ФITO、禁带宽度、本征层厚度、掺杂浓度、缺陷态密度等因素对太阳电池性能的影响.模拟得到,在功函数达到5.1 eV,禁带宽度1.8 eV,本征层厚度265 nm等最优化条件下,非晶硅太阳能电池转化效率达到9.855%,比一般非晶硅太阳能电池转化效率高近2%.     

肖特基钙钛矿太阳电池结构设计与优化

有机-无机杂化钙钛矿材料有高吸收系数、低廉的制作成本以及较为简单的制备工艺,在近年来表现出良好的发展前景.本文采用wx-AMPS模拟软件对平面结构钙钛矿太阳电池和肖特基钙钛矿太阳电池进行建模仿真对比,从理论上分析无载流子传输层的肖特基钙钛矿太阳电池的优势.结果显示,器件两侧电极功函数和吸收层的能带分布是提高太阳电池效率的关键.在对电极使用Au(功函数为5.1 eV)的前提下,透明导电电极功函数为3.8 eV,可以得到肖特基钙钛矿太阳电池转换效率为17.93%.对器件模型吸收层进行优化,通过寻找合适的掺杂浓度,抑制缺陷密度,确定合适的厚度,可以获得理想的转换效率(20.01%),是平面异质结结构(理论转换效率31%)的63.84%.肖特基钙钛矿太阳电池在简单的器件结构下可以获得优异的光电性能,具有较好的应用潜力.     

非晶硅太阳电池结构模拟设计

为了从理论上分析提高非晶硅太阳能电池的转化效率,运用微电子和光子结构分析一维器件模拟程序模拟非晶硅太阳电池a-SiC:H/a-Si:H/a-Si:H结构,分析比较了不同前端接触透明导电层的功函数ΦITO、禁带宽度、本征层厚度、掺杂浓度、缺陷态密度等因素对太阳电池性能的影响.模拟得到,在功函数达到5.1 eV,禁带宽度1...     

载流子选择性接触:高效硅太阳电池的选择

太阳电池可看成由光子吸收层和接触层两个基本单元组成,接触层是高复合活性金属界面和光子吸收层之间的区域.为了进一步提高硅太阳电池的转换效率,关键是降低光子吸收层和接触之间的复合损失.近年来,载流子选择性接触引起了光伏界的研究兴趣,其被认为是接近硅太阳电池效率理论极限的最后的障碍之一.本文分析了三种类型的载流子选择性接触:在光子吸收层与金属界面之间引入薄的重掺杂层,即所谓的发射极或背面场;利用两种材料之间的导带或价带对齐;利用高功函数的金属氧化物与晶硅接触从而在晶硅中感应能带弯曲.基于一维太阳电池模拟软件wx AMPS,模拟了扩散同质结硅太阳电池[结构为(p~+)c-Si/(n)c-Si/(n~+)c-Si]、非晶硅薄膜硅异质结太阳电池[结构为(p~+)a-Si/(i)a-Si/(n)c-Si/(i)a-Si/(n~+)a-Si]和氧化物薄膜硅异质结太阳电池[结构为(n)MoO_x/(n)c-Si/(n)TiO_x]暗态下的能带结构和载流子浓度的空间分布,其中c-Si为晶硅;a-Si为非晶硅;(i),(n)和(p)分别表示本征、n型掺杂和p型掺杂.模拟结果表明:载流子选择性接触的核心是在接触处晶硅表面附近形成载流子浓度空间分布的不对称进而使得电导率的不对称,形成了对电子的高阻和空穴的低阻或者对空穴的高阻和电子的低阻,从而让空穴轻松通过同时阻挡电子,或者让电子轻松通过同时阻挡空穴,形成空穴选择性接触或者电子选择性接触.     

硅异质结太阳电池的物理机制和优化设计

硅异质结太阳电池是一种由非晶硅薄膜层沉积于晶硅吸收层构成的高效低成本的光伏器件,是一种具有大面积规模化生产潜力的光伏产品.异质结界面钝化品质、发射极的掺杂浓度和厚度以及透明导电层的功函数是影响硅异质结太阳电池性能的主要因素.针对这些影响因素已经有大量的研究工作在全世界范围内展开,并且有诸多研究小组提出了器件效率限制因素背后的物理机制.洞悉物理机制可为今后优化设计高性能的器件提供准则.因此及时总结硅异质结太阳电池的物理机制和优化设计非常必要.本文主要讨论了晶硅表面钝化、发射极掺杂层和透明导电层之间的功函数失配以及由此形成的肖特基势垒;讨论了屏蔽由功函数失配引起的能带弯曲所需的特征长度,即屏蔽长度;介绍了硅异质结太阳电池优化设计的数值模拟和实践;总结了硅异质结太阳电池的研究现状和发展前景.     

模拟分析少子复合速率及吸收层对HIT太阳电池性能的影响

采用AMPS-1D程序模拟分析了前后接触少子复合速率以及吸收层的厚度和少子迁移率对非晶硅/单晶硅异质结太阳电池光伏性能的影响.模拟发现,与太阳电池的前接触少子复合速率相比,背接触少子复合速率对太阳电池光伏性能的影响更为显著.吸收层单晶硅的厚度对太阳电池光伏性能的影响要受到单晶硅隙间缺陷态密度以及背接触少子复合速率的制约.当背接触复合占主要地位时,吸收层越厚电池的转换效率越高;当吸收层隙间缺陷复合占主要地位时,电池的转换效率在某一厚度处达到峰值.吸收层的少子迁移率对太阳电池性能的影响,也要受到背接触少子复合速率的制约.当背接触复合速率较低时,少子迁移率越大,电池的转换效率越高;当背接触复合速率较高时,少子迁移率越小,电池的转换效率越高.     

模拟分析少子复合速率及吸收层对HIT太阳电池性能的影响

采用AMPS-1D程序模拟分析了前后接触少子复合速率以及吸收层的厚度和少子迁移率对非晶硅/单晶硅异质结太阳电池光伏性能的影响.模拟发现,与太阳电池的前接触少子复合速率相比,背接触少子复合速率对太阳电池光伏性能的影响更为显著.吸收层单晶硅的厚度对太阳电池光伏性能的影响要受到单晶硅隙间缺陷态密度以及背接触少子复合速率的制约.当背接触复合占主要地位时,吸收层越厚电池的转换效率越高;当吸收层隙间缺陷复合占主要地位时,电池的转换效率在某一厚度处达到峰值.吸收层的少子迁移率对太阳电池性能的影响,也要受到背接触少子复合速率的制约.当背接触复合速率较低时,少子迁移率越大,电池的转换效率越高;当背接触复合速率较高时,少子迁移率越小,电池的转换效率越高.     

Cu_2O/ZnO氧化物异质结太阳电池的研究进展

介绍了近年来低成本Cu_2O/ZnO氧化物异质结太阳电池方面的研究进展.应用于光伏器件的吸收层材料Cu_2O是直接带隙半导体材料,天然呈现p型;其原材料丰富,且对环境友好.Cu_2O/ZnO异质结太阳电池结构主要有平面结构和纳米线/纳米棒结构.纳米结构的Cu_2O太阳电池提高了器件的电荷收集作用;通过热氧化Cu片技术获得的具有大晶粒尺寸平面结构Cu_2O吸收层在Cu_2O/ZnO太阳电池应用中展现出了高质量特性.界面缓冲层(如i-ZnO,a-ZTO,Ga_2O_3等)和背表面电场(如p~+-Cu_2O层等)可有效地提高界面处能级匹配和增强载流子输运.10 nm厚度的Ga_2O_3提供了近理想的导带失配,减少了界面复合;Ga_2O_3非常适合作为界面层,其能够有效地提高Cu_2O基太阳电池的开路电压V_(oc)(可达到1.2 V)和光电转换效率.p~+-Cu_2O(如Cu_2O:N和Cu_2O:Na)能够减少器件中背接触电阻和形成电子反射的背表面电场(抑制电子在界面处复合).利用p型Na掺杂Cu_2O(Cu_2O:Na)作为吸收层和Zn_(1-x)Ge_x-O作为n型缓冲层,Cu_2O异质结太阳电池(器件结构:MgF_2/ZnO:Al/Zn_(0.38)Ge_(0.62)-O/Cu_2O:Na)光电转换效率达8.1%.氧化物异质结太阳电池在光伏领域展现出极大的发展潜力.     

双面HIT太阳电池TCO与非晶硅界面势垒的模拟优化

采用美国滨州大学研发的AMPS-1D软件,模拟了TCO与非晶硅界面势垒对TCO/a-Si:H(p+)/a-Si:H(i)/c-Si(n) /a-Si:H(i) /a-Si:H(n+) /TCO双面HIT异质结太阳电池光伏特性的影响。结果表明太阳电池的TCO/p+前接触界面势垒（对于电子）越高,越易形成欧姆接触,且电池的短波响应增强,使电池性能变好。模拟还发现,n+ /TCO背接触界面势垒（对于电子）越低,电池性能越好。若背场重掺杂,在背接触势垒小于等于0.5ev时,电池的转换效率不会受到背接触势垒的影响;若背场低掺杂,在背接触势垒很小的情况下,也能达到与重掺杂相同的转换效率。     

双面HIT太阳电池TCO与非晶硅界面势垒的模拟优化

采用美国滨州大学研发的AMPS-1D软件,模拟了TCO与非晶硅界面势垒对TCO/a-Si:H(p+)/a-Si:H(i)/c-Si(n)/a-Si:H(i) /a-Si:H(n+)/TCO双面HIT异质结太阳电池光伏特性的影响.结果表明太阳电池的TCO/p+前接触界面势垒(对于电子)越高,越易形成欧姆接触,且电池的短波响应增强,使电池性能变好.模拟还发现,n+/TCO背接触界面势垒(对于电子)越低,电池性能越好.若背场重掺杂,在背接触势垒小于等于0.5 eV时,电池的转换效率不会受到背接触势垒的影响;若背场低掺杂,在背接触势垒很小的情况下,也能达到与重掺杂相同的转换效率.     

Doping graphene with metal contacts

Making devices with graphene necessarily involves making contacts with metals. We use density functional theory to study how graphene is doped by adsorption on metal substrates and find that weak bonding on Al, Ag, Cu, Au, and Pt, while preserving its unique electronic structure, can still shift the Fermi level with respect to the conical point by approximately 0.5 eV. At equilibrium separations, the crossover from p-type to n-type doping occurs for a metal work function of approximately 5.4 eV, a value much larger than the graphene work function of 4.5 eV. The numerical results for the Fermi level shift in graphene are described very well by a simple analytical model which characterizes the metal solely in terms of its work function, greatly extending their applicability.     

Performance assessment of Cu2SnS3 (CTS) based thin film solar cells by AMPS-1D

A relative performance assessment of copper tin sulfide (CTS) thin film solar cells with different phases such as, cubic, tetragonal, and orthorhombic as an absorber layer has been carried out by AMPS-1D simulation software. Based on the proposed device architecture, the effects of thickness and carrier concentration for the absorber layer as well as the back metal contact with various work function are studied in order to improve the performance of CTS solar cell. It is found that 10¹⁸ cm⁻³ and 2500–3000 nm are optimum values for carrier concentration and thickness for all the investigated CTS absorber layer phases, respectively. On the other hand, back contact metal work function of 5.28 eV, 5.67 eV and 5.71 eV are identified to be the optimal values for cubic, tetragonal, and orthorhombic phases, respectively. We have analyzed in detail the output performance of CTS thin film solar cell with respect to its fabrication, which can serve a constructive research pathway for the thin film photovoltaic industry.     

Tuning the Schottky barrier in the arsenene/graphene van der Waals heterostructures by electric field

Using density functional theory calculations, we investigate the electronic properties of arsenene/graphene van der Waals (vdW) heterostructures by applying external electric field perpendicular to the layers. It is demonstrated that weak vdW interactions dominate between arsenene and graphene with their intrinsic electronic properties preserved. We find that an n-type Schottky contact is formed at the arsenene/graphene interface with a Schottky barrier of 0.54 eV. Moreover, the vertical electric field can not only control the Schottky barrier height but also the Schottky contacts (n-type and p-type) and Ohmic contacts (n-type) at the interface. Tunable p-type doping in graphene is achieved under the negative electric field because electrons can transfer from the Dirac point of graphene to the conduction band of arsenene. The present study would open a new avenue for application of ultrathin arsenene/graphene heterostructures in future nano- and optoelectronics.     

用电化学沉积法制备ZnO/Cu2O异质p-n结

由于P型ZnO的制备仍然存在一定的困难,限制了ZnO在光电方面的应用,尤其是在发光二极管和激光器的实际应用,目前利用P型的透明半导体氧化物与n型ZnO制备异质p-n结,成为新的研究热点。选择P型导电Cu2O与ZnO制备出异质p-n结。Cu2O是一种典型的P型半导体材料,禁带宽度为2．1eV,可见光范围的吸收系数较高。首次利用电化学沉积的方法制备了ZnO／Cu2O异质p-n结,研究了电沉积ZnO,Cu2O的生长机制和ZnO／Cu2O异质结的结构、光学和电学特性。     

Fabrication and characterization of Fe-doped titania semiconductor electrodes with p-n homojunction devices

The nano-TiO₂ electrode with a p-n homojunction device was designed and fabricated by coating of the Fe³⁺-doped TiO₂ (p-type) film on top of the nano-TiO₂ (n-type) film. These films were prepared from synthesized sol-gel TiO₂ samples which were verified as anatase with nano-size particles. The semiconductor characteristics of the p-type and n-type films were demonstrated by current-voltage (I-V) measurements. Results show that the rectifying curves of undoped TiO₂ and Fe³⁺-doped TiO₂ sample films were observed from the I-V data illustration for both the n-type and p-type films. In addition, the shapes of the rectifying curves were influenced by the fabrication conditions of the sample films, such as the doping concentration of the metal ions, and thermal treatments. Moreover, the p-n homojunction films heating at different temperatures were produced and analyzed by the I-V measurements. From the I-V data analysis, the rectifying current of this p-n junction diode has a 10 mA order higher than the current of the n-type film. The p-n homojunction TiO₂ electrode demonstrated greater performance of electronic properties than the n-type TiO₂ electrode.     

Rb吸附石墨烯纳米带电子性质和光学性质的研究

本文基于密度泛函理论的第一性原理方法了计算了Rb、O和H吸附石墨烯纳米带的差分电荷密度、能带结构、分波态密度和介电函数,调制了石墨烯纳米带的电子性质和光学性质,给出了不同杂质影响材料光学特性的规律.结果表明本征石墨烯纳米带为n型直接带隙半导体且带隙值为0.639 eV;Rb原子吸附石墨烯纳米带之后变为n型简并直接带隙半导体,带隙值为0.494eV;Rb和O吸附石墨烯纳米带变为p型简并直接带隙半导体,带隙值增加为0.996eV;增加H吸附石墨烯纳米带后,半导体类型变为n型直接带隙半导体,且带隙变为0.299eV,带隙值相对减小,更有利于半导体发光器件制备.吸附Rb、O和H原子后,石墨烯纳米带中电荷密度发生转移,导致C、Rb、O和H之间成键作用显著.吸附Rb之后,在费米能级附近由C-2p、Rb-5s贡献;增加O原子吸附之后,O-2p在费米能级附近贡献非常活跃,杂化效应使费米能级分裂出一条能带;再增加H原子吸附之后,Rb-4p贡献发生蓝移,O-2p在费米能级附近贡献非常强,费米能级分裂出两条能带.Rb、O和H的吸附后,明显调制了石墨烯纳米带的光学性质.     

Analysis of the generation mechanism of the S-shaped J—V curves of MoS2/Si-based solar cells

Amorphous-microcrystalline MoS$_{2}$ thin films are fabricated using the sol-gel method to produce MoS$_{2}$/Si-based solar cells. The generation mechanisms of the S-shaped current density-voltage ($J$-$V$) curves of the solar cells are analyzed. To improve the performance of the solar cells and address the problem of the S-shaped $J$-$V$ curve, a MoS$_{2}$ film and a p$^+$ layer are introduced into the front and back interfaces of the solar cell, respectively, which leads to the formation of a p-n junction between the p-Si and the MoS$_{2}$ film as well as ohmic contacts between the MoS$_{2}$ film and the ITO, improving the S-shaped $J$-$V$ curve. As a result of the high doping characteristics and the high work function of the p$^+$ layer, a high-low junction is formed between the p$^+$ and p layers along with ohmic contacts between the p$^+$ layer and the Ag electrode. Consequently, the S-shaped $J$-$V$ curve is eliminated, and a significantly higher current density is achieved at a high voltage. The device exhibits ideal p-n junction rectification characteristics and achieves a high power-conversion efficiency (CE) of 7.55%. The findings of this study may improve the application of MoS$_{2}$ thin films in silicon-based solar cells, which are expected to be widely used in various silicon-based electronic and optical devices.     

Zinc oxide, a multifunctional material: from material to device applications

In this paper we report on some of the recent advances in transparent thin film oxide semiconductors, specifically zinc oxide produced by radio frequency magnetron sputtering at room temperature, with multifunctional properties. By controlling the deposition parameters it is possible to produce undoped material with electronic semiconductor properties, or by doping it to get either n-type or p-type semiconductor behavior. In this work we refer to our experience in producing n-type doped zinc oxide as transparent electrode to be used in optoelectronic applications such as solar cells and position sensitive detectors, while the undoped zinc oxide can be used as active layer of fully transparent thin film transistors.     

过渡金属W、Mn、V、Ti掺杂二维材料MoSi2N4的第一性原理计算

本文基于密度泛函理论(DFT)的第一性原理计算了W、Mn、V、Ti替位掺杂二维MoSi₂N₄后的几何结构、电子结构以及光学性质的变化.电子结构分析表明W、Mn、W、Ti替位掺杂二维MoSi₂N₄后的禁带宽度分别为1.806 e V、1.003 e V、1.218 e V和1.373 e V;四种过渡金属掺杂后MoSi₂N₄的带隙类型没有发生改变,均为间接带隙半导体;W掺杂后的杂质能级靠近价带顶,费米能级靠近价带顶,为p型半导体,杂质能级为受主能级;Mn掺杂后的杂质能级靠近导带底,费米能级靠近导带底,为n型半导体;V和Ti掺杂后杂质能级位于费米能级附近,为复合中心;光学性质分析表明,在2 e V～4 e V的能量区间内,W掺杂结构的吸收波长为336 nm,体系发生红移;Mn、V和Ti替位掺杂后的吸收波长分别为320 nm、358 nm和338 nm,且掺杂体系均发生蓝移.     

Low temperature photoluminescence and photoacoustic characterization of Zn-doped InxGa1−xAsySb1−y epitaxial layers for photovoltaic applications

In this paper we present results on the characterization of Zn-doped InGaAsSb epitaxial layers to be used in the development of stacked solar cells. Using the liquid phase epitaxy technique we have grown p-type InGaAsSb layers, using Zn as the dopant, and n-type Te-doped GaSb wafers as substrates. A series of Zn-doped InGaAsSb samples were prepared by changing the amount of Zn in the melt in the range: 0.1-0.9 mg to obtain different p-type doping levels, and consequently, different p-n region characteristics. Low temperature photoluminescence spectra (PL) were measured at 15 K using at various excitation powers in the range 80-160 mW. PL spectra show the presence of an exciton-related band emission around 0.642 eV and a band at 0.633 eV which we have related to radiative emission involving Zn-acceptors. Using the photoacoustic technique we measured the interface recombination velocities related to the interface crystalline quality, showing that the layer-substrate interface quality degrades as the Zn concentration in the layers increases.