Optimum design of InGaP/GaAs dual-junction solar cells with different tunnel diodes

We design the InGaP/GaAs dual-junction (DJ) solar cells by optimizing short-circuit current matching between top and bottom cells using the Silvaco ATLAS. The relatively thicker base layer of top cell exhibits a larger short-circuit current density (J _sc) while the thicker base layer of bottom cell allows for a smaller J _sc. The matched J _sc of 10.61±0.05 and 13.25±0.06 mA/cm ² under AM1.5G and AM0 illuminations, respectively, are obtained, leading to the increased conversion efficiency. The base thicknesses of top InGaP cells are optimized at 0.8 and 0.65 μm for AM1.5G and AM0 illuminations, respectively, and the base thicknesses of bottom GaAs cells are optimized at 2 μm. For the optimized solar cell structure, the maximum J _sc = 10.66 mA/cm ² (13.31 mA/cm ²), V _oc =  2.34 V (2.35 V), and fill factor =  87.84% (88.1%) are obtained under AM1.5G (AM0) illumination, exhibiting a maximum conversion efficiency of 25.78% (23.96%). The effect of tunnel diode structure, i.e, GaAs/GaAs, AlGaAs/AlGaAs, and InGaP/InGaP, on the characteristics of solar cells is investigated. The photogeneration rate in the DJ solar cell structure is also obtained by incident light of different wavelengths.     

Composition modulation analysis of InxGa1−xP layers grown on (0 0 1) germanium substrates

The development of new photovoltaic approach to improve costs and efficiencies is focused on the new materials and new technologies. InGaP is, in this sense, a key material for solar conversion. In particular, in the solar concentration approach, this material is part of multiple junction solar cells. Its low lattice mismatch with germanium and its adequate bandgap make it very promising. This paper shows how compositional modulation can affect the InGaP emitter and the AlGaAs tunnel junctions. The influence of the growth conditions, on the compositional modulation and misfit and threading dislocations, in In_0.49Ga_0.51P layers is demonstrated by TEM on purposely grown single InGaP layers. High resolution electron microscopy (HREM) intensity profiles showed no elastic lattice related modulation.     

Tunneling and injection in ferromagnetic structures InGaAs/GaAs/(Ga,Mn)As and InGaAs/<Emphasis Type="Italic">n</Emphasis> <Superscript>+</Superscript>-GaAs/(Ga,Mn)As

The spin light-emitting diodes based on InGaAs/GaAs heterostructures with a quantum well and an injector in the form of a (Ga,Mn)As ferromagnetic layer have been studied. It has been demonstrated that the efficiency of electron spin injection in the structure with a (Ga,Mn)As/n⁺-GaAs tunneling barrier can be controlled by varying the parameters of n⁺-GaAs. The spin injection control mechanisms associated with the thermal activation and tunneling of carriers have been discussed.     

Prediction of lateral barrier height in identically prepared Ni/n-type GaAs Schottky barrier diodes

We have identically prepared Ni/n-GaAs/In Schottky barrier diodes (SBDs) with doping density of 7.3 × 10¹⁵ cm⁻³. The barrier height for the Ni/n-GaAs/In SBDs from the current-voltage characteristics have varied from 0.835 to 0.856 eV, and ideality factor n from 1.02 to 1.08. We have determined a lateral homogeneous barrier height value of 0.862 eV for the Ni/n-GaAs/In SBD from the experimental linear relationship between barrier heights and ideality factors.     

Organic p-i-n solar cells

We introduce a p-i-n-type heterojunction architecture for organic solar cells where the active region is sandwiched between two doped wide-gap layers. The term p-i-n means here a layer sequence in the form p-doped layer, intrinsic layer and n-doped layer. The doping is realized by controlled co-evaporation using organic dopants and leads to conductivities of 10^-4 to 10^-5 S/cm in the p- and n-doped wide-gap layers, respectively. The photoactive layer is formed by a mixture of phthalocyanine zinc (ZnPc) and the fullerene C₆₀ and shows mainly amorphous morphology. As a first step towards p-i-n structures, we show the advantage of using wide-gap layers in M-i-p-type diodes (metal layer–intrinsic layer–p-doped layer). The solar cells exhibit a maximum external quantum efficiency of 40% between 630-nm and 700-nm wavelength. With the help of an optical multilayer model, we optimize the optical properties of the solar cells by placing the active region at the maximum of the optical field distribution. The results of the model are largely confirmed by the experimental findings. For an optically optimized device, we find an internal quantum efficiency of around 82% under short-circuit conditions. Adding a layer of 10-nm thickness of the red material N,N-dimethylperylene-3,4:9,10-dicarboximide (Me-PTCDI) to the active region, a power-conversion efficiency of 1.9% for a single cell is obtained. Such optically thin cells with high internal quantum efficiency are an important step towards high-efficiency tandem cells. First tandem cells which are not yet optimized already show 2.4% power-conversion efficiency under simulated AM 1.5 illumination of 125 mW/cm² . PACS 73.61.Ph; 78.30.Jw; 89.30.Cc     

Al2O3增强的Co2-C98/Al2O3/Si异质结的光伏效应

随着能源危机的加剧,太阳能电池作为开发和利用太阳能的一种普遍形式, 日益受到世界各国的重视.随着太阳能电池向着高效率、薄膜化、无毒性和原材料丰富的方向发展, 单纯的硅系太阳能电池已经无法达到这样的要求,因此新的材料和工艺的开发利用迫在眉睫. 本文研究了碳材料在硅异质节上实现光伏效应的改善及其可能在太阳能电池上的应用. 采用脉冲激光沉积方法制备的Co₂-C₉₈/Al₂O₃/Si异质结构在标准日光照射 (AM1.5, 100 mW/cm²)条件下,可获得0.447 V的开路电压和18.75 mA/cm²的电流密度, 转换效率可达3.27%.通过电容电压特性和暗条件下的电输运性能测量, 证明了氧化铝层的引入不但对单晶硅的表面起到了物理钝化作用,减小了反向漏电流, 使异质结界面缺陷、界面能级和复合中心减少,还起到了场效应钝化作用, 增加了异质结界面的势垒高度,增加了开路电压,使异质结的光伏效应显著增强.     

新型MIp~+-Al_(0.3)Ga_(0.7)As/p-n-n~+-GaAs太阳电池的设计与I-V特性理论分析

为充分利用太阳光的短波部分,将AlxGa1-xAs设计为电池的又一个光伏工作层,并引入固定负电荷,建立界面感应势垒,形成MIp -AlGaAs感应结,有效降低界面对光生电子的复合。以制作工艺简单的p -AlGaAs／p-GaAs界面,将感应结与p／n-GaAs部分连接起来,构成新型高效率复合结构MIp -Al0.3Ga0.7As／p-n-n -GaAs太阳电池。其I-V特性理论研究绐果表明,选择合适的负电荷面密度数和Al0.3Ga0.7As层的掺杂浓度,即:建立合适高度的感应势垒,可显著降低界面复合速度近8个数量级。优化设计得到的整个电池的效率为31.5％,较传统的窗口层电池有明显提高。     

Impact of rough silicon buffer layer on electronic quality of GaAs grown on Si substrate

The electronic and the structural properties of n-GaAs layers grown on rough surface of silicon substrate by molecular beam epitaxy (MBE) has been investigated by photoluminescence (PL), time resolved photoluminescence (TRPL) and high resolution X-ray diffraction (HRXRD). The relationship between electronic and structural properties of the n-GaAs layer was checked, showing that the defect density is a strong cause for trapping the minority carriers. The impact of introducing intermediate rough silicon layer between silicon substrate and n-GaAs layer on the electronic properties was observed, showing that the structure grown on rough Si involves higher lifetime than those developed on flat silicon substrate. Such structure could be used for economic solar cells fabrication.     

Spectral-splitting concentrator photovoltaic modules based on AlGaAs/GaAs/GaSb and GaInP/InGaAs(P) solar cells

A concentrator photovoltaic module with sunlight spectral splitting by Fresnel lens and dichroic filters is developed. The photoelectric conversion efficiency of such a module is estimated at a level of 49.4% when three single-junction cells are used and may reach 48.5–50.6% when a tandem two-junction cell is combined with narrow-band cells. Single-junction AlGaAs, GaAs, GaSb, and InGa(P)As solar sells are fabricated by zinc diffusion from the vapor phase into an n-type epitaxial layer. GaInP/GaAs cascade solar cells are prepared by MOS hydride epitaxy. The overall efficiency of the three single-junction solar cells developed for the spectral-splitting module is 38.1% (AM1.5D) at concentration ratio K _c = 200x. The combination of the solar cells with the cascade structure demonstrates an efficiency of 37.9% at concentrations of 400–800 suns. The parameters of the spectral-splitting photovoltaic module are measured. The photovoltaic efficiency of this module reaches 24.7% in the case of three single-junction cells and 27.9% when the two-junction and single-junction cells are combined.     

Thin macroporous silicon heterojunction solar cells

We demonstrate the processing of a heterojunction solar cell from a purely macroporous silicon (MacPSi) absorber that is generated and separated from a monocrystalline n‐type Cz silicon wafer by means of electrochemical etching. The etching procedure results in straight pores with a diameter of (4.7 ± 0.2) µm and a distance of 8.3 µm. An intrinsic amorphous Si (a‐Si)/p⁺‐type a‐Si/indium tin oxide (ITO) layer stack is on the front side and an intrinsic a‐Si/n⁺‐type a‐Si/ITO layer stack is on the rear side. The pores are open when depositing the layers onto the 3.92 cm²‐sized cell. The conductive layers do not cause shunting through the pores. A silicon oxide layer passivates the pore walls. The energy‐conversion efficiency of the (33 ± 2) µm thick cell is 7.2%. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

宽沟道SI-GaAs衬底上适于光发射机的BH激光器

目前,光发射机中的激光器有采用MOCVD和MBE方法生长的多量子阱激光器,用LPE法生长的BH激光器。我们根据现有的实验条件,为了制作单片集成的光发射机,在沟道SI-GaAs衬底上采用两次液相外延生长BH激光器,实现了表面平面化。在800℃一次外延生长四层。第一层n⁺-GaAs缓冲层,第二层N-GaAlAs下限制层,第三层非掺杂构GaAs有源层,第四层为P-GaAlAs上限制层。采用适当的腐蚀条件刻蚀出有源区最窄的燕尾形隐埋条。在二次外延中,我们仅装一槽GaAlAs源液,在晶片上仅停留一次便生长出两个掩埋层,且层间界面与有源区自对准。上层为N-GaAlAs,载流子浓度为10¹⁶cm^-3,下层为高阻伴随生长层。由于高阻伴随层的存在对电流产生了有有效的侧向限制作用,因此避免了通常的SiO₂膜沉积等一系列工艺,提高了成品率,减化了工艺程序。利用n型掩埋层和隐埋条区P型上限制层之间铝组分及载流子类型、浓度的差异,虽然做一种宽接触电极,但由于隐埋条区上有良好的欧姆接触,而在掩埋层上为非良欧姆接触,所以起到了一定的电流外限制作用。n型电极是从n⁺-GaAs层引出的。 这种沟道SI-GaAs衬底正装GaAlAs/GaAs BH激光器室温连续工作阈值电流为55mA,P-I曲线在100℃仍有良好的线性关系。     

渐变带隙氢化非晶硅锗薄膜太阳能电池的优化设计

利用一维微电子-光电子结构分析软件(AMPS-1D)在AM1.5G(100 mW/cm2)、室温条件下模拟和比较了有、无渐变带隙氢化非晶硅锗(a-SiGe:H)薄膜太阳能电池的各项性能.计算结果表明:渐变带隙结构电池具有较高的开路电压(V oc)和较好的填充因子(FF),转换效率(E ff)比非渐变带隙电池提高了0.477%.研究了氢化非晶硅(a-Si:H)、氢化非晶碳化硅(a-SiC:H)和氢化纳米晶硅(nc-Si:H)三种不同材料的窗口层对a-SiGe:H薄膜太阳能电池性能的影响.结果显示:在以nc-Si:H为窗口层的电池能带中,费米能级E F已经进入价带,使得窗口层电导率及电池开路电压有所提高,又由于ITO与p-nc-Si:H的接触势垒较低,使得接触处的电场降低,更有利于载流子的收集.另一方面,窗口层与a-SiGe:H薄膜之间存在较大的带隙差,在p/i界面由于能带补偿作用形成了价带势垒(带阶)?E v,阻碍了空穴的迁移,因此我们在p/i界面引入缓冲层,使得能带补偿作用得到释放,更有利于空穴的迁移和收集,得到优化后单结渐变带隙a-SiGe:H薄膜结构太阳能电池的转换效率达到了9.104%.     

Study of the Hanle effect with the transverse component of the electron spin orientation in III–V semiconductors

The Hanle effect in n-GaAs and p-AlGaAs is studied in the longitudinal and transverse geometries of the experiment, in which the emission is recorded parallel and perpendicular to the spin direction of optically oriented electrons, respectively. The factors responsible for the error in determining the sign of the electron g factor in GaAs studied in the transverse geometry of the experiment are considered. It is shown that the results obtained from measurements of the transverse spin component of the orientation are useful in determining the parameters of semiconductor structures.     

Geometry-induced electron doping in periodic semiconductor nanostructures

Recently, new quantum features have been observed and studied in the area of nanostructured layers. Nanograting on the surface of the thin layer imposes additional boundary conditions on the electron wave function and induces G-doping or geometry doping. G-doping is equivalent to donor doping from the point of view of the increase in electron concentration n. However, there are no ionized impurities. This preserves charge carrier scattering to the intrinsic semiconductor level and increases carrier mobility with respect to the donor-doped layer. G-doping involves electron confinement to the nanograting layer. Here, we investigate the system of multiple nanograting layers forming a series of hetero- or homojunctions. The system includes main and barrier layers. In the case of heterojunctions, both types of layers were G-doped. In the case of homojunctions, main layers were G-doped and barrier layers were donor-doped. In such systems, the dependence of n on layer geometry and material parameters was analysed. Si and GaAs homojunctions and GaAs/AlGaAs, Si/SiGe, GaInP/AlGAs, and InP/InAlAs heterojunctions were studied. G-doping levels of 10¹⁸–10¹⁹ cm⁻³ were obtained in homojunctions and type II heterojunctions. High G-doping levels were attained only when the difference between band gap values was low.     

Injection electroluminescence from quantum-size InGaAs/GaAs structures with metal/semiconductor and metal-oxide-semiconductor junctions

Electroluminescence from forward-biased diode structures with Au(Ni)/GaAs and Au(Ni)/tunneling-thin oxide/GaAs junctions has been studied. The possibility of luminescence amplification from the Schottky diodes by introducing a tunneling-thin anode-oxide or heavily doped p ⁺-GaAs layer between the metal and semiconductor have been demonstrated. The studies of the temperature dependence of electroluminescence and the I-W curves indicate that the amplification of the electroluminescence intensity from the above structures may be associated with lowering the potential barrier for the minority carriers under the forward bias of the Schottky barrier.     

Effect of the thickness on the optoelectronic properties of SnS films and photovoltaic performance of SnS/i-a-Si/n-a-Si solar cells

Different thick orthorhombic SnS films were successfully fabricated by sulfurization of various sputtered different thick Sn precursor layers. All the absorption coefficients of different thick SnS films are higher than 2 × 10⁴ cm^?1 in the visible light region of 400–800 nm, and the direct band gaps of these SnS films were estimated to be about 1.2 eV. Furthermore, SnS/i-a-Si/n-a-Si solar cells with 205-, 420-, 635-, 845- and 1,060-nm-thick SnS-absorber layers were fabricated, and the 845-nm-thick SnS-absorber-based SnS/i-a-Si/n-a-Si solar cell shows the highest conversion efficiency of 0.42 %, a short-circuit current density of 2.4 mA/cm², and an open-circuit voltage of 362 mV.     

n-ZnO:Al/i-ZnO/n-CdS/p-Cu2ZnSnS4太阳能电池光伏特性的分析

具有高光吸收系数的半导体Cu₂ZnSnS₄ (CZTS)薄膜是一种新型太阳能电池材料. 本文对n-ZnO:Al/i-ZnO/n-CdS/p-CZTS结构的CZTS薄膜太阳能电池进行分析, 讨论CZTS薄膜的掺杂浓度、厚度、缺陷态和CdS薄膜的掺杂浓度、 厚度对太阳能电池转换效率的影响以及太阳能电池的温度特性. 分析表明, CZTS薄膜作为太阳能电池的主要光吸收层, CZTS薄膜的掺杂浓度和厚度的取值对太阳能电池的转换效率有显著影响, CZTS薄膜结构缺陷态的存在会导致太阳能电池性能的下降. CdS缓冲层的掺杂浓度、厚度对太阳能电池光伏特性的影响较小. 经结构参数优化得到的n-ZnO:Al/i-ZnO/n-CdS/p-CZTS薄膜太阳能电池的最佳光 伏特性为开路电压1.127 V、短路电流密度27.39 mA/cm²、填充因子87.5%、 转换效率27.02%,转换效率温度系数为-0.14%/K.     

Electrical and photovoltaic properties of Cd1? x Zn x S/ p -GaAs heterojunctions

Cd_1−x Zn _x S/p-GaAs heterojunctions for solar cell applications have been prepared by growing single crystal Cd_1−x Zn _x S epitaxial layers on (111)GaAs substrates through a vapour phase chemical transport method using the close-spaced geometry and H₂ as a transport agent. Electrical and photovoltaic properties of the heterojunctions have been investigated and discussed in connection with the main features of the growth technique. AM1 power conversion efficiencies up to 6.2% have been measured and possible improvements have been examined.     

Virtual Anderson transition in a narrow impurity band of doped <Emphasis Type="Italic">p</Emphasis>-GaAs/AlGaAs layers

In highly doped uncompensated layers of p-GaAs/AlGaAs quantum wells, activation conduction with low activation energies is observed at low temperatures and this conduction is not explained by known mechanisms (ε₄ conduction). Such behavior is attributed to the delocalization of electron states near the maximum of a narrow impurity band in the sense of the Anderson transition. In this case, conduction is implemented due to the activation of minority carriers from the Fermi level to the indicated delocalized-state band.