Advantages of InGaN/GaN multiple quantum well solar cells with stepped-thickness quantum wells

InGaN/GaN multiple quantum well (MQW) solar cells with stepped-thickness quantum wells (SQW) are designed and grown by metal-organic chemical vapor deposition. The stepped-thickness quantum wells structure, in which the well thickness becomes smaller and smaller along the growth direction, reveals better crystalline quality and better spectral overlap with the solar spectrum. Consequently, the short-circuit current density (Jsc) and conversion efficiency of the solar cell are enhanced by 27.12% and 56.41% compared with the conventional structure under illumination of AM1.5G (100 mW/cm2). In addition, approaches to further promote the performance of InGaN/GaN multiple quantum well solar cells are discussed and presented.     

基于GaAs/InAs-GaAs/ZnSe量子点太阳电池结构的优化

基于GaAs/InAs-GaAs/ZnSe的P-i-N量子点太阳电池结构, 根据光学原理和扩散理论建立了光生电流密度与膜层厚度相关的数学模型, 定量分析了量子点层厚度等参数对太阳电池性能的影响,以期达到提高量子 点太阳电池转换效率的目的.理论模拟表明:在i层厚度取3000 nm时,优化后P(GaAs)型、N(ZnSe)型层 薄膜的最佳膜厚为1541 nm, 78 nm, 并在单一波长下太阳电池转换效率为20.1%;同时量子 点体积和温度对于量子点太阳电池I-V特性也会产生影响, 当量子点体积和温度逐渐增大时, 开路电压呈现减小趋势,使得转换效率降低.     

Delta-doped quantum wire tunnel junction for highly concentrated solar cells

We propose a novel structure for tunnel junction based on delta-doped AlGaAs/GaAs quantum wires. Higher spatial confinement of quantum wires alongside the increased effective doping concentration in the delta-doped regions extremely increase the peak tunneling current and enhance the performance of tunnel junction. The proposed structure can be used as tunnel junction in the multijunction solar cells under the highest possible thermodynamically limited solar concentration.The combination of the quantum wire with the delta-doped structure can be of benefit to the solar cells' advantages including higher number of sub-bands and high degeneracy. Simulation results show a voltage drop of 40 mV due to the proposed tunnel junction used in a multijunction solar cell which presents an extremely low resistance to the achieved peak tunneling current.     

不同周期数的GaInAs/GaAsP多量子阱太阳能电池

为了研究不同量子阱周期数下GaInAs/GaAsP多量子阱太阳能电池性能的变化规律,利用金属有机化学气相沉积技术(MOCVD)制备了不同周期数的双结多量子阱太阳能电池样品以及无量子阱双结结构的参考样品,利用高分辨率X射线衍射仪(HXRD)和高分辨率透射电镜(TEM)测试了样品的晶体质量,同时在AM0(1×)光谱条件下测试了样品的I-V特性曲线和相应子电池的外量子效率。最终得到了高晶体质量、吸收截止波长在954 nm的Ga_(0.89)In_(0.11)As/GaAs_(0.92)P_(0.08)多量子阱结构,扩展波段的外量子效率最高达到75.18%,电池光电转换效率相对于无量子阱结构提升2.77%。通过对比测试结果发现,随着量子阱结构周期数的增加,太阳能电池在扩展波段(890~954 nm)的外量子效率不断提高,常规波段的短波响应(300~700 nm)会出现下降,长波响应(700~890 nm)会出现上升,短路电流和转换效率相应提升并趋于饱和。     

GaAs量子阱太阳能电池量子效率的研究

将量子阱结构引入到单结GaAs太阳能电池中能够有效扩展吸收光谱.为了研究量子阱结构在GaAs太阳能电池中的作用机理,本文采用实验和理论的方法研究了InGaAs/GaAsP量子阱结构对电池量子效率的影响.实验结果表明,量子阱结构的窄带隙阱层材料将电池的吸收光谱从890 nm扩展到1000 nm.同时,量子阱结构的引入提高了680—890 nm波长范围内的量子效率,降低了波长在680 nm以下的量子效率.通过计算得到的量子阱结构和GaAs材料的光吸收系数,可以用来解释量子阱结构对太阳能电池量子效率的影响.     

ZnS/CdS复合窗口层对CdTe太阳能电池短波光谱响应的影响

采用磁控溅射法制备了ZnS/CdS复合窗口层,并将其应用于CdTe太阳能电池。对所制备薄膜的形貌和结构等进行了研究。测试了具有不同窗口层的CdTe太阳电池的量子效率和光Ⅰ-Ⅴ特性,分析了ZnS薄膜制备条件对CdTe电池器件性能影响;研究了CdS薄膜厚度和ZnS/CdS复合窗口层对短波区透过率以及CdTe太阳电池的光谱响应的影响。着重研究了具有ZnS/CdS复合窗口层的CdTe太阳电池的短波光谱响应。结果表明,CdS窗口层厚度从100 nm减至50 nm后,其对短波区光子透过率平均提高了18.3%,CdTe太阳电池短波区光谱响应平均提高了27.6%。衬底温度250 ℃条件下制备的ZnS晶粒尺寸小于室温下制备的ZnS。具有ZnS/CdS复合窗口层的CdTe电池中,采用衬底温度250 ℃沉积ZnS薄膜来制备窗口层的电池器件,其性能要优于室温下沉积ZnS制备窗口层的电池器件。这说明晶粒尺寸的大小对电子输运有一定影响。在相同厚度CdS的前提下,具有ZnS/CdS复合窗口层的CdTe电池比具有CdS窗口层在短波的光谱响应提高了约2%。这说明ZnS/CdS复合窗口层能够做到减少对短波光子的吸收,从而使更多的光子被CdTe电池的吸收层吸收。     

硅锗量子阱结构在硅异质结太阳电池中应用的数值模拟

利用半导体工艺和器件仿真软件silvaco TCAD(Technology Computer Aided Design),模拟研究了采用硅/硅锗合金(silicon/silicon germanium alloy,Si/Si_(1-x)Ge_x)量子阱结构作为吸收层的薄膜晶体硅异质结太阳电池各项性能.模拟结果显示,长波波段光学吸收随锗含量的增加而增加,而开路电压则因Si_(1-x)Ge_x)层带隙的降低而下降.锗含量为0.25时,短路电流密度的增加补偿了开路电压的衰减,效率提升0.2%.氢化非晶硅/晶体硅(a-Si:H/c-Si)界面空穴密度以及Si_(1-x)Ge_x)量子阱的体空穴载流子浓度制约着空穴费米能级的位置,进而影响到开路电压的大小.随着锗含量增加,a-Si:H/c-Si界面缺陷对开压的影响降低,Si_(1-x)Ge_x)量子阱的体缺陷对开压的影响则相应增加.高效率含Si_(1-x)Ge_x)量子阱结构的硅异质结太阳电池的制备需要a-Si:H/c-Si界面缺陷的良好钝化以及高质量Si_(1-x)Ge_x)量子阱的生长.     

Direct observation of the carrier transport process in InGaN quantum wells with a pn-junction

A new mechanism of light-to-electricity conversion that uses InGaN/GaN QWs with a p-n junction is reported.According to the well established light-to-electricity conversion theory,quantum wells(QWs) cannot be used in solar cells and photodetectors because the photogenerated carriers in QWs usually relax to ground energy levels,owing to quantum confinement,and cannot form a photocurrent.We observe directly that more than 95% of the photoexcited carriers escape from InGaN/GaN QWs to generate a photocurrent,indicating that the thermionic emission and tunneling processes proposed previously cannot explain carriers escaping from QWs.We show that photoexcited carriers can escape directly from the QWs when the device is under working conditions.Our finding challenges the current theory and demonstrates a new prospect for developing highly efficient solar cells and photodetectors.     

Recent progress of colloidal quantum dot based solar cells

Colloidal quantum dot(CQD) solar cells have attracted great interest due to their low cost and superior photo-electric properties. Remarkable improvements in cell performances of both quantum dot sensitized solar cells(QDSCs) and PbX(X = S, Se) based CQD solar cells have been achieved in recent years, and the power conversion efficiencies(PCEs) exceeding 12% were reported so far. In this review, we will focus on the recent progress in CQD solar cells. We firstly summarize the advance of CQD sensitizer materials and the strategies for enhancing carrier collection efficiency in QDSCs, including developing multi-component alloyed CQDs and core-shell structured CQDs, as well as various methods to suppress interfacial carrier recombination. Then, we discuss the device architecture development of PbX CQD based solar cells and surface/interface passivation methods to increase light absorption and carrier extraction efficiencies. Finally, a short summary, challenge, and perspective are given.     

An analysis of quantum coherent solar photovoltaic cells

A new hypothesis (Scully et al., Proc. Natl. Acad. Sci. USA 108 (2011) 15097) suggests that it is possible to break the statistical physics-based detailed balance-limiting power conversion efficiency and increase the power output of a solar photovoltaic cell by using “noise-induced quantum coherence” to increase the current. The fundamental errors of this hypothesis are explained here. As part of this analysis, we show that the maximum photogenerated current density for a practical solar cell is a function of the incident spectrum, sunlight concentration factor, and solar cell energy bandgap and thus the presence of quantum coherence is irrelevant as it is unable to lead to increased current output from a solar cell.     

新一代太阳电池概述

文章对新一代太阳电池的基本概念、研究现状和研究目标进行了详细的介绍.从"充分吸收光能,减少能量转换损失"的角度,分析了新一代太阳电池的结构设计特征.以纳米技术与叠层电池结构为基础,就高能光子的利用,介绍了宽带隙吸收层窗口电池、量子点热载流子电池和多重激子激发(MEG)的量子点电池;为解决低能光子损失,介绍了窄带隙光伏材料和中间带光伏器件包括量子点中间带和高失配构建的中间带电池;探讨了利用光-光转换的模式,对上转换和下转换的电池体系以及可能的极限效率进行了阐述.     

Efficient design of perovskite solar cell using mixed halide and copper oxide

Solar cells based on perovskites have emerged as a transpiring technology in the field of photovoltaic. These cells exhibit high power conversion efficiency. The perovskite material is observed to have good absorption in the entire visible spectrum which can be well illustrated by the quantum efficiency curve. In this paper, theoretical analysis has been done through device simulation for designing solar cell based on mixed halide perovskite. Various parameters have efficacy on the solar cell efficiency such as defect density, layer thickness, doping concentration, band offsets, etc. The use of copper oxide as the hole transport material has been analyzed. The analysis divulges that due to its mobility of charge carriers, it can be used as an alternative to spiro-OMeTAD. With the help of simulations, reasonable materials have been employed for the optimal design of solar cell based on perovskite material. With the integration of copper oxide into the solar cell structure, the results obtained are competent enough. The simulations have shown that with the use of copper oxide as hole transport material with mixed halide perovskite as absorber, the power conversion efficiency has improved by 6%.The open circuit voltage has shown an increase of 0.09 V, short circuit current density has increased by 2.32 m A/cm~2, and improvement in fill factor is 8.75%.     

Field-enhanced charge flow in nanorod heterostructure solar cells

Recent studies on organic heterostructure solar cells have indicated that interface morphology plays an important role in determining the quantum efficiency. Hybrid heterostructure mixing donor and acceptor semiconductors appear to offer the best opportunity in achieving superior performance and there are indications that a network of percolated heterojunctions can be quite effective in promoting light absorption and exciton quenching. Charge transport and collection efficiency, however, appear to be more complex in the bulk heterostructure and the nature of charge flow depends largely on the type of current paths in existence. We report in this work the possible existence of field-assisted charge flow in the nanorod heterostructure solar cells when carriers of different polarity move in close proximity. The field-effect associated with the charge density gradients can exert a force on the nearby carriers resulting in an increase in the short-circuit current. The model is used to explain data reported in the literature on solar cells composed of TiO₂ nanorods embedded in a conjugated polymer.     

碲化镉薄膜太阳能电池电学特性参数分析

用inline方式全部近空间升华方法制备n-CdS/p-CdTe取得了～11%的转换效率(AM1.5). 把其中n-CdS层采用磁控溅射方法取得了～10%的转换效率(AM1.5). 基于其电流密度-电压(J-V)曲线和外量子效率曲线, 分析了其拟合关键参数对于电池性能的影响程度, 并从理论分析上把目前器件性能参数与当今前沿性能参数以及其理论值进行比较, 指出了如何提高电池转换效率(η)的方法: 提高开路电压(V_oc)、短路电流(J_sc)和填充因子(FF). 关键词： 碲化镉电池 电流密度-电压曲线 外量子效率曲线 电学特性     

PIN型和NIP型硅薄膜太阳电池中绒面陷光结构和陷光性能研究

对于硅薄膜太阳电池来说, 无论是PIN型还是NIP型太阳电池, 采用绒面陷光结构来提高入射光的有效利用率是提高太阳电池效率的重要方法之一.本文采用标度相干理论对PIN和NIP型电池的绒面结构的陷光性能进行了数值模拟. 结果表明: PIN电池中前电极和NIP电池中背电极衬底粗糙度分别为160和40 nm时可获得理想的陷光效果; 在不同粗糙度背电极衬底上制备a-SiGe:H电池发现, 使用40和61.5 nm 背电极可获得相当的短路电流密度, 理论分析和实验得到了一致的结果. 关键词： 陷光结构 光散射能力 标量相干理论 硅基薄膜太阳电池     

工业级纳米绒面多晶硅太阳电池的制备及其性能研究

基于产线工艺制备了纳米绒面多晶硅太阳电池,并表征其光电转换性能。研究结果表明：相对传统微米绒坑,纳米绒面能够提升多晶硅太阳电池的短路电流,相应的光电转换效率绝对值提升大于0.4%,产线均值光电转换效率超过了19.1%。结合漫反射光谱和外量子效率测试结果,改进的光电转换的原因归结为纳米绒面能够有效地诱捕短波和长波太阳光子,增强短波和长波太阳光响应。本研究证实纳米绒面多晶硅太阳电池可利用产线工艺制备且具有较高的光电转换效率,能够实现产业化。     

Highly effective III-V solar cells by controlling the surface roughnesses

An advanced approach to minimize the light loss was discussed for III-V solar cells, by controlling the roughnesses of the device surface. Adhesives with different viscosities were applied to bond the III-V solar cells with the supporting substrate before the epitaxial lift-off process. The surface roughness of the III-V solar cells with epoxy adhesive (R_rms = 15.4 nm) is one order of magnitude higher than that with acrylic adhesive (R_rms = 1.6 nm), due to the differences in viscosity, resulting from the spreadability while being hardened. This roughness has increased the reflectance in the wavelength between 650 and 900 nm, implying that this reflectance is influenced by the rear surface of the solar cell. The device performance of the double-junction solar cells (Ga_0.5In_0.5P- and GaAs- based) also reflects the effect of the reflectance. The solar cell with the epoxy adhesive exhibited ~2% increase of the conversion efficiency than that with the acrylic adhesive, mainly due to the increased current density. The integrated current density from the external quantum efficiency (EQE) also exhibited ~2% increase only in the bottom (GaAs-based) cell, corresponding to the higher reflectance for red and near-infrared wavelength ranges.     

Influence of InAs quantum dots on the transport properties of GaAs-based solar cell devices

We investigated both the photovoltaic and transport properties of GaAs based solar cells with and without InAs quantum dots (QDs). In small forward bias region, humps in the local ideality factor are found in the QD-embedded devices at low temperatures. This might be caused by the charges captured in the QD-induced defect states. The temperature dependence of the ideality factor, extracted from large voltage regions, was well explained by the tunneling-mediated interface recombination process. The reverse-bias current also exhibited a signature of trap-mediated tunneling. All these results suggested that the presence of trap states could cause the degraded photovoltaic performance of our QD-embedded solar cells.     

n型窗口层材料及其在高速沉积微晶硅太阳电池中的应用研究

采用常规的射频等离子体增强化学气相沉积技术制备了可以用于微晶硅薄膜太阳电池的n型的掺杂窗口层材料.通过掺杂窗口层材料在电池中的应用发现：微晶硅薄膜太阳电池由于其电子和空穴的迁移率相差比较小而显示出磷掺杂的n型的微晶硅材料也可以像硼掺杂的p型的微晶硅材料一样,可作为微晶硅薄膜太阳电池的窗口层材料;两种窗口层制备电池的效率差别不大,而且量子效率（QE）测试结果显示两种电池的n/i和p/i界面没有明显的区别;电池的双面不同波长拉曼光谱的测试结果给出：不论是n/i/p还是p/i/n型的电池,在起始生长本征层阶段均 关键词： n型的掺杂窗口层 p型的掺杂窗口层 微晶硅薄膜太阳电池