Improving power conversion efficiency of perovskite solar cells by cooperative LSPR of gold-silver dual nanoparticles

Enhancing optical and electrical performances is effective in improving power conversion efficiency of photovoltaic devices. Here, gold and silver dual nanoparticles were imported and embedded in the hole transport layer of perovskite solar cells. Due to the cooperative localized surface plasmon resonance of these two kinds of metal nanostructures, light harvest of perovskite material layer and the electrical performance of device were improved, which finally upgraded short circuit current density by 10.0%, and helped to increase power conversion efficiency from 10.4% to 11.6% under AM 1.5G illumination with intensity of 100 m W/cm~2. In addition, we explored the influence of silver and gold nanoparticles on charge carrier generation, dissociation, recombination, and transportation inside perovskite solar cells.     

Concept of epitaxial silicon structures for edge illuminated solar cells

A new concept of edge illuminated solar cells (EISC) based on silicon epitaxial technique has been proposed. In this kind of photovoltaic (PV) devices, sun-light illuminates directly a p-n junction through the edge of the structure which is perpendicular to junction surface. The main motivation of the presented work is preparation of a working model of an edge-illuminated silicon epitaxial solar cell sufficient to cooperation with a luminescent solar concentrator (LSC) consisted of a polymer foil doped with a luminescent material. The technological processes affecting the cell I–V characteristic and PV parameters are considered.     

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.     

TiO_2 composite electron transport layers for planar perovskite solar cells by mixed spray pyrolysis with precursor solution incorporating TiO_2 nanoparticles

Perovskite solar cells with planar structure are attractive for their simplified device structure and reduced hysteresis effect. Compared to conventional mesoporous devices, TiO_2 porous scaffold layers are removed in planar devices. Then,compact TiO_2 electron transport layers take the functions of extracting electrons, transporting electrons, and blocking holes.Therefore, the properties of these compact TiO_2 layers are important for the performance of solar cells. In this work, we develop a mixed spray pyrolysis method for producing compact TiO_2 layers by incorporating TiO_2 nanoparticles with different size into the precursor solutions. For the optimized nanoparticle size of 60 nm, a power conversion efficiency of 16.7% is achieved, which is obviously higher than that of devices without incorporated nanoparticles(9.9%). Further investigation reveals that the incorporation of nanoparticles can remarkably improve the charge extraction and recombination processes.     

Charge carrier dynamics in CdSe nanocrystals: implications for the use of quantum dots in novel photovoltaics

The dynamics of photo-generated electrons and holes in CdSe quantum dots have been studied using the femtosecond fluorescence upconversion technique, permitting an unambiguous examination of the excited state. The band edge emission shows an expected size dependence on the decay rate. We find that the deep trap emission is coupled to the band edge fluorescence, implicating surface states as important factors in the excited state lifetime of the hole. As a factor of the overall efficiency of solar cells, the rate of charge separation and the fate of the exciton are important considerations in the design of nanocrystal-based photovoltaic devices. Received 30 November 2000     

Photo-electronic phenomena in narrow gap Hg1−xCdxTe

The photo-electronic properties of Hg_1−xCd_xTe grown by molecular beam epitaxy (MBE) or by liquid phase epitaxy (LPE) were investigated using Fourier transform transmission spectroscopy, Fourier transform photoluminescence measurements, spectroscopic ellipsometry (SE), as well as magneto-optics and magnetic-field-dependent Hall studies. The investigation was carried out from liquid helium to room temperatures in the infrared band up to 10 μm. Some important impurities and defects states, including As, Sb, Ag, Fe impurities and Hg vacancy as well as their complexes in Hg_1−xCd_xTe, were carefully studied. We obtained the energy levels of the impurity states and their optical, electric and magnetic behaviors. By SE measurement, a number of very useful parameters, such as the real and the imaginary part of dielectric constant, gap energies corresponding to important critical points, were extracted. Mobility spectra and multi-carrier fitting procedure were used to separate the contributions to the measured mobility from the light holes, heavy holes, and electrons. As a result, the sign change of transverse conductivity component with applied magnetic-field is explained according to multi-carrier process.Hg_1−xCd_xTe (MCT) is one of the most important infrared materials, which is subjected to intensive studies. Its optical and electrical properties are widely used for the fabrication of high performance photoconductive and photovoltaic detectors. Some of characteristics that directly affect device performance, such as impurities, defects, as well as the lifetime of the minority carriers, remain as the major concern. Recently, the quality of the MCT material grown by MBE and LPE has been improved and accurate control over the doping levels for several dopants have been realized [1], [2], [3]. Following the progresses made in material preparation and doping, we are able to study the material systematically.In this paper, we report the recent progress made on the investigation of the electrical and optical properties of both doped and undoped MCT in our laboratory using Fourier transform spectroscopy (FTIR), photoluminescence, magneto-photoconductivity, transport measurement, as well as SE.     

Investigation of non-equilibrium electron-hole plasma in nanowires by THz spectroscopy

Efficient emission of THz radiation by AlGaAs nanowires via excitation of photocurrent by femtosecond optical pulses in nanowires was observed. Dynamics of photoinduced charge carrier was studied via influence of electron-hole plasma on THz radiation by optical pump THz probe method. It was found that characteristic time of screening of contact field is about 15 ps. Recombination of non-equilibrium occurs in two stages: fast recombination of free electron and holes (with relaxation time about 700 ps), and slow recombination (with relaxation time about 15 ns), which involves a capture of electrons and holes on the defects of crystalline structure of nanowires.     

Simulation of a Single-Mode Tunnel-Junction-Based Long-Wavelength VCSEL

We investigate the physics of an internal device for a high-performance, vertical-cavity surface-emitting laser operating at 1.305 μm. Experimental results are analyzed using as the simulation software a photonic-integrated-circuit simulator in 3D (PICS3D), which is a state-of-the-art 3D simulator for surface- and edge-emitting laser diodes, semiconductor optical amplifiers, and other similar active waveguide devices. The 2D/3D semiconductor equations are coupled to the optical modes in both lateral and longitudinal directions. Optical properties such as the quantum well/wire/dot optical gain and spontaneous emission rates are computed self-consistently. Careful adjustments of material parameters led to an excellent agreement between simulation and measurements. Simulation results show that the maximum output power is limited by electron leakage from quantum wells.     

基于CPV技术的LED路灯聚光器的研究

以120W大功率LED路灯太阳能电池板为研究对象,通过聚光光伏技术,利用光学透镜(聚光器)提高太阳能电池的光电转换效率。利用聚焦作用增大光照密度,有效地降低了太阳能光照面积,极大地减少了光电材料的使用量,大幅度降低了太阳能电池的成本。通过光学仿真软件TracePro进行仿真,验证了其可行性。     

量子阱结构对有机电致发光器件效率的影响

实验中共制备了五种有机量子阱结构电致发光器件,分别对这五种量子阱结构器件的电致发光特性进行了研究,分析了量子阱结构的周期数和势垒层的厚度对器件电学性能的影响.实验结果表明适当周期数的量子阱结构器件的亮度和电流效率比传统的三层结构器件的要大,主要原因是量子阱结构对电子和空穴的限制作用,这种限制作用提高了电子和空穴在发光层中形成激子和复合的概率,从而提高了发光的亮度和效率.当改变阱结构器件中势阱层的厚度时,也会对器件的亮度和效率产生影响,采用适当的势阱层厚度能够提高器件的亮度和效率. 关键词： 量子阱结构 电致发光 电流效率 光谱     

Application of millimeter-sized polymer cylindrical lens array concentrators in solar cells

A unique method is proposed to encapsulate solar cells and improve their power conversion efficiency by using a millimeter-sized cylindrical lens array concentrator. Millimeter-sized epoxy resin polymer(ERP) cylindrical lens array concentrators are fabricated by the soft imprint technique based on polydimethylsiloxane stamps. The photovoltaic measurements show that millimeter-sized ERP cylindrical lens array concentrators can considerably improve the power conversion efficiency of silicon solar cells. The validity of the proposed method is proved by the coupled optical and electrical simulations. The designed solar cell devices with the advantages of high-efficiency and convenient cleaning are very useful in practical applications.     

In掺杂h-LuFeO3光吸收及极化性能的第一性原理计算

h-LuFeO3是一种窄带隙铁电半导体材料,已被证明在铁电光伏领域有较好的应用前景.然而,较低的极化强度使光生电子-空穴对复合率大,限制了h-LuFeO3基铁电光伏电池效率的提高.为改善h-LuFeO3的极化强度,提高光吸收性质,本文利用第一性原理计算方法研究了In原子在h-LuFeO3不同位置的掺杂形成能,得到最稳定...     

Ultrafast Terahertz Probes of Charge Transfer and Recombination Pathway of CH_3NH_3PbI_3 Perovskites

We use transient terahertz photoconductivity measurements to demonstrate that upon optical excitation of CH_3NH_3PbI_3 perovskite, the hole transfer from CH_3NH_3PbI_3 into the organic hole-transporting material(HTM)Spiro-OMe TAD occurs on a sub-picosecond timescale. Second-order recombination is the dominant decay pathway at higher photo-excitation fluences as observed in neat CH_3NH_3PbI_3 films. In contrast, under similar experimental conditions, second-order recombination weakly contributes the relatively slow recombination between the electrons in the perovskite and the injected holes in HTM, as a loss mechanism at the CH_3NH_3PbI_3/Spiro-OMe TAD interface. Our results offer insights into the intrinsic photophysics of CH_3NH_3PbI_3-based perovskites with direct implications for photovoltaic devices and optoelectronic applications.     

光器件应用改性Ge的能带结构模型

Ge为间接带隙半导体,通过改性技术可以转换为准直接或者直接带隙半导体.准/直接带隙改性Ge半导体载流子辐射复合效率高,应用于光器件发光效率高;同时,准/直接带隙改性Ge半导体载流子迁移率显著高于Si半导体载流子迁移率,应用于电子器件工作速度快、频率特性好.综合以上原因,准/直接带隙改性Ge具备了单片同层光电集成的应用潜力.能带结构是准/直接带隙改性Ge材料实现单片同层光电集成的理论基础之一,目前该方面的工作仍存在不足.针对该问题,本文主要开展了以下三方面工作:1)揭示了不同改性条件下Ge材料带隙类型转化规律,完善了间接转直接带隙Ge实现方法的相关理论; 2)研究建立了准/直接带隙改性Ge的能带E-k模型,据此所获相关结论可为发光二极管、激光器件仿真模型提供关键参数; 3)提出了准/直接带隙改性Ge的带隙调制方案,为准/直接带隙改性Ge单片同层光电集成的实现提供了理论参考.本文的研究结果量化,可为准/直接带隙改性Ge材料物理的理解,以及Ge基光互连中发光器件有源层研究设计提供重要理论依据.     

Degradation of Safranine T dye-based photo electrochemical organic photovoltaic devices

In this work, we studied the degradation of different photovoltaic parameters of Safranine T (ST) dye-doped organic photo electrochemical cell (PEC). Different photovoltaic parameters were measured for as-prepared device. The same measurement was repeated with time at 24-h regular interval for five successive days. During the measurement, the devices were unencapsulated and kept in an open environment. The photovoltaic parameters degraded up to 90% of its initial value. Along with moisture, humidity was the main reason for the degradation considered to be the reduction of work function difference of two electrodes in contact with organic blend.     

Simulation of IPV effect in In-doped c-Si with optimized indium concentration and layer thickness

Impurity photovoltaic effect(IPV) is one of the attempts to improve efficiency of solar cells and is the idea of exploiting three step generation via impurity states within the band gap to utilize sub-band gap photons. The three transitions are of electrons from valence band (VB) to conduction band (CB), valence band to impurity level and impurity level to conduction band. In the present simulation, we have used the p⁺nn⁺ structure in order to achieve higher photogenerated current and efficiency without loosing the open circuit voltage. Compared to other group-III elements in silicon solar cell, Indium is the most suitable material to achieve higher benefit in IPV. In this simulation, the model of IPV is considered to achieve the maximum benefit from the impurity state in a solar cell. To simulate we have used the one dimensional simulation program, SCAPS-1D. Again light trapping is an important part of IPV solar cell that has been considered in this simulation. Using IPV we have numerically demonstrated, an increase in efficiency, by 2.79% over that without-IPV effect and a 3.23% increase over the efficiency, 30.9% as reported by Schmeits and Mani [1].     

Theory of the double heterostructure laser: I. Numerical solution of the charge transport equations

As a first stage in self-consistent calculations of the optical and electrical properties of the double heterostructure laser, a numerical integration procedure has been developed for the solution of the charge transport equations. The procedure is capable of integrating the equations for a range of device parameters without excessive demands upon computing facilities. The calculated distributions of electrons and holes across the device reveal the inadequacies of analytical solutions to approximate forms of the equations. It is found to be essential to a proper treatment of the transport problem to include the variation of the electric field by way of Poisson's equations. The retention of Poisson's equation in the scheme of transport equations introduces difficulties in an integration routine. It is these difficulties that are successfully overcome by the procedure described in this paper.     

Optical, electrical and photovoltaic properties of thermally annealed PPHT:DDE blend thin films

We have investigated the optical, electrical and photovoltaic properties of devices based on 1,2-diazoamino diphenyl ethane (DDE) and poly(3-phenyl hydrazone thiophene) (PPHT):DDE blend. It is observed from the J-V characteristics of the Al/DDE/ITO (ITO—indium tin oxide) device that the electron current injected from Al contact was shown to be space charge limited (SCL), indicating that Al forms nearly ohmic contact for electron injection into lowest unoccupied molecular orbital (LUMO) of DDE. The effect of thermal annealing and composition, on the optical, electrical and photovoltaic response of blend of PPHT and DDE sandwiched between a transparent ITO electrode and an Al back contact are investigated. The observed absorption quenching in the PPHT:DDE blend is attributed to the disordering of PPHT chains and charge transfer between PPHT and DDE as evidenced by FTIR spectra. The observed red shift in the absorption peak on thermal annealing is due to the improvement in the ordering and increases in conjugation length in PPHT. The observed dark current-voltage curves agree well with trap-controlled SCL transport theory. The photophysics of the blend material and influence of thermal annealing on the performance and morphology of these devices were discussed. Annealing process results in the formation of PPHT:DDE complex and increase in the ordering of polymer chain, that increases the incident photon to current efficiency (IPCE) and power conversion efficiency of the photovoltaic devices.     

平面异质结有机-无机杂化钙钛矿太阳电池研究进展

高效低成本太阳电池的研发是太阳能光伏技术大规模推广应用的关键. 近年来兴起的有机- 无机杂化钙钛矿(以下简称钙钛矿)太阳电池因具有光电能量转换效率高、制备工艺简单等优点, 引起了学术界和产业界的广泛关注, 具有广阔的发展前景. 其中平面异质结钙钛矿太阳电池因具有结构简单, 可低温制备等诸多优点, 成为目前研究的一个重要方向. 平面异质结钙钛矿太阳电池分为n-i-p型和p-i-n型两种结构. 其中钙钛矿分别与电子传输层和空穴传输层形成两个界面, 在这两个界面上实现电子和空穴的快速分离. 电子传输层和空穴传输层分别为电子和空穴提供了独立的输运通道. 平面异质结结构有利于钙钛矿太阳电池中电子和空穴的分离、传输和收集. 此外, 该结构不需要高温烧结的多孔结构氧化物骨架, 扩大了电子和空穴传输材料的选择范围. 可以根据钙钛矿材料的能带分布及载流子传输特性, 来选择能级和载流子传输速率更为匹配的传输材料. 本文对钙钛矿的材料特性, 平面异质结结构的由来及发展进行了简要的概述. 其中重点介绍了平面异质结钙钛矿太阳电池的结构特征、工作机理、钙钛矿/电荷传输层的界面特性, 以及电池性能的优化, 包括钙钛矿薄膜制备、空穴和电子传输层的优化等. 最后对钙钛矿电池的发展前景及存在问题进行了阐述, 为今后高效、稳定钙钛矿太阳电池的研究提供参考.     

Engineering the electronic band structure for multiband solar cells

Using the unique features of the electronic band structure of GaN(x)As(1-x) alloys, we have designed, fabricated and tested a multiband photovoltaic device. The device demonstrates an optical activity of three energy bands that absorb, and convert into electrical current, the crucial part of the solar spectrum. The performance of the device and measurements of electroluminescence, quantum efficiency and photomodulated reflectivity are analyzed in terms of the band anticrossing model of the electronic structure of highly mismatched alloys. The results demonstrate the feasibility of using highly mismatched alloys to engineer the semiconductor energy band structure for specific device applications.