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Low Cost Amorphous Silicon Intrinsic Layer for Thin-Film Tandem Solar Cells  [PDF]
Ching-In Wu,Shoou-Jinn Chang,Kin-Tak Lam,Shuguang Li,Sheng-Po Chang
International Journal of Photoenergy , 2013, DOI: 10.1155/2013/183626
Abstract: The authors propose a methodology to improve both the deposition rate and SiH4 consumption during the deposition of the amorphous silicon intrinsic layer of the a-Si/μc-Si tandem solar cells prepared on Gen 5 glass substrate. It was found that the most important issue is to find out the saturation point of deposition rate which guarantees saturated utilization of the sourcing gas. It was also found that amorphous silicon intrinsic layers with the same value will result in the same degradation of the fabricated modules. Furthermore, it was found that we could significantly reduce the production cost of the a-Si/μc-Si tandem solar cells prepared on Gen 5 glass substrate by fine-tuning the process parameters. 1. Introduction In recent years, silicon-based thin-film solar cells have been studied extensively due to their potential benefits in low cost, high efficiency, and low pollution during production. It has been shown that these silicon-based thin-film solar cells are scalable for full-sized commercial production [1]. However, the fundamental challenge of silicon thin-film solar cells is light-induced degradation known as the Staebler-Wronski Effect (SWE) [2]. There are currently two major types of silicon thin-film solar cells in the market. One is the amorphous silicon (a-Si) only module, which could achieve an approximately 7% energy conversion efficiency with a degradation ratio of around 23%. The other is the amorphous silicon tandem microcrystalline silicon (a-Si/μc-Si) tandem device, which could achieve more than 10% energy conversion efficiency with a smaller degradation ratio of around 15%. It is generally believed that increasing the ratio of hydrogen gas in the process of forming the intrinsic layers could improve the module stability. However, increasing hydrogen dilution ratio during the formation of the intrinsic layers suffers from two major drawbacks. First, hydrogen treatment could easily compromise p-layer interface in front of the intrinsic layer. Second, increasing the hydrogen dilution ratio of the total process gas also means decreasing the ratio of SiH4 used for forming the silicon film. This could result in a reduction in deposition rate. It has been reported previously that one can tune the distance of the electrodes to increase both the utilization of the depositing gas and the deposition rate [3]. However, it is necessary to adjust the hardware of the deposition system which depends strongly on the system used. It has also been reported that one can introduce triode to control the dissociation of reacting gas and the
Optimization of Recombination Layer in the Tunnel Junction of Amorphous Silicon Thin-Film Tandem Solar Cells  [PDF]
Yang-Shin Lin,Shui-Yang Lien,Chao-Chun Wang,Chia-Hsun Hsu,Chih-Hsiang Yang,Asheesh Nautiyal,Dong-Sing Wuu,Pi-Chuen Tsai,Shuo-Jen Lee
International Journal of Photoenergy , 2011, DOI: 10.1155/2011/264709
Abstract: The amorphous silicon/amorphous silicon (a-Si/a-Si) tandem solar cells have attracted much attention in recent years, due to the high efficiency and low manufacturing cost compared to the single-junction a-Si solar cells. In this paper, the tandem cells are fabricated by high-frequency plasma-enhanced chemical vapor deposition (HF-PECVD) at 27.1?MHz. The effects of the recombination layer and the i-layer thickness matching on the cell performance have been investigated. The results show that the tandem cell with a p+ recombination layer and i2/i1 thickness ratio of 6 exhibits a maximum efficiency of 9.0% with the open-circuit voltage ( ) of 1.59?V, short-circuit current density ( ) of 7.96?mA/cm2, and a fill factor (FF) of 0.70. After light-soaking test, our a-Si/a-Si tandem cell with p+ recombination layer shows the excellent stability and the stabilized efficiency of 8.7%. 1. Introduction Amorphous silicon (a-Si)/a-Si tandem solar cells have attracted extensive interest among solar cell because of the less light-induced degradation [1, 2] (Stabler-Wronski effect) compared to their single-junction solar cell counterparts. The n-p junction between the two subcells is often referred to as a tunnel junction but actually functions as a recombination junction in electrically connecting the two p-i-n junctions of the tandem structure. For high stabilized efficiency tandem cell applications, a good n/p junction must have very high recombination rates, negligible optical absorption, and an ohmic characteristic with a low series resistance in order to improve the carrier transport [3–6]. Various recombination layers, such as a-SiC:H [7], metal oxides [8], microcrystalline layer [9], and / recombination layer [10] have been introduced between the n and p layers to promote carrier recombination. The thickness of intrinsic- (i-) layer of individual subcell is another key parameter because of the current matching limitation imposed by series connection. In addition, reducing the i-layer thickness of top cell as possible as it is important to stabilize against light degradation [11, 12]. In this paper, we use a recombination layer as the recombination layer inserted in a tandem solar cell to investigate the effect on the cell performance. Furthermore, the tandem cells with different i-layer thickness matching ratio are also fabricated and their photovoltaic characteristics are also discussed. 2. Experimental In this study, we prepared double-junction (a-Si/a-Si) solar cells by high-frequency (27.1?MHz) plasma-enhanced chemical vapor deposition (HF-PECVD). The
High efficiency amorphous/microcrystalline silicon tandem solar cells deposited in a single chamber system

Zhang Xiao-Dan,Zheng Xin-Xi,Wang Guang-Hong,Xu Sheng-Zhi,Yue Qiang,Lin Quan,Wei Chang-Chun,Sun Jian,Zhang De-Kun,Xiong Shao-Zhen,Geng Xin-Hua,Zhao Ying,

物理学报 , 2010,
Abstract: Based on the previous research on the deposition of amorphous/microcrystalline (micromorph) silicon tandem solar cells, silane concentration for the deposition of microcrystalline bottom cell is selected to further optimize the performance for micromorph tandem solar cells by using very high frequency technique. Finally, micromorph silicon tandem solar cell with 11.02% (Area=1.0cm2) initial conversion efficiency is fabricated at a certain silane concentration, and it has a structure suitable for trapping light. Furthermore, 100cm2 micromorph module with 9.04% initial conversion efficiency is also successfully obtained.
Effect of n Doped Layers in an Amorphous Silicon Top Solar Cell on the Performance of "Micromorph" Tandem Solar Cells

Han Xiaoyan,Li Guijun,Hou Guofu,Zhang Xiaodan,Zhang Dekun,Chen Xinliang,Wei Changchun,Sun Jian,Xue Junming,Zhang Jianjun,Zhao Ying,Geng Xinhua,

半导体学报 , 2008,
Abstract: Pin/pin "micromorph" tandem solar cells were deposited by very high frequency plasma enhanced chemical vapor deposition (VHF-PECVD).Tunnel recombination junctions of the "micromorph" tandem solar cells consisting of two microcrystalline-doped layers with a defect rich interface were developed.While the solar cells performed reasonably well under AM 1.5 lights,we found through spectral response measurements that the first deposited cell of the tandem structures was leaking under low light conditions.The insertion of a thin protection layer of n-type amorphous silicon is presented in this paper.The results shown that the introduced n-type amorphous silicon could improve the leakage phenomenon.The leakage phenomenon disappeared when the thickness of the n-type amorphous silicon was 6nm,leading to an increase in open-circuit voltage.The open-circuit voltage increased from 1.27 to 1.33V and FF increased from 60% to 63%.
Three-Terminal Amorphous Silicon Solar Cells  [PDF]
Cheng-Hung Tai,Chu-Hsuan Lin,Chih-Ming Wang,Chun-Chieh Lin
International Journal of Photoenergy , 2011, DOI: 10.1155/2011/813093
Abstract: Many defects exist within amorphous silicon since it is not crystalline. This provides recombination centers, thus reducing the efficiency of a typical a-Si solar cell. A new structure is presented in this paper: a three-terminal a-Si solar cell. The new back-to-back p-i-n/n-i-p structure increased the average electric field in a solar cell. A typical a-Si p-i-n solar cell was also simulated for comparison using the same thickness and material parameters. The 0.28?μm-thick three-terminal a-Si solar cell achieved an efficiency of 11.4%, while the efficiency of a typical a-Si p-i-n solar cell was 9.0%. Furthermore, an efficiency of 11.7% was achieved by thickness optimization of the three-terminal solar cell. 1. Introduction Amorphous silicon (a-Si) for photovoltaic applications can be deposited using the techniques of plasma-enhanced chemical vapor deposition (PECVD) [1–3], catalytic CVD (Cat-CVD) [4, 5], photo-CVD [6, 7], sputtering [8], and so forth. Since it is usually deposited at a low temperature, low-cost or flexible materials like glass, plastic, or stainless steel can be adopted as the substrate. Amorphous Si also has the advantages of an abundant supply on the earth and a high-absorption coefficient at visible wavelengths [9, 10]. These advantages make it promising for applications in thin-film photovoltaics. Amorphous Si can be applied to many types of solar cells, such as single-junction [11, 12], multijunction [13, 14], and HIT [15] (heterojunction with intrinsic thin layer) solar cells. In 2000, the stable efficiency of a single-junction a-Si solar cell (area of 1?cm2) was 9.0% [16]. In 2009. a single-junction a-Si solar cell has achieved an efficiency of 10.1% [17]. Multijunction solar cells were usually able to achieve higher efficiencies. For example, the stable efficiency of a triple-junction solar cell (a-Si/a-Si/a-SiGe tandem solar cell) was 12.1% [18], and the efficiencies of micromorph Si solar cells (a-Si/μc-Si tandem solar cells) were larger than 11% [19–21]. Multijunction solar cells are composed of two or more subcells. The working mechanism of multijunction solar cells is by way of tunnel-recombination junctions, and the final efficiency is limited by the smallest photogenerated current among all subcells [22]. This is because each subcell of a multijunction solar cell must pass through the same current. Therefore, the defects inside the a-Si may reduce the efficiencies of solar cells whether for a single-junction cell or a multijunction cell. The efficiencies are reduced due to the recombination of photogenerated carriers via
A microscopic description of light induced defects in amorphous silicon solar cells  [PDF]
Lucas K. Wagner,Jeffrey C. Grossman
Physics , 2008, DOI: 10.1103/PhysRevLett.101.265501
Abstract: Using a combination of quantum and classical computational approaches, we model the electronic structure in amorphous silicon in order gain understanding of the microscopic atomic configurations responsible for light induced degradation of solar cells. We demonstrate that regions of strained silicon bonds could be as important as dangling bonds for creating traps for charge carriers. Further, our results show that defects are preferentially formed when a region in the amorphous silicon contains a hole and a light-induced excitation. These results agree with the puzzling dependencies on temperature, time, and pressure observed experimentally.
Hybrid Dielectric-Metallic Back Reflector for Amorphous Silicon Solar Cells  [PDF]
James G. Mutitu,Shouyuan Shi,Allen Barnett,Dennis W. Prather
Energies , 2010, DOI: 10.3390/en3121914
Abstract: In this paper, we present the design and fabrication of hybrid dielectric-metallic back surface reflectors, for applications in thin film amorphous silicon solar cells. Standard multilayer distributed Bragg reflectors, require a large number of layers in order to achieve high reflectance characteristics. As it turns out, the addition of a metallic layer, to the base of such a multilayer mirror, enables a reduction in the number of dielectric layers needed to attain high reflectance performance. This paper explores the design, experimental realization and opportunities, in thin film amorphous silicon solar cells, afforded by such hybrid dielectric-metallic back surface reflectors.
Computational design of high performance hybrid perovskite on silicon tandem solar cells  [PDF]
A. Rolland,L. Pedesseau,A. Beck,M. Kepenekian,C. Katan,Y. Huang,S. Wang,C. Cornet,O. Durand,J. Even
Physics , 2015,
Abstract: In this study, the optoelectronic properties of a monolithically integrated series-connected tandem solar cell are simulated. Following the large success of hybrid organic-inorganic perovskites, which have recently demonstrated large efficiencies with low production costs, we examine the possibility of using the same perovskites as absorbers in a tandem solar cell. The cell consists in a methylammonium mixed bromide-iodide lead perovskite, CH3NH3PbI3(1-x)Br3x (0 < x < 1), top sub-cell and a single-crystalline silicon bottom sub-cell. A Si-based tunnel junction connects the two sub-cells. Numerical simulations are based on a one-dimensional numerical drift-diffusion model. It is shown that a top cell absorbing material with 20% of bromide and a thickness in the 300-400 nm range affords current matching with the silicon bottom cell. Good interconnection between single cells is ensured by standard n and p doping of the silicon at 5.10^19cm-3 in the tunnel junction. A maximum efficiency of 27% is predicted for the tandem cell, exceeding the efficiencies of stand-alone silicon (17.3%) and perovskite cells (17.9%) taken for our simulations, and more importantly, that of the record crystalline Si cells.
Amorphous Silicon Solar cells with a Core-Shell Nanograting Structure  [PDF]
L. Yang,L. Mo,Y. Okuno,S. He
Physics , 2011,
Abstract: We systematically investigate the optical behaviors of an amorphous silicon solar cell based on a core-shell nanograting structure. The horizontally propagating Bloch waves and Surface Plasmon Polariton (SPP) waves lead to significant absorption enhancements and consequently short-circuit current enhancements of this structure, compared with the conventional planar one. The perpendicular carrier collection makes this structure optically thick and electronically thin. An optimal design is achieved through full-field numerical simulation, and physical explanation is given. Our numerical results show that this configuration has ultrabroadband, omnidirectional and polarization-insensitive responses, and has a great potential in photovoltaics.
A Silicon-Singlet Fission Parallel Tandem Solar Cell Exceeding 100 % External Quantum Efficiency  [PDF]
Luis M. Pazos,Ju Min Lee,Anton Kirch,Maxim Tabachnyk,Richard H. Friend,Bruno Ehrler
Physics , 2015,
Abstract: Silicon solar cells dominate the solar cell market with record lab efficiencies reaching almost 26%. However, after 60 years of research, this efficiency saturated close to the theoretical limit for silicon, and radically new approaches are needed to further improve the efficiency. Here we present parallel-connected tandem solar cells based on down-conversion via singlet fission. This design allows raising the theoretical power conversion efficiency limit to 45% with far superior stability under changing sunlight conditions in comparison to traditional series tandems. We experimentally demonstrate a silicon/pentacene parallel tandem solar cell that exceeds 100% external quantum efficiency at the main absorption peak of pentacene, showing efficient photocurrent addition and proving this design as a realistic prospect for real-world applications.
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