受体浓度影响体异质结有机太阳能电池复合损耗研究

制备基于P3HT:PCBM的复合体异质结太阳能电池 ,研究受体浓度对载流子复合特性的影响。测试结果表明, 受体浓度影响器件的电荷收集和复合损耗, 从而直接影响体异质结有机太阳能电池的光电性能; 光生电流随偏 置电压的增加而下降,光生电流下降趋势反映了载流子的复合损耗特性。理论分析进一步 表明,给体中电子与受体中 电子的密度比与受体浓度有直接关系,受体浓度改变双分子复合常数的大小,从而影响载流 子的复合特性。     

Energy characteristics of excitons in structures based on InGaN alloys

Samples containing ultrathin InGaN layers that emit radiation in the spectral range from the ultraviolet to yellow region are studied. The samples are grown by metal-organic vapor-phase epitaxy. The Urbach energy, the localization energy of excitons, and the activation energy of charge carriers are determined to characterize radiative and nonradiative processes in the quantum dots and barriers of the structures. It is shown that these energy parameters are linearly dependent on the photon energy in the range from 3.05 to 2.12 eV. It is established that temperature variations in the emission intensity are due to the increase in the number of charge carriers thermally activated from the quantum wells into barriers as well as due to the enhancement of scattering of free excitons at defects.     

Enhanced photovoltaic characteristics of solar cells based on n-type triphenodioxazine derivative

Polymer solar cells based on poly (2-methoxy-5-(2′-ethyl-hexyloxy)-1, 4-phenylene vinylene) (MEH-PPV):1-(3-methoxycarbonyl)-propyl-1-1-phenyl-(6,6)C61(PCBM):3, 10-di(trifluoromethane) triphenodioxazine (TFTD) was fabricated using spin coating technology. The absorption spectra of MEH-PPV: PCBM: TFTD film coated from chlorobenzene solution was broadened and showed higher intensity compared with that of the pure MEH-PPV. The TFTD acting as electron acceptors in combination with PCBM induced the photoluminescence (PL) quenching of MEH-PPV, which were associated with the photoinduced charge transfer characteristics of composite film. Further, a photovoltaic conversion efficiency up to 1.03% under 16.7 mW/cm² white light illumination was achieved in the MEH-PPV: PCBM: TFTD system.     

Effects of contact electrode size on the characteristics of polycrystalline-Si p-i-n solar cells

The effects of contact electrode size on the photo-voltaic characteristics of polycrystalline-Si p-i-n solar cells have been studied,with respect to a unit-cell pitch size of 1μm width.For the non-transparent Al contact electrode with a contact width of 0.05-0.2μm,the short-circuit current is obviously reduced with increasing contact width,due to a larger area of optical reflection by the electrode.On the other hand,even when using a transparent ITO(indium-tin-oxide) electrode,a larger width of contact e...     

Effects of grain boundaries on the current-voltage characteristics of polycrystalline silicon solar cells

The current components associated with the grain boundaries of diffused p/n junction polysilicon solar cells made on n- and p-type Wacker substrates are analyzed and experimentally identified. New electrical methods for determining the presence or absence of preferential diffusion along the grain boundaries and for determining the average doping density of preferentially diffused regions along the grain boundaries are described. For p-type substrates, these methods revealed preferential phosphorus diffusion along grain boundaries; no preferential boron diffusion along grain boundaries was observed. The recombination current components were analyzed for the cells in which preferential diffusion occurred. The analysis shows that the dominant current component at small bias levels (0-300 mV) is the recombination current at the grain boundaries within the p/n junction space-charge region. At higher bias levels (V simeq V_{OC} simeq 500-600mV), both this current component and the current component due to recombination at that part of the grain boundary below the preferentially diffused region are important. The grain-boundary shunt resistance does not contribute a significant current component. It is shown that the preferential diffusion makes negligible the recombination current injected into the sidewall of the preferentially diffused region. This is consistent with a model in which the phosphorus diffusion significantly lowers the surface recombination velocity at the grain boundaries and in which the retarding built-in electric field further decreases the recombination current.     

Effects of contact electrode size on the characteristics of polycrystalline-Si p-i-n solar cells

The effects of contact electrode size on the photo-voltaic characteristics of polycrystalline-Si p-i-n solar cells have been studied,with respect to a unit-cell pitch size of 1μm width.For the non-transparent Al contact electrode with a contact width of 0.05-0.2μm,the short-circuit current is obviously reduced with increasing contact width,due to a larger area of optical reflection by the electrode.On the other hand,even when using a transparent ITO(indium-tin-oxide) electrode,a larger width of contact electrode may also cause a smaller short-circuit current, due to a larger area of optical absorption by the electrode.However,for this ITO electrode,the contact electrode of 0.05μm width causes a smaller short-circuit current than that of 0.1μm width,primarily ascribed to a smaller area for collecting carrier and a larger contact resistance.As a result,while using the ITO contact electrode to enhance the conversion efficiency of the solar cell,a proper width of contact electrode should be employed to optimize the photo-voltaic characteristics.     

Modeling of polarization charge in N-face InGaN/GaN MQW solar cells

The present work reports on a theoretical study of spontaneous and piezoelectric polarization effects on the photovoltaic characteristics of InGaN/GaN multiple quantum well solar cells. More especially, it will prove that the use of heterostructures with N-face as a surface polarity can further improve the photovoltaic conversion. A new model including piezoelectric polarization is developed. In this paper, a part of simulation is also paid to analyze the dependence of the photocurrent density, the open circuit voltage, the output power and the efficiency versus the In composition and the number of quantum well units. As has been found, a maximum of energy conversion is expected to achieve 19 percent for optimum alloy composition. An attempt to explain the photovoltaic behavior of the solar cells in correlation of obtained results will be attempted.     

Features of the light current-voltage characteristics of bifacial solar cells based on thin CdTe layers

It is shown that the features of the illuminated current-voltage characteristics of bifacial solar cells glass/SnO₂:F/CdS/CdTe/Cu/ITO with a thin base layer are associated with the photovoltaic effect at the back contact. An equivalent circuit of the device structure under study, which takes into account the existence of two illuminated diodes—a frontal diode (main separating barrier) and a diode at a back contact—is suggested.     

Numerical simulation of InGaN Schottky solar cell

The Indium Gallium Nitride (InGaN) III-Nitride ternary alloy has the potentiality to allow achieving high efficiency solar cells through the tuning of its band gap by changing the Indium composition. It also counts among its advantages a relatively low effective mass, high carriers' mobility, a high absorption coefficient along with good radiation tolerance. However, the main drawback of InGaN is linked to its p-type doping, which is difficult to grow in good quality and on which ohmic contacts are difficult to realize. The Schottky solar cell is a good alternative to avoid the p-type doping of InGaN. In this report, a comprehensive numerical simulation, using mathematically rigorous optimization approach based on state-of-the-art optimization algorithms, is used to find the optimum geometrical and physical parameters that yield the best efficiency of a Schottky solar cell within the achievable device fabrication range. A 18.2% efficiency is predicted for this new InGaN solar cell design.     

Failure analysis of electrical-thermal-optical characteristics of LEDs based on AlGaInP and InGaN/GaN

The electrical-thermal-optical characteristics of AlGaInP yellow and InGaN/GaN blue LEDs under electrical stresses were studied. Since the increase of effective acceptor concentration on p-type side, the forward voltages of AlGaInP decrease after 3155 h aging. And the operating voltage of high forward bias expansion for InGaN/GaN is due to the increase of the series resistance. Compared with InGaN/GaN, AlGaInP LEDs display different trend for the relationship between optical output and ideality factors. The relationship between ideality factor and radiative recombination is also studied and established. The characteristic of different intermediate adhesive is compared during aging period based on transient thermal test.     

Dye-sensitized solar cells based on ZnO nanotetrapods

In this paper, we reviewed recent systematic studies of using ZnO nanotetrapods for photoanodes of dye-sensitized solar cells (DSSCs) in our group. First, the efficiency of power conversion was obtained by more than 3.27% by changes of conditions of dye loading and film thickness of ZnO nanotetrapod. Short-circuit photocurrent densities (Jsc) increased with the film thickness, Jsc would not be saturation even the film thickness was greater than 35 μm. The photoanode architecture had been charactered by good crystallinity, network forming ability, and limited electron-hopping interjunctions. Next, DSSCs with high efficiency was devised by infiltrating SnO2 nanoparticles into the ZnO nanotetrapods photoanodes. Due to material advantages of both constituents described as above, the composite photoanodes exhibited extremely large roughness factors (RFs), good charge collection, and tunable light scattering properties. By varying the composition of the composite photoanodes, we had achieved an efficiency of 6.31% by striking a balance between high efficiency of charge collection for SnO2 nanoparticles rich films and high light scattering ability for ZnO nanotetrapods rich films. An ultrathin layer of ZnO was found to form spontaneously on the SnO2 nanoparticles, which primarily was responsible for enhancing open-circuit photovoltage (Voc). We also identified that recombination in SnO2/ZnO composite films was mainly determined by ZnO shell condition on SnO2, whereas electron transport was greatly influenced by the morphologies and sizes of ZnO crystalline additives. Finally, we applied the composite photoanodes of SnO2 nanoparticles/ZnO nanotetrapods to flexible DSSCs by low temperature technique of "acetic acid gelation-mechanical press-ammonia activation." The efficiency has been achieved by 4.91% on ITO-coated polyethylenenaphtalate substrate. The formation of a thin ZnO shell on SnO2 nanoparticles, after ammonia activation, was also found to be critical to boosting Voc and to improving inter-particles contacts. Mechanical press, apart from enhancing film durability, also significantly improved charge collection. ZnO nanotetrapods had been demonstrated to be a better additive than ZnO particles for the improvement of charge collection in SnO2/ZnO composite photoanodes regardless of whether they were calcined.     

图形衬底对InGaN/GaN多量子阱太阳能电池性能的提升

In this paper, the enhanced performance of InGaN/GaN multiple quantum well solar cells grown on patterned sapphire substrates （PSS） was demonstrated. The short-circuit current （Jsc） density of the solar cell grown on PSS showed an improvement of 60%, compared to that of solar cells grown on conventional sapphire substrate. The improved performance is primarily due to the reduction of edge dislocations and the increased light absorption path by the scattering from the textured surface of the PSS. It shows that the patterned sapphire technology can effectively alleviate the problem of high-density dislocations and low Jsc caused by thinner absorption layers of the InGaN based solar cell, and it is promising to improve the efficiency of the solar cell.     

Theoretical analysis on GaAs sub-cell doping concentration for triple-junction solar cells irradiated by proton based on TCAD simulation

The degradation on the GaInP/GaAs/Ge triple-junction solar cells was irradiated by proton, and the solar cells with various GaAs sub-cell doping concentrations are modeled by the technology computer aided design (TCAD) simulation. The degradation results of related electrical parameters and external quantum efficiency (EQE) are studied. The degradation mechanism irradiated by proton is discussed. The short-circuit current, maximum power and conversion efficiency decrease with the increasing of GaAs sub-cell doping concentration. When the base doping concentration of GaAs sub-cell is 1×1016 cm-3, the degradation of short-circuit current is less than that of other base doping concentrations. Furthermore, under proton irradiation, with the increase of doping concentration of GaAs sub-cell, the open-circuit voltage first increases and then decreases. Meanwhile, when the base doping concentration of GaAs sub-cell is 2×1017 cm-3, the degradation of open-circuit voltage is less than that of other base doping concentrations. The research will provide the basic theories and device simulation method for GaInP/GaAs/Ge triple-junction solar cells radiation damage evaluation study and radiation hardening, and can provide guidance for the production of triple-junction solar cells in orbit.     

Performance of front contact silicon solar cells under concentration

The first realization of a new type of silicon solar cell intended for operation at very high concentration, with all the contacts at its front face, is presented. Although the efficiencies achieved are not outstanding, the feasibility of the structure is proven by the fabrication of several thousands of cells with similar performance. Modeling has evidenced the main routes for improvement. Efficiencies close to 25% for a range of efficiencies from 80 to 560 suns are predicted as achievable for cells with state‐of‐the‐art technology and appropriate layout. Copyright © 2004 John Wiley & Sons, Ltd.     

Molecular doping of low-bandgap-polymer:fullerene solar cells: Effects on transport and solar cells

We show how molecular doping can be implemented to improve the performance of solution processed bulk heterojunction solar cells based on a low-bandgap polymer mixed with a fullerene derivative. The molecular dopant 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ) is introduced into blends of poly[2,6(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b:3,4-b0]-dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)] (PCPDTBT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) via co-solution in a range of concentrations from 0% to 1%. We demonstrate that the hole conductivity and mobility increase with doping concentration using field-effect measurements. Photoinduced absorption (PIA) spectroscopy reveals that the polaron density in the blends increases with doping. We show that the open circuit voltage and short circuit current of the corresponding solar cells can be improved by doping at 0.5%, resulting in improved power conversion efficiencies. The increase in performance is discussed in terms of trap filling due to the increased carrier density, and reduced recombination correlated to the improvement in mobility.     

晶体硅太阳能电池片老化特性研究

利用铝背场材料水煮特性的差异性,对4种铝背场多晶太阳能电池片的水煮特性进行了研究,详细分析了4种不同铝背场电池片老化特性(冷-热循环特性和湿热特性)与水煮特性的关系,同时也探讨了单晶与多晶电池片老化特性的差异性。结果表明:铝背场水煮特性较好的电池片表现出较好的湿热老化特性,但电池片的冷-热循环老化特性与其水煮特性无直接关系;单晶电池老化特性略优于多晶,且冷-热循环约40周后电池效率衰减基本稳定,湿热老化450~500 h后电池效率衰减基本稳定。     

Low-cost solar cells based on large-area unconventional silicon

Low-cost approaches to solar cell manufacture require the use of inexpensive low-grade nonsingle crystalline silicon. Earlier experimental results indicate that conventional polysilicon, as it is used as ingot for the single crystal growing process, leads to solar cells of poor photovoltaic performance. These problems were overcome by utilizing unconventional nonsingle crystalline silicon, which is characterized by controlled size and structure of the individual grains. With modified processing, optimized in respect to the unique structure of the material, large-area solar cells could be realized under production scheme methods. Cells exhibiting dimensions up to 11 cm × 11 cm were fabricated, AM0 efficiencies of 8 percent could be achieved corresponding to AM1 values exceeding 10 percent. On test samples of 2 cm × 2 cm area AM0 efficiency Of 12.5 percent (AM1 value equivalent 14.0 percent) could be reached. The new material together with the optimized processes offer potentials for significant cost reduction by virtue of their being applicable to volume production and to automated fabrication techniques.     

基于钙钛矿材料的新型结构太阳能电池器件

基于钙钛矿材料的太阳能电池是一种受到广泛关注的新型太阳能电池。根据钙钛矿太阳能电池结构的不同将其分为四类,综述了钙钛矿太阳能电池的研究现状和最新进展。详细介绍了各类钙钛矿太阳能电池的结构和性能,分析总结了其优缺点。最后展望了钙钛矿太阳能电池未来的发展趋势。     

Nano-sphere surface arrays based on GaAs solar cells

In this paper,we present our efforts on simulating and analyzing the effect of two-dimensional nano-sphere surface array on the characteristic of GaAs solar cells.Based on the scattering and diffraction theory of the photonic crystals,the simulation results show that the distance of adjacent nano-spheres(D)has the pronounced influence on the conversion efficiency and exhibits much poor tolerance,the absolutely conversion efficiency is reduced by exceeding of 2%as the D varies from 0 to 1μm,in addition,the lower conversion efficiency(<18%)is exhibited and almost remains unaltered when the D is of>2μm.The radius(R)of nano-spheres demonstrates much great tolerance.For D=0,the solar cells exhibit high conversion efficiency(>20%)and the efficiency is only varied by less than 1%when R is varied in a very wide region of 0.3-1.2μm.One can also find out that there is good tolerance for efficiency around the optimal value of refractive index and there is only about 0.2%decrease in final cell efficiency for around±24%variation in the optimal values,which implys that it does not demand high precision processing equipment and the whole nano-sphere array could be fully complemented using self-assembled chemical methods.     

Double-parallel-junction hybrid solar cells based on silicon nanocrystals

A novel type silicon nanocrystal-based hybrid solar cell is demonstrated here, where two individual junctions are designed carefully and arranged in parallel with each other. It is found that complementary absorption can be realized by double parallel junctions, and more photons in a wide energy range can be absorbed. As a result, device efficiency has been enhanced more than twice compared to single junction reference device. In addition, its working principles are also studied extensively.