Potential of light trapping in microcrystalline silicon solar cells with textured substrates

The real and potential benefits of light trapping in microcrystalline silicon single‐junction solar cells are studied theoretically. Effects of a hypothetical high haze parameter of textured transparent conductive oxide on quantum efficiency and short‐circuit current of the solar cell are analysed by numerical simulation. The role of the angular distribution function of scattered light as a second important scattering parameter is shown. The potential thickness reductions of the intrinsic layer due to enhanced light trapping are demonstrated. Copyright © 2003 John Wiley & Sons, Ltd.     

Cyanine tandem and triple-junction solar cells

Ultrathin bilayer heterojunction solar cells using cyanine electron donors and electron acceptor C₆₀ are used to fabricate monolithically stacked tandem and triple junction devices. Sub-cell stack sequences as well as C₆₀ layer thicknesses are optimized by optical modeling and maximum efficiency is corroborated experimentally. The highest power conversion efficiency of 4.3% under full sun irradiation is achieved with a tandem cell where heptamethine and trimethine cyanine dyes are used in the front and back cell, respectively. The open circuit voltage matches the sum of the two respective open circuit voltages of the individual single junction solar cells within 3%. Triple junction cells using an additional sub-cell with a pentamethine cyanine suffer from electrical series resistance. At low light irradiation intensity, however, both triple and tandem solar cells reach power conversion efficiencies above 5% in agreement with the performance increase predicted from numerical simulation.     

Investigations on the temperature dependence of CPV modules equipped with triple‐junction solar cells

This paper deals with the temperature impact on the IV curve of concentrator photovoltaic (CPV) modules equipped with III–V triple‐junction solar cells. The electrical parameters of three FLATCON^® type CPV modules are investigated using a sun simulator, where the module temperatures are varied by heating with infrared (IR) bulbs. It is found that all electrical parameters vary linearly to a change of temperature. The open circuit voltages and the fill factors (FFs) of the CPV modules decrease with increasing temperature. The relative decrease in open circuit voltage of the CPV modules is similar to the value of individual triple‐junction solar cells. In contrast, the short circuit current temperature coefficients are found to be different. The experimental results can be explained by considering thermal expansion effects in the module and temperature dependencies of the optical efficiencies of the Fresnel lenses. Copyright © 2010 John Wiley & Sons, Ltd.     

Novel Nano Structure for Green Energy Harvesting at 10 μm Thermal Radiation

In recent years, the potential of renewable green energy sources has been extensively studied. The proven technology which is photovoltaic solar cells strictly depends on daylight and produces low-efficiently. To overcome the restrictions, one technology studied is through harvesting the thermal radiation energy which can provide a 24-hour energy source. The continuity of energy sources promises very good energy conversion especially for military applications. This article presents a new structure that can harvest the abundant thermal radiation energy into usable energy at the wavelength of 10 m. A rectangular structure with a perturbation slit was designed to integrate with a rectifier circuit for green energy conversion. The slit tunnel junction guided the electromagnetic field into a junction where the energy could be collected and converted. An enhancement factor of approximately 110.6 can be achieved by a perturbation slit length of 1.0 m. The results extracted from the proposed design promise a better candidate to overcome the disadvantages of photovoltaic solar cells for energy harvesting devices.     

Theoretical effects of surface diffused region lifetime models on silicon solar cells

A computer simulation of silicon solar cells has indicated that the combination of band gap reduction due to heavy doping and certain spatial forms of lifetime dependence can combine to form severe limitations to the open circuit voltage of silicon solar cells. The interaction of these effects tends to shift the active region of the diffused surface layer away from the injecting junction resulting in an increase in the current density injected into the surface region. Reductions in open circuit voltage as great as 10% over models which do not include these effects can be seen.     

HITTM cells—high‐efficiency crystalline Si cells with novel structure

Our unique, high‐efficiency c‐Si solar cell, named the HIT cell, has shown considerable potential to improve junction properties and surface passivation since it was first developed. The improved properties in efficiency and temperature dependence compared to conventional p – n diffused c‐Si solar cells are featured in HIT power 21^TM solar cell modules and other applications which are now on the market. In the area of research, further improvement in the junction properties of the a‐Si/c‐Si heterojunction has been examined, and the highest efficiency to date of 20.1% has recently been achieved for a cell size of 101 cm². The high open circuit voltage exceeding 700 mV, due to the excellent surface passivation of the HIT structure, is responsible for this efficiency. In this paper, recent progress in HIT cells by Sanyo will be introduced. Copyright © 2000 John Wiley & Sons, Ltd.     

Analysis of Ge junctions for GaInP/GaAs/Ge three‐junction solar cells†

We study Ge solar cells with epitaxial GaInP windows for application as the third junction of GaInP/GaAs/Ge three‐junction solar cells. We demonstrate Ge junctions with open‐circuit voltages above 230 mV, fill factors above 65%, and internal quantum efficiencies of ∼90%. By varying separately the base and emitter contributions to the junction dark current, we deduce the factors limiting the performance of this device, and we project the improvement to the device performance that may be obtainable if key limiting factors such as the emitter surface‐recombination velocity can be mitigated. Published in 2001 by John Wiley & Sons, Ltd.     

Studies of the micro- and nanostructure of polycrystalline CdTe and CuInSe2 using atomic force and scanning tunneling microscopy

Atomic force microscopy (AFM) and scanning tunneling microscopy (STM) have been used to study the micro- and nanostructure of CdTe and CuInSe₂ thin films used for photovoltaic cells. Topographic images are comparable with those reported previously using conventional scanning electron microscopy (SEM)—to the limit of spatial resolution of the SEM technique. For higher magnifications, nanoscale structures and features have been observed for the first time with AFM and STM, and these observations have implications for the suitability and preparation of these semiconductors for high-efficiency solar cell realization.     

Experimental evidence of parasitic shunting in silicon nitride rear surface passivated solar cells

Many solar cells incorporating SiN_x films as a rear surface passivation scheme have not reached the same high level of cell performance as solar cells incorporating high‐temperature‐grown silicon dioxide films as a rear surface passivation. In this paper, it is shown by direct comparison of solar cells incorporating the two rear surface passivation schemes, that the performance loss is mainly due to a lower short‐circuit current while the open‐circuit voltage is equally high. With a solar cell test structure that features a separation of the rear metal contacts from the passivating SiN_x films, the loss in short‐circuit current can be reduced drastically. Besides a lower short‐ circuit current, dark I–V curves of SiN_x rear surface passivated solar cells exhibit distinct shoulders. The results are explained by parasitic shunting of the induced floating junction (FJ) underneath the SiN_x films with the rear metal contacts. The floating junction is caused by the high density of fixed positive charges in the SiN_x films. Other two‐dimensional effects arising from the injection level dependent SRV of the Si/SiN_x interfaces are discussed as well, but, are found to be of minor importance. Pinholes in the SiN_x films and optical effects due to a different internal rear surface reflectance can be excluded as a major cause for the performance loss of the SiN_x rear surface passivated cells. Copyright © 2002 John Wiley & Sons, Ltd.     

Effect of Sb on the quantum efficiency of GaInP solar cells

The energy bandgap of GaInP solar cells can be tuned by modifying the degree of order of the alloy. In this study, we employed Sb to increase the energy bandgap of the GaInP and analyzed its impact on the performance of GaInP solar cells. An effective change in the cutoff wavelength of the external quantum efficiency of GaInP solar cells and an effective increase of 50 mV in the open‐circuit voltage of GaInP/Ga(In)As/Ge triple junction solar cells were obtained with the use of Sb. Copyright © 2016 John Wiley & Sons, Ltd.     

Recent progress in MIS solar cells

Metal–insulator–semiconductor (MIS)-type solar cells have an inherent cost advantage compared to p-n junction solar cells. First-generation MIS–inversion layer (MIS–IL) solar cells, already successfully produced in an industrial pilot line, are restricted to efficiencies of 15–16%. With the second-generation MIS–IL silicon solar cells, based on drastically improved surface passivation by plasma-enhanced chemical vapour-deposited silicon nitride, simple technology can be combined with very high efficiencies. The novel inversion layer emitters have the potential to outperform conventional phosphorus-diffused emitters of Si solar cells. A 17.1% efficiency could already be achieved with the novel point-contacted ‘truncated pyramid’ MIS–IL cell. A new surface-grooved line-contact MIS–IL device presently under development using unconventional processing steps applicable for large-scale fabrication is discussed. By the mechanical grooving technique, contact widths down to 2 μm can be achieved homogeneously over large wafer areas. Bifacial sensitivity is included in most of the MIS-type solar cells. For a bifacial 98 cm² Czochralski (Cz) Si MIS-contacted p-n junction solar cell with a random pyramid surface texture and Al as grid metal, efficiencies of 16.5% for front and 13.8% for rear side illumination are reported. A 19.5% efficiency has been obtained with a mechanically grooved MIS n⁺p solar cell. The MIS-type silicon solar cells are able to significantly lower the costs for solar electricity due to the simple technology and the potential for efficiencies well above 20%.©1997 John Wiley & Sons, Ltd.     

一种改进太阳能计算器芯片二极管稳压电路设计

对于太阳能计算器,稳压电路的设计是串联三个PN结二极管以达到稳压目的。这种设计会出现以下问题:当外部光线太强时,太阳能电池板的供电电压较高,而稳压电路由于正向饱和压降过高,不能及时将高电压释放掉,会造成计算器不能正常工作。文章研究了改进二极管稳压电路的设计,通过只变更其中的一层mask(P+),将其中一个PN结二极管改为肖特基二极管,使其正向饱和压降处于一个合理的区间,并且研究了通过该变动后不同的Ti金属厚度以及不同温度对该稳压电路的影响。结果显示该种优化完全符合应用需求。     

Antireflection coating design for series interconnected multi‐junction solar cells

Antireflection coating design for multi‐junction solar cells can be more challenging than in the single‐junction case. Reasons for this are discussed. Analytical expressions used to optimize antireflection (AR) coatings for single junction solar cells are extended for use in monolithic, series interconnected multi‐junction solar cell AR coating design. The result is an analytical expression which relates the solar cell performance (through J_sc) directly to the AR coating design through the device reflectance. It is also illustrated how AR coating design can be used to provide an additional degree of freedom for current matching multi‐junction devices. Published in 2000 by John Wiley & Sons, Ltd.     

Circuit modeling of the emitter-wrap-through solar cell

Back-contact solar cells have the potential to reduce module assembly costs and give a higher conversion efficiency. Such a device must be simple to fabricate on an industrial scale and be tolerant of low minority-carrier diffusion lengths. The emitter-wrap-through (EWT) cell is a device design that can meet these goals. In this device, the diffused junction is present on both sides and is connected by laser-drilled holes through the silicon. EWT cells were frequently found to have poor fill factors (FFs) due to shunt-like behavior. The holes were found to possess no defects that adversely affect device performance. However, detailed equivalent circuit modeling of the EWT cell was able to explain the shunt-like behavior. Experiments were performed to confirm the physical mechanisms described by the equivalent circuit model. Device optimization guided by the equivalent circuit model has led to the demonstration of a large area EWT cell with a FF of 77.64% and efficiency of 18.2%     

High efficiency triple junction thin film silicon solar cells with optimized electrical structure

We report on improving the performance of pin‐type a‐Si:H/a‐SiGe:H/µc‐Si:H triple‐junction solar cells and corresponding single‐junction solar cells in this paper. Based on wet‐etching sputtered aluminum‐doped zinc oxide (ZnO:Al) substrates with optimized surface morphologies and photo‐electrical material properties, after adjusting individual single‐junction solar cells utilized in triple‐junction solar cells with various optimization techniques, we pay close attention to the optimization of tunnel recombination junctions (TRJs). By means of the optimization of individual a‐Si:H/a‐SiGe:H and a‐SiGe:H/µc‐Si:H double‐junction solar cells, we compensated for the open circuit voltage (V_oc) loss at the a‐Si:H/a‐SiGe:H TRJ by adopting a p‐type µc‐Si:H layer with a low activation energy. By combining the optimized single‐junction solar cells and top/middle, middle/bottom TRJs with little electrical losses, an initial efficiency of 15.06% was achieved for pin‐type a‐Si:H/a‐SiGe:H/µc‐Si:H triple‐junction solar cells. Copyright © 2014 John Wiley & Sons, Ltd.     

Characteristics of Polyaniline/Si Heterojunction Solar Cell By Electrochemical Dye Sensitization

Using the electrochemical polymerization dye sensitization （ECDS） method, polyaniline （PAn）, which is used as top region material in solar cells, is sensitized with direct blue dye（DS）, and sensitized Al grid/DS-PAn/n-Si/Al heterojunction solar cells is prepared by ECDS. Influences of the ECDS on the absorption spectrum and the junction characteristics of the solar cell were discussed, and the output characteristics were measured. The results show that the absorption spectrum of the sensitized PAn films is much wider and stronger in Vis-range; the diode quality factor is about 6.3 and the height of latent barrier potential of p-n junction is 0.89 eV; the short-circuit current and the conversion efficiency of sensitized DS- PAn/Si heterojunction solar cells are greatly improved, which the short-circuit current can increase 6 times, the fill factor is 57% and the efficiency can reach 1.42 % under the illumination of 37.2 W/m^2 , respectively.     

太阳能光伏汇流箱监测系统设计

光伏汇流箱是光伏发电的重要组成部分,主要用于太阳能光伏组件与直流控制柜间的连接。文中设计的光伏汇流箱主电路以单片机STC12C5A60S2为控制核心,由电流检测电路、温度检测电路、通信电路和电源电路等组成,主要实现光伏汇流箱温度检测;利用霍尔传感器实现了太阳能光伏组件阵列的电流巡检;同时利用DC-DC原理实现了高电压到低电压的转换,并以此为主控电路提供电源。此外,还实现了光伏汇流箱与PC机的通信。该设计简单实用,且具有成本低、可靠性高的优点。     

The effect of crystal defects on the performance of gaas solar cells

The nature and the effect of crystal defects on the performance of GaAs/GaAlAs solar cells fabricated by MOCVD production reactors have been evaluated. Intrinsic threading dislocations from the GaAs substrates propagate through the junction and are believed to act as recombination centers reducing both the short circuit current density and the open circuit voltage of the device. These defects, at a concentration level exceeding 2 × 10⁴ cm⁻², detrimentally affect the electrical performance of the solar cells.     

GaAs基GaInNAs太阳电池研究进展

在研究新型高效GaAs基三结和四结太阳电池过程中,研究者努力寻找一种既满足能隙约为1eV,同时又与GaAs衬底晶格匹配的半导体材料。通过调节组分,GaInNAs可同时满足上述两个特性,因此GaInNAs被认为是制备新型高效多结GaAs基太阳电池的理想材料。但实际上,制备高晶体质量GaInNAs材料十分困难,造成所制备的器件性能低下,未能达到实际要求。探讨了导致GaInNAs材料生长困难的机理,并对当前GaAs基GaInNAs太阳电池材料的研究历程和技术现状进行了概述。在此基础上,展望了GaInNAs技术的未来走向。     

Analysis of the EWT‐DGB solar cell at low and medium concentration and comparison with a PESC architecture

Silicon represents an interesting material to fabricate low‐cost and relatively simple and high‐efficient solar cells in the low and medium concentration range. In this paper, we discuss a novel cell scheme conceived for concentrating photovoltaic, named emitter wrap through with deep grooved base (EWT‐DGB), and compare it with the simpler passivated emitter solar cell. Both cells have been fabricated by means of a complementary metal–oxide–semiconductor‐compatible process in our laboratory. The experimental characterization of both cells is reported in the range 1–200 suns in terms of conversion efficiency, open circuit voltage, short circuit current density and fill factor. In particular, for the EWT‐DGB solar cells, we obtain an encouraging 21.4% maximum conversion efficiency at 44 suns. By using a calibrated finite‐element numerical electro‐optical simulation tool, validated by a comparison with experimental data, we study the potentials of the two architectures for concentrated light conditions considering possible realistic improvements with respect to the fabricated devices. We compare the solar cell figures of merit with those of the state‐of‐the‐art silicon back‐contact back‐junction solar cell holding the conversion efficiency record for concentrator photovoltaic silicon. Simulation results predict a 24.8% efficiency at 50 suns for the EWT‐DGB cell and up to 23.9% at 100 suns for the passivated emitter solar cell, thus confirming the good potential of the proposed architectures for low to medium light concentration. Finally, simulations are exploited to provide additional analysis of the EWT‐DGB scheme under concentrated light. Copyright © 2017 John Wiley & Sons, Ltd.