The improved photovoltaic response of commercial monocrystalline Si solar cell under natural and artificial light by using water flow lens (WFL) system

The performances of a photovoltaic system based on high‐efficiency commercial monocrystalline Si solar cell associated with the water flow lens (WFL) system are investigated. This system enables the cooling of the surface of the cell, indirectly cooling the surrounding, and, on the other hand, it allows us to investigate, depending on the position of the cell and the WFL system, the influence of larger and smaller intensities of the light with the inevitable change in the spectrum. All of these effects are very important and can greatly contribute to the better photovoltaic performance of the used cells. Indoor characterization at higher and lower light intensities is performed using both different spectra and intensity of the light. The obtained results show that at low/lower light intensity, spectra are more dominant than the intensity of light itself and that the used WFL system always improves the photovoltaic response leading to a higher efficiency of the tested solar cell. It was found that the ratios of the short circuit current (I_sc) and the input light energy (P_input) are 4.42 and 8.96 without and with the use of the WFL system in the measurements, respectively. The same Si solar cell is also tested in outdoor condition, but this time using the WFL system to concentrate sunlight to produce a larger amount of power and water flow for cooling the surface of the solar cell. Again, a higher efficiency (an increase from 25.7% to 33.5%) by using the WFL system was obtained.     

The effect of the series resistance on the photovoltaic properties of In-doped CdTe(p) thin film homojunction structure

The photovoltaic properties of In-doped CdTe(p) thin film homojunction structure have been investigated; the effect of the series resistance on the short circuit current has especially been discussed in detail. A simulation of the fabricated device is achieved successfully using the PSPICE computer program. Mathematical derivations are implemented in order to interpret the results. It is found that the deteriorative effect of the series resistance on the short circuit current vs light intensity characteristics increases by increasing the light intensity. A new factor has been suggested to be a measure of how the series resistance affects the solar cell behavior at low and high light intensities.     

Intensity modulated short circuit current spectroscopy for solar cells

Understanding charge separation and transport is momentously important for the rectification of solar cell performance. To probe photo-generated carrier dynamics, we implemented intensity modulated short circuit current spectroscopy (IMSCCS) on porous Si and Cu(In_x,Ga_1−x)Se₂ solar cells. In this experiment, the solar cells were lightened with sinusoidally modulated monochromatic light. The photocurrent response of the solar cell as a function of modulation frequency is measured as the optoelectronic transfer function of the system. The optoelectronic transfer function introduces the connection between the modulated light intensity and measured AC current of the solar cell. In this study, interaction of free carriers with the density of states of the porous Si and Cu(In_x, Ga_1−x)Se₂ solar cells was studied on the basis of charge transport time by IMSCCS data.     

Determination of the interfacial dynamic velocity in silicon solar cells

A detailed theoretical method is presented for the determination of the interfacial dynamic velocity (IDV) S_d introduced at the edge of the space-charge region in the base of a solar cell. The method is based on a dynamic measurement at an arbitrary point on the I–V curve and exploits measurements carried out on a solar cell under illumination. A transient regime between two steady states around the operating point is investigated. The theory takes into account the carrier generation and recombination rates. The measured values of S_d are shown to depend on the cell operating conditions, and the error in the determination of S_d increases with the light intensity that is kept constant during measurements. The interfacial dynamic velocity characterizes the junction as an active interface related to the current flow through the device and appears to allow solar cell quality control since it also depends on the cell structure parameters.     

太阳能电池最大功率跟踪的线性近似法分析

对太阳能电池最大功率的跟踪方法——线性近似法进行了实验分析,考察单晶硅、多晶硅、非晶硅三种材料的太阳能电池最佳工作电压Um、最佳工作电流,Im和最大输出功率Pm随光照强度的变化情况.结果发现:对同一种太阳能电池,光照强度改变时,Um可以认为基本不变;Im和Pm与光照强度均呈线性关系.同一光照强度下,单晶硅电池最佳工作点...     

Effect of spatial variation of incident radiation on spectral response of a large area silicon solar cell and the cell parameters determined from it

Effect of spatial variation of incident monochromatic light on spectral response of an n⁺–p–p⁺ silicon solar cell and determination of diffusion length of minority carriers (L_b) in the base region and the thickness of the apparent dead layer (x_d) in the n⁺ emitter from the spectral response have been investigated. Spectral response of a few 10 cm diameter and 10×10 cm² pseudo-square silicon solar cells was measured with the help of a standard silicon solar cell of 2×2 cm² area in 400–1100 nm wavelength range. Different areas (4, 9, 16, 25 and total area 78.6 or 96 cm²) were exposed. The effect of the radial variation of incident radiation was determined quantitatively by defining a parameter f₁ as the ratio of the average intensity falling on the reference cell to that on the exposed area of the test cell. The value of f₁ varied between 1 and 1.15 (1.25) as the exposed area of the cell varied from 4 cm² to 78.6 (96) cm² indicating that the spatial inhomogeneity of intensity increased with the increase in the exposed cell area. Short-circuit current densities, J_sc, computed from spectral response data for AM1.5 spectrum were less compared to the directly measured values by a factor which was nearly equal to f₁. However, radial variation of intensity does not affect the determination of diffusion length of minority carriers in the base region (by the long wavelength spectral response, LWSR method using the measured spectral response data in 0.85<λ<1.05 μm range) and the thickness of the dead layer (by the method of Singh et al. using the data of 0.45<λ<0.65 μm range) significantly.     

Defects localization research in photovoltaic cells: Methods and devices

The article presents a method to determine local defects in solar photovoltaic cells (PVC). It is based on the non-contact measurement of PVC area temperature distribution by a special thermovision system when applying forward and reverse voltage to the cell. Distribution of PVC surface temperature is determined by nonuniformity of current density (because of local defects) and reveals itself in the intensity of thermal radiation in the infrared spectrum (IR). The difference between the light detector signals when applying a forward or reverse voltage to PV cells and in the absence of applied voltage to the PVC is used to eliminate the effect of IR light patch, surface irregularities emissivity of solar cells, heterogeneity sensitivity light detector array. The hardware and software implementation techniques using the focal plane array of infrared 3–5 micron spectral range and 320 × 256 elements size are presented.     

Near-band-edge photoluminescnce in Cu(In,Ga)Se2 solar cells

Photoluminescence (PL) and PL decay characteristics of the near-band-edge (NBE) PL at room temperature have been studied on the Cu(In,Ga)Se₂ (CIGS) solar cells. The carrier recombination process has been discussed with emphasis on the photovoltaic properties of the solar cell. It has been found that: (i) PL intensity of the CIGS solar cells is much stronger than that in the corresponding CIGS thin films, (ii) the PL decay time of the cell is longer than that of the CIGS film, and (iii) the PL decay time of the CIGS solar cell exhibits strong dependence on the PL excitation intensity. In the CIGS solar cell, intense PL is obtained under the open circuit condition (oc), in contrast to the very low PL yield under the short circuit (sc) condition. The PL decay time under the sc condition is much shorter than that under the oc condition. Excitation intensity dependence of PL intensity and the PL decay time have been studied, and they are discussed with relation to the photo-voltage due to the PL excitation light. PL and injection EL under the external DC bias have been studied. The mapping image of NBE-PL intensity has been compared with that of the laser beam induced current (LBIC), and the PL intensity image reflects the photovoltaic properties of the CIGS solar cells. We demonstrated that NBE-PL of the CIGS solar cell reflects the photovoltaic effect, and it can be utilized as a powerful characterization method.     

Microwave detection of minority carriers in solar cell silicon wafers

Techniques measuring photoconductive decay by means of microwaves (μ-PCD) can be used to detect free carriers in semiconductors. The instrument as developed at ECN for characterization of the solar cell material is described. The experimental details of two measurement techniques and the theoretical background are discussed. In the decay method the effective mean lifetime of the minority carriers is measured. In the harmonic modulation technique information about the lifetime of the minorities is contained in the phase-shift of the microwave signal relative to the phase of the light intensity. The aim of this research is to determine the bulk mean lifetime of the minority carriers and the surface recombination velocities of solar cell silicon wafers by a non-destructive and contactless technique. Typical experiments will be presented.     

考虑多变量因素影响的光伏PEM制氢系统建模与分析

针对复杂工况对光伏制氢系统性能产生不确定性的影响,提出考虑多变量因素影响的光伏制氢系统模型,探索辐照度、温度、膜厚、压力等因素对光伏质子交换膜（PEM）制氢系统的影响。系统首先建立考虑辐照度、温度、膜厚、压力等因素影响的光伏-质子交换膜电解槽-氢储罐的光伏制氢模型,之后对系统进行定量计算和定性分析,并依据实际光伏数据进行实验验证。结果表明,在额定功率范围内,太阳电池输出电流和功率随辐照度的增加而增大,随温度的升高而降低。质子交换膜电解槽电压随辐照度、膜厚、压力的增加而增大,随温度的升高而减小。太阳电池输出功率、质子交换膜电解槽电压的变化趋势与辐照度变化趋势具有一致性。最终计算得到太阳电池系统、质子交换膜电解槽系统和总系统效率分别为16.8%、72.2%和12.1%。     

Quantum dot integration in heterostructure solar cells

InAs self-assembled quantum dots (SA-QDs) were incorporated into GaAlAs/GaAs heterostructure for solar cell applications. The structure was fabricated by molecular beam epitaxy on p-GaAs substrate. After the growth of GaAs buffer layer, multi-stacked InAs QDs were grown by self-assembly with a slow growth rate of 0.01 ML/s, which provides high dot quality and large dot size. Then, the structure was capped with n-GaAs and wide band gap n-GaAlAs was introduced. One, two or three stacks of QDs were sandwiched in the p–n heterojunction. The contribution of QDs in solar cell hetero-structure is the quantized nature and a high density of quantized states. I–V characterization was conducted in the dark and under AM1 illumination with 100 mW/cm² light power density to confirm the solar cell performance. Photocurrent from the QDs was confirmed by spectral response measurement using a filtered light source (1.1-μm wavelength) and a tungsten halogen lamp with monochromator with standard lock-in technique. These experimental results indicate that QDs could be an effective part of solar cell heterostructure. A typical I–V characteristic of this yet-to-be-optimized solar cell, with an active area of 7.25 mm², shows an open circuit voltage V_oc of 0.7 V, a short circuit current I_sc of 3.7 mA, and a fill factor FF of 0.69, leading to an efficiency η of 24.6% (active area).     

A simple approach to determine the solar cell diode ideality factor under illumination

A simple approach, which can estimate the diode ideality factor of a high efficiency pn junction solar cell under illumination by using its current-voltage data, is explained. We have proposed that an analytical method based on Lambert W-function is sufficient for the extraction of the diode ideality factor of a solar cell modeled by double junction behavior with considerable compliance. Various illumination intensities are also considered in order to specify the reliable limit of the method. The dependence of the ideality factor and the reverse saturation current with light intensity has also been investigated in order to provide insight into the alteration of electrical conduction at junction interface at room temperature.     

A study on the influence of the spatial distribution of metastable defects on the properties of a-Si:H p-i-n and n-i-p solar cells: Experiment and numerical simulation

The keV-electron irradiation technique is used to study the influence of different spatial distributions of metastable defects on the properties of a-Si:H p-i-n and n-i-p solar cells. The energy dependence of the penetration depth of the keV-electrons is utilized to introduce metastable defects in different regions of the solar cells. A strong influence of the induced defect profiles on the open-circuit voltage and the short-circuit current of the solar cells is found. Internal collection efficiency measurements and modelling show that the relative alteration of the cell parameters contains information about the spatial distribution of the induced metastable defects in the case of standard p-i-n and n-i-p a-Si:H solar cells. On the basis of this result it is concluded that bulk rather than interface degradation is the dominant effect after light soaking and current injection for the solar cells investigated in this study.     

Fast LBIC in-line characterization for process quality control in the photovoltaic industry

The photovoltaic industry asks for fast, non-destructive techniques for in-line characterization tools in solar cells production. We shall show in this paper that the use of the light beam induced current technique (LBIC) is capable to get in a few seconds time photocurrent maps of large area solar cells and to correlate these data with the cell efficiency. The samples analysed in this study are industrial 10×10 cm² multicrystalline silicon solar cells. The LBIC setup works with three laser sources at 633, 780 and 830 nm, taking the laser beam power below 1 mW. The laser beams are moved on the wafer surfaces using a galvanometer x–y scanner system and the beam size on the focus has a diameter of about 65 μm. We demonstrated the possibility to obtain quantitative information about the cell quality in <3 s from the photocurrent maps with a pretty good correlation with the efficiency data.     

A new protocol for characterization of dislocations in photovoltaic polycrystalline silicon solar cells

Main photovoltaic properties of polycrystalline silicon solar cells are often affected by dislocation effects. Dislocations degrade functional photocurrent and considerably alter relevant parameters such as short-circuit current density, dark current intensity and open-circuit voltage. In this study, we have developed an enhanced photothermal technical protocol for diagnosing dislocation spatial distribution inside photovoltaic polycrystalline silicon solar cells. We tried to establish a qualitative and quantitative correlation between the local thermal properties alteration and dislocation spatial range. Experimental imaging profiles, yielded by this technique are compared to other diagnostic techniques results.     

Review and tests of methods for the determination of the solar cell junction ideality factors

Up to 22 methods for the determination of the solar cell ideality factor, n, have been presented in this paper. Most of them use the single-exponential diode model, static mode, dc regime, forward bias and a single I–V data set.Mostly, n is estimated simultaneously with other parameters and the methods apply to p–n and/or MS and MIS diodes. The disparities in model assumptions, structures investigated and operation conditions are too large to allow simple comparison of the efficiencies of those methods.Thus, the authors have expressed some considerations on those assumptions and operation conditions, together with comments on strengths and weaknesses of the different techniques. Thirteen methods have been assessed experimentally using a commercial c-Si solar cell. The resulting n values range from 1.26 to 1.50 for the temperature and light intensity intervals of [295; 328] K and [0; 1000] W m⁻², respectively. A discussion on the overall results of this work has also been made, showing notably that (i) the assumption of a constant n for any temperature, light intensity and biasing voltage has been found inappropriate by various workers; (ii) dark condition methods give slightly lower n than light condition ones; (iii) n ranges from 1 to 2 for most of the structures published in this work, except for some MIS structures, hetero-junction semiconductors solar cells, metal contacts with amorphous semiconductors, texturized Si devices, and c-Si (second diode in the two-exponential diodes model); (iv) n, I_s and thus Φ_B for Schottky diodes can be determined by different techniques on dark condition, and may be commonly used as evaluating criteria of metal/semiconductor (MS) and metal/insular/semiconductor (MIS) interfacial properties.     

Characterization of screen printed Ti/CdS and Ti/CdSe photoelectrodes for photoelectrochemical hydrogen production

Authors report preparation and characterization of CdSe/Ti and CdS/Ti photoelectrodes for their application in photoelectrochemical hydrogen production using a semiconductor septum solar cell configuration. The septum electrodes were characterized structurally, optoelectronically and photoelectrochemically for their use in septum solar cells for hydrogen production. Both these septum electrodes exhibited high photosensitive current in the solid-state and the photoelectrochemical solar cell configuration. The j–E (current density-potential) characteristics of the semiconductors in the photoelectrochemical cell configuration indicated promising photo-chemcial energy conversion current (photocurrent).     

Study of the photon down‐conversion effect produced by thin silicon‐rich oxide films on silicon solar cells

In the present work, we studied the photon down‐conversion effect produced by thin films of silicon oxide with embedded silicon nanocrystals also called silicon‐rich oxide (SRO). These films have been used to absorb high energy light and the re‐emission of two or more low energy photons (~1.1 eV) with the goal of improving the external quantum efficiency and consequently the conversion efficiency of silicon solar cells. According to our results, the incorporation of a thin SRO film on the solar cell surface increases the short circuit current and the FF of the silicon solar cells; the enhancement of spectral response is due to the high photoluminescence intensity of the SRO in the visible region when irradiated with UV light. An improvement of 38% in the solar cell efficiency has been observed in our particular solar cell fabrication process by the use of an SRO film with high photoluminescence intensity, which replaces the conventional silicon dioxide film. Copyright © 2016 John Wiley & Sons, Ltd.     

Evaluation of external quantum efficiency of a 12.35% tandem solar cell comprising dye-sensitized and CIGS solar cells

A tandem solar cell is constructed by series connection of a semi-transparent dye-sensitized solar cell (DSSC) as a top cell and a Cu(In, Ga)Se₂ (CIGS) solar cell as a bottom cell, where the isolated DSSC and CIGS cells show the conversion efficiency of 8.27% and 11.71%, respectively. The DSSC/CIGS tandem cell exhibits the improved conversion efficiency of 12.35% with photocurrent density of 14.1 mA/cm², open-circuit voltage of 1.435 V and fill factor of 0.61. External quantum efficiency (EQE) of the tandem cell is investigated under DC and AC modes. EQE of the isolated DSSC and CIGS cell can be measured by either DC mode or AC mode, whereas EQE for the tandem cell is detected only under AC mode with bias light. Bias light intensity is found to play the crucial role in determining the precise EQE of the tandem cell. At the given chopping frequency as low as 10 Hz, the measured EQE at bias light corresponding to 1 sun intensity is consistent with the simulated EQE data.