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Issue
Eur. Phys. J. Appl. Phys.
Volume 88, Number 2, November 2019
Article Number 20401
Number of page(s) 13
Section Nanomaterials and Nanotechnologies
DOI https://doi.org/10.1051/epjap/2019190146
Published online 05 February 2020

© EDP Sciences, 2020

1 Introduction

On the efficiency of nano-sized solar cells and its applications, extensive research has been carried out so far that in each process, we have seen relative changes in the device in terms of efficiency and quality.

Here, considering how to improve the performance of a solar cell by applying new layers to its structure, it is attempted to take into account the conditions that can be implemented to simulate new structures in the solar cell. One of the most important issues in the field of solar cells is to achieve high efficiency based on the number of photons shifted to the surface. In the case of the production of a device with suitable conditions, the photon absorption capability and the photovoltaic transformation function in low ambient light can also be achieved. But the point to consider in this regard is how to create a process to improve efficiency by making changes in the structure of the solar cell. One of the ways to increase the efficiency of these devices is to reduce the barrier of light transmission, which is the conductor of the current carrier by using transparent or semi-transparent conductors; it ensures the light is transmitted to the energy absorber plate. This process, which can be achieved by carbon structures, can help improve device efficiency [1].

Carbon nanotubes are useful electronic features in the light of specific characteristics and are capable of absorbing photons‏. These properties allow the creation of heterojunction devices such as solar cells‏. It can be used as a conductive network for transmitting loads and as a transparent electrode for collecting flux‏. The relationship between interface composition and characteristic parameters of the solar cell strategy based on single-wall carbon nanotubes has been used as a GaAs-compatible absorbent‏. It was found that with the increase of the common surface, the open circuit voltage decreases [2].

To increase the efficiency of the photoelectric transformation process and reduce the cost with widespread use, thin-layer solar cells are among the most widely used topics. Based on the results of a study, third-generation solar cells that have carbon nanotube enhancement layers were used to achieve great progress [3].

Charge collection layers are an essential part of this type of solar cell. Carbon nanotubes (CNTs) were introduced as a very good choice for this role. The CNTs have a wide range of transmitting properties that are very beneficial. For this reason, CNTs can be used as a conduction layer in solar cells [4].

The single-walled CNTs (SWCNTs) are a useful ingredient to produce high-performance photovoltaic devices due to their excellent optical and electrical properties. It can be improved by making changes in the process of producing CNTs to conditions of low resistance and high transparency for light transmission, which has been doubled in comparison to the silicon type [5].

Due to the fact that polymer nanocomposites of CNTs are diverse and widely used materials, they have increased demand for various applications. These results are widely used in the production of useful compound materials such as graphene, gold nanotubes and carbon black nanocomposites [6].

CNTs have good stability and good optical properties as a direct sunlight absorber. The analysis of the stability of the relative absorption spectra in the optical and thermal properties of nanotubes to increase the efficiency of solar absorbers is very convenient [7].

According to extensive research, high-purity semiconductor CNTs are expected to be contaminated with high-performance electronic devices. For this reason, one of the uses of these types of structures is introduced to improve the performance of solar cells [8].

In a study based on the impact of the combination of highly transparent and conductive CNTs, the synchronization rate generated in the combined solar cells and the increase in power conversion efficiency was obtained [9].

Doping of CNTs can provide various possibilities for controlling the physical properties of CNTs. In a study, the effect of doping CNTs with non-metals, alkali metals, transition metals, and clusters was carried out. This study showed that there is a possibility of control and change in electronic properties, magnetic properties, transitions and optical properties of CNTs [10].

By measuring the conductivity of the CNTs and the amount of light absorption, it was found that the guidance mechanism in the SWCNT is comparable to that of the conductive polymers [11].

In a study that was carried out using non-destructive X-ray dispersion on CNTs, its structural characteristics were completely analyzed. The results show that for multiplicity growth and production, directly related to the density of adjacent dimensions [12].

In a numerical analysis using simulation tools, the combined properties of CNTs in solar cells were investigated. The results showed that the open circuit voltage changes with the change in electronic properties, while the rest of the electrical parameters reach the optimum value [13].

In an investigation of the result of a study, it became clear that the CNT has excellent conductivity in the hole. Performance measurement was based on the AM 1.5G light spectrum. The exact research showed that the increase in efficiency in the solar cell is very different from that of the non-layered SWCNT model [14].

In an investigation on a solar cell covered by a transparent conductive CNT network, the effect of this layer was investigated as a vortex hole collector and transparent electrode for light transmission. In this work, according to the standard AM 1.5, the power conversion efficiency was investigated and the magnitude of the increase in this change was observed on the efficiency of the solar cell [15].

In fact, CNTs have an organic photovoltaic function. By comparing the function of solar cells, a cell that has photovoltaic performance improvement layers also results in a significant increase in lower dark current conditions [16]. By investigating third-order optical nonlinearities, the average contribution of a carbon atom to optical instability was determined and compared. It was found that the smaller diameter of a graphene nanotube has the largest contribution to its electrical performance. This method is used to construct photonic conductor materials [16].

The kinetics of the carrier, in the process of charge separation, is covered up to four orders in the density of the volumetric hole, which is created by a recombinant process. The results show that there are several potential ways to improve photovoltaic devices in transporting and reconstructing both charges and excitons in thin film SWCNT [17]. Research results showed that the best photovoltaic performance for CNT weight percentages is between 0.2% and 0.4%, and the presence of CNTs can improve the load. It sharply reduces the electron-hole noise in the anode and increases photon absorption in the solar cell [18].

Semiconductor photocatalysts were used to overcome serious defects and to quickly rebuild the load and to remove light absorption constraints. The photocatalytic properties of the multi-junction system have also been examined for environmental and energy efficiency and it has been shown that improvements in defects can be achieved through these elements [19]. In an evaluation of the photocatalytic process that was performed under visible light exposure, the performance of the composite and carbon nanotubes was obtained to improve photocatalytic activity. Also, it has been shown that an electron transport pathway can be generated to transfer electrons. This can be considered as a new method for photon absorption [20].

The electrical properties of the CNT layers in recent studies simulated by heterogeneous networks were investigated for electrical and optical conductivity resistance and compared with the data extracted by experimental experiments [21,22]. In the process of reviewing the improvement of solar cell performance, we are referring to wavelengths and how photons are absorbed in different frequencies and energies. Because, based on the relationships governing photon energy, for absorbing light and converting to electrical energy, the proportion of wavelength to structure and impurity of the device is very effective [23].

By studying the electrical and optical properties of doped CNTs, it showed that CNTs can be used as a good conductive semiconductor structure. Electrical and optical studies were carried out by changing the rate between nanotubes with the doped nanotube in thin films of CNTs. These findings clearly showed that by changing the composition of the nanotube, new optical and electrical properties could be achieved in CNTs [24].

In this paper, an improved process is produced for the production of single-junction solar cells with higher efficiency and a broad-based application in which a transparent CNT conductor is used as an electrical conductor as well as photon energy absorber at certain wavelengths. This process can results in the production of solar cells with multilayered composite elements.

2 Methodology

At the first step, the governing equations on the device's physics are simulated [25]. Considering the nonlinear optical properties of CNTs, the photon absorption can be changed by using the armchair and zigzag nanotubes [10]. With the variation of the electron and hole mobility based on the added CNT improver layer, the photon absorption would be changed. In the present work, the variation of the mentioned parameters has been done for the 75 Ω/squ CNTs layer and the photon absorption is computed.

Third-order optical nonlinearities, arranged by second-order hyperpolarizabilities, have examined the chiral conditions of graphene nanotubes, and based on the information received from one carbon atom, the third-order optical instability of each of the nanotubes has been calculated and determined. According to the nonlinear optical conditions that can be realized, the absorption of the desired photon can be obtained [26].

In SWCNT, the high-frequency mobility of holes is less than that of multi-chiral films. The results show that there is a fundamental shift in the transportation and reconstruction of both charges and excitants in thin film SWCNT. Accordingly, several potential ways to improve photovoltaic devices can be identified [17].

In this study, the simulation results were compared to the data obtained from each layer, and certain values for the parameters of the layers in the device were calculated. In order to measure and access the surface ohmic resistance, based on the primary thickness, the investigations were carried out and then the electron and hole capabilities were obtained and finally compared with each other. In fact, the electrical conductivity is significantly dependent on oxidative factors, which leads to an increase in electrical conductivity and conduction change in the SWCNT1 [11].

In this process, a layer of a solar cell-compatible nanostructure network is added to the original model. The creation of a superficial layer of CNTs in a high precision solar cell can have a comparable performance difference with cells lacking it [27].

In order to achieve the final results in this study, CNT structures were investigated and the approved values for semiconducting nanosized conductivity, the concentration of semiconductors should be moderated to an optimum extent. Then, the ability to move the electrons and the holes were calculated for each layer strength value, which was matched to the results of the experiments contained in valid papers [28].

Different substrates of high density, high purity, and uniform diameter CNTs can be obtained interconnected, with mechanical and physical properties acceptable for use as an energy absorber layer [25]. Nanostructure networks were modeled as a semiconductor with a small energy band for further absorption at desired wavelengths.

To increase the energy efficiency of light-sensitive cells, one can use the addition of electrolyte to the nanotube [29]. Since the main goal of this study is to examine the flow of material through transparent solids, the use of CNT layers as a semiconductor is desirable because in software analysis, there are no problems in solving energy carrier problems towards the electrode in semiconductors, although, according to the preliminary studies, it is possible to select other nanostructures in it.

This can be achieved in the copper structure, which is used as a transparent conductor at the junction of the solar cell so that there is no barrier to light reaching the cell surface and the photovoltaic transformation process. The light transmission in this model is almost constant in all spectra [30].

In this paper, the base structure is initially simulated and the changed are made to reach the improved efficiency. The initial structure is a solar cell with different windows and structures which is composed of materials from group III-V of the periodic table [31]. The different layers of the considered model for the solar cell can be seen in Figure 1. The numerical simulation of the standard parameters according to Table 1 was also used to define the elements used in this solar cell [21].

Here, 4H-SiC was selected as a semiconductor that was used based on the function of CNT bonding work. In order to create an acceptable and accurate model of a CNT network, the properties of the 4H-SiC were modified to match the properties of metal materials while meeting the test resistivity values if the optical properties were unaltered [28] and to absorb more photons without changing the electrical properties based on the nonlinear optical performance [10], Some of the parameters required for simulation have been used.

The electron and hole are capable of adapting to the tested CNT plate resistivity with different modified conditions of 75 Ω/squ and 128 Ω/squ. In fact, these conditions are defined by the following equations [21]: (1) (2)

In which q is the charge of an electron or hole, µn and µp are the electron and hole mobility coefficients, and t is the thickness of that material.

Since the light intensity of the input means the photon entering and producing the electron, the short circuit current (Isc) depends on the intensity of the light. On the other hand, Isc is proportional to the area of the solar cell, the short-circuit current density (Jsc), which is usually used for comparing the performance of solar cells with the short circuit current value of Jsc = Isc. Then, by setting the value of J = 0, which means the cutoff current, the calculation of the open circuit voltage (Voc) value is as follows [32]: (3) (4)

Here J0 is a constant value, q is the electron charge and V is the voltage between the terminals, and the efficiency of the solar cell (Eff) is defined as follows [32]: (5) where the amount of fill factor (FF) is calculated for Eff calculation from the following equation [32]:

(6)

In general, the FF value is used to measure the current–voltage squared curve (JV). Because Voc and Jsc increase the lifespan of minority carriers, the maximum voltage and current densities will ultimately determine the JV curve. Thus, it is possible to obtain the maximum current and voltage density [33].

thumbnail Fig. 1

Gallium arsenide solar cell structure model with two thin CNTs as double load collector.

Table 1

Some of the parameters used in numerical simulation [21].

3 Results

In the studies, changing the thickness and the location of each of these two layers, their effects on the efficiency of the solar cell are investigated. The differences between the considered layers are in their optical properties which are given in Table 1.

The simulated model of the GaAs solar cell with one CNT layer added on its surface as a double load collector is represented in Figure 2. The CNT layer can be composed of 75 Ω/squ, 128 Ω/squ or combination of 75 Ω/squ and 128 Ω/squ, whose properties are given Table 2.

Figure 3 illustrates the meshing approach of the device according which the load dispersion process is predicted. Caused by more sensitivity at the central part of the solar cell, more accurate analysis should be performed at the surrounding area. Hence, the meshing is finer at this area. Furthermore, as the superficial layer has been created at the upper area, great deal of details should be computed at this region reach more accurate results without extra computational cost. Therefore, this area is also meshed by finer elements.

The standard sunlight spectrum and the transmitted spectrum from the CNT layer with a small difference reach to the solar cell surface [28]. In Figure 4, the standard range of AM1.5G is shown and the standard sunlight and transmitted spectrum of CNT are compared with the simulated spectra in the present work.

The dimensions of the device are also considered as the dimensions given in AM1.5G standard optical spectra. The voltage and current received from the device are recorded. The changed are applied to the CNT layers in order to reach the largest efficiency.

In order to run the exact simulation based on the curves shown in Figure 4, the curves for the standard AM1.5G spectrum as well as the associated wavelet spectra transmitted to the surface of the solar cell by the passage of the CNT layer are shown in Figure 5.

This diagram was calculated based on the light transmission data in CNTs against the transmission of the standard AM1.5G wave spectrum and extracted after simulation.

Figure 6 shows the current–voltage diagram of the solar cell without the CNT enhancement layer. The efficiencies of the GaAs solar cell with and without CNT layer are given in Table 2. As it can be seen in this table with the addition of the CNT enhancer layer on the solar cell structure, the flow of the device is significantly increased compared to the same solar cell without CNT layer.

According to Figure 7 in which the IV curve is shown, with the addition of the CNT layer, the open circuit voltage significantly increases. This improvement results in improving the efficiency of the solar cell [33].

As it can be seen in Table 2, the obtained results are in good agreement with the results reported previously [28]. Therefore, the simulation approach is employed in the following sections.

Defining the solar cell with and without CNT layer in the programming environment and the construction of the solar cell structure, the needed outputs are obtained and presented subsequently. The surface current absorption of the solar cell with the CNT layer is computed and compared with the same device without the CNT layer.

In Figures 8 and 9, the difference in current density is shown in the solar cell. In the case of a device without a CNT layer, the dispersion rate is not uniform and the maximum flow flux extends from the midpoint of the solar cell (the electrode's location on the cell surface), but in another modeling based on the CNT layers as the load collector is designed and simulated to see the uniformity of the flow current density.

This uniformity in the dispersion of electrical loads made it possible to use the all of the cell's surface to the same extent, and this participation in the production of the current eventually increased the efficiency of the device.

Figure 10 shows the effect of solar cell efficiency on the thickness of the surface-enhancing CNT layer, which is extracted and plotted in accordance with Table 3 [28].

Based on the research, it was found that all of the CNTs of the zigzag model have been identified as semiconductors, and their energy band gap is highly dependent on the size of the nanotube, and in the laboratory studies, the armchair model nanotubes also come from a variety of nanotubes The semiconductor chain has a great deal of dependency on the previous model, between the energy band gap and the size of the nanotubes [34]. Therefore, it can be expected that the change in the absorption process will change with the change in the structure of the nanotube as well as the dimensions used in the structure of this solar cell.

As shown in this table, the maximum solar cell efficiency was obtained in the case where a surface enhancement layer with a thickness of 100 nm was obtained and, if its thickness was increased or decreased, there was a decrease in efficiency in the solar cell. These changes are also visible in the graph shown in Figure 10.

With regard to the results obtained from the effect of the superficial layer and the choice of 100 nm thickness as the best-operating conditions of the solar cell, other parameters applicable to this structure were investigated.

In Figures 1114, several examples of simulated images related to different layers have been shown to analyze the effect of the number of CNT layers on the performance of the device.

The changes of these CNT enhancement layers with different thickness and sequence conditions on the solar cell were investigated and performance and efficiency analysis for each of these conditions were performed. As shown in Figure 11, changing the type of surface enhancer layer from type 128 Ω/squ to type 75 Ω/squ leads to a slight change in solar cell efficiency. However, in Figure 12 in which two surface layers have been used to increase the efficiency, more significant difference is observed in the device efficiencies with enhancer layers of types 128 Ω/squ and 75 Ω/squ. All the results obtained from this displacement and the number of layers can be seen and compared in Table 4 and Figure 17.

Here, a comparison of the performance of a base solar cell and a similar cell has been made with an enhancer layer or more CNT layers that were considered in this model. The results showed that the best performance can be given from a dual enhancer layer are obtained at the top of the cell. Its current–voltage diagram is shown in Figure 15.

In order to further illustrate this increase in efficiency, it can be seen in Figure 15, which in fact represents an improvement in the amount of flow in the solar cell with a double-improver layer.

In Table 4, the difference between the performance of the device and the numbers of improver layers of CNTs are shown. According to the information displayed in this section, there is a very small difference in various situations.

The diagram is shown in Figure 16 also shows the efficiency of the different states for the number of CNT layers. By comparing these small differences between double, triple, quad, and five layers, the best conditions were observed in the presence of two surface layers. This difference was further investigated with more emphasis on maximizing efficiency.

It should be noted that all parameters of the CNT layers shown in Table 4 are based on the information given in Table 1 for the simulation process.

As the results of the studies on the number of improvers' CNT layers were found, the best conditions for the yield in the two-layer mode were observed, this was considered in the same layering condition.

In the process of investigation, the efficiency and other parameters of the output parameters were investigated by different thickness percentages. Table 5 shows the effect of changes in efficiency due to changes in the thickness of the upper layer compared to the lower layer.

As already mentioned, by making more photon absorption in CNT type 75 Ω/squ [10], and by using electrical transfer capability in CNT type 128 Ω/squ [11], the best efficiency can be achieved using a double-layer composite on the solar cell. This was accomplished by shrinking the layer thickness of 128 Ω/squ, which was placed on the 75 Ω/squ layer. However, with less thickness of the top layer from 10 nm, the efficiency of the solar cell decreases due to the reduction of electrical transmission value. Therefore, in order to have maximum efficiency, it is necessary to consider the optimum thickness for the upper layer and the lower layer obtained in the simulation results, as shown in Table 5.

These efficiencies were all extracted based on a double CNT layer with a total thickness of 100 nm. As the results of the investigations show, the maximum yields were observed with a small difference in the range of 10% to 90% for this surface layer of the solar cell. In fact, the best performance conditions for this solar cell are shown in Figure 17.

In this curve, the upper curve is based on the conditions that the 4H-Sic layer is located on the CNT layer and the lower graph for the case in which the layers are displaced. This situation actually resulted in the best available extraction from a single-junction solar cell with the CNTs Improvement layers, which used a very thin layer of 10nm for a high-density 128 Ω/squ CNTs structure, which is named here 4H-Sic was introduced. In the lower layer, a thick layer of 90 nm CNTs of 75 Ω/squ type were introduced, which was named CNT here.

In another study on photon absorption rates, improving absorption conditions with regard to the presence of nanotube enhancement layers is presented in Figure 18. In this figure, as in the preceding sections, the same dispersion of photon absorption in a solar cell was observed, and the reason for this is the same as the absorption coefficient of the load by the enhancement layers.

In the picture shown in Figure 19, the impurities used in this solar cell are shown. In this solar cell, which is based on the semiconductor structure of the p-type on the n-type semiconductor (P on N), it has a top double layer, with a non-uniformity on the cell surface (as shown in Tab. 1) With a total thickness of 100 nm and below is a semiconductor layer of AlGaAs with a thickness of 500 nm as a window. Subsequently, a 400 nm thickness GaAs composite semiconductor layer is used as an emitter. The lower layer that plays the role of the base in this cell is GaAs with a thickness of 8 µm, and all of which lay on a substrate of GaAs with a thickness of 10 µm (Fig. 1), the impurities created in this structure are in Figure 19. Impurities used in this cell can be seen in Table 6.

To compare the results of this research with the results of other studies on single-junction solar cells and to determine the output location derived from this study, we can refer to the information presented in Table 7.

In Figure 20, we can compare the current–voltage curves of several different models of solar cells. These charts were extracted based on the results of the simulations carried out in this study as well as the reproduction of the work done by other researchers.

By comparing these diagrams, the trend of increasing the amount of short circuit current and open circuit voltage was observed.

In this study, considering that the modified CNTs structure was used as a surface enhancer, the main objectives of the study were introduced, the results of this study show that it is possible to use the application of multiple surface layers It is more favorable to absorb photon energy than the single-layer mode.

thumbnail Fig. 2

Simulation of the initial model in the Silvaco software for analyzing the structure of the solar cell layers.

Table 2

Verifying the regenerated parameters.

thumbnail Fig. 3

Solar cell meshing model for numerical simulation.

thumbnail Fig. 4

International Standard AM1.5G wavelength for Simulation of the Sunlight Spectrum (a) without CNT and (b) with CNT.

thumbnail Fig. 5

Standard wavelength curve AM1.5G alongside curve of transmitted light spectrum of semi-transparent CNTs.

thumbnail Fig. 6

Voltage–current curve of a solar cell without a CNT as improver layer (Voc = 1.01 V, Isc = 30.44 mA/cm2, FF = 86.35%, Eff = 25.40%).

thumbnail Fig. 7

Voltage–current curve of the solar cell has a CNTs recovery improver layer (Voc = 1.039 V, Isc = 32.08  mA/cm2, FF = 87.89%, Eff = 28.38%).

thumbnail Fig. 8

Current density without surface improver layer.

thumbnail Fig. 9

Current density with CNT surface improver layer.

thumbnail Fig. 10

Efficiency dependence on the thickness of the CNT layer [28].

Table 3

Results of the change in the thickness of the CNT layer [28].

thumbnail Fig. 11

Surface-level modeling with only one type of CNT (a) 128 Ω/squ and (b) 75 Ω/squ.

thumbnail Fig. 12

Two-layer surface-enhancement layer modeling with the difference in the arrangement of CNT layers without changing their thickness (a: 128 Ω/squ type on top and b: 75 Ω/squ type on top).

thumbnail Fig. 13

Three-layer superficial layer improvement modeling with the difference in the arrangement of CNT layers (a: 128 Ω/squ type in middle layer and b: 75 Ω/squ type in middle layer).

thumbnail Fig. 14

Five-layer superficial layer improvement modeling with the difference in the layout arrangement of CNT layers (a: double 75 Ω/squ type in middle layers and b: double 128 Ω/squ type in middle layers).

Table 4

Comparison of the results obtained from the number of CNT layers.

thumbnail Fig. 15

Voltage-current curve of the solar cell has a double CNT improver layer (Voc = 1.053 V, Isc = 33.05  mA/cm2, FF = 86.35%, Eff = 29.99%).

thumbnail Fig. 16

Comparison of solar cell efficiency with regard to the number of layers of surface CNTs.

Table 5

The effect of changing the thickness of layers in a 100 nm double-layer CNT.

thumbnail Fig. 17

Dependence of thickness efficiency and displacement of double layer CNTs.

thumbnail Fig. 18

Photon absorption rate in a solar cell with CNT improver layers.

thumbnail Fig. 19

Impurity of Solar Cell with double Nanotubes Layers.

Table 6

The thickness and impurity levels of the final solar cell layers.

Table 7

Comparison of final results obtained from single-junction solar cell performance with a Gallium-Arsenide structure.

thumbnail Fig. 20

Four current–voltage curves comparison (a non CNT layer, a 75 Ω/Squ CNT layer, a 128 Ω/Squ CNT layer and a double-CNT layer).

4 Conclusion

In this study, a solar cell without a CNT improver layer was first simulated using two-dimensional Silvaco software. Then, with the addition of the CNT improver layer, a one-step increase in efficiency was achieved due to the uniformity of the surface flow density of the solar cell and the same use of the entire surface of the device. Afterward, the effect of the number of CNT layers on the solar cell efficiency was studied for the conditions of one to five layers. It was observed that the maximum efficiency was obtained by using the two different improver layers. It was shown here that in order to have the maximum efficiency in a single-junction solar cell, it is possible to obtain a multilayer semi-transparent CNT semiconductor surface layer.

Author contribution statement

S.N. Jafari designed the model and the computational framework and analyzed the data. S.N. Jafari and A. Ghadimi carried out the implementation. S.N. Jafari and A. Ghadimi performed the calculations. S.N. Jafari and A. Ghadimi wrote the manuscript with input from all authors. S.N. Jafari, A. Ghadimi and S. Rouhi conceived the study and were in charge of overall direction and planning.

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1

Single Wall Carbon Nanotube.

Cite this article as: Seyed Nooreddin Jafari, Abbas Ghadimi, Saeed Rouhi, Improving the efficiency of GaAs solar cells using a double semi-transparent carbon nanotubes thin layer, Eur. Phys. J. Appl. Phys. 88, 20401 (2019)

All Tables

Table 1

Some of the parameters used in numerical simulation [21].

Table 2

Verifying the regenerated parameters.

Table 3

Results of the change in the thickness of the CNT layer [28].

Table 4

Comparison of the results obtained from the number of CNT layers.

Table 5

The effect of changing the thickness of layers in a 100 nm double-layer CNT.

Table 6

The thickness and impurity levels of the final solar cell layers.

Table 7

Comparison of final results obtained from single-junction solar cell performance with a Gallium-Arsenide structure.

All Figures

thumbnail Fig. 1

Gallium arsenide solar cell structure model with two thin CNTs as double load collector.

In the text
thumbnail Fig. 2

Simulation of the initial model in the Silvaco software for analyzing the structure of the solar cell layers.

In the text
thumbnail Fig. 3

Solar cell meshing model for numerical simulation.

In the text
thumbnail Fig. 4

International Standard AM1.5G wavelength for Simulation of the Sunlight Spectrum (a) without CNT and (b) with CNT.

In the text
thumbnail Fig. 5

Standard wavelength curve AM1.5G alongside curve of transmitted light spectrum of semi-transparent CNTs.

In the text
thumbnail Fig. 6

Voltage–current curve of a solar cell without a CNT as improver layer (Voc = 1.01 V, Isc = 30.44 mA/cm2, FF = 86.35%, Eff = 25.40%).

In the text
thumbnail Fig. 7

Voltage–current curve of the solar cell has a CNTs recovery improver layer (Voc = 1.039 V, Isc = 32.08  mA/cm2, FF = 87.89%, Eff = 28.38%).

In the text
thumbnail Fig. 8

Current density without surface improver layer.

In the text
thumbnail Fig. 9

Current density with CNT surface improver layer.

In the text
thumbnail Fig. 10

Efficiency dependence on the thickness of the CNT layer [28].

In the text
thumbnail Fig. 11

Surface-level modeling with only one type of CNT (a) 128 Ω/squ and (b) 75 Ω/squ.

In the text
thumbnail Fig. 12

Two-layer surface-enhancement layer modeling with the difference in the arrangement of CNT layers without changing their thickness (a: 128 Ω/squ type on top and b: 75 Ω/squ type on top).

In the text
thumbnail Fig. 13

Three-layer superficial layer improvement modeling with the difference in the arrangement of CNT layers (a: 128 Ω/squ type in middle layer and b: 75 Ω/squ type in middle layer).

In the text
thumbnail Fig. 14

Five-layer superficial layer improvement modeling with the difference in the layout arrangement of CNT layers (a: double 75 Ω/squ type in middle layers and b: double 128 Ω/squ type in middle layers).

In the text
thumbnail Fig. 15

Voltage-current curve of the solar cell has a double CNT improver layer (Voc = 1.053 V, Isc = 33.05  mA/cm2, FF = 86.35%, Eff = 29.99%).

In the text
thumbnail Fig. 16

Comparison of solar cell efficiency with regard to the number of layers of surface CNTs.

In the text
thumbnail Fig. 17

Dependence of thickness efficiency and displacement of double layer CNTs.

In the text
thumbnail Fig. 18

Photon absorption rate in a solar cell with CNT improver layers.

In the text
thumbnail Fig. 19

Impurity of Solar Cell with double Nanotubes Layers.

In the text
thumbnail Fig. 20

Four current–voltage curves comparison (a non CNT layer, a 75 Ω/Squ CNT layer, a 128 Ω/Squ CNT layer and a double-CNT layer).

In the text

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