Light-Trapping Characteristics of Ag Nanoparticles for Enhancing the

Subscriber access provided by Nanyang Technological Univ

Article

Light Trapping Characteristics of Ag Nanoparticles for Enhancing the Energy-Conversion Efficiency in Hybrid Solar Cells Zhi-qiang Fan, Wei-jia Zhang, Qiang Ma, Lanqin Yan, Lihua Xu, and Yao-long Fu ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.7b10347 • Publication Date (Web): 22 Sep 2017 Downloaded from http://pubs.acs.org on September 24, 2017

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

ACS Applied Materials & Interfaces is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 23

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Applied Materials & Interfaces

Light Trapping Characteristics of Ag Nanoparticles for Enhancing the Energy-Conversion Efficiency in Hybrid Solar Cells Zhiqiang Fan,† Weijia Zhang,*,† Qiang Ma,† Lanqin Yan,‡ Lihua Xu,‡ Yaolong Fu§ †

Center of Condensed Matter and Material Physics, School of Physics and Nuclear Energy Engineering, Beihang University, Beijing 100191, China ‡

National Center for Nanoscience and Technology, Beijing 100190, China

§

China Ordnance Industrial Standardization Research Institute, Beijing, 100189, China

*

Corresponding author. E-mail: [email protected]. Telephone number: 011+86+10+82338147

Abstract In this paper, we investigated the optical and electrical characteristics of the hybrid solar cells using silicon pyramid/Ag nanoparticles and nanowire/Ag nanoparticles nanocomposite structures, which are obtained by the Ag-assisted electro-less etching method. And we introduced the application of the physical and chemical properties for Ag nanoparticles on four kinds of solar cells: silicon pyramid, silicon pyramid /PEDOT:PSS silicon nanowrie, silicon nanowire/PEDOT:PSS. We simulated these structures with the absorption for different parameters. Furthermore, we also show the result of the current density- voltage (J-V) measurement with Ag nanoparticles which exhibits an improvement of power conversion efficiency in contrast to the samples without Ag nanoparticles. It was found that the properties of trapping light for Ag nanoparticles have a prominent impact on the improvement of power conversion efficiency in the hybrid solar cells.

Keywords: Ag nanoparticles, silicon nanowire, pyramid, solar cell, combined structure 1. Introduction Optical losses and electricity losses are the primary factors which affect the efficiency of solar cells1-6 and the main reason behind the optical losses is the reflection of silicon surface, 34% of optical losses are from the surface of polished silicon wafer. To improve the efficiency of solar cells, the reflectance must be reduced to 10% or less. Therefore, it is necessary to enhance the absorption of solar spectrum in the range of 0.3µm ~2.5µm from the earth surface.7-9 Light reflection and diffusion of surface or interface for the photovoltaic device may cause more energy loss，so an effective way to enhance the efficiency is to reduce the reflection of the incident light from the solar cell interface. Up to now, two methods have been applied. One way is to prepare the anti-reflection film on the solar cell surface. As the anti-reflection film, the silicon dioxide or silicon nitride transparent film with a quarter of incident light wavelength must be prepared by using the physical or chemical procedure on the upper surface of solar cells.10-12The other way is to prepare the anti-reflection structure on the upper surface of solar cell. This structure is prepared by using the traditional methods including acid or alkali wet etching, reactive ion etching, the 1

ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

photon/electron beam lithography and mechanical grooving method on the silicon surfaces.13-15 Fabrication of crystalline silicon solar cells consists of wafer slicing and texturing of its surface, and the texturing structure may reduce the light reflection. This means that more incident light has been absorbed by multiple reflections and refractions on the surface of the valid texturing structure, and more and more photon-generated carriers have also been obtained by the light trapping.15The application of silicon solar cell is limited by its high cost of raw material and low efficiency. Therefore, the reducing costs and energy-efficiency improvements in solar cells are the main directions of current research field. In addition to the attribution of material, the loss of efficiency in the silicon solar cell is caused by the physical design.16-17 i) Reflection loss: a fraction of the incident light has been reflected off the material surface, which leads to the efficiency loss. To improve the efficiency, we need to find a way to reduce the reflection. ii) Surface recombination loss: the photon-generated of electron-hole pairs may cause the recombination phenomenon on the surface. It leads to the reducing of the electron-hole pairs’ apart and the decrease in the current density. iii) Internal recombination loss: the photon-generated carries may cause the recombination phenomenon within the material by the material defects. iv) Increase the life time: the minority carrier lifetime can be increased with the addition of magnetic nanoparticles on the solar cell. v) Series resistor loss: the cause may produce the joule heat by the internal resistance of solar cell or the resistance of the circuit. vi) Voltage factor loss: the photon-generated carries may move because of the influence of internal electric field for depletion region on the p-n junction interface. Therefore, the moving carries produce the polarized electric charges, and a new electric field is obtained. Besides, it affects the value of internal voltage by the diffused of dopants. In order to improve the efficiency, it needs to reduce the light reflection. The efficiency has been increased by the light-trapping technology. The silicon nanowire with light trapping scheme has great potential solar energy utilization field.18-22 To achieve a high light absorption, the light field has been managed by this structure with the optimal shape. Because of the superior optical and electrical performance, the silicon nanowire is one of the hot topics in the research field of the nanometer materials.20, 23 Several methods have been developed to synthesize nanowire, including VLS( vapor-liquid-solid ) growth method,24 reactive ion etching method,25 electrochemical etching26-27 and metal-assisted chemical etching method.28-31 The metal-assisted chemical etching method has many advantages, such as simple equipment, easy and fast operation, low-cost manufacture, high productivity and high controllability. In the chemical reaction processing, deposition of Ag nanoparticle on the silicon surface and silicon etching all belong to the chemical battery reaction. In the initiation of reaction, the silver ions obtained an electron into the silver nanoparticles and attach to the silicon surface. The process of the silver icon deposition and the silicon wafer etching are simultaneous. The oxidation and reduction reaction proceed between the silver nanoparticle and silicon surface which are formed the primary battery can take place in the solution. The positive ion from silver layer is always transferred to the silicon surface. And then the silicon atom from the silicon wafer surface has reacted with the F- from the etching of solution to SiF62- , and the SiF62- is immediately dissolved into the solution. Furthermore, the silicon atom that attaches to the silver layer is dissolving into the solution with the etching reaction progress. The part of the silicon atom that is not attached to the silver layer and is not etched by the reactions and changed into the silicon nanowires. Finally, with the etching time on the silicon surface，a large-area nanowire arrays with a similar height are obtained.32 Therefore, this research 2


Page 2 of 23

Page 3 of 23

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


field attracts more and more attention from researchers all over the world. There are two primary factors that affect the reflection of silicon nanowire.28, 30 i) The nanowire silicon has a lot of small openings, these index is smaller than that of the planar silicon. Thus, the light reflection has been reduced on the interface of air/naowire. ii) The larger surface of nanowire may cause the multiple reflections between the adjacent nanowires. And the ability of light absorption for this structure has been improved by the extension of light propagation path. The light trapping characteristic of the nanowire structure is better than that of the planar silicon. The synthesis of nanowire and one to two dimensional structure for the composite structure have been already obtained, and the new structure for the metal nanoparticles doped into the nanowire has been applied in the solar cells.33-36 The Ag nanoparticles have many advantages: low cost manufacturing, simple equipment, high conductivity and plasmonic effect. Because of the plasmonic effect for the Ag nanoparticles, the efficiency of the solar cell may be improved by the increasing light absorption. It has been reported that the short-wavelength spectral and opto-electronic conversion properties of the inorganic/organic hybrid cells were enhanced by using Ag nanoparticles/Si nanoholes nanocomposite. Additionally, they found that the reason for the increasing efficiency of solar cell was mainly attributed to the localized surface plasmonic effect of Ag nanoparticles. 36M anisha Sharma and Pushpa Raj Pudasaini et al.34 also reported that the multipode Au/Ag bimetallic nanostructure was incorporated on the rear surface of an ultrathin planar c-silicon/organic polymer hybrid solar cell, and a power conversion efficiency value as high as 7.7% has been measured in the combined structure. However, because of the poor electrode contact and the bulk or surface recombination, the efficiency of combined structure is lower. In this paper, in order to reduce the loss of poor electrode contact and the bulk or surface recombination, the positive photoresist and TMAH( Tetramethylammonium hydroxide) solution have been applied in our experiment.3 We introduced the application of the physical and chemical properties for Ag nanoparticles on four kinds of solar cells: silicon pyramid, silicon pyramid /PEDOT:PSS, silicon nanowrie,37 and silicon nanowire/PEDOT:PSS, respectively.38-39 In addition, the combined light-trapping structure with the adding of Ag nanoparticle arrays on the silicon pyramid or nanowire solar cells have also been simulated. In the whole simulation, we defined that the radius of Ag nanoparticles (r = 10 nm) and the different height of silicon pyramid or nanowire array solar cell. The lower absorption for combined structure is more than the higher of absorption for pyramid or nanowire structure. Furthermore, the optical and electrical characteristics of the hybrid solar cells with or without Ag nanoparticles were investigated.

3



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 1. (a) and (b): schematic diagrams of the process flow in obtaining silicon pyramid and the combined structure of solar cells. Figure (c) and (d): Schematic diagrams of the process flow in obtaining silicon nanowire and the combined structure of solar cells. Figure (e) and (f): Schematic diagrams of the process flow in obtaining silicon nanowire / PEDOT:PSS and the combined structure of solar cells. The PEDOT:PSS layer was coated by the spin coater at 500rpm for 15s and 6000rpm for 45s to form Si/PEDOT:PSS heterojunction structure.

2. Experimental details 2.1 Silicon Pyramid Array Fabrication. In the experiment, n- type (100) silicon wafers (resistivity 1-10 Ω•cm) were used in the experiments. The back of silicon wafers were coated with several layers of positive photoresist (KMP-BP212-30) about approximately thickness of 420 nm and cured at 90°C for 60s (see Figure 1a). To obtain the silicon pyramid structure, the silicon wafers were then etched in a mixed solution of IPA, Na(OH) and deionized water with the ratio 64ml, 30g, 970ml for 45min under 90°C. Soon after the experiment, to remove the silicon dioxide, the pyramid wafers were immersed into a solution of 5% HF. Then, leaving behind photoresist for the back of sample, it was also immediately placed into the acetone solution. And then, a large-area pyramid arrays with a similar height are obtained on the silicon surface.

2.2 Silicon Nanowire Array Fabrication. The etching solution for silicon nanowire is different from the pyramid structure. Firstly, the silicon wafers were also coated with several layers of positive photoresist about approximately thickness of 420 nm and cured at 90°C for 60s (see Figure 1c). Secondly, to obtain the silicon nanowire structure, the samples were immediately placed into a solution containing 0.01M AgNO3 and 9.6M HF and stirred for 1.5min. And then the samples were immersed in an etchant composed of 9.6M HF and 0.6M H2O2 after Ag nanoparticles were deposited on the samples’ surface for 1h in the dark at the room temperature. Finally, the Ag catalyst and silicon dioxide were dissolved with dilute nitric acid solution 4


Page 4 of 23

Page 5 of 23

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(V /V O=1:1) and 5% HF at room temperature, respectively. To remove the photoresist for the back of sample, it was immediately placed into the acetone solution. And then, a large-area pyramid arrays with a similar height are obtained on the silicon surface. Then the samples has been treated by the solution of TMAH at 30s~60s.

2.3 Silicon Pyramid and Nanowire of Solar Cell. The nanowire-coated wafers and pyramid wafers were all diffused at 900°C with duration of 30 min by using liquid BBr3 as boron source. And then the depth of formed p-n junction was no more than 1µm. Consequently, the p-type region form via diffusion only occupied the upper surface and the lower surface was still n-type. After the removal of borosilicate glass from the upper surface and edge isolation, the electrode of back and front sides for the two structures were all deposited with approximately thickness of 400 nm silver using a thermal evaporator under a vacuum pressure of 4.5×10-4 mbar.37, 40-41 2.4 Silicon combined structure of Solar Cell. For the combined structure (pyramid + Ag nanoparticles and nanowire+ Ag nanoparticles ) solar cell, the samples were placed into a silver coating solution containing 0.001M AgNO3，9.6M HF，0.002M sodium citrate (C6H5Na3O7) and 1.0g.L-1 PVP for 5min, where were stirred in the magnetic water bath attached to a constant speed for 1.5min under the ambient atmosphere (see Figure.1b, 1d). The size of Ag nanoparticles has been controlled by the concentration, reaction time of the reaction solution. In order to study the application of the physical and chemical properties for Ag nanoparticles on the solar cells (silicon pyramid and silicon nanowrie), in the whole experiment, the process of Ag nanoparticles deposition is carried out under indentical experiment conditions. So the size of Ag nanoparticles from the combined structure (pyramid + Ag nanoparticles and nanowire+ Ag nanoparticles) is the same. And the size of Ag nanoparticles is approximately 96nm, as shown in Figure 3e1 and 3f1.

2.5 Silicon Pyramid, Nanowire and Combined/ PEDOT:PSS Solar Cell. In the experiment, clean n- type (100) silicon wafers (resistivity 1-10 Ω•cm) were used in the experiments. The back of samples were also coated with several layers of positive photoresist (KMP-BP212-30), whose thickness is approximately 420 nm and is cured at 90°C for 60s (see Fig.1e). And then the silicon pyramid, nanowire, combined (nanowire +Ag nanoparticles) structure was prepared by the chemical etching method. Then the samples were also treated by the solution of TMAH at 30s~60s.To improve the hydrophilicity of samples, they also were treated by the UV-ozone cleaner at 15mim. The PEDOT:PSS mixed with 1wt% Triton X-100 and 5 wt% dimethyl sulphoxide solution was stirred in the closed container for 1h before the samples were coated with this solution at 500rpm for 15s and 6000rpm for 45s to form Si/PEDOT:PSS heterojunction structure. Soon after the coating, the samples were thermal annealed to remove the solvent at 140°C in a dry atmosphere for 15min. To remove the photoresist for the sample, it was immediately placed into the acetone/methanol/deionized water. Finally, the electrode of back and front sides for the three structures were all deposited with approximately thickness of 200 nm gallium-indium alloy (Ga/In) and silver using a thermal evaporator under a vacuum pressure of 4.5×10-4 mbar, respectively (see Figure.1e,1f). 2.6 Characterization. The detailed procedure for fabricating ordered and uniform silicon pyramid, nanowire and combined structure of solar cells were presented in Figure 1. The simulations and experiments of solar cells will be discussed in detail in the following paragraphs. By the simulation based on Finite element method (FEM), the power flow distribution is simulated by 2D model and the TM illumination is discussed in different cells. The morphology of 5



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

silicon pyramid or nanowire array was characterized by field emission scanning electron microscope (FESEM, JSM-7500F, Japan). The reflectance of the samples was measured by Ultraviolet Photometer-1601. The performances of solar cells were characterized by using illuminated current-voltage under one sun global spectrum of AM1.5.

3、Results and discussion Firstly, we examined the light absorption at wavelengths of 300nm~700nm of the silicone solar cell with three different structures: pyramid, nanowire and combined array, as shown in Figure 2. By the simulation based on Finite element method (FEM),10, 42-44 the power flow distribution is simulated by 2D model and TM illumination is discussed in different physical thickness of silicon pyramid or different height of nanowire solar cell. The effect of this light-trapping structure on absorption of nanowire structure with the adding of Ag nanoparticles is also investigated, and all parameters are inspected. We assumed that the thickness of n layer and Al layer for all structures is 80nm and 50nm, respectively. The effect of incident light perpendicular to the surface of solar cells on the absorption was optimal, so the simulation based on vertically incident light. In the simulation, we defined the absorption of incident light for the silicon solar cell is α λ :

α λ =

|| |!" #×# |

Where S is the surface area of integrating region,

& '

|Re E+ × H+ | is the average energy

density, ω is the angular frequency of incident light, ε/ is the permittivity of vacuum, Imε ω is the imaginary part of material permittivity, E is the electric field intensity, V is the volume of calculation area. V0 is the volume of n layer and Al layer of solar cell, V1 is the volume of n layer, Al layer and p layer or p layer with Ag nanoparticels of solar cell. The absorption spectra of material under AM 1.5 spectrum is δ/ λ =

1 λ α λ

δ/ λ is the standard of photon flux density under AM1.5 spectrum. The total photons of absorption by integral to the whole range M λ of incident light wave (λ& to λ' ) are ;

M67689 = ; M λdλ

We define the model of Figure 2a as the reference model (M& ) and the pyramid structure of figure 2(b) is the new model (M2). In the numerical simulation, two models of solar cells M1 and M2 are the same volume. And the increased percent of light absorption for two models is Mabs.

M8 ?> >

× 100%

3.1 The optical characteristics of the silicon pyramid and nanowire solar cells.

6


Page 6 of 23

Page 7 of 23

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


（b1）

(a1)

(a2)

(b2)

(a3)

(a4)

(b4)

(b3)

(b5)

(c2)

(c1)

7



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(c3)

(c4)

(c5)

(d1)

(d3)

Page 8 of 23

(d2)

(d4)

(d5)

Figure 2. (a1) and (b1): schematic diagrams of the pyramid structure and the combined structure with the absorption for different height of pyramid arrays ( L = 40nm, 80nm, 120nm). Figure (b2): schematic diagrams of the percent increase of light absorption between the pyramid structure and the combined structure. The distribution of electric field intensity for pyramid and combined structure ( L= 40nm ) is also illustrated in the figure(a2)- (a4) and (b3)- (b5)with the incident wavelength ( λ = 315nm, 460nm, 700nm ), respectively. Figure (c1), (c2) and (d1), (d2): Schematic diagrams of the nanowire structure and combined structure with the absorption for different height of nanowire arrays ( L = 40nm, 80nm, 120nm, 160nm, 200nm ); The distribution of electric field intensity for nanowire structure and combined structure ( L= 160nm ) is also illustrated in the Figure c3- c5 and d3- d5with the incident wavelength ( λ = 315nm, 460nm, 700nm ), respectively.

Figure 2a1 and 2b1 illustrate the absorption spectra of silicon pyramid and the combined structure (silicon pyramid with Ag nanoparticles) with the absorption for different thickness or height (L = 40nm, 80nm, 120nm) of pyramid arrays. As observed in the Figure 2a1 and 2b1, in this 8


Page 9 of 23

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


two structures, the average absorptions of L=120 nm with the wavelength range of 300 – 700 nm based on silicon hybrid solar cells are 21.96% and 33.31%, the average absorptions of L=80 nm are 19.96% and 31.05%, the average absorptions of L=40 nm are 17.52% and 28.21%, respectively. As inspected, the light absorption of L=40 or L=80 nm is less than that of light L=120 nm in the three light absorption layer thickness. The film thickness of n region and Al region used in silicon solar cells are the same. The film thickness of silicon solar cell for L=40 nm or L=80 nm is less than the film thickness for L=120 nm. In the Figure 2b2, the percent increase of light absorption Mabs with three light absorption layer thickness is calculated. The maximum value of Mabs of L=120 nm is 157.05%，and then 69.4% of photon number for the combined solar cell was absorbed under AM 1.5 spectrum. It is more than the maximum value of Mabs of L=40 or L=80 nm. Moreover, the minimum value of Mabs of L=40nm with the light wavelength in the range of 400nm -700nm is 136.04%. Therefore, in the light wavelength in the range of 300nm -700nm, the absorption for combined solar cell is all higher than the pyramid structure. As inspected, the light absorption of L=40 or L=80 nm is less than the light absorption L=120 nm in the three light absorption layer thickness. In the Figure 2(a1, b1), due to the thicker film of p region and Ag nanoparticles, the pyramid Si solar cell or the combined structure increase the absorption of light. Furthermore, figure (a2)- (a4) and (b3)- (b5) present the distribution of electric field intensity for pyramid or combined structure (L= 40nm ) is illustrated with the incident wavelength ( λ = 315nm, 460nm, 700 nm ), respectively. Compared to the pyramid structure, the distribution of electric field intensity with the incident wavelength (λ = 315nm, 460nm, 700 nm ) absorbed markedly higher amounts of incident light , it is mainly attributable to the optimal of light trapping at the front sides of pyramid array with Ag nanoparticels. Figure 2c1 and 2d1 illustrate silicon nanowire arrays structure and the combined structure with the absorption for different height of nanowire arrays. In those two structures, we define the thickness of n region and Al region is 80nm and 50nm, respectively. In p region, we define the diameter and periodicity of silicon nanowire arrays is 17nm and 21 nm. In this simulation, the incident light is also vertical. Figure 2c2 and 2d2 illustrate the absorption spectra of silicon nanowire arrays structure and the combined structure with the absorption for different height of nanowire arrays (L = 40nm, 80nm, 120nm, 160nm and 200nm). The effect of this light-trapping structure on absorption of nanowire structure with the adding of Ag nanoparticles is also investigated, and all parameters are inspected. As observed in the Figure 2c2 ，the average absorption of height (L = 40nm, 80nm) for the silicon nanowire solar cell with the light wavelength range 300 nm -700 nm are 18.43% and 19.09%, the average absorption of height (L = 120nm, 160nm, 200nm) are 17.54% , 18.81% and 19.77%, respectively. As inspected, the light absorption of height (L = 40nm, 80nm, 120nm, 160nm) is less than the light absorption of height (L = 200nm) for the silicon nanowire solar cell. Thus, with the bigger height, the silicon nanowire solar cell is increasing the ability to absorb light. Figure 2c3 –c5 present the distribution of electric field intensity for this structure (L= 160 nm) is illustrated with the incident wavelength ( λ = 315nm, 460nm, 700 nm ), respectively. The distribution of electric field intensity with the incident wavelength (λ = 315nm) absorbed markedly higher amounts of incident light rather than the incident wavelength (λ = 460nm, 700 nm). Figure 2d1 illustrates the absorption on the combined structure with Ag nanoparticles decorated on the surface and the radius of Ag nanoparticles (r = 10 nm) and the height (L = 40nm, 80nm, 120nm, 160nm, 200nm) of silicon nanowire array solar cell has been applied．In this 9



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 2b 551 56 57 58 2b2 59 60

simulation, we define the model of Figure 2c1 as the reference model and the structure of Figure 2d1 as the combined model. As observed in the Figure 2d2，the average absorptions of Ag nanoparticles (r = 10 nm) for the height (L = 40nm, 80nm) of the combined model with the light wavelength range 300 nm -700 nm are 27.51% and 31.51%, the average absorptions of height (L = 120nm, 160nm, 200nm) are 34.82% , 35.85% and 36.92%, respectively. As inspected, the light absorption of height (L = 40nm, 80nm, 120nm, 160nm) is less than the light absorption height (L = 200nm) for the combined model. Moreover, compared to the nanowire structure, the lower absorption for combined structure is more than the higher of absorption for nanowire structure. It is mainly attributable to the optimal light trapping with Ag nanoparticles. Because the higher amounts of Ag nanoparticles have been decorated on the silicon nanowire solar cell, and it has caused the localized surface plasmon resonance (LSPR) phenomenon. L. Britnell et al.45 have reported the photovoltaic device with gold nanoparicles spattered on top of the top grapheme layer for plasmonic enhancement of light absorption. G.Santoro et al.46 have also reported correlate the morphological parameters of silver nanostructured thin films with silicon wafer with their Surface Enhanced Raman Scattering activity. In addition, Neelima Paul et al.47 have investigated the mechanism of gold nanostructure growth on a tailored CdSe quantum dot array to probe the templating possibilities. Their research has demonstrated that the use of metal nanoparticles in solar cell results in optical field enhancement and improvement of the optical absorption. The metal nanoparticles not only can confine the light surrounding the surface of solar cells, but also scatter and couple the incident light into the solar cell. And this performance may lead to the light absorption enhancement of solar cells. The localized surface plasmon resonance (LSPR) is the main mechanisms for the plasmonic light trapping systems.42,43-44 The LSPR is a characteristic of small metal nanoparticles and yilds very high field enhancement within a few nanometers from the metal nanoparticles surface. In the Figure 2d2, the peak absorption of combined structure by LSPR phenomenon with the incident light wavelength in the range of 400nm-450nm and 525nm-625nm has been changed with the blue shift on the size of Ag nanoparticles. Figure 2d3 –d5 present the distribution of electric field intensity for this structure (L= 160 nm) is illustrated with the incident wavelength (λ = 315nm, 460nm, 700 nm), respectively. The distribution of electric field intensity with the incident wavelength (λ = 315nm) also absorbed markedly higher amounts of incident light rather than the incident wavelength (λ = 460nm, 700 nm). The combined structure also causes strong field enhancement by the localized surface plasmon modes excited between the Ag nanoparticles and active layer on the surface. As a result, the absorption of silicon combined solar cell is enhanced around the edges of Ag nanoparticles.

3.2 The electrical characteristics of the silicon pyramid and nanowire solar cells.

10


Page 10 of 23

Page 11 of 23

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


a1

b1

c1

a2

b2

c2

a3

b3

c3

d1

e1

f1

d2

e2

f2

11



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

d3

e3

Page 12 of 23

f3

Figure 3. (a1)-(a2), (b1)-(b2) and (c1)-(c2): Schematic diagrams of surface and cross-sectional SEM images of silicon nanowire structure with different etching time (10min,15min and 20min). Figure (a3)-(c3): Schematic diagrams of reflectance spectra of three kinds of silicon nanowire structure. Figure (d1)-(d2), (e1)-(e2) and (f1)-(f2): Schematic diagrams of surface and cross-sectional SEM images of silicon nanowire structure for the silicon pyramid and combined structure (pyramid with Ag nanoparticles, nanowire with Ag nanoparticles) solar cells. Figure (d3)-(f3): Schematic diagrams of reflectance spectra of three kinds of structure.

Next, we examined the effects of light reflectance at wavelengths of 300nm~110nm on the silicone solar cell with four different structures: pyramid, nanowire and two combined arrays, which can be observed in Figure 3. Figure 3a1-f1 show scanning electron micrographs SEM images of silicon nanowire, pyramid, combined (pyramid with Ag nanoparticles, nanowire with Ag nanoparticles) structure. Figures 3(a1-c1) displays the SEM for three contrast groups with different etching time 10min, 15min and 20min, respectively. So many factors for the etching condition (such as define type, doping type, time, temperature, components of etchant) have been identified in affecting the surface morphologies of samples.48 With the almost of conditions unchanged, the length of nanowire have been determined by etching time. As can be seen in Figure 3d1 and 3d2, a tight and ordered silicon pyramid array was deposited on the silicon wafer. As shown in Figure 3(a1-d1), the surface color of silicon nanowire appeared black rather than pyramid structure, after the removal of the Ag nanoparticles by placing them into the dilute nitric acid solution (V /V O=1:1) for 2h. As shown in Figure 3(e1-f1), the surface and cross- sectional SEM image for the two combined structures(pyramid with Ag nanoparticles, nanowire with Ag nanoparticles) show that the Ag nanoparticles were deposited on the upper and lower surface of silicon pyramid and silicon nanowire (15min), respectively. And the surface color of combined structure appeared white rather than nanowire array, after Ag nanoparticles were deposited on the samples’ surface in the dark at the room temperature. Furthermore, panel’s a3 – f3 of Figure 3 also show the total reflections of four structures. Figure 3a3 -3d3 presents the total reflections of three contrast groups of nanowire array and pyramid structure. The average reflection of the pyramid array with the light wavelength in the range of 300nm-1100nm is 0.851%, the average reflection of three contrast groups for nanowire structure is 0.425%, 0.397% and 0.392%, respectively. The reflection of the silicon nanowire is much less than the pyramid structure. And then the silicon nanowire array with a lower reflection would trap the incident light more than the pyramid array. Moreover, Figure 3e3 and 3f3 also present the total reflection of two combined structures, the average reflection of three contrast groups (10min, 15min and 20min) for the combined structure is 0.406%, 0.373% and 0.339%, the average reflection of pyramid with Ag nanoparticles is 0.680%, respectively. The 12


Page 13 of 23

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


reflection of the combined structure is much less than the pyramid structure or nanowire array. Although the combined structure with a lower reflection would trap the incident light rather than the pyramid or nanowire array, whether the power conversion efficiency of solar cell based on the combined structure is better than the pyramid or nanowire array? To address this problem, we performed the experiment as following.

Table 1. Photovoltaic properties of the hybrid Si pyramid, nanowire and combined structures of solar cells with different etching time JSC

VOC

FF

（mA/cm2 ）（V）（%） Nanowire/10 min Nanowire/15 min Nanowire/20 min (Nanowire + Ag)/ 15min Pyramid Pyramid+ Ag

26.50 23.72 25.22 26.28 27.10 29.78

0.556 0.550 0.544 0.540 0.562 0.556

57 59 43 62 62 64

PCE （%）

8.40 7.70 5.90 8.80 9.40 10.6

Figure.4 J-V characteristics of the four structures of heterojunction solar cell based on the untreated and treated Si pyramid or nanowire with Ag nanoparticle under illumination.

All solar cells based on different structures were measured under AM 1.5G illumination, as shown in the current density- voltage (J-V) characterization in Figure 4 and Table 1. Table 1 shows the results of the J-V measurements of pyramid solar cell and nanowire solar cells under the standard test condition. The maximum current density JSC of silicon nanowire solar cells appears in nanowire/10min, of which the mean value of JSC is higher than nanowire/15min or 20min by 2.78 or 1.28 mA/cm' . But the mean value of JSC for pyramid is higher than nanowire/10min by 0.6 mA/cm' and is larger than nanowire/15min or 20min by3.38 or 1.88 mA/cm' . Moreover, it can be observed that the JSC of the solar cell with the pyramid and nanowire/15min is 27.1 mA/cm' and 23.72 mA/cm' . While that of the combined structures with (pyramid +Ag) and (nanowire + Ag)/15min are 29.78 mA/cm'and 26.28 mA/cm' . Thus, there was a significant increasing for light absorption from the combined solar cells to the untreated structures. On the 13



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

other hand, the performances of the combined solar cells were better than that of the untreated solar cells. This was in accordance with the markedly higher of light absorbed and lower of reflection by the structure, as shown in Figure 2(b1), 2(d2) and Figure 3(e3), 3(f3). It can be seen that the combined structure (nanowire/15min+ Ag) exhibited a power conversion efficiency of 8.8% (JSC =26.28 mA/cm', VOC =540 mV, FF = 62%). In contrast, one fabricated on the untreated structure has a conversion efficiency of 7.7% (JSC =23.72 mA/cm', VOC =550 mV, FF = 59%). And the pyramid structure exhibited a high conversion efficiency of 9.4% (JSC =27.1 mA/cm' , VOC =562 mV, FF = 62%). But the combined structure (pyramid+ Ag) exhibited a higher power conversion efficiency of 10.6% (JSC =29.78 mA/cm' , VOC =556 mV, FF = 64%). Compared to the silicon nanowire solar cells, the light trapping of silicon pyramid solar cell is low but the performance is not disappointing. And the conversion efficiency of nanowire/10min, nanowire/15min and nanowire/20min is reduced by 4%, 12.5% and 32.9% respectively, in contrast to the combined structure (nanowire/15min + Ag) solar cell, as shown in the set of Table 1. Moreover, the conversion efficiency of silicon pyramid solar cell is reduced by 11.3%, in contrast to the combined structure (pyramid + Ag) solar cell. Although the structure with the nanowire/15min and (nanowire + Ag)/15min exhibited a better light trapping ability, both the mean value of FF and V0C of the solar cell were similar and lower than that of the cell based on pyramid structure and (pyramid +Ag) , as shown in Table 1. This situation for the four structures can be attributed to two reasons: the poor electrode contact and the bulk or surface recombination.37 Firstly, the front surface of cells is usually destroyed in the certain area. In contrast to the pyramid solar cell, the front surface is rough, especially for the long etching time of nanowire solar cell. In the experiment, the front surface field is usually created by firing aluminum paste. The front surface field is the most important in forming the ohmic contact and passivating the front surface, and the absence of the front surface field may result in the increasing the front surface recombination. This situation for the front surface is as same as the back surface. Therefore, in our experiment, the back surface of silicon wafers was coated with several layers of positive photoresist before obtaining the silicon nanowire structure. When the samples were placed into the etchant solution, the back surface can be isolated from the etchant solution by the positive photoresist. Moreover, as shown in Table 1 and Figure 4, the fill factor (FF) of nanowire solar cell is worse than that of pyramid solar cell as the statistics showed. This is related to the poor electrode contact of nanowire -cells. The nanowire array decorated the surface of solar cell. Therefore, only the tips of nanowire arrays contacted with the Al electrode. The contact area has been reduced, and then the series resistance of nanowire solar cell has been increased. Consequently, the FF was correspondingly worsened. Secondly, the bulk and surface recombination is one of the possible reasons for the lower performance of the silicon nanowire solar cells than the silicon pyramid solar cell. As shown in Figures 3a1-3d1, the volume and surface area of silicon nanowire solar cell is more than the silicon pyramid solar cell. Assuming that the minority carrier lifetime and hole diffusion constant is not going to change, the photogenerated carriers has been collected after they transport a long distance along the nanowire. And then the process of carriers’ collection causes a larger bulk recombination in the silicon nanowire solar cell, although the silicon nanowire solar cell possesses the lowest reflectance compared with the silicon pyramid solar cell, as shown in Figure 3a3-3d3. Furthermore, the value of VOC is also related to the surface recombination of silicon nanowire and pyramid solar cells. As shown in Table 1 and Figure 4, the maximum open-circuit voltage VOC of silicon nanowire solar 14


Page 14 of 23

Page 15 of 23

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


cells appears in nanowire/10min, of which the value of VOC is 0.556 V. The open-circuit voltage VOC of silicon pyramid solar cell is 0.562 V, and it is more than the open-circuit voltage VOC of silicon nanowire solar cells. The total surface area of silicon nanowire solar cells is larger than that of silicon pyramid solar cells. Therefore, the surface recombination of silicon nanowire solar cells is higher than that of pyramid ones. Accordingly, the value of open-circuit voltage VOC for the silicon nanowire solar cells is reduced. Moreover, the length of nanowire/20min is the longest compared with the length of nanowire/10min or 15min. The density of nanowire arrays becomes larger with the increasing of etching time. Consequently, the surface recombination is strongly dependent on the surface area of the wafer, which may result in a great surface recombination with the increasing of etching time. As shown in Table 1, it can be observed that the VOC of the nanowire solar cells with three kinds of etching time is 0.556V , 0.550 V and 0.544 V. The minimum open-circuit voltage VOC of silicon nanowire solar cells appears in nanowire/20min, of which the value of VOC is 0.544 V. The solar cells with nanowire/20min arrays of smaller diameter have the largest surface area, which consequently exhibited lowest VOC.

3.3 The optical characteristics of the Silicon nanowire / PEDOT:PSS solar cell

(a2)

(a1)

(a3)

(a4)

(a5)

15



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(b1)

(b3)

(b2)

(b4)

(b5)

Figure 5. (a1) and (a2): schematic diagrams of the nanowire/PEDOT:PSS structure with the absorption for different height of nanowire arrays ( L = 40nm, 80nm, 120nm, 160nm and 200nm ); The distribution of electric field intensity for this structure ( L= 80nm ) is also illustrated in the Figure(a3), (a4) and (a5) with the incident wavelength ( λ = 300nm, 400nm and 700 nm ), respectively. (b1) and (b2):schematic diagrams of the combined structure (nanowire/PEDOT:PSS+ Ag nanoparticles) with the absorption for different height nanowire arrays ( L = 40nm, 80nm, 120nm, 160nm and 200nm ); The distribution of electric field intensity for this structure ( L= 80nm ) is illustrated in the Figure (b3) ,(b4) and (b5) with the incident wavelength (λ = 300nm, 400nm and 700 nm ).

Figure 5a1 and 5b1 illustrate the structure of silicon nanowire/PEDOT:PSS arrays structure and the combined structure with the absorption for different height of nanowire/PEDOT:PSS arrays. In two structures, we defined the thickness of PEDOT:PSS, n region and Ga/In region is 40nm, 80nm and 50nm, respectively. In n region, we defined the periodicity and diameter of silicon nanowire arrays is 26.7nm and 20 nm. In this simulation, the incident light is also vertical. Figure 5a2 and 5b2 illustrate the absorption spectra of silicon nanowire/PEDOT:PSS arrays structure and the combined structure with the absorption for different height of nanowire arrays (L = 40nm, 80nm, 120nm, 160nm, 200nm). As observed in the Figure 5a2，the average absorptions of height(L = 40nm, 80nm and 120nm)for the silicon nanowire solar cells with the incident light wavelength range 300 nm -700 nm are 22.69% and 22.71% and 22.85%, the average absorptions of height(L =160nm, 200nm) are 22.41% and 21.62%, respectively. As inspected, the light absorption of height (L = 40nm, 80nm, 160nm and 200nm) is less than the light absorption of height (L = 120nm) for the silicon nanowire/PEDOT:PSS solar cell. Figure 5a3 –a5 presents the distribution of electric field intensity for this structure (L= 80nm) is illustrated with the incident wavelength ( λ = 16


Page 16 of 23

Page 17 of 23

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


300nm, 400nm, 700 nm ), respectively. The distribution of electric field intensity with the incident wavelength (λ = 300nm) absorbed markedly higher amounts of incident light rather than the incident wavelength (λ = 400nm, 700 nm). Therefore, with the optimal height, the silicon nanowire/PEDOT:PSS solar cell increases the ability to absorb light. Figure 5b1 illustrates the absorption on the combined structure with Ag nanoparticles decorated on the surface and the radius of Ag nanoparticles (r = 10 nm) and the height (L = 40nm, 80nm, 120nm, 160nm and 200nm) of silicon nanowire/PEDOT:PSS array solar cell has been applied．As observed in the Figure 5b2，the average absorptions of Ag nanoparticles (r = 10 nm) for the height( L = 40nm, 80nm and 120nm)of the combined model with the light wavelength range 300 nm -700 nm are 23.13% and 23.69% and 23.63%, the average absorptions of height(L = 160nm and 200nm)are 23.81% and 24.03%, respectively. As inspected, the light absorption of height (L = 40nm, 80nm, 120nm, 160nm) is less than the light absorption height (L = 200nm) for the combined model. Moreover, compared to the nanowire/PEDOT:PSS structure, the lower of absorption for combined structure is more than the higher of absorption for nanowire/PEDOT:PSS strcture. It is mainly attributable to the optimal of light trapping with Ag nanoparticles. In the figure 5b2, the peak absorption of combined structure by LSPR phenomenon with the incident light wavelength in the range of 300nm-400nm has been changed more than nanowire/PEDOT:PSS structure. Figure 5b3 –b5 presents the distribution of electric field intensity for this combined structure (L= 80nm) is illustrated with the incident wavelength ( λ = 300nm, 400nm, 700 nm ), respectively. The distribution of electric field intensity with the incident wavelength (λ = 300nm) absorbed markedly higher amounts of incident light rather than the incident wavelength (λ = 400nm, 700 nm) with the addition of Ag nanoparticles. Moreover, the combined structure also causes strong field enhancement by the localized surface Plasmon modes excited between the Ag nanoparticles and the surface active layer. Consequently, the absorption of silicon combined solar cell is also enhanced around the edges of Ag nanoparticles. Whether the power conversion efficiency of solar cell based on the combined structure is also better than the nanowire/PEDOT:PSS array? To address this problem, we performed the experiment as following.

3.4 The electrical characteristics of the Silicon nanowire / PEDOT:PSS solar cell Table 2. Solar cells performance of the hybrid solar cells fabricated from Si pyramid ,nanowire and two combined structures. JSC VOC FF PCE

（mA/cm2 ）（V）（%） Nanowire (10min)/ PEDOT:PSS Nanowire (15min)/ PEDOT:PSS Nanowire (20min)/ PEDOT:PSS (Nanowire + Ag)(15min)/ PEDOT:PSS Pyramid / PEDOT:PSS (Pyramid + Ag) / PEDOT:PSS

25.10 25.30 25.10 26.10 25.20 26.82

0.358 0.520 0.382 0.506 0.556 0.530

17


63 49 61 53 60 64

（%） 5.66 6.55 5.90 7.00 8.44 9.10


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure

6.

J-V

characteristics

under

illumination

of

the

silicon

Page 18 of 23

pyramid/PEDOT:PSS

or

nannowire/PEDOT:PSS heterojunction solar cell based on the untreated and treated Si (pyramid+Ag or nanowire +Ag) /PEDOT:PSS.

Figure 6 shows the results of the J-V characteristics of pyramid/PEDOT:PSS solar cell and nanowire/PEDOT:PSS solar cells with different lengths under the standard test condition. All the characteristics parameters of the four kinds of cells are summarized in Table 2. The silicon nanowire(15min)/PEDOT:PSS solar cells possess the highest short circuit current density(JSC) of 25.3 mA/cm' and highest open circuit voltage(VOC) of 520 mV, rather than nanowire(10min or 20min)/PEDOT:PSS solar cells, which results in the highest power conversion efficiency of 6.55% among the three nanowire/PEDOT:PSS cells. The optoelectronic performance of shorter and longer length of silicon nanowires is poor. The reason is that the longer silicon nanowire is easy to form aggregation at the upper surface to prevent the organism going into the space of nanowires. Then comparing with the longer nanowire, the shorter silicon nanowire did not obtain large area for the silicon nanowire/PEDOT:PSS (core-shell) structure. The proper size of nanowire length may provide ideal environment for optoelectronic performance. To improve the solar efficiency for hybrid solar cells, most factors have been discussed in16 ， such as reducing carrier recombination, improving free carrier transport, enchancing the optical anti-reflection response and improving the open-circuit voltage and short-circuit current density. And the key factor is directly associated with the short-circuit current density. What’s more, it can be observed that the JSC of the solar cell with the combined structure with (nanowire + Ag)( 15min) PEDOT:PSS is 26.10 mA/cm' , it is higher than nanowire (15min) by 0.8 mA/cm' , and more than nanowire(10min) or (20min) by 1.0 mA/cm' . The JSC of the solar cell with the combined structure with (pyramid+ Ag) PEDOT:PSS is 26.82 mA/cm' , it is higher than pyramid structure by1.62mA/cm'. Thus, there was a significant increase for light absorption from the combined solar cell to the untreated structure. On the other hand, the performance of the combined/PEDOT:PSS solar cells were better than that of nanowire/PEDOT:PSS solar cells. This is in accordance with the markedly higher of light absorbed by the structure, as shown in Figure 5(b2). It can be seen that the combined (nanowire + Ag) /PEDOT:PSS structure exhibited a power conversion efficiency of 7% (JSC =26.1 mA/cm' , VOC =506 mV, FF = 53%). In contrast, the one fabricated on the untreated structure has a conversion efficiency of 6.55% (JSC =25.3 mA/cm' , VOC =520 mV, FF = 49%). Furthermore, the pyramid/PEDOT:PSS structure also exhibited a high conversion efficiency of 8.44% (JSC =25.2 mA/cm' , VOC =556 mV, FF = 60%), but the combined 18


Page 19 of 23

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


structure (pyramid+ Ag) /PEDOT:PSS exhibited a higher power conversion efficiency of 9.1% (JSC =26.82 mA/cm', VOC =530 mV, FF = 64%). Thus, there was a significant increasing for power conversion efficiency from the combined solar cell to the untreated structure. Compared to the untreated structure (the structure without Ag nanoparticles) of the solar cell, the combined structure (the structure with Ag nanoparticles) of solar cells light trapping of is high but the performance is also not disappointing. The conversion efficiency of (nanowire + Ag)( 15min) PEDOT:PSS is increased by 6.4%, in contrast to the silicon nanowire(15min) PEDOT:PSS solar cell. Moreover, in contrast to the pyramid/PEDOT:PSS, the conversion efficiency of (pyramid+ Ag) /PEDOT:PSS is increased by7.2%, as shown in the set of Table 2. This means that the properties of trapping light for Ag nanoparticles have a prominent impact on the improvement of power conversion efficiency for the hybrid solar cells. As shown in the Figure 4, Table 1and Figure 6 and Table 2, the power conversion efficiency of solar cell based on the combined structure is better than the untreated structure. The power conversion efficiency of solar cells is increased with the adding of Ag nanoparticle arrays. The changed tread of silicon- PEDOT:PSS solar cells is the same as the solar cells without PEDOT:PSS which means that the silver nanoparticles have been deposited on the two different structures of solar cell, it will be affected on the power conversion efficiency of solar cells. Additionally, the power conversion efficiency presents increasing trend.

4. Conclusions In this paper, we introduced the application of the physical and chemical properties for Ag nanoparticles on four kinds of solar cells: silicon pyramid, silicon pyramid/PEDOT:PSS, silicon nanowrie and silicon nanowire/PEDOT:PSS. We have simulated the absorption of silicon pyramid and pyramid with Ag nanoparticles structure for different height of pyramid arrays. We also defined that the pyramid structure is the reference model. The increase percent of light absorption Mabs with three light absorption layer thickness for the two models is investigated. Moreover, we have simulated a combined light-trapping structure with the adding of Ag nanoparticle arrays on the silicon nanowire solar cell. The structure without Ag nanoparticles is the reference model. By comparing the absorption and the optimal electric field intensity distribution of the two models, the ability to absorb light of combined model is better than that of reference model. In the whole simulation, the trapping-light method of Ag nanoparticles is an essential technique. Finally, we have experimentally demonstrated the current density- voltage characterization of four structures. The power conversion efficiency of solar cell based on the combined structure is better than that of untreated structure. Furthermore, similar to the silicon nanowire solar cell, the silicon nanowire/PEDOT:PSS is also simulated and experimentally demonstrated with the adding of Ag nanoparticle arrays. In the whole experiment, the properties of trapping light for Ag nanoparticles have a prominent impact on the improvement of power conversion efficiency for the hybrid solar cells.

Acknowledgment This study was supported by the National Natural Science Foundation of China (Grant no. 51572008). 19



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Reference 1.

Chen, Y.; Xu, Z. D.; Gartia, M. R.; Whitlock, D.; Lian, Y. G.; Liu, G. L., Ultrahigh Throughput Silicon

Nanomanufacturing by Simultaneous Reactive Ion Synthesis and Etching. Acs Nano 2011, 5 (10), 8002-8012. 2.

Wang, H. P.; Lin, T. Y.; Hsu, C. W.; Tsai, M. L.; Huang, C. H.; Wei, W. R.; Huang, M. Y.; Chien, Y. J.;

Yang, P. C.; Liu, C. W.; Chou, L. J.; He, J. H., Realizing High-Efficiency Omnidirectional n-Type Si Solar Cells via the Hierarchical Architecture Concept with Radial Junctions. Acs Nano 2013, 7 (10), 9325-9335. 3.

Wang, F. Y.; Jiang, Y. J.; Li, T. T.; Zhao, Y.; Zhang, X. D., Increasing Efficiency of Hierarchical

Nanostructured Heterojunction Solar Cells to 16.3% Via Controlling Interface Recombination. J.Mater.Chem.A 2015, 3 (45), 22902-22907. 4.

Kim, D. R.; Lee, C. H.; Rao, P. M.; Cho, I. S.; Zheng, X., Hybrid Si Microwire and Planar Solar Cells:

Passivation and Characterization. Nano Lett. 2011, 11 (7), 2704-2708. 5.

Liu, Y.; Zhang, Z.-g.; Xia, Z.; Zhang, J.; Liu, Y.; Liang, F.; Li, Y.; Song, T.; Yu, X.; Lee, S.-t.; Sun, B., High

Performance Nanostructured Silicon–Organic Quasi p–n Junction Solar Cells via Low-Temperature Deposited Hole and Electron Selective Layer. Acs Nano 2016, 10 (1), 704-712. 6.

Kelzenberg, M. D.; Boettcher, S. W.; Petykiewicz, J. A.; Turner-Evans, D. B.; Putnam, M. C.; Warren,

E. L.; Spurgeon, J. M.; Briggs, R. M.; Lewis, N. S.; Atwater, H. A., Enhanced Absorption and Carrier Collection in Si Wire Arrays for Photovoltaic Applications. Nat. Mater. 2010, 9 (3), 239-244. 7.

Yoon, S.; Turner, G.; Garboushian, V.; Ieee, Thin, Lightweight, 18% Efficient Space Silicon Solar Cell

and Array. IEEE Photovoltaic Spec. Conf., 25th. 1996; p 259-262. 8.

Kurtz, S. R.; Oneill, M. J.; Ieee, Estimating and Controlling Chromatic Aberration Losses for

Two-junction, Two-terminal Devices in Refractive Concentrator Systems. IEEE Photovoltaic Spec. Conf., 25th.1996; p 361-364. 9.

Hegedus, S. S.; Deng, X. M.; Ieee, Analysis of 0ptical Enhancement in a-Si n-i-p Solar Cells Using A

Detachable Back Reflector. IEEE Photovoltaic Spec. Conf., 25th. 1996; p 1061-1064. 10. Jia, Y. K.; Yang, S. E.; Guo, Q. N.; Chen, Y. S.; Gao, X. Y.; Gu, J. H.; Lu, J. X., Optimal Design of Light Trapping Structure for Broadband Absorption Enhancement in Amorphous Silicon Solar Cell. Acta Phys. Sin. 2013, 62 (24), 247801. 11. Huo, F. R.; Li, Y. F.; To, S.; Liu, T. C.; Xue, C. X., Optimal Design of Broadband Antireflective Subwavelength Gratings for Solar Applications. Optik 2015, 126 (20), 2626-2628. 12. Jung, J. Y.; Um, H. D.; Jee, S. W.; Park, K. T.; Bang, J. H.; Lee, J. H., Optimal Design for Antireflective Si Nanowire Solar Cells. Sol. Energy Mater. Sol. Cells 2013, 112, 84-90. 13. Lee, S. G.; Lee, K. I.; Seo, C. K.; Lee, J. U.; Choi, Y.; Nam, B.; Yu, J. Y.; Jeong, J. K., Optimal Design of Antireflective Layer for DUV Lithography and Their Experimental Results. IEEE Advances in Res.Tech.Process. Conf., 14th.1997; Vol. 3049, p 409-418. 14. Deinega, A.; Valuev, I.; Potapkin, B.; Lozovik, Y., Antireflective Properties of Pyramidally Textured Surfaces. Opt. Lett. 2010, 35 (2), 106-108. 15. Krc, J.; Smole, F.; Topic, M., Advanced Optical Design of Tandem Micromorph Silicon Solar Sells. J. Non-Cryst. Solids 2006, 352 (9-20), 1892-1895. 16. Moiz, S. A.; Nahhas, A. M.; Um, H.-D.; Jee, S.-W.; Cho, H. K.; Kim, S.-W.; Lee, J.-H., A Stamped PEDOT:PSS-Silicon Nanowire Hybrid Solar Cell. Nanotechnology 2012, 23 (14), 145401. 17. Zhao, J. H.; Wang, A. H.; Altermatt, P. P.; Zhang, G. C., Peripheral Loss Reduction of High Efficiency 20


Page 20 of 23

Page 21 of 23

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Silicon Solar Cells by MOS Gate Passivation, by Poly-Si Filled Grooves and by Cell Pattern Design. Prog. Photovoltaics 2000, 8 (2), 201-210. 18. Lin, C. X.; Povinelli, M. L., Optical Absorption Enhancement in Silicon Nanowire Arrays with A Large Lattice Constant for Photovoltaic Applications. Opt. express 2009, 17 (22), 19371-19381. 19. Zhu, J.; Yu, Z. F.; Burkhard, G. F.; Hsu, C. M.; Connor, S. T.; Xu, Y. Q.; Wang, Q.; McGehee, M.; Fan, S. H.; Cui, Y., Optical Absorption Enhancement in Amorphous Silicon Nanowire and Nanocone Arrays. Nano Lett. 2009, 9 (1), 279-282. 20. Khan, F.; Baek, S. H.; Kim, J. H., Novel Approach for Fabrication of Buried Contact Silicon Nanowire Solar Cells with Improved Performance. Sol. Energy 2016, 137, 122-128. 21. Garnett, E.; Yang, P. D., Light Trapping in Silicon Nanowire Solar Cells. Nano Lett. 2010, 10 (3), 1082-1087. 22. Li, J. S.; Yu, H. Y.; Li, Y. L., Aligned Si Nanowire-based Solar Cells. Nanoscale 2011, 3 (12), 4888-4900. 23. Xie, W. Q.; Oh, J. I.; Shen, W. Z., Realization of Effective Light Trapping and Omnidirectional Antireflection in Smooth Surface Silicon Nanowire Arrays. Nanotechnology 2011, 22 (6), 065704. 24. Misra, S.; Yu, L. W.; Foldyna, M.; Cabarrocas, P. R. I., High Efficiency and Stable Hydrogenated Amorphous Silicon Radial Junction Solar Cells Built on VLS-grown Silicon Nanowires. Sol. Energy Mater. Sol.Cells 2013, 118, 90-95. 25. Cho, C.; Kong, D.; Oh, J. H.; Kim, B.; Lee, B.; Lee, J., Surface Texturing Method for Silicon Solar Cell Using Reactive Ion Etching with Metal Mesh. Phys. Status Solidi A 2014, 211 (8), 1844-1849. 26. Liu, J.; Zhang, X. S.; Dong, G. Q.; Liao, Y. X.; Wang, B.; Zhang, T. C.; Yi, F. T., Fabrication of Silicon Nanopillar Arrays by Cesium Chloride Self-assembly and Wet Electrochemical Etching for Solar Cell. Appl. Surf. Sci. 2014, 289, 300-305. 27. Wang, R. C.; Chao, C. Y.; Su, W. S., Electrochemically Controlled Fabrication of Lightly Doped Porous Si Nanowire Arrays with Excellent Antireflective and Self-cleaning Properties. Acta Mater. 2012, 60 (5), 2097-2103. 28. Fang, H.; Wu, Y.; Zhao, J. H.; Zhu, J., Silver Catalysis in the Fabrication of Silicon Nanowire Arrays. Nanotechnology 2006, 17 (15), 3768-3774. 29. Zhang, M.-L.; Peng, K.-Q.; Fan, X.; Jie, J.-S.; Zhang, R.-Q.; Lee, S.-T.; Wong, N.-B., Preparation of Large-area Uniform Silicon Nanowires Arrays Through Metal-Assisted Chemical Etching. J. Phy. Chem. C 2008, 112 (12), 4444-4450. 30. Fan, Z.; Zhang, W.; Fu, Y.; Yan, L.; Ma, X., Facile Synthesis of Silicon Micropillar Arrays Using Extreme Ultraviolet Lithography and Ag-Assisted Chemical Etching Method. J. Phy. Chem. C 2016, 120 (12), 6824-6834. 31. Peng, K. Q.; Hu, J. J.; Yan, Y. J.; Wu, Y.; Fang, H.; Xu, Y.; Lee, S. T.; Zhu, J., Fabrication of Single-Crystalline Silicon Nanowires by Scratching A Silicon Surface with Catalytic Metal Particles. Adv. Funct. Mater. 2006, 16 (3), 387-394. 32. Huang, Z. P.; Geyer, N.; Werner, P.; de Boor, J.; Gosele, U., Metal-Assisted Chemical Etching of Silicon: A Review. Adv. Mater. 2011, 23 (2), 285-308. 33. Bai, F.; Li, M.; Huang, R.; Song, D.; Jiang, B.; Li, Y., Template-free Fabrication of Silicon Micropillar/Nanowire Composite Structure by One-Step Etching. Nanoscale Res. Lett. 2012, 7, 557. 34. Sharma, M.; Pudasaini, P. R.; Ruiz-Zepeda, F.; Vinogradova, E.; Ayon, A. A., Plasmonic Effects of Au/Ag Bimetallic Multispiked Nanoparticles for Photovoltaic Applications. ACS Appl. Mater. interfaces 2014, 6 (17), 15472-15479. 21



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

35. Ishwor, K.; Qiming, L.; Keiji, U.; Hajime, S., Improved Performance of Poly(3,4-ethylenedioxythiophene):Poly(stylene sulfonate)/n-Si Hybrid Solar Cell by Incorporating Silver Nanoparticles. Jpn. J. Appl. Phys. 2014, 53 (11), 110305. 36. Liu, Z. X.; Xu, L.; Zhang, W. P.; Ge, Z. Y.; Xu, J.; Su, W. N.; Yu, Y.; Ma, Z. Y.; Chen, K. J., Extended Short-Wavelength Spectral Response of Organic/(Silver Nanoparticles/Si Nanoholes Nanocomposite Films) Hybrid Solar Cells Due to Localized Surface Plasmon Resonance. Appl. Surf. Sci. 2015, 334, 110-114. 37. Li, H.; Jia, R.; Chen, C.; Xing, Z.; Ding, W.; Meng, Y.; Wu, D.; Liu, X.; Ye, T., Influence of Nanowires Length on Performance of Crystalline Silicon Solar Cell. Appl. Phys. Lett. 2011, 98 (15), 151116. 38. Gong, X.; Jiang, Y.; Li, M.; Liu, H.; Ma, H., Hybrid Tapered Silicon Nanowire/PEDOT:PSS Solar Cells. Rsc Adv. 2015, 5 (14), 10310-10317. 39. Zhang, F.; Song, T.; Sun, B., Conjugated Polymer-Silicon Nanowire Array Hybrid Schottky Diode for Solar Cell Application. Nanotechnology 2012, 23 (19), 194006. 40. Dou, B.; Jia, R.; Li, H.; Chen, C.; Ding, W.; Meng, Y.; Xing, Z.; Liu, X.; Ye, T., High Performance Radial p-n Junction Solar Cell Based on Silicon Nanopillar Array with Enhanced Decoupling Mechanism. Appl. Phys. Lett. 2012, 101 (18), 829-889. 41. Oh, I.; Kye, J.; Hwang, S., Enhanced Photoelectrochemical Hydrogen Production from Silicon Nanowire Array Photocathode. Nano Lett. 2012, 12 (1), 298-302. 42. Shen, H. H.; Bienstman, P.; Maes, B., Plasmonic Absorption Enhancement in Organic Solar Cells with Thin Active Layers. J. Appl. Phys. 2009, 106 (7), 073109. 43. Shan, F.; Zhang, T.; Zhu, S.-Q., Effects of Ag Nanocubes with Different Corner Shape on the Absorption Enhancement in Organic Solar Cells. J. Nanomater. 2014, 827658. 44. Li, X.; Hylton, N. P.; Giannini, V.; Lee, K.-H.; Ekins-Daukes, N. J.; Maier, S. A., Bridging Electromagnetic and Carrier Transport Calculations for Three-dimensional Modelling of Plasmonic Solar Cells. Opt. express 2011, 19 (14), A888-A896. 45. Britnell, L.; Ribeiro, R. M.; Eckmann, A.; Jalil, R.; Belle, B. D.; Mishchenko, A.; Kim, Y. J.; Gorbachev, R. V.; Georgiou, T.; Morozov, S. V.; Grigorenko, A. N.; Geim, A. K.; Casiraghi, C.; Castro Neto, A. H.; Novoselov, K. S., Strong Light-Matter Interactions in Heterostructures of Atomically Thin Films. Sci. 2013, 340 (6138), 1311-1314. 46. Santoro, G.; Yu, S.; Schwartzkopf, M.; Zhang, P.; Vayalil, S. K.; Risch, J. F. H.; Rubhausen, M. A.; Hernandez, M.; Domingo, C.; Roth, S. V., Silver Substrates for Surface Enhanced Raman Scattering: Correlation Between Nanostructure and Raman Scattering Enhancement. Appl. Phys. Lett. 2014, 104 (24), 243107. 47. Paul, N.; Metwalli, E.; Yao, Y.; Schwartzkopf, M.; Yu, S.; Roth, S. V.; Muller-Buschbaum, P.; Paul, A., Templating Growth of Gold Nanostructures with a CdSe Quantum Dot Array. Nanoscale 2015, 7 (21), 9703-9714. 48. Zhang, M. L.; Peng, K. Q.; Fan, X.; Jie, J. S.; Zhang, R. Q.; Lee, S. T.; Wong, N. B., Preparation of Large-area Uniform Silicon Nanowires Arrays Through Metal-Assisted Chemical Etching. J. Phy. Chem. C 2008, 112 (12), 4444-4450.

22


Page 22 of 23

Page 23 of 23

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Table of Contents

23


Light-Trapping Characteristics of Ag Nanoparticles for Enhancing the

Recommend Documents