Article_RefinedOptoelectronicPropertie

See discussions, stats, and author profiles for this publication at https//www.researchgate.net/publication/348161236 Refined optoelectronic properties of silicon nanowires for improving photovoltaic properties of crystalline solar cells a simulation study Article in Journal of Materials Science Materials in Electronics February 2021 DOI 10.1007/s10854-020-05031-w CITATION1 READS127 6 authors, including Some of the authors of this publication are also working on these related projects Organic Solar Cell View project ARC on silicon solar cell View project Deb Kumar Shah Chonbuk National University 21 PUBLICATIONS 40 CITATIONS SEE PROFILE Devendra Kc UiT - The Arctic University of Norway, campus Narvik 16 PUBLICATIONS 17 CITATIONS SEE PROFILE M. Shaheer Akhtar Chonbuk National University 259 PUBLICATIONS 5,340 CITATIONS SEE PROFILE All content following this page was uploaded by Deb Kumar Shah on 26 January 2021. The user has requested enhancement of the downloaded file. Refined optoelectronic properties of silicon nanowires for improving photovoltaic properties of crystalline solar cells a simulation study Deb Kumar Shah 1 , Jaeho Choi 2 , Devendra KC 3 , M. Shaheer Akhtar 1,2,4, * , Chong Yeal Kim 2 , and O-Bong Yang 1,2,4, * 1 School of Semiconductor and Chemical Engineering, Jeonbuk National University, Jeonju 54896, Republic of Korea 2 New and Renewable Energy Materials Development Center NewREC, Jeonbuk National University, Jeonbuk 56332, Republic of Korea 3 Electrical Department, Gabriel Elektro AS, 9700 Lakselv, Norway 4 Graduate School of Integrated Energy-AI, Jeonbuk National University, Jeonju 54896, Republic of Korea Received 17 August 2020 Accepted 1 December 2020 C211 The Authors, under exclusive licence to Springer ScienceBusiness Media, LLC part of Springer Nature 2021 ABSTRACT Tremendous works have been devoted on reducing the materials costs and searching a low-cost antireflection AR layer in silicon Si solar cells. This work reports on the surface architectural of Si wafer p-type by growing the nano- wires NWs-like structures through cost-effective wet-controlled etching method. The nanostructures over Si wafer were optimized in terms of sizes, lengths and densities by changing the etching conditions and thoroughly examined their growth and optoelectrical properties. The well-defined grown NWs textured on Si wafer exhibited the low average reflectance of * 2.25 in the full visible-NIR spectrum from 400 to 1000 nm which was well matched to the simulated average reflectance of 2.23. A model was designed using PC1D simulation to evaluate the photovoltaic PV parameters of NWs textured Si wafer-based solar cells without AR layer. In this simulation, the length of SiNWs and reflectance were selected as input parameters to instigate the power con- version and quantum efficiencies of solar cells. The highest conversion efficiency of * 16.2 is observed when the average length of SiNWs and reflectance were * 2.52 lm and * 2.25, respectively. Experimentally, the fabricated SiNWs- based solar cell with etching time of 20 min attained the highest conversion efficiency of 15.9 and the value was very close to simulated results. PV parameters of SiNWs-based solar cells without AR layer were comparable to commercial c-Si solar cells with SiNx AR layer. Thus, the controlled wet etching is an easy, facile method for fabrication of nanowires on Si wafer with low reflectance. The enhancement in optical and electrical properties would be Address correspondence to E-mail shaheerakhtarjbnu.ac.kr; obyangjbnu.ac.kr https//doi.org/10.1007/s10854-020-05031-w J Mater Sci Mater Electron expected to a great prospect in developing low-cost c-Si solar cells without AR layer. 1 Introduction In search of invaluable renewable source, the crys- talline silicon c-Si solar cell technology has been established as prosperous renewable technology for supplying the commercial energy [1, 2]. So far, the c-Si-based PV technology is leading in the PV market with maximum power conversion efficiency PCE over *20 and life span of 25-year guarantee [3]. In recent year, the PCE of c-Si solar cells is being con- stant and there is no significant improvement in PV performances. Until now, the c-Si solar cells are fac- ing the reflection losses, exciton generation losses and improper light absorbance [4]. The reduction in the reflection losses on Si surface is the possible and effective way to enhance the light absorbance and rate generation of electron–hole pairs [5, 6]. The bare silicon wafer surface generally presents the 30 reflection which can be reduced less than 10 by creating the AR layer on Si wafer [4]. In commercial c-Si solar cells, the AR coating was performed by deposition of Si 3 N 4 layer through an expensive and complex process of plasma-enhanced chemical vapor deposition PECVD, which would cause the increase of production cost of solar cell. However, a problem of low short-circuit current density J SC is associated to Si 3 N 4 AR layer, because the high amount of fixed positive charges in Si 3 N 4 layer facilitates to create an inversion layer at Si/Si 3 N 4 interface. Hence, the effective tool for improving the surface losses and conversion efficiency of c-Si solar cells is the surface texturing of Si wafer, which might reduce the reflection of light and improved the optoelectronic properties [7]. In c-Si solar cell, the surface texturing on Si wafer is crucial step, as it enhances the light absorption with less front surface reflection, internal multiple reflec- tion, and increased light path lengths inside the cell [8]. In commercial c-Si solar cell, the pyramidal tex- tured Si wafers have been used, but sometimes they have a tendency to show light diffraction and become apparent in the long wavelength range [9, 10]. SiNWs, one-dimensional 1D semiconductors, are optically and electronically very active compared to 2D or 3D surfaces. Typically, the SiNWs on Si wafer effectively suppressed reflection and improved the light scattering and trapping behavior in Si wafer due to its elevated absorption of incident light [11, 12]. The SiNWs under illumination pose the serious recombination of photogenerated electron–hole pairs, which normally results in the low efficiency com- pared to pyramidal surface textured in Si wafer [13]. To overcome this serious problem, a proper surface passivation on SiNWs is necessary for achieving high PCE of solar cells. The surface texturing by chemical method such as controlled chemical etching might be the process to make NWs as well as surface passi- vation at the same time. Several texturing processes, such as acid texturization, reactive ion etching, mechanical texturization, have been used for the surface texturing of Si wafer [14]. The reactive ion etching methods, especially wet etching, show the ease of 1D growth, good reproducible results, and highly uniform nanowires or nanorods growth on Si surface. The optical and electrical properties of SiNWs are normally relied on the wire diameter, length and periodicity [15, 16]. Therefore, the precise control of conditions during wet reactive ion etching is needed to obtain high-quality passivated SiNWs for solar cell applications. In this work, the controlled wet reactive ion etching of p-type Si wafer was con- ducted to grow uniform NWs and the simulation study to evaluate the PV parameters of SiNWs-based solar cells without AR layer was performed. The influence of etching parameters like time on the morphological and optical properties of SiNWs is investigated to know the optimum Si wet etching. The fabricated SiNWs on Si solar cell was thoroughly characterized in terms of morphology, structure, crystalline nature, optical and photovoltaic properties PC1D simulation. The PV parameters of SiNWs wafer were further characterized through Personal Computer One-Dimensional PC1D simulation tool [17] by choosing length of SiNWs and average reflectance as input parameters. The optimum PCE of 16.2 is achieved at 2.52 lm of SiNW length with minimum reflectance 2.25 by this simulation tool. J Mater Sci Mater Electron 2 Experimental details 2.1 Fabrication of SiNWs via wet-chemical etching Commercial p-type c-Si wafers 40 9 40 mm 2 witha thickness of 120 lm and sheet resistance of 1–3 X cm were used as a substrate. Before performing the etching, the c-Si wafer was thoroughly cleaned by the sonication using ethanol, isopropanol and DI water for 15 min each. For silver metal layer deposition, the mixture of 0.17 g of AgNO 3 , 10 ml of HF and 90 ml of DI water was used wherein the cleaned c-Si wafer was dipped until the color of Si surface changed to light yellow color. During formation of Ag layer, silver ions in the vicinity of Si surface that captured electrons from Si and metallic Ag nuclei were uni- formly formed, as shown in Fig. 1. On the other hand, the etching solution was prepared by mixing of 10 ml of HF 48 wt, 1 ml of H 2 O 2 30 wt and 40 ml of H 2 O. The formed Ag covered c-Si wafer was immersed in the etching solution with the etching time varied from 5 to 50 min. As illustrated in Fig. 1, the Si atom near Ag nanoparticles were first oxidized to SiO 2 and then dissolved by HF to form SiF 6 2- , leading to the etching of Ag nanoparticles into the wafer to obtain the SiNWs. The lengths of SiNWs were optimized by controlling the etching time 5 to 50 min with definite concentration of etching solu- tion. The residual Ag nanoparticles were removed from the nanowires surfaces by carefully washing with DI water and then it was treated with diluted HNO 3 solution 65 wt for 15 min for further removal of residual Ag nanoparticles. Finally, the fabricated SiNWs were dried in oven at 70 C176C for 2 h. 2.2 Fabrication of SiNWs solar cells The fabricated p-type SiNWs wafer from the wet- chemical etching was utilized for the fabrication of solar cells. During the etching process, well-defined nanowires-like textures were grown on p-type Si wafer. In order to create the PN junction, the SiNWs wafers were placed into the quartz boat and the boat was placed in the middle of quartz tube for per- forming the phosphorus diffusion in a quartz fur- nace. The diffusion process was carried out by elevated the furnace temperature to 780 C176C along with a POCl 3 gas flow of 1200 sccm. After diffusion, p-doped n-layer on both Si surfaces was formed and the resistance of *75 X/h which was the indication of n–p–n junction formation was obtained. The phosphorous glass PSG over the surface of n–p–n structure was removed by 5 HF solution. To com- plete the cell fabrication, the screen printing was applied to perform the front side metallization of p–n junction SiNWs using Ag paste SOL-9610, Heraeus materials Singapore PTE Ltd. and rear side was screen printed by Al paste SOLMA-A153, Dongjin Semichem Co., Ltd., Korea. The metal-coated p–n Fig. 1 Schematic diagram of fabricating SiNWs on the surface of Si wafer J Mater Sci Mater Electron junction SiNWs was placed on the conveyor belt for co-firing at 700–800 C176C which usually results in the proper bonding between Ag to Si surface. 2.3 Parameters of PC1D simulation The numerical modeling software PC1D has been used to simulate photovoltaic properties of c-Si solar cells, which was developed by the University of New South Wales, Australia [18]. PC1D allows to simulate the behavior of photovoltaic structures based on semiconductor by regarding to one-dimensional ax- ial symmetry. The PC1D contains libraries files with the parameters of the crystalline semiconductors used in various photovoltaic technologies such as the GaAS, a-Si, AlGaAs, Si, InP and Ge. The files of the solar spectrum are also available in this software mainly AM0 and AM1.5 spectrum [19]. The simula- tion of Si solar cell is carried out by setting up key parameters, which include device area, thickness, bulk recombination time, carrier concentration, bandgap, dielectric constant, etc. It can simulate the reflection and light trapping for alkaline-textured solar cells and predict the electrical performance of textured solar cell devices [20]. These tools enable higher level solar cell production line simulators, such as the Virtual Production Line VPL to relate the effects of different texturing conditions e.g., chemical composition, time and temperature on final device electrical performance [21]. In this work, the area and thickness of c-Si wafers were chosen as 16 cm 2 and 120 lm, respectively. The simulation was performed under AM 1.5 solar radiation and constant light intensity of 0.1 W/cm 2 one sun at 300 K tem- perature. For all PV simulation, the bulk recombina- tion time was set to 10 ls and p-type background doping concentration of the solar cell was set as 1.153 9 10 16 cm -3 and first front diffusion N-type 2.87 9 10 20 cm -3 peak. The details of input parame- ters in PC1D simulation are summarized in Table 1. 2.4 Characterizations The fabricated SiNWs on Si substrates were charac- terized by a variety of analytical, spectroscopic and photovoltaic measurement techniques. For microstructure and surface morphology, the field emission scanning electron microscopy FESEM, Hitachi 4800, Japan, FESEM coupled energy disper- sive X-Ray EDAX and transmission electron microscopy TEM, JEM-2010, JEOL, Japan analyses were used. A piece of SiNWs substrate was put into ethanol and strongly sonicated for NWs dispersion which was finally dispersed on the copper grid for TEM analysis. The optical property such as reflec- tance of fabricated SiNWs was investigated by ultraviolet diffuse reflectance spectroscopy UV-DRS, Shimadzu MPC-3100 in the wavelength range of 300–1200 nm. The lifetime mapping of fabricated SiNWs was measured to explain the surface bulk charge carrier lifetime and sheet resistance of fabri- cated silicon substrate has been measured. The sub- strates are also characterized by Photo-luminance spectroscopy for the measurement of absorbance. The details photovoltaic properties were estimated by PC1D simulation by taking length of SiNWs and average reflectance as input key parameters. The photovoltaic parameters of fabricated SiNWs-based solar cells were carried out by taking the current I– voltage V characteristics using ABET Technologies sun 3000-solar simulator. 3 Results and discussion The growth and length of SiNWs were measured by FESEM and TEM analysis tools. Figure 2 shows the cross-sectional view of SiNWs with respect to the etching time ranging from 1 to 50 min. The vertically Table 1 Summary of all the primary parameters used in the PC1D simulation Parameters Values Device area 16 cm 2 Front surface texture depth 0–5 lm Front reflectance 2–4 Thickness of Si solar cell 120 lm Dielectric constant 11.9 Energy band gap 1.124 eV Background doping P-type 1.513 9 10 16 cm -3 First front diffusion N-type 2.87 9 10 20 cm -3 Refractive index 3.58 Excitation