Porous Silicon Solar Cells Research Articles

Performance stability of porous silicon solar cells using reduced graphene oxide for applications in harsh environments

The impact of graphene on the photovoltaic stability of solar cells made of porous silicon (PSi) is discussed in this research. Here, reduced graphene oxide (rGO) capping layers electrophoretically deposited on PSi substrates were used to regulate the photoluminescence (PL) quenching of the PSi substrates. The samples' morphology showed that after graphene transfer, the porosity structure remained unaltered, and rGO layers completely covered the PSi surface. The rGO layers were successfully deposited on PSi substrates, according to the Raman analysis of the rGO/PSi, which revealed two prominent peaks corresponding to the G and D graphene bands. Additionally, the D-mode intensity was higher than the G-band intensity, showing that the deposited rGO layers had fewer structural defects and irregularities. The stability of the optical properties of PSi substrates was tested by comparing the PL spectra before and after graphene deposition. The findings demonstrated that the PL quenching of rGO-capped PSi structure was mitigated even after prolonged exposure to laser light. Therefore, the optical consistency of PSi samples was enhanced through deposition of graphene layers. Then, bare and rGO-covered PSi substrates were used to fabricate heterojunction solar cells, and their current-voltage results were measured under a solar light simulator at various temperatures. The optoelectrical tests showed that the availability of unstable species, such as hydrogen bonds on the PSi surface, caused a reduction in the efficiency of bare PSi devices at high temperatures. These terminations changed due to temperature changes, which decreased the photovoltaic performance of PSi substrates. This deterioration was moderated when graphene was transferred, which improved the photovoltaic stability of PSi-based solar cells. The rGO capping layer increased the electrical stability of fabricated solar cell based on PSi substrate during temperature changes.

Effect of increasing etching time on the efficiency of porous silicon solar cells

In this work, p-type silicon wafers were electrochemically etched to create nanocrystalline silicon (porous silicon (PS)) films. Different etching periods (5, 10, 15, and 20 minutes) were investigated to see how they affected the development of a nanosized pore array with a constant etching current density (10 mA/cm2). To prevent oxidation, PS samples were stored in methanol after preparation. PS is characterized by X-ray diffraction (XRD), and atomic force microscopy (AFM). At varied etching times (5, 10, 15, and 20 min), the crystallite size as determined by XRD was equal to (66.39, 88.13, 31.2, and 21.21) nm, respectively. The nanometric size was verified via AFM. The porosity of PS increased as the etching time increased; the maximum value was obtained at a 20-minute etching time. The C-V characteristic of PS/Si heterojunction describes control factors like built-in potential (Vbi) and the kind of connection, a linear relationship of 1/C2 with bias voltage indicating that the junction is an abrupt type. Vbi was calculated for PS/p-Si/Al heterojunction at different etching times, and it was between (1.1-1.8) volt. I-V characteristics under illumination showed an enhancement in the efficiency of the PS/Si/Al solar cells. The maximum value of the solar cell efficiency was 6.79% occurs at 15 min time of etching.

Enhancing Photovoltaic Performance of Porous Silicon Solar Cells with Al2O3 Nanoparticles prepared by electrolysis method

In this work nanocrystalline porous silicon (PSi) prepared by electrochemical etching of p type silicon wafers. PSi is characterised by means of XRD, FTIR and AFM. Crystallites length become expected with the aid of X-Ray diffraction. Atomic Force microscopy confirmed the nanometric size. Colloidal Al2O3 nanoparticles prepared via electrolysis method and deposited using drop-casting method as a thin film. The structural, morphological, optical homes of Al2O3 NPs were investigated. The effect of Al2O3 NPs diffusion at the holes of PSi sun mobile have stated which exhibits an improvement in (Ag/Al2O3/PSi/Si/Al) solar cell performance.

Porous silicon solar cells with 13.66% efficiency achieved by employing graphene-quantum-dots interfacial layer, doped-graphene electrode, and bathocuproine back-surface passivation layer

Formation of Porous Si (PSi) enhances the light absorption of Si thanks to the increased surface-to-volume ratio, useful for improving the power conversion efficiency (PCE) of Si-based solar cells. Here, we first employ graphene quantum dots (GQDs) as an interfacial layer for better band alignment at the graphene (GR) transparent conductive electrode (TCE)/PSi interface. The PCE exhibits a maximum of 13.66%, highest ever achieved in GR/PSi solar cells, by doping the GR TCE and passivating the Si back surface in addition to the GQDs interfacial layer. The use of the interfacial and the passivating layers results in the reduction of the carrier recombination at the GR TCE/PSi and Si/cathode interfaces, respectively. The cell also shows excellent long-term stability by maintaining 84% of its original PCE even in air for 30 days.

Nanostructure of Porous Si and Anodic SiO2 Surface Passivation for Improved Efficiency Porous Si Solar Cells.

The photovoltaic effect in the anodic formation of silicon dioxide (SiO2) on porous silicon (PS) surfaces was investigated toward developing a potential passivation technique to achieve high efficiency nanostructured Si solar cells. The PS layers were prepared by electrochemical anodization in hydrofluoric acid (HF) containing electrolyte. An anodic SiO2 layer was formed on the PS surface via a bottom-up anodization mechanism in HCl/H2O solution at room temperature. The thickness of the oxide layer for surface passivation was precisely controlled by adjusting the anodizing current density and the passivation time, for optimal oxidation on the PS layer while maintaining its original nanostructure. HRTEM characterization of the microstructure of the PS layer confirms an atomic lattice matching at the PS/Si interface. The dependence of photovoltaic performance, series resistance, and shunt resistance on passivation time was examined. Due to sufficient passivation on the PS surface, a sample with anodization duration of 30 s achieved the best conversion efficiency of 10.7%. The external quantum efficiency (EQE) and internal quantum efficiency (IQE) indicate a significant decrease in reflectivity due to the PS anti-reflection property and indicate superior performance due to SiO2 surface passivation. In conclusion, the surface of PS solar cells could be successfully passivated by electrochemical anodization.

Effect of ZnO nanoparticles deposition on porous silicon solar cell

Zinc Oxide (ZnO) thin film was prepared by using a Pulse Laser Deposition (PLD) method which was deposited on a porous silicon layer. The structural and morphological properties of the deposited film were characterized. The results showed that the optical properties analyses have high absorption in ultra violate region and wide bandgap within a value around (3.7) e.V. the results obtained that the structural feature film has a crystalline hexagonal structure and its grain size around 17.5 nm. Furthermore, the solar cell efficiency improved after ZnO nanoparticle deposition to be around 15.6% compared to 10.56% for porous silicon solar cells.

Investigation of Porous Silicon Layers Properties Using Speckle Techniques for Photovoltaic Applications

Speckle imaging technique (SIT) is used as non-destructive testing to obtain indicative speckle patterns with the aim to be applied for photovoltaic solar cells. These speckle patterns are mainly characterized by their contrast and optical density (OD), which give indications for the properties of the solar cell. In the current work, the porous silicon layers (PSLs) acting as an anti-reflection coating (ARC) formed with different surface porosities are prepared on n+p textured crystalline CZ- silicon by electrochemical etching (ECE) in HF-based electrolyte using different current densities. The morphological properties of the PSLs are investigated by scanning electron microscopy (SEM). The optical properties of the textured surfaces are studied using photoluminescence “PL” and reflectivity measurements. The band gap energy of the prepared PSLs increases to 1.89 eV. The reflectivity of the PSLs decreases to 0.75% in a wavelength range (350–750) nm. The current-voltage (I-V) characteristics of Ag/PS/n + p/Ag junction are investigated which reveal an increment in the resulting short-circuit current density and the open-circuit voltage up to 2.96 mA/cm2 and 0.385 V, respectively. These results show an improvement in the fill factor by 48.5%. The inspected properties of the porous silicon solar cells exhibit a correlation with the contrast and the OD of the speckle patterns imaged from these cells.

Optical Properties of Porous Silicon Solar Cells for Use in Transport

Porous silicon (pSi) samples were prepared by electrochemical etching of p-type silicon (p-type Si) substrate. Three pSi samples with different parameters of electrochemical etching (electrical potential, etching time, etching current) were prepared and analyzed. We studied the influence of electrochemical etching parameters on spectral reflectance of pSi structure. A modification of interference pattern was observed due to changes of microstructure. We determined the thickness of pSi layers from spectral reflectance. Solar cells with a porous structure achieve high efficiency and long life. These solar cells are predestined for use in transport.

IMPROVING THE PHOTORESPONSE OF POROUS SILICON FOR SOLAR CELL APPLICATIONS BY EMBEDDING OF CdTe NANOPARTICLES

The present work is concerned with the preparation of thin films of nanocrystalline porous silicon (PSi) by the method of electrochemical etching. CdTe nanoparticles (NPs) have been prepared by utilizing the pulsed laser ablation in liquid. The measurements of tunneling microscopy, X-ray diffraction (XRD), Fourier transformation infrared spectroscopy (FTIR) and atomic force microscopy (AFE) were carried out and revealed that the PSi was nanostructured and the produced CdTe NPs were ball shaped, having good disposability. The diffusion of CdTe NPs on the properties of PSi solar cell assures that there was an improvement upon their properties. The relationship between [Formula: see text] and the reverse bias voltage was observed to be linear. Values of the built-in potential were observed to be dependent on the laser fluence, current density and the etching time.

POROUS SILICON SOLAR CELL WITH ANTI-REFLECTION COATING LAYER FOR EFFICIENCY IMPROVED

Ponte Academic JournalMay 2016, Volume 72, Issue 5 POROUS SILICON SOLAR CELL WITH ANTI-REFLECTION COATING LAYER FOR EFFICIENCY IMPROVEDAuthor(s): Khalid Omar ,Khaldun A. SalmanJ. Ponte - May 2016 - Volume 72 - Issue 5 doi: 10.21506/j.ponte.2016.5.32 Abstract:A porous silicon layer was prepared by electrochemical etching and a zinc oxide film was deposited on a porous silicon layer using a radio frequency sputtering system. The surface morphology of the porous silicon and zinc oxide/porous silicon layers was characterized using scanning electron microscopy. Nano-pores were produced in the porous silicon layer with an average diameter of 5.8 nm, which increased the porosity to 83%. The photoluminescence emission spectra of the zinc oxide/porous silicon layers present three emission peaks, two peaks located at 385 and 603 nm due to the zinc oxide nanocrystalline film and a third located at 638 nm due to nanocrystalline porous silicon. Optical reflectance for all the layers was obtained using an optical reflectometer. The lowest effective reflectance was obtained for the zinc oxide/porous silicon layers. The fabrication of crystalline silicon solar cells based on the zinc oxide/porous silicon anti-reflection coating layers was performed. The I-V characteristics of the solar cells were studied. The zinc oxide/porous silicon layers were found to be an excellent anti-reflection coating and to exhibit exceptional light-trapping at wavelengths ranging from 400 to 1000 nm, which led to a high efficiency of the crystalline silicon solar cell of 15.49 % compared to 12.35% efficiency for the crystalline silicon solar cell with a porous silicon anti-reflection coating layer. The zinc oxide/porous silicon anti-reflection coating layers enhance and increase the efficiency of the crystalline silicon solar cell. Download full text:Check if you have access through your login credentials or your institution Username Password

Concept and Nanostructure Control of Plasmonic Porous Silicon Solar Cells

[Introduction]A multi-junction solar cell can generate high open current voltage by each layer absorbing a different wavelength light, although lattice mismatch between materials is one of its problems. A possible new type of solar cell is an all-Si tandem solar cell, which will have no mismatch. Our laboratory noticed that porous silicon is a light-absorbing material for short wavelengths. Its nano-scale holes on its surface increases its band gap due to the quantum size effect. Because this porous structure, however, leads to high resistivity and low absorption coefficient, the porous layer must be made thinner by enhancing light absorption. To improve light absorption, we propose using localized surface plasmon of metal nanoparticles [1, 2]. By such introduction of these particles into the holes of porous silicon, a thinner porous layer can be also achieved. Here, we proposed this plasmonic porous silicon solar cell (or PPSSC), and aimed to control the structure of porous silicon. To determine guidelines for fabricating PPSSCs, we created solar cells consisting of porous silicon, and then measured their I-Vcharacteristics. By simulation, we estimated the enhancement of light absorption of porous silicon with metal nanoparticles. [Experimental]1. Preparation of porous silicon: Here, p-type monocrystalline silicon wafers with three different resistivities were anodized for different times and current density. The surfaces and cross-sections were then observed by field emission scanning electron microscopy (FE-SEM) and evaluated using UV-vis spectrum. Several wafers were also treated with Ar dry etching, and its effect on their surface structure observed. 2. Fabrication of solar cells: An n-type silicon layer was deposited on top of the porous silicon by chemical vapor deposition (CVD) using SiH4 and PH3 in H2. Silver electrodes were fabricated using RF sputtering, and then their rectification property and quantum efficiency were measured. 3. FDTD simulation: With the Finite-Different-Time-Domain (FDTD) method, we created a simulation model in which silver nanoparticles exist in the holes on the silicon surface. The simulation showed how the light absorption in this combined material is enhanced by adding silver nanoparticles to the porous silicon. Then, the necessary layer thickness of porous layer was estimated by the model, and the influence of localized surface plasmon was verified by investigating the strength of the electrical field near the interface between the silicon and silver nanoparticles. [Results and Discussion] 1.Structure control of porous silicon: By changing the anodization time and current density, we successfully fabricated porous silicon of various pore size, depth, and porosity. Figure 1 shows the relationship between current density I and pore diameter. In addition, results reveal that dry etching expands the pore size of a porous silicon surface (Fig. 2), indicating that dry etching might facilitate both the introduction of metal nanoparticles and the control of band gaps. 2.Evaluation of porous silicon solar cells: Figure 3 shows that a thin n-type silicon layer was successfully deposited on the porous silicon by CVD. Figure 4 shows that p-n junctions were also formed by this deposition. However, compared with a monocrystalline silicon solar cell (Fig.5), porous silicon solar cells tended to have a smaller increase rate of I than that of V. One factor in this trend is the high resistivity of porous silicon, indicating that making the porous silicon layer thinner is important to increase the efficiency of PPSSCs. Figure 6 compares the quantum efficiency of porous silicon and monocrystalline silicon solar cells, revealing that porous silicon solar cells have lower quantum efficiency. One explanation is that insufficient deposition of n-type silicon onto the porous silicon accelerates surface recombination. This surface recombination can be improved by performing passivation. 3.Evaluation of combined materials by simulation: FDTD simulation indicated that the light absorption of the combined materials can be improved when the silver nanoparticles exist in the holes of porous silicon, and that a strong electrical field is injected into the silicon around the interface between silicon and the silver nanoparticles. These results indicate that localized surface plasmon might improve light absorption and enhance thinner porous silicon as a light absorption layer. [Conclusion] Current density, resistivity of wafers, and dry etching can be factors in controlling the structure of porous silicon. We successfully formed p-n junctions with porous silicon, and based on the measured I-Vcharacteristics and quantum efficiency of porous silicon solar cells, the porous silicon needs to be thinner and needs passivation. The simulations suggest that metal nanoparticles enhance the light absorption.

(Invited) Nanometer-Distance Control in Plasmonic Dye-Sensitized Solar Cells and Applications of Localized Surface Plasmon to Next Generation of Solar Cells

When metal nanoparticles (NP), such as silver (Ag) and gold (Au), are irradiated by sunlight, their localized surface plasmon is excited, thus causing light scattering and light absorption. The ratio of light absorption to scattering strongly depends on the particle size. In general, when the nanoparticles are larger than 100 nm in diameter, the extinction of light is dominated by scattering; this property is applied to anti-reflection or light trapping for solar cells. When the metal nanoparticles are smaller than several tens of nanometers, light extinction is dominated by light absorption, and this light absorption generates near-field light accompanied by a strong electric field. In 1997, we previously introduced the concept of a dye-sensitized solar cell that utilizes localized surface plasmons and is thus called a “plasmonic DSSC” [1]. In this DSSC, near-field light is used to enhance both the photoabsorption of Ru-dye and the generation of photoelectrons. By introducing AgNPs into a film of N3 dye, the absorbance of the dye can be increased by a factor of 149. Absorption enhancement has also been reported when the composite films are formed with AuNPs and black dye (BD). A key factor for enhancing the photoabsorption of a plasmonic DSSC with such a composite film is an overlap in the photoabsorption spectra between the metal nanoparticles and the dye. [2] In this paper, we summarized our enhancements of DSSCs by using localized surface plasmon with focusing on the nanometer-distance control between metal NP, dyes and TiO2. Furthermore, the applications of localized surface plasmon to next generation of solar cells will be introduced. The types of solar cells suitable for applying localized surface plasmon will comprehensively be discussed. Plasmonic dye-sensitized solar cells DSSC with AgNPs showed improved photoelectric conversion efficiency (Eff ) of 2.5%, compared with about 1.5% for a DSSC without AgNPs [3]. In that study, to clarify the effect of AgNPs on the power generation characteristics, the TiO2 film of the DSSC was 2 μm thick, which is thinner than that for a typical DSSC (~10 μm). An optimal thickness of the TiO2 film should exist for capturing sunlight while preventing back charge transfer. The dependence of TiO2 thickness on the performance of a DSSC with metal nanoparticles had been investigated. [4] The level of electric field enhancement around AuNPs strongly depends on parameters such as the dielectric constant, distance from the surface of the particle, particle size, particle shape, and light wavelength, and thus depends on the combination of materials and their surface state. The length and conformation of the surface modulator is critical to determine the distance between the dyes, metal nanoparticles and TiO2. [5] Figure 1 shows the schematic of nanometer-distance control using a surface modulator in DSSC. Attempting to highly control the distance, the hybridization of the peptide nucleic acide (PNA), which has similar structure to deoxyribonucleic acid (DNA), was used to improve the efficiency of DSSC. The Eff of DSSC was enhanced from 3.1% to 4.0% by the incertion of Ag NP with PNA bonded with TiO2. [6] Applications of localized surface plasmon to next generation of solar cells The following applications of localized surface plasmon to several kinds of solar cell (Plasomonic unti-reflecting coating for silicon solar cells [7], Plasmonic extremely thin absorber (ETA) solar cells [8, 9], Plasmonic interlayer for multijunction solar cells [10], and Plasmonic porous silicon solar cells) will be sumarized. At same time, the suitable type of solar cells for the applying will be discussed with considering the principle of each solar cell. Finally, I will introduce the concept of silicon nanowire tandem solar cells under the project of “FUTURE-PV Innovation”. Acknowledgement A part of this work was supported by the MEXT, FUTURE－PV Innovation Project.

A New Method of Reduce Monocrystalline Silicon Solar Cells Surface Reflection by Silver Mirror Reaction

A new approach is in the pretreatment polishing silicon surface formed silver electrode through silver mirror reaction and put them into HF and hydrogen peroxide to reach electrochemical corrosion conditions according to the chemical cell reaction, formed the porous structure of silicon surface. The porous silicon solar cells in a wavelength region of 400–800nm showed a surface reflectance below 15% milder than the conventional solutions.

Sensitization of Porous Silicon with Germanium Quantum Dots for Up-Conversion of Low Energy Photons via Intermediate Band for Third Generation Solar Cells

Incorporation of germanium quantum dots (QDs) in porous silicon (PS) promises foundation of efficient intermediate band (IB) within the bandgap of the host material. We have developed the idealized model for such material system intended to be used for third generation solar cells. We solved Schrodinger equation for a chain of Ge nanodots embedded in a pore of columnar porous silicon material. We have shown that holes induce narrow energy band lined up with the forbidden band gap of Si and spreads over some distance from the chain into Si. The last feature is very desirable for efficient operation of IB structure associated with PS solar cells.

Current improvement of porous silicon photovoltaic devices by using double layer porous silicon structure: applicable in porous silicon solar cells

The photoluminescence (PL) phenomena of porous silicon (PS) samples with different etching times were examined to find out a relationship between PL emission energy (experimental value of PS band gap energy) and the etching time for fabrication of double (two) layer porous silicon sample on one silicon substrate. The dependence of PL Peak energy with etching time was discussed. A double layer PS structure was formed by using two electrochemical reactions with different etching times of 20 and 10 min, respectively. The photovoltaic (PV) properties of mono layer and double layer porous silicon PV devices were examined and compared. The main result is the enhanced short-circuit current (Isc) of double layer PS structure compared to monolayer ones.

Erbium doped stain etched porous silicon

In this work a simple erbium doping process applied to stain etched porous silicon layers (PSLs) is proposed. This doping process has been developed for application in porous silicon solar cells, where conventional erbium doping processes are not affordable because of the high processing cost and technical difficulties. The PSLs were formed by immersion in a HF/HNO 3 solution to properly adjust the porosity and pore thickness to an optimal doping of the porous structure. After the formation of the porous structure, the PSLs were analyzed by means of nitrogen BET (Brunauer, Emmett and Teller) area measurements and scanning electron microscopy. Subsequently, the PSLs were immersed in a saturated erbium nitrate solution in order to cover the porous surface. Then, the samples were subjected to a thermal process to activate the Er 3+ ions. Different temperatures and annealing times were used in this process. The photoluminescence of the PSLs was evaluated before and after the doping processes and the composition was analyzed by Fourier transform IR spectroscopy.

Effects of illumination and 60Co γ-ray irradiation on the electrical characteristics of porous silicon solar cells

A new approach for hybrid metal–insulator–semiconductor (MIS) Si solar cells is adopted by Institute of Fundamental Problems for High Technology, Ukrainian Academy of Sciences. In order to interpret the effect of illumination and 60Co γ-ray radiation dose on the electrical characteristics of solar cells are studied at room temperature. Before the solar cells are subjected to stressed irradiation six different illumination levels of forward and reverse bias I– V measurements are carried out at room temperature. The solar cells are irradiated with 60Co γ-ray source irradiation, with a dose rate of 2.12 kGy/h and an over dose range from 0 to 500 kGy. Experimental results shows that both the values of capacitance and conductance increase with increasing illumination levels and give the peaks at high illumination levels. γ-ray irradiation induces an increase in the barrier heights Φ b( C– V) which are obtained from reverse-bias C– V measurements, whereas barrier heights Φ b( I– V) which are deducted from forward-bias I– V measurements remain essentially constant. This negligible change of Φ b( I– V) is attributed to the low barrier height (BH) in regions associated with the surface termination of dislocations. Both the I– V and C– V characteristics indicate that the total-dose radiation hardness of the Si solar cells cannot be neglected according to illumination levels.

Low-porosity porous silicon nanostructures on monocrystalline silicon solar cells

In this work we present a study of low-porosity porous silicon (PS) nanostructures stain etched on monocrystalline silicon solar cells. The PS layers reduce the reflectance, improve the diffusion of dopants by rapid thermal processes, and increase the homogeneity of the sheet resistance. Some samples were subjected to chemical oxidation in HNO 3 to reduce the porosity of the surface layer. After the diffusion process, deposition of a SiN x antireflection layer, and screen printing of the samples, an efficiency of 15.5% is obtained for low-porosity PS solar cells, compared with an efficiency of 10.0% for standard PS cells and 14.9% for the reference Cz cells.

High-efficiency solar cell using a thin porous silicon layer

The performance improvement of solar cells due to the formation of a porous silicon layer on deep-junction n +/p silicon structures has been investigated. The photovoltaic properties of two identical sample groups with and without porous silicon layer are compared. More than a 50% improvement in I sc and about a 5% increase in V oc was demonstrated in structures with PS layer. No change in the fill factor was observed. The performance of the porous silicon solar cell has been found to be sensitive to the PS layer thickness. Optimal thickness was determined using the electrical measurement. The main result is that the photovoltaic energy conversion efficiency of solar cells can be increased by the PS layer. This low-cost PS formation process can be applied in the photovoltaic cell technology as a standard procedure. © 1997 Elsevier Science S.A.