Absorption enhancement in thin film a-Si solar cells with double-sided SiO_2 particle layers

Light absorption enhancement is very important for improving the power conversion efficiency of a thin film a-Si solar cell. In this paper, a thin-film a-Si solar cell model with double-sided SiO2 particle layers is designed, and then the underlying mechanism of absorption enhancement is investigated by finite difference time domain(FDTD) simulation;finally the feasible experimental scheme for preparing the SiO2 particle layer is discussed. It is found that the top and bottom SiO2 particle layers play an important role in anti-reflection and light trapping, respectively. The light absorption of the cell with double-sided SiO2 layers greatly increases in a wavelength range of 300 nm–800 nm, and the ultimate efficiency increases more than 22% compared with that of the flat device. The cell model with double-sided SiO2 particle layers reported here can be used in varieties of thin film solar cells to further improve their performances.     

Effect of emitter layer doping concentration on the performance of a silicon thin film heterojunction solar cell

A novel type of n/i/i/p heterojunction solar cell with a-Si:H(15nm)/a-Si:H(10nm)/ epitaxial c-Si(47μm)/epitaxial c-Si(3μm) structure is fabricated by using the layer transfer technique, and the emitter layer is deposited by hot wire chemical vapour deposition. The effect of the doping concentration of the emitter layer S d (Sd =PH3 /(PH3 +SiH4 +H2 )) on the performance of the solar cell is studied by means of current density-voltage and external quantum efficiency. The results show that the conversion efficiency of the solar cell first increases to a maximum value and then decreases with S d increasing from 0.1% to 0.4%. The best performance of the solar cell is obtained at S d = 0.2% with an open circuit voltage of 534 mV, a short circuit current density of 23.35mA/cm2 , a fill factor of 63.3%, and a conversion efficiency of 7.9%.     

The study of a new n/p tunnel recombination junction and its application in a-Si：H/μc-Si：H tandem solar cells

This paper reports that a double N layer (a-Si:H/μc-Si:H) is used to substitute the single microcrystalline silicon n layer (n-μc-Si:H) in n/p tunnel recombination junction between subcells in a-Si:H/μc-Si:H tandem solar cells. The electrical transport and optical properties of these tunnel recombination junctions are investigated by current-voltage measurement and transmission measurement. The new n/p tunnel recombination junction shows a better ohmic contact. In addition, the n/p interface is exposed to the air to examine the effect of oxidation on the tunnel recombination junction performance. The open circuit voltage and FF of a-Si:H/μc-Si:H tandem solar cell are all improved and the current leakage of the subcells can be effectively prevented efficiently when the new n/p junction is implemented as tunnel recombination junction.     

Indium–tin oxide films obtained by DC magnetron sputtering for improved Si heterojunction solar cell applications

The indium–tin oxide(ITO) film as the antireflection layer and front electrodes is of key importance to obtaining high efficiency Si heterojunction(HJ) solar cells. To obtain high transmittance and low resistivity ITO films by direct-current(DC) magnetron sputtering, we studied the impacts of the ITO film deposition conditions, such as the oxygen flow rate,pressure, and sputter power, on the electrical and optical properties of the ITO films. ITO films of resistivity of 4×10-4?·m and average transmittance of 89% in the wavelength range of 380–780 nm were obtained under the optimized conditions:oxygen flow rate of 0.1 sccm, pressure of 0.8 Pa, and sputtering power of 110 W. These ITO films were used to fabricate the single-side HJ solar cell without an intrinsic a-Si:H layer. However, the best HJ solar cell was fabricated with a lower sputtering power of 95 W, which had an efficiency of 11.47%, an open circuit voltage(V oc) of 0.626 V, a filling factor(FF) of 0.50, and a short circuit current density(J sc) of 36.4 m A/cm2. The decrease in the performance of the solar cell fabricated with high sputtering power of 110 W is attributed to the ion bombardment to the emitter. The V oc was improved to 0.673 V when a 5 nm thick intrinsic a-Si:H layer was inserted between the(p) a-Si:H and(n) c-Si layer. The higher V oc of 0.673 V for the single-side HJ solar cell implies the excellent c-Si surface passivation by a-Si:H.     

非晶Si1-xGex:H薄膜太阳能电池研究

The AMPS-ID program is used to investigate electrical and optical properties of the thin film solar cell of a-SiC:H/a-Si1-xGex:H/a-Si:H. The short circuit current density, open circuit voltage, fill factor and efficiency of the solar cell are investigated. The efficiency of the solar cell is 9.19% as thickness of a-Si1-xGex:H is 340 nm with Ge content x=0.1. In addition, we also discuss the factors which affect solar cell efficiency.     

Numerical simulation of a triple-junction thin-film solar cell based on μc-Si_(1-x)Ge_x :H

In this paper, a-Si:H/a-SiGe:H/μc-SiGe:H triple-junction solar cell structure is proposed. By the analyses of microelectronic and photonic structures (AMPS-1D) and our TRJ-F/TRJ-M/TRJ-B tunneling-recombination junction (TRJ) model, the most preferably combined bandgap for this structure is found to be 1.85 eV/1.50 eV/1.0 eV. Using more realistic material properties, optimized thickness combination is investigated. Along this direction, a-Si:H/a-SiGe:H/μc-SiGe:H triple cell with an initial efficiency of 12.09% (Voc = 2.03 V, FF = 0.69, Jsc = 8.63 mA/cm2 , area = 1 cm2 ) is achieved in our laboratory.     

Enhanced Efficiency of Metamorphic Triple Junction Solar Cells for Space Applications

Metamorphic In_(0.55)Ga_(0.45)P/In_(0.06)Ga_(0.94)As/Ge triple-junction(3J-MM) solar cells are grown on Ge(100) substrates via metal organic chemical vapor deposition. Epi-structural analyses such as high resolution x-ray diffraction, photoluminence, cathodoluminescence and HRTEM are employed and the results show that the high crystal quality of 3J-MM solar cells is obtained with low threading dislocation density of graded buffer(an average value of 6.8×10~4/cm~2). Benefitting from the optimized bandgap combination, under one sun, AMO spectrum,25℃ conditions, the conversion efficiency is achieved about 32%, 5% higher compared with the lattice-matched In_(0.49)Ga_(0.51)P/In_(0.01)Ga_(0.99)As/Ge triple junction(3J-LM) solar cell. Under 1-MeV electron irradiation test, the degradation of the EQE and Ⅰ-Ⅴ characteristics of 3 J-MM solar cells is at the same level as the 3J-LM solar cell.The end-of-life efficiency is ~27.1%. Therefore, the metamorphic triple-junction solar cell may be a promising candidate for next-generation space multi-junction solar cells.     

Evaluation of electrical and optical characteristics of ZnO/CdS/CIS thin film solar cell

In this study, device modeling and simulation are conducted to explain the effects of each layer thickness and temperature on the performance of ZnO/CdS/CIS thin film solar cells. Also, the thicknesses of the CIS and CdS absorber layers are considered in this work theoretically and experimentally. The calculations of solar cell performances are based on the solutions of the well-known three coupling equations: the continuity equation for holes and electrons and the Poisson equation. Our simulated results show that the efficiency increases by reducing the CdS thickness. Increasing the CIS thickness can increase the efficiency but it needs more materials. The efficiency is more than 19% for a CIS layer with a thickness of 2 μm. CIS nanoparticles are prepared via the polyol route and purified through centrifugation and precipitation processes.Then nanoparticles are dispersed to obtain stable inks that could be directly used for thin-film deposition via spin coating.We also obtain x-ray diffraction(XRD) peak intensities and absorption spectra for CIS experimentally. Finally, absorption spectra for the CdS window layer in several deposition times are investigated experimentally.     

Photoluminescence Analysis of Electron Damage for Minority Carrier Diffusion Length in GaInP/GaAs/Ge Triple-Junction Solar Cells

Photoluminescence(PL) measurements are carried out to investigate the degradation of GaInP top cell and GaAs middle cell for GaInP/GaAs/Ge triple-junction solar cells irradiated with 1.0, 1.8 and 11.5 MeV electrons with fluences ranging up to 3 × 10~(15), 1 × 10~(15) and 3 × 10~(14) cm-2, respectively. The degradation rates of PL intensity increase with the electron fluence and energy. Furthermore, the damage coefficient of minority carrier diffusion length is estimated by the PL radiative efficiency. The damage coefficient increases with the electron energy. The relation of damage coefficient to electron energy is discussed with the non-ionizing energy loss(NIEL), which shows a quadratic dependence between damage coefficient and NIEL.     

Influence of p-layer on the performance of n-i-p μc-Si:H thin film solar cells

The high pressure radio frequency plasma enhanced chemical vapor deposition (RF-PECVD) process was adopted to prepare the n-i-p microcrystalline silicon solar cells,the influence of p-type layers on the performance of the solar cells was investigated,and the optimum p layer suited to the n-i-p microcrystalline silicon solar cells was obtained.The experimental results demonstrate that the performance of the solar cells can be highly affected by the structural and optical properties of the p-layers,and the performance of solar cells can be greatly improved by optimizing p layers.We have achieved an initial active-area efficiency of 8.17% (V oc =0.49 V,J sc =24.9 mA/cm 2 ,FF=67%) for the μc-Si:H single-junction n-i-p solar cells and an initial active-area efficiency of 10.93% (V oc =1.31 V,J sc =13.09 mA/cm 2 ,FF=64%) for the a-Si:H/μc-Si:H tandem n-i-p solar cells.     

Improved performance of microcrystalline silicon solar cell with graded-band-gap silicon oxide buffer layer

Microcrystalline silicon(μc-Si:H) solar cell with graded band gap microcrystalline silicon oxide(μc-Si Ox:H) buffer layer is prepared by plasma enhanced chemical vapor deposition and exhibits improved performance compared with the cell without it. The buffer layer moderates the band gap mismatch by reducing the barrier of the p/i interface, which promotes the nucleation of the i-layer and effectively eliminates the incubation layer, and then enhances the collection efficiency of the cell in the short wavelength region of the spectrum. The p/i interface defect density also decreases from 2.2 × 1012cm-2to 5.0 × 1011cm-2. This graded buffer layer allows to simplify the deposition process for the μc-Si:H solar cell application.     

Micromorph tandem solar cells: optimization of the microcrystalline silicon bottom cell in a single chamber system

We report on the development of single chamber deposition of microcrystalline and micromorph tandem solar cells directly onto low-cost glass substrates. The cells have pin single-junction or pin/pin double-junction structures on glass substrates coated with a transparent conductive oxide layer such as SnO₂ or ZnO. By controlling boron and phosphorus contaminations, a single-junction microcrystalline silicon cell with a conversion efficiency of 7.47% is achieved with an i-layer thickness of 1.2 μm. In tandem devices, by thickness optimization of the microcrystalline silicon bottom solar cell, we obtained an initial conversion efficiency of 9.91% with an aluminum (Al) back reflector without a dielectric layer. In order to enhance the performance of the tandem solar cells, an improved light trapping structure with a ZnO/Al back reflector is used. As a result, a tandem solar cell with 11.04% of initial conversion efficiency has been obtained.     

An effective reflectance method for designing broadband antireflection films coupled with solar cells

The solar spectrum covers a broad wavelength range,which requires that antireflection coating(ARC) is effective over a relatively wide wavelength range for more incident light coming into the cell.In this paper,we present two methods to measure the composite reflection of SiO2/ZnS double-layer ARC in the wavelength ranges of 300-870 nm(dualjunction) and 300-1850 nm(triple-junction),under the solar spectrum AM0.In order to give sufficient consideration to the ARC coupled with the window layer and the dispersion effect of the refractive index of each layer,we use multidimensional matrix data for reliable simulation.A comparison between the results obtained from the weighted-average reflectance(WAR) method commonly used and that from the effective-average reflectance(EAR) method introduced here shows that the optimized ARC through minimizing the effective-average reflectance is convenient and available.     

Detailed balance limit efficiency of silicon intermediate band solar cells

The detailed balance method is used to study the potential of the intermediate band solar cell (IBSC), which can improve the efficiency of the Si-based solar cell with a bandgap between 1.1 eV to 1.7 eV. It shows that a crystalline silicon solar cell with an intermediate band located at 0.36 eV below the conduction band or above the valence band can reach a limiting efficiency of 54% at the maximum light concentration, improving greatly than 40.7% of the Shockley—Queisser limit for the single junction Si solar cell. The simulation also shows that the limiting efficiency of the silicon-based solar cell increases as the bandgap increases from 1.1 eV to 1.7 eV, and the amorphous Si solar cell with a bandgap of 1.7 eV exhibits a radiative limiting efficiency of 62.47%, having a better potential.     

Light trapping enhancement with combined front metal nanoparticles and back diffraction gratings

In this letter, a design with both metal nanoparticles and back diffraction gratings is put forward for enhancing the efficiency of thin film silicon solar cells. The coupling mechanism between the metal nanoparticles and silicon absorber layer, and that between the incident light and the modes of the silicon absorption layer through the grating layer are both analyzed. The interaction between the front metal nanoparticles and back gratings is analyzed, which substantially increases the light trapping by 58% com- pared to fiat solar cell.     

Efficiency Enhancement of Dye-Sensitized Solar Cells： Using Salt CuI as an Additive in an Ionic Liquid

Energy conversion efficiency of the dye-sensitized solar cell is improved from 3.5% to 4.5% by adding a small amount of CuI into an ionic liquid electrolyte. It is found that other copper-I salts, for example, CuBr, have the same effect for the dye-sensitized solar cell. Experimental results show that no Cu^2＋ ions exist in this electrolyte. It is suggested that this improvement is caused by the adsorption of Cu^＋ onto the TiO2 porous film.     

Resonant energy transfer from nanocrystal Si to β-FeSi2 in hybrid Si/β-FeSi2 film

The photoluminescence （PL） characteristics of hybrid β-FeSi2/Si and pure β-FeSi2 films fabricated by pulsed laser deposition at 20 K are investigated. The intensity of the 1.54-μm PL from the former is enhanced, but the enhancement vanishes when the excitation wavelength is larger than the widened band gap of Si nanocrystal. Time-resolved PL decay measurements reveal that the lifetime of the photo-excited carriers in the hybrid β-FeSi2/Si film is longer than that in the pure β-FeSi2 film, providing evidence that the PL enhancement results from the resonant charge transfer from nanocrystalline Si to β-FeSi2.     

Simulation of near-infrared photodiode detectors based on β-FeSi_2/4H-SiC heterojunctions

In this paper,we propose a near-infrared p-type β-FeSi2/n-type 4H-SiC heterojunction photodetector with semiconducting silicide(β-FeSi2) as the active region for the first time.The optoelectronic characteristics of the photodetector are simulated using a commercial simulator at room temperature.The results show that the photodetector has a good rectifying character and a good response to near-infrared light.Interface states should be minimized to obtain a lower reverse leakage current.The response spectrum of the β-FeSi2/4H-SiC detector,which consists of a p-type β-FeSi2 absorption layer with a doping concentration of 1×1015cm-3 and a thickness of 2.5 μm,has a peak of 755 mA/W at 1.42 μm.The illumination of the SiC side obtains a higher responsivity than that of the β-FeSi2 side.The results illustrate that the β-FeSi2/4H-SiC heterojunction can be used as a near-infrared photodetector compatible with near-infrared optically-activated SiC-based power switching devices.     

Low platinum loading PtNPs/graphene composite catalyst with high electrocatalytic activity for dye-sensitized solar cells

Platinum nanoparticles(PtNPs)/graphene composite materials are synthesized by a controlled chemical reduction of H2PtCl6 on graphene sheets.The electrocatalytic activity of a PtNPs/graphene composite counter electrode for a dye-sensitized solar cell(DSSC) is investigated.The results demonstrate that the PtNPs/graphene composite has high electrocatalytic activity for the dye-sensitized solar cell.The cell employing PtNPs(1.6 wt%)/graphene counter electrode reaches an conversion efficiency(η)of 3.89% upon the excitation of 100 mW/cm2 AM 1.5 white light,which is comparable to that of the cell with a Pt-film counter electrode(η=3.76%).It suggests that one can use only 14% Pt content of the conventional Pt-film counter electrode to obtain a comparable conversion efficiency.It may be possible to obtain a high performance DSSC using the PtNPs/graphene composite with a very low Pt content as a counter electrode due to its simplicity,low cost,and large scalability.     

Significant Improvement of Passivation Performance by Two-Step Preparation of Amorphous Silicon Passivation Layers in Silicon Heterojunction Solar Cells

The key feature of amorphous/crystalline silicon heterojunction solar cells is extremely low surface recombination,which is related to superior passivation on the crystalline silicon wafer surface using thin hydrogenated amorphous silicon(a-Si:H)layers,leading to a high open-circuit voltage.In this work,a two-step method of a-Si:H passivation is introduced,showing excellent interface passivation quality,and the highest effective minority carrier lifetime exceeds 4500 μs.By applying a buffer layer deposited through pure silane plasma,the risk of film epitaxial growth and plasma damage caused by hydrogen diluted silane plasma is effectively reduced.Based on this,excellent passivation is realized through the following hydrogen diluted silane plasma process with the application of high density hydrogen.In this process,hydrogen diffuses to a-Si/c-Si interface,saturating residual dangling bonds which are not passivated by the buffer layer.Employing this two-step method,a heterojunction solar cell with an area of 239 cm~2 is prepared,yielding to open-circuit voltage up to 735 mV and total-area efficiency up to 22.4%.