Experimental and theoretical radiation damage studies on crystalline silicon solar cells

An experimental facility was developed to asses in situ the degradation of crystalline silicon solar cells, fabricated by the Solar Energy Group of the National Atomic Energy Commission (CNEA), by measuring the current–voltage characteristic curve. The cells were irradiated with 10 MeV protons and fluences between 10⁸ and 10¹³ p/cm², using an external beam of the linear tandem accelerator TANDAR, at CAC-CNEA. Furthermore, theoretical simulations were performed to establish the relation between the variation of the electrical parameters and the degradation of the lifetime of minority carriers in the base. The damage constant for 10 MeV proton irradiated silicon solar cells of n⁺–p–p⁺ structure and 1 Ω cm base resistivity was determined. Finally, a proposal of a new model of radiation damage for silicon solar cells is discussed.     

Analysis for superior radiation resistance of InP-based solar cells

Better radiation resistance of InP-based solar cells such as InGaP and InGaAsP cells, and minority-carrier-injection-enhanced annealing phenomena of radiation-induced defects in those materials previously found by the authors has been analyzed by considering introduction rates and annealing behavior of radiation-induced defects in InP-related materials. Radiation resistance of InP-related materials is found to be explained by lower damage coefficients and band-gap energy effects on solar cell degradation compared to other materials.     

Copper metallization for crystalline Si solar cells

Cu metallization for crystalline Si solar cells was investigated using either Ti or Ti/TiN diffusion barriers. The resistivity and the specific contact resistance change were measured for both Ti(30 nm)/Cu(100 nm) and Ti(30 nm)/TiN(30 nm)/Cu(100 nm) contact structures under various annealing conditions. As the annealing temperature increased, the efficiency of the cells increased mainly due to the increase in fill-factor and I_SC, which was correlated with the series resistance (R_S) of the metal layer. The solar cells with Ti/TiN/Cu contacts generally showed the higher efficiencies than those with Ti/Cu, because in Ti/Cu contacts Cu diffused through Ti and increased R_S.     

Mechanism for the anomalous degradation of Si solar cells induced by high-energy proton irradiation

High-energy and high-fluence proton irradiation of Si space solar cells has provoked an anomalous increase in short-circuit current, followed by its abrupt decrease and cell failure. A model is proposed which explains the phenomena by expressing a reduction in the carrier concentration of the base region, in addition to a decrease of minority-carrier diffusion length. The reduction in carrier concentration due to majority-carrier trapping by radiation-induced defects has the effect of (1) broadening the depletion region width and (2) increasing the resistivity of the base layer. The anomalous change in the quantum efficiency of the cells under high-fluence ( 10¹⁴cm⁻²) irradiation is also explained by considering the generation of a donor-type defect level with the irradiation.     

Radiation response of InP/Si and InGaP/GaAs space solar cells

An analysis of the radiation response of state-of-the-art InP/Si, InGaP, and dual junction (DJ) InGaP/GaAs space solar cells under both electron and proton irradiated is presented. The degradation data are modeled using the theory of displacement damage dose. For each technology, a characteristic curve which describes the cell degradation in any radiation environment is determined, and the characteristic curves are used to compare the radiation resistance of the different technologies on an absolute scale. The radiation data are used as input to a code which predicts the end-of-life (EOL) performance of a solar panel in earth orbit. The results show that in orbits outside the earth's radiation belts, the high-efficiency DJ InGaP/GaAs solar panels provide the highest EOL specific power. However, in orbits which pass through the belts, the radiation hard InP/Si panels provide the highest specific power by as much as 30%.     

Optical confinement of the intermediate layer between Si and alumina substrate in thin film Si solar cells

Enhancement of the optical confinement effect by an intermediate layer (IML) between Si and alumina substrate in thin film Si solar cells was studied. The dependence of the optical confinement effect on refractive index of the IML and on thickness of Si was separately investigated by hemispherical reflectance measurement of the following two series of samples. In the first case, SiO_xN_y, SiN_x or TiO₂ was deposited as the IML in the multilayer, Si/IML/alumina. In the second case, Si layers with different thicknesses were formed. The study showed that in certain conditions the IML could enhance the optical absorption of Si layer in thin film Si solar cells.     

Impurity diffusion from uncoated foreign substrates during high temperature CVD for thin-film Si solar cells

In this paper, we study the diffusion of impurities from three types of foreign substrates (graphite, alumina and mullite) during thermal chemical vapour deposition (CVD) of a polycrystalline Si film. For this we use a rapid thermal CVD (RTCVD) system and characterization techniques such as secondary ion mass spectroscopy (SIMS) and deep level transient spectroscopy (DLTS). Results show that, in the case of materials like graphite, metallic contaminants can freely outdiffuse into the deposited layer and the environment. In contrast, the ceramic substrates release only a very limited amount of contaminants during the CVD process, making the need of a diffusion barrier much less severe.     

Antireflective coating fabricated by chemical deposition of ZnO for spherical Si solar cells

ZnO thin films as an antireflective (AR) coating have been successfully fabricated on spherical Si solar cells by chemical deposition, which enables uniform film formation. ZnO films were prepared chemically by immersing the cell in an aqueous solution of zinc nitrate and dimethylamineborane maintained at 80 °C. The current–voltage measurements of the solar cells confirmed the increase in short circuit current induced by the AR effect. The open circuit voltage and fill factor were improved by surface passivation. As a result, the conversion efficiency of cells without an AR coating (9.45%) increased to 11.8%, which represents a 25% (relative) increase. The results indicate that the chemical deposition of ZnO is effective for the AR coating of spherical Si solar cells.     

Aluminium-induced crystallisation of silicon on glass for thin-film solar cells

Aluminium-induced crystallisation of amorphous silicon is studied for the formation of continuous polycrystalline silicon thin-films on low-temperature glass substrates. It is shown to be a promising alternative to laser crystallisation and solid-phase crystallisation. Silicon grain sizes of larger than 10 μm are achieved at temperatures of around 475°C within annealing times as short as 1 h. The Al doping concentration of the poly-Si films depends on the annealing temperature, as revealed by Hall effect measurements. A poly-Si/Al/glass structure presented here can serve as a seeding layer for the epitaxial growth of polycrystalline silicon thin-film solar cells, or possibly as the base material with the back contact incorporated.     

Control of μc-Si/c-Si interface layer structure for surface passivation of Si solar cells

Outstanding passivation properties for p-type crystalline silicon surfaces were obtained by using very thin n-type microcrystalline silicon (μc-Si) layers with a controlled interface structure. The n-type μc-Si layers were deposited by the RF PE-CVD method with an insertion of an ultra-thin oxide (UTO) layer or an n-type amorphous silicon (a-Si : H) interface layer. The effective surface recombination velocity (SRV) obtained was very small and comparable to that obtained using thermal oxides prepared at 1000°C. The structural studies by HRTEM and Raman measurements suggest that the presence of UTO produces a very thin a-Si : H layer under the μc-Si. A crystal lattice discontinuity caused by these interface layers is the key to a small SRV.     

The novel usage of spectroscopic ellipsometry for the development of amorphous Si solar cells

We present the novel use of spectroscopic ellipsometry (SE) for the development of a-Si:H solar cell. SE is a very fast and useful tool to measure various optical properties of thin film. In the case of a-Si:H thin film analysis, generally, SE is used to estimate the film thickness, roughness, void fraction, optical constants such as (n,k), and so forth. In this study, optical parameters from SE measurements were analyzed with relation to structural and electrical properties of a-Si:H thin film for solar cell. By analyzing IR absorption spectra and conductivity measurements, it was affirmed that <ε₂> and parameter A by Tauc-Lorentz model fitting of SE data are representative parameters qualifying a-Si:H thin film, and that they have close relationships with FF and light induced degradation property of solar cells. Based on the analysis, solar cells that have i-layers with various E_g were optimized. By this research, easier and faster methodology to develop a-Si:H thin film for thin film Si solar cells using SE measurements was established.     

Status and research development of Si NWs/PEDOT∶PSS hybrid solar cells

硅基太阳电池作为当前主流的光伏器件,进一步降低成本并提升效率仍是人们努力的方向.基于此,一方面,可以从太阳电池材料入手,用硅纳米线阵列代替平板硅,硅纳米线阵列具有优异的光学和电学性能,可大幅减少光反射,增加光的吸收和利用,有望提高光伏器件的效率,并可降低硅原料消耗,降低材料成本;另一方面,将硅微纳结构与有机材料进行复合,充分利用两种材料的优势,制备杂化太阳电池,以达到增强稳定性,提高效率和降低成本的目的.本文概括了Si纳米线阵列SiNWs/PEDOT∶PSS杂化太阳电池的发展现状和存在的问题,并针对相应问题的解决思路和发展方向进行了讨论.     

非晶硅薄膜太阳能电池应用分析

介绍非晶硅薄膜太阳能电池,分析其光致衰退效应与影响光电性能的各种因素。总结并展望了优化非晶硅太阳能电池的各种技术。     

Reliability assessment of silicone coated silicon concentrator solar cells by accelerated aging tests for immersing in de-ionized water

Direct de-ionized (DI) water immersion cooling has been verified to be an effective method for managing the operating temperature of silicon solar cells under concentration. However, the stable electrical performance was difficult to be achieved. The following investigation on mechanism indicated that galvanic corrosion occurred on cells. In this study, silicone coating was proposed to apply for the silicon concentrator (CPV) solar cells to eliminate or minimize the degradation when operated in DI water for a long time. The reliability of the selected silicone coatings and the silicone coated silicon CPV cells was assessed through designed accelerated aging tests, which include damp heat test, thermal cycling test and DI water immersion test. The selected silicone coatings exhibited excellent optical transparency. The tests results showed that no issues related with the selected silicone coatings’ reliability were observed. Some variations in the electrical performance of the silicone coated cells were detected, but the results gave confidence of the reliable performance of coated cells since they represented less than the total degradation allowed for the module under these tests. The simulation results indicated that temperature of the coated cell in DI water can be still maintained lower than that of conventionally encapsulated cell.