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1.
In the present paper, the authors discuss the application of amorphous p–i–n solar cells containing i-layers which are deposited at high substrate temperatures as top cells in amorphous silicon/microcrystalline silicon tandem (“micromorph”) solar cells. Increasing the substrate temperature for the deposition of intrinsic a-Si : H results in a reduced optical gap. The optical absorption is enhanced and thereby the current generation. A high-current generation within a relatively thin amorphous top cell is very interesting in the context of micromorph tandem cells, where the amorphous top cell should contribute a current of at least 13 mA/cm2 for a total cell current density of 26 mA/cm2. A detailed study of the intrinsic material deposited by VHF-GD at 70 MHz at substrate temperatures between 220°C and 360°C is presented, including samples deposited from hydrogen-diluted silane plasmas. The stability of the films against light soaking is investigated employing the μ0τ0 parameter, which has been shown to be directly correlated to the cell performance. The paper discusses in detail the technological problems arising from the insertion of i-layers deposited at high substrate temperatures into solar cells. These problems are specially pronounced in the case of cells in the p–i–n (superstrate) structure. The authors demonstrate that an appropriate interface layer at the p/i-interface can largely reduce the detrimental effects of i-layer deposition at high temperatures. Finally, the application of such optimized high-temperature amorphous cells as top cells in micromorph tandem cells is discussed. Current densities of 13 mA/cm2 in the top cell are available with a top cell i-layer thickness of only 250 nm.  相似文献   

2.
A numerical investigation of the intrinsic layer effect on the improvement of GaAs n–i–p solar cell performances is presented. Solution of Poisson's equation together with continuity equations for electrons and holes allows the determination of carrier's density, electric field and recombination profiles within the i-layer. The analysis examines the effect of i-layer thickness on the electric field, recombination rate and collection efficiency. It is found that increasing the i-layer thickness increases the absorption while it reduces the electric field and increases the recombination rate. The three competing parameters have to be monitored simultaneously so as to obtain an optimal thickness. To achieve this, the variation of the total photocurrent is used as indicator. The photocurrent shows a sharp increase in the domain of very thin i-layers (<0.5 μm) then a saturation is reached for thicker layers (>1 μm), the simulation is performed for thicknesses up to 2 μm.  相似文献   

3.
Intrinsic microcrystalline silicon films have been deposited at high-power–high-pressure regime. Effects of pressure and hydrogen dilution on the microstructures of the films have been investigated. Crystalline size decreases at high pressure although the deposition rate increases up to 10 Å/s. Microstructure depends sensitively on pressure as well as on hydrogen dilution of silane. Single junction solar cells have been fabricated with Si films having different degrees of crystallinity and grain size and the performances have been studied.  相似文献   

4.
The paper reviews the material requirements of microcrystalline silicon (μc-Si) in terms of the device operation and configuration for thin film solar cells and thin film transistors (TFTs). We investigated the material properties of μc-Si films deposited by using 13.56 MHz plasma-enhanced chemical vapor deposition (PECVD) from a conventional H2 dilution in SiH4. Two types of intrinsic μc-Si films deposited at the high pressure narrow electrode gap and the low pressure wide electrode gap were studied for the solar cell absorption layers. The material properties were characterized using dark conductivity, Raman spectroscopy, and transmission electron microscope (TEM) measurements. The μc-Si quality and solar cell performance were mainly determined by microstructure characteristics. Solar cells adopting the optimized μc-Si film demonstrated high stability with no significant changes in solar cell performance after air exposure for six months and subsequent illumination for over 300 h. The results can be explained that low ion bombardment and high atomic hydrogen density under the PECVD condition of the high pressure narrow electrode gap produce high-quality μc-Si films for solar cell application.  相似文献   

5.
Double porous silicon (d-PS) layers formed by acid chemical etching on a top surface of n+/p multi-crystalline silicon solar cells were investigated with the aim to improve the performance of standard screen-printed silicon solar cells. First a macro-porous layer is formed on mc-Si. The role of this layer is texturization of surface. Next, the cells have been manufactured using standard technology based on screen-printing metallization. Finally, a second mezo-porous layer in n+ emitter of cell has been produced. The role of this PS layer is to serve as an antireflection coating. In this way, we have obtained d-PS layers on these solar cells. The paper present observation of d-PS microstructure with SEM as well as measurements of its effective reflectance at the level of 2.5% in the 400–1000 nm length wave range. The efficiency of the solar cells with this structure is about 12%.  相似文献   

6.
The dependence of the maximum power output PM and short-circuit current JSC on the form (relative variation with position) of the optical generation rate profile in an a-Si:H p–i–n solar cell has been investigated computationally. It was found that there was an optimal form for the generation profile, and that PM increased from 4.64 to 5.29 mWcm−2, an increase of about 14%, when this optimal generation profile was used in the simulation. Optimal doping of the i-layer of the cell with phosphorous led to a PM of 5.60 mWcm−2, and when the optimal generation profile for this P-profiled cell was found, it yielded a PM of 7.86 mWcm−2, an increase of about 40%. This suggests that the combination of P-profiling and optimal generation could lead to significant improvements in cell performance. Moreover, it was found that for both cells the form of the optimal generation profile could be associated with the position of the peak in the external quantum efficiency, obtained from the spectral response. The possibility of using band-gap grading to achieve an optimal generation rate profile has been suggested.  相似文献   

7.
The aim of this work is to investigate the electrical uniformity of monolithic polycrystalline silicon solar cells prepared by various process techniques. By a series of experiments such as P and Al impurity gettering and silicon nitride passivation, a new conclusion is that the application of P and Al gettering as well as silicon nitride passivation enhances the electrical uniformity of small area solar cells diced from the same polycrystalline silicon solar cells, even if impurity gettering is not effective when the dislocation density is above a threshold value of about 106 cm−2. The experiments give us some hints that when we cut large area polycrystalline silicon solar cells into small pieces needed for application, we should modify production process slightly.  相似文献   

8.
The results of numerical device simulations for p–i–n diodes and the closed-form expression of the current–voltage characteristics developed for p–n diodes are compared. It is shown that the closed-form expression correctly predicts the functional relationship between material parameters and device performance of p–i–n diodes. The ideality factor between 1 and 2 is analyzed in detail. The effect of the defect density, the intrinsic carrier concentration, the mobility and the built-in potential on device performance are demonstrated. These insights are applied to analyze microcrystalline silicon thin-film solar cells deposited by chemical vapor deposition at temperatures below 250 °C.  相似文献   

9.
The antireflection properties of electrochemically formed porous silicon (PS) layers in the 0.3 μm thick n+ emitter of Si p–n+ junctions, have been optimized for application to commercial silicon photovoltaic cells. The porosity and thickness of the PS layers are easily adjusted by controlling the electrochemical formation conditions (current density and anodization time). The appropriate PS formation conditions were determined by carrying out a two steps experiment. A first set of samples allowed to determine the optimal porosity and a second one to adjust the thickness of the PS layers, by evaluating the interference features of the reflectance produced by the layers. A PS layer with optimal antireflection coating (ARC) characteristics was obtained in 30% HF in only 3.5 s. The effective reflectance is reduced to 7.3% between 400 and 1150 nm which leads to a gain of up to 33% in the theoretical short circuit current of a p–n+ shallow junction compared to a reference junction without a PS layer. The effective reflectance with optimized PS layers is significantly less than that obtained with a classical TiO2 ARC on a NaOH pretextured multicrystalline surface (11%).  相似文献   

10.
High conversion efficiency for (amorphous/microcrystalline) "micromorph" tandem solar cells requires both a dedicated light management, to keep the absorber layers as thin as possible, and optimized growth conditions of the microcrystalline silicon (μc-Si:H) material. Efficient light trapping is achieved here by use of textured front and back contacts as well as by implementing an intermediate reflecting layer (IRL) between the individual cells of the tandem. This paper discusses the latest developments of IRLs at IMT Neuchâtel: SiOx based for micromorphs on glass and ZnO based IRLs for micromorphs on flexible substrates were successfully incorporated in micromorph tandem cells leading to high, matched, current above 13.8 mA/cm2 for p-i-n tandems. In n-i-p configuration, asymmetric intermediate reflectors were employed to achieve currents of up to 12.5 mA/cm2. On glass substrates, initial and stabilized efficiencies exceeding 13% and 11%, respectively, were thus obtained on 1 cm2 cells, while on plastic foils with imprinted gratings, 11.2% initial and 9.8% stable efficiency could be reached. Recent progress on the development of effective front and back contacts will be described as well.  相似文献   

11.
In this study, the indoor evaluation of amorphous silicon modules was conducted using extended visual inspection and various electrical characterisation tools. The visual inspection, which included low-magnification optical microscopy, revealed several defects resulting from physical damage and bad scribing. These defects, as well as poor material quality, are likely contributors to the degradation in performance observed during the measurement of current–voltage characteristics under standard conditions, as well as at different temperature and irradiance levels. The observed degradation is carefully analysed in this paper.  相似文献   

12.
We have developed thin film silicon double-junction solar cells by using micromorph structure. Wide bandgap hydrogenated amorphous silicon oxide (a-SiO:H) film was used as an absorber layer of top cell in order to obtain solar cells with high open circuit voltage (Voc), which are attractive for the use in high temperature environment. All p, i and n layers were deposited on transparent conductive oxide (TCO) coated glass substrate by a 60 MHz-very-high-frequency plasma enhanced chemical vapor deposition (VHF-PECVD) technique. The p-i-n-p-i-n double-junction solar cells were fabricated by varying the CO2 and H2 flow rate of i top layer in order to obtain the wide bandgap with good quality material, which deposited near the phase boundary between a-SiO:H and hydrogenated microcrystalline silicon oxide (μc-SiO:H), where the high Voc can be expected. The typical a-SiO:H/μc-Si:H solar cell showed the highest initial cell efficiency of 10.5%. The temperature coefficient (TC) of solar cells indicated that the values of TC for conversion efficiency ) of the double-junction solar cells were inversely proportional to the initial Voc, which corresponds to the bandgap of the top cells. The TC for η of typical a-SiO:H/μc-Si:H was −0.32%/ °C, lower than the value of conventional a-Si:H/μc-Si:H solar cell. Both the a-SiO:H/μc-Si:H solar cell and the conventional solar cell showed the same light induced degradation ratio of about 20%. We concluded that the solar cells using wide bandgap a-SiO:H film in the top cells are promising for the use in high temperature regions.  相似文献   

13.
Device modeling for p–i–n junction basis thin film microcrystalline Si solar cells has been examined with a simple model of columnar grain structure utilizing two-dimensional device simulator. The simulation results of solar cell characteristics show that open-circuit voltage (Voc) and fill factor considerably depend on structural parameters such as grain size and acceptor doping in intrinsic layer, while short-circuit current density (Jsc) is comparatively stable by built-in electric field in the i-layer. It is also found that conversion efficiency of more than 16% could be expected with 1 μm grain size and well-passivated condition with 10 μm thick i-layer and optical confinement.  相似文献   

14.
The hot-wire chemical vapour deposition (HWCVD) has been used to prepare highly conducting p- and n-doped microcrystalline silicon thin layers as well as highly photoconducting, low defect density intrinsic microcrystalline silicon films. These films were incorporated in all-HWCVD, all-microcrystalline nip and pin solar cells, achieving conversion efficiencies of η=5.4% and 4.5%, respectively. At present, only the nip-structures are found to be stable against light-induced degradation. Furthermore, microcrystalline nip and pin structures have been successfully incorporated as bottom cells in all-hot-wire amorphous–microcrystalline nipnip- and pinpin-tandem solar cells for the first time. So far, the highest conversion efficiencies of the “micromorph” tandem structures are η=5.7% for pinpin-solar cells and 7.0% for nipnip solar cells.  相似文献   

15.
The presence of a pair of peaks in the high wavenumber infrared (IR) absorption region of hydrogenated microcrystalline silicon (μc-Si:H) has been recently proposed as a strong indicator of poor quality material that is prone to oxidation and is therefore unsuitable for thin-film, photovoltaic applications. In this work, we show that these peaks located at 2083 and 2100 cm−1 are also present in the Raman scattering spectra of μc-Si:H and therefore can be directly measured on substrates that are suitable for solar cells. We present results for material grown by matrix-distributed electron-cyclotron resonance (MD-ECR) plasma-enhanced chemical vapour deposition (PECVD) on both crystalline silicon and borosilicate glass substrates. The narrow, twinned peaks detected by Raman disappear with time—presumably due to oxidation—although a broad peak at 2100 cm−1 remains.  相似文献   

16.
Main photovoltaic properties of polycrystalline silicon solar cells are often affected by dislocation effects. Dislocations degrade functional photocurrent and considerably alter relevant parameters such as short-circuit current density, dark current intensity and open-circuit voltage. In this study, we have developed an enhanced photothermal technical protocol for diagnosing dislocation spatial distribution inside photovoltaic polycrystalline silicon solar cells. We tried to establish a qualitative and quantitative correlation between the local thermal properties alteration and dislocation spatial range. Experimental imaging profiles, yielded by this technique are compared to other diagnostic techniques results.  相似文献   

17.
In this study we report for the first time a method for simple, precise and single-step generation of thin film of amorphous silicon (a-Si) on silicon substrate induced by laser pulses with the frequency of megahertz under ambient conditions for solar cell fabrication. Also, the effect of laser parameters such as pulse width is investigated by developing an analytical model for the calculation of the non-dimensional surface temperature with various pulse widths; it was found from experimental and analytical results that for a constant power and repetition rate, an increase in the pulse duration corresponds to a significant increase in the surface temperature which results in an increase in the amount of amorphorized material as well as improvement of light absorption. A Scanning Electron Microscope (SEM), scanning near-field optical microscope (SNOM), a Micro-Raman, Energy Dispersive X-ray (EDX) spectroscopy and an optical spectrometer were used to analyze the optical and material properties of the amorphorized thin layer on Si-substrate.  相似文献   

18.
The effects of the silane concentration f on the structural, optical and electrical properties of undoped hydrogenated silicon films prepared in a plasma-enhanced chemical vapour deposition system have been studied. The electrical conductivity and Hall mobility appear to be controlled by microstructures induced by silane concentration and a clear electrical transport transition from crystalline to amorphous phase has been found when 3%<f<4%. A two-phase model has been used to discuss the electrical properties.  相似文献   

19.
An experimental study of the effect of degradation of the metal-semiconductor contact by current pulses on the IV characteristics of silicon solar cells allows us to discuss the two-diode model as a function of series and shunt resistances. It is shown that contact degradation is the unique factor deteriorating the fundamental parameters. The recombination, diffusion and photocurrent terms remain unchanged with adherence loss between metal contact and silicon semiconductor.  相似文献   

20.
The paper reports on the effects of a proton irradiation campaign on a series of thin-film silicon solar cells (single- and double-junction). The effect of subsequent thermal annealing on solar cells degraded by proton irradiation is investigated. A low-temperature annealing behaviour can be observed (at temperatures around 100 to 160°C) for microcrystalline silicon solar cells. To further explore this effect, a second proton irradiation campaign has been carried out, but this time on microcrystalline silicon layers. The effect of proton irradiation and subsequent thermal annealing on the optical and electronic properties of microcrystalline silicon is, thus, thoroughly investigated.  相似文献   

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