共查询到20条相似文献,搜索用时 31 毫秒
1.
In this paper effective surface recombination velocities Seff at the rear Si---SiO2 interface of the presently best one -sun silicon solar cell structure are calculated on the basis of measured oxide parameters. A new cell design is proposed allowing for a control of the surface space charge region by a gate voltage. It is shown that the electric field introduced by the positive fixed oxide charge density typically found at thermally oxidized silicon surfaces and the favorable work function difference between the gate metal aluminum and silicon leads to a reduction of Seff to values well below 1 cm/s at AM1.5 illumination for n-type as well as p-type silicon. At low illumination levels, however, oxidized n-type silicon has much better surface passivation properties than p-type silicon due to the small hole capture cross section (σn/gsp ≈ 1000 at midgap). Only at small illumination intensities for p-type substrates or in the case of poor Si---SiO2 interface quality the incorporation of a gate electrode on the rear surface is a promising tool for further reducing surface recombination losses. 相似文献
2.
Low surface recombination velocity and significant improvements in bulk quality are key issues for efficiency improvements of solar cells based on a large variety of multicrystalline silicon materials. It has been proven that PECVD silicon nitride layers provide excellent surface and bulk passivation and their deposition processes can be executed with a high throughput as required by the PV industry. The paper discusses the various deposition techniques of PECVD silicon nitride layers and also gives results on material and device properties characterisation. Furthermore the paper focuses on the benefits achieved from the passivation properties of PECVD SiNx layers on the multi-Si solar cells performance. This paper takes a closer look at the interaction between bulk passivation of multi-Si by PECVD SiNx and the alloying process when forming an Al-BSF layer. Experiments on state-of-the-art multicrystalline silicon solar cells have shown an enhanced passivation effect if the creation of the alloy and the sintering of a silicon nitride layer (to free hydrogen from its bonds) happen simultaneously. The enhanced passivation is very beneficial for multicrystalline silicon, especially if the defect density is high, but it poses processing problems when considering thin (<200 μm) cells. 相似文献
3.
Direct epitaxial crystalline silicon thin film (CSiTF) solar cells on low-cost silicon sheets from powder (SSP) ribbons have been prepared using rapid thermal chemical vapour deposition (CVD) growth. The characterisation of CSiTF solar cells was investigated by electron and spectrally resolved light beam induced current (EBIC and SR-LBIC, respectively). All EBIC measurements were performed on both the front-side surface as well as on the cross-section of CSiTF solar cells. The electrical recombination was detected by EBIC and compared with their morphologies. The results of EBIC scan show that recombination centres are situated at grain boundaries (GBs); higher the density of grain, higher the recombination activities (higher contrast). Recombination of different intensity (strong and weak) takes place at vertical GBs. Compared with the high recombination at GBs, the contrast in intragrain is low. The dark contrast of the GBs and intragrain defects is clearly reduced near the surface due to the passivation by hydrogen, which indicates that the minority carrier diffusion length decreases gradually with the depth perpendicular to the surface. The diffusion length was determined by SR-LBIC. The results show that the diffusion length distribution is quite inhomogeneous over the whole cell area. A maximum Leff of about 25 μm and mean values around 15 μm are calculated for the best solar cell. 相似文献
4.
Suresh Kumar Dhungel Jinsu Yoo Kyunghae Kim Somnath Ghosh Sungwook Jung Junsin Yi 《Renewable Energy》2008,33(2):282
Back surface passivation becomes a key issue for the silicon solar cells made with thin wafers. The high surface recombination due to the metal contacts can be lowered by reducing the back contact area and forming local back surface field (LBSF) in conjunction with the passivation with dielectric layer. About 3×10-7 m thick porous silicon (PS) layer with pore diameter mostly of 1×10-8–5×10-8 m was formed by chemical etching of silicon using the acidic solution containing hydrofluoric acid (HF), nitric acid (HNO3) and De-ionized water in the volume ratio 1:3:5 at 298 K for which etching time was kept constant for 360 s. Electrical properties of oxidized PS was studied through the current–voltage (I–V) and capacitance–voltage (C–V) characteristics of the metal–insulator–semiconductor (MIS) device in which the oxidized PS was used as an insulating layer and the results were further analyzed. The C–V curves of all the studies MIS devices showed the negative flatband voltage varying from -2 to , confirming that the oxidized layer of PS has fixed positive charge. 相似文献
5.
We investigated a simple field effect passivation of the silicon surfaces using the high-pressure H2O vapor heating. Heat treatment with 2.1×106 Pa H2O vapor at 260°C for 3 h reduced the surface recombination velocity from 405 cm/s (before the heat treatment) to 38 cm/s for the thermally evaporated SiOx film/Si. Additional deposition of 140 nm-SiOx films (x<2) with a high density of fixed positive charges on the SiO2/Si samples further decreased the surface recombination velocity to 22 cm/s. We also demonstrated the field effect passivation for n-type silicon wafer coated with thermally grown SiO2. Additional deposition of 210 nm SiOx films on both the front and rear surfaces increased the effective lifetime from 1.4 to 4.6 ms. Combination of thermal evaporation of SiOx film and the heat treatment with high-pressure H2O vapor is effective for low-temperature passivation of the silicon surface. 相似文献
6.
A method of determination of recombination velocity Sf of minority carriers at the front surface of an n+–p–p+(p+–n–n+) silicon solar cell in which the n+(p+) front emitter is made by diffusion of dopant impurity in the p(n) region is presented. This method uses the short-wavelength spectral response of the cell to determine Sf and is applicable if the front emitter of the cell has a linearly varying built-in field. It was applied to a p+–n–n+ solar cell that had a Gaussian distribution of the dopant impurity in the p+ front emitter up to a depth of 0.078 μm from the surface. Using the spectral response data of cell in 380 nm<λ< 500 nm range Sf was found to have a nearly constant value 6×105 cm s−1 in 400 nm<λ<460 nm range. Below and above this wavelength range the value of Sf was found to be slightly smaller. For comparison the value of Sf was also determined assuming the p+ region to be uniformly doped, and this value was found to be significantly smaller than based on the diffused emitter model. The analysis showed that for a diffused junction cell, the assumption that the front emitter is uniformly doped, ignores the presence of the built-in field in the emitter region and leads to overestimation of minority carrier recombination in the emitter. Consequently for a given contribution of the front emitter region to the spectral response of the cell, this assumption underestimates the front surface recombination and determines a smaller value of Sf. On the other hand, the present method can be expected to determine a realistic value of Sf independent of λ for most diffused junction silicon solar cells using the spectral response data in a suitable short-wavelength range since each such cell indeed has a built-in electric field in the emitter region. 相似文献
7.
G. Agostinelli A. Delabie P. Vitanov Z. Alexieva H.F.W. Dekkers S. De Wolf G. Beaucarne 《Solar Energy Materials & Solar Cells》2006,90(18-19):3438-3443
Surface recombination velocities as low as 10 cm/s have been obtained by treated atomic layer deposition (ALD) of Al2O3 layers on p-type CZ silicon wafers. Low surface recombination is achieved by means of field induced surface passivation due to a high density of negative charges stored at the interface. In comparison to a diffused back surface field, an external field source allows for higher band bending, that is, a better performance. While this process yields state of the art results, it is not suited for large-scale production. Preliminary results on an industrially viable, alternative process based on a pseudo-binary system containing Al2O3 are presented, too. With this process, surface recombination velocities of 500–1000 cm/s have been attained on mc-Si wafers. 相似文献
8.
Satoshi Shimizu Akihisa Matsuda Michio Kondo 《Solar Energy Materials & Solar Cells》2008,92(10):1241-1244
In this study, highly stabilized hydrogenated amorphous silicon films and their solar cells were developed. The films were fabricated using the triode deposition system, where a mesh was installed between the cathode and the anode (substrate) in a plasma-enhanced chemical vapor deposition system. At a substrate temperature of 250 °C, the hydrogen concentration of the resulting film (Si–H=4.0 at%, Si–H2<1×1020 cm−3) was significantly less than that of conventionally prepared films. The films were used to develop the i-layers of solar cells that exhibited a significantly low degradation ratio of 7.96%. 相似文献
9.
This work is a contribution towards the understanding of the properties of hydrogenated silicon nitride (SiNx:H) that lead to efficient surface and bulk passivation of the silicon substrate. Considering the deposition system used (low-frequency plasma-enhanced chemical vapour deposition (PECVD)), we report very low values of surface recombination velocity Seff. As-deposited Si-rich SiNx:H leads to the best results (n-type Si: Seff=4 cm/s - p-type Si: Seff=14 cm/s). After annealing, the surface passivation quality is drastically deteriorated for Si-rich SiNx:H whereas it is lightly improved for low refractive index SiNx:H (n∼2-2.1). The chemical analysis of the layers highlighted a high hydrogen concentration, regardless the SiNx:H stoichiometry. However, the involved H-bond types as well as the hydrogen desorption kinetics are strongly dependent on the SiNx:H composition. Furthermore, “N-rich” SiNx:H appears to be denser and thermally more stable than Si-rich SiNx:H. When subjected to a high-temperature treatment, such a layer is believed to induce the release of hydrogen in its atomic form, which consequently leads to an efficient passivation of surface and bulk defects of the Si substrate. The results are discussed and compared with the literature data reported for the different configurations of PECVD reactors. 相似文献
10.
S.R. Jadkar J.V. Sali A.M. Funde Nabeel Ali Bakr P.B. Vidyasagar R.R. Hawaldar D.P. Amalnerkar 《Solar Energy Materials & Solar Cells》2007,91(8):714-720
Hydrogenated amorphous silicon (a-Si:H) thin films were deposited from pure silane (SiH4) using hot-wire chemical vapor deposition (HW-CVD) method. We have investigated the effect of substrate temperature on the structural, optical and electrical properties of these films. Deposition rates up to 15 Å s−1 and photosensitivity 106 were achieved for device quality material. Raman spectroscopic analysis showed the increase of Rayleigh scattering in the films with increase in substrate temperature. The full width at half maximum of TO peak (ΓTO) and deviation in bond angle (Δθ) are found smaller than those obtained for P-CVD deposited a-Si:H films. The hydrogen content in the films was found <1 at% over the range of substrate temperature studied. However, the Tauc's optical band gap remains as high as 1.70 eV or much higher. The presence of microvoids in the films may be responsible for high value of band gap at low hydrogen content. A correlation between electrical and structural properties has been found. Finally, the photoconductivity degradation of optimized a-Si:H film under intense sunlight was also studied. 相似文献
11.
J. Degoulange I. Prichaud C. Trassy S. Martinuzzi 《Solar Energy Materials & Solar Cells》2008,92(10):1269-1273
A solution to the problem of the shortage of silicon feedstock used to grow multicrystalline ingots can be the production of a feedstock obtained by the direct purification of upgraded metallurgical silicon by means of a plasma torch. It is found that the dopant concentrations in the material manufactured following this metallurgical route are in the 1017 cm−3 range. Minority carrier diffusion lengths Ln are close to 35 μm in the raw wafers and increases up to 120 μm after the wafers go through the standard processing steps needed to make solar cells: phosphorus diffusion, aluminium–silicon alloying and hydrogenation by deposition of a hydrogen-rich silicon nitride layer followed by an annealing. Ln values are limited by the presence of residual metallic impurities, mainly slow diffusers like aluminium, and also by the high doping level. 相似文献
12.
Highest-quality surface passivation of low-resistivity p-type silicon using stoichiometric PECVD silicon nitride 总被引:1,自引:0,他引:1
The surface passivation properties of silicon nitride (SiN) films fabricated by high-frequency direct plasma-enhanced chemical vapour deposition (PECVD) on low-resistivity (1 Ω cm) p-type silicon solar cell substrates have been investigated. The process gases used were ammonia and a mixture of silane and nitrogen. In order to find the optimum set of SiN deposition parameters, a large number of carrier lifetime test structures were prepared under different deposition conditions. The optimised deposition parameters resulted in outstandingly low surface recombination velocities (SRVs) below 10 cm/s. Interestingly, we find the lowest SRVs for stoichiometric SiN films, as indicated by a refractive index of 1.9. In former studies similarly low SRVs had only been obtained for silicon-rich SiN films. The fundamentally different passivation behaviour of our SiN films is attributed to the addition of nitrogen to the process gases. 相似文献
13.
Surface passivation is one of the primary requirements for high efficient silicon solar cells. Though the current existed passivation techniques are effective, expensive equipments are required. In this paper, a comprehensive understanding of the SiO2 passivation layer grown by liquid phase deposition (LPD) was presented, which was cost-effective and very simple. It was found that the post-annealing process could significantly enhance the passivation effect of the LPD SiO2 film. Besides, it was revealed that both chemical passivation and field-effect passivation mechanisms played important roles in outstanding passivation effect of the LPD SiO2 film through analyzing the minority carrier lifetime and the surface recombination velocity of n-type and p-type silicon wafers. Although the deposition parameters had little influence on the passivation effect, they affected the deposition rate. Therefore, appropriate deposition parameters should be carefully chosen based on the compromise of the deposition rate and fabrication cost. By utilizing the LPD SiO2 film as surface passivation layer, a 19.5%-efficient silicon solar cell on a large-scale wafer (156 mm × 156 mm) was fabricated. 相似文献
14.
In this work, we have investigated three different surface passivation technologies: classical thermal oxidation (CTO), rapid thermal oxidation (RTO) and silicon nitride by plasma enhanced chemical vapor deposition (PECVD). Eight different passivation properties including SiO2/SiNx stacks on phosphorus diffused (100 and 40 Ω/Sq) and non-diffused 1 Ω cm FZ silicon were compared. Both types of SiO2 layers, CTO and RTO, yield a higher effective lifetime on the emitter surface than on the non-diffused surface. For the SiNx layers the situation is reverted. On the other hand, with SiO2/SiNx stacks high lifetimes are obtained not only non-diffused surface but also on the diffused surface. Thus, we have chosen the RTO/SiNx stack layers as front and rear surface passivation in solar cells, which passivate relatively good on the surface and has very low-weighted reflection. On planar cells passivated with RTO/SiNx a very high Voc of 675.6 mV and a Jsc of 35.1 mA/cm2 was achieved. Compared to a planar cell using CTO the efficiency of RTO/SiNx cell is 0.8% higher (4.5% relative). It can be concluded that the RTO/SiNx layers are the optimal passivation for the front and rear surface. On the other hand, for textured cells, the Jsc and FF of RTO/SiNx cells are lower than those of CTO cells. The main reasons of these Jsc and FF losses were also discussed systematically. 相似文献
15.
A. Rohatgi V. Yelundur J. Jeong A. Ebong M. D. Rosenblum J. I. Hanoka 《Solar Energy Materials & Solar Cells》2002,74(1-4)
A low-cost, manufacturable defect gettering and passivation treatment, involving simultaneous anneal of a PECVD SiNx film and a screen-printed Al layer, is found to improve the lifetime in Si ribbon materials from 1–10 μs to over 20 μs. Our results indicate that the optimum anneal temperature for SiNx-induced hydrogenation is 700°C for EFG and increases to 825°C when Al is present on the back of the sample. This not only improves the degree of hydrogenation, but also forms an effective back surface field. We propose a three-step physical model, based on our results, in which defect passivation is governed by the release of hydrogen from the SiNx film due to annealing, the generation of vacancies during Al–Si alloying, and the retention of hydrogen at defect sites due to rapid cooling. Controlled rapid cooling was implemented after the hydrogenation anneal to improve the retention of hydrogen at defect sites by incorporating an RTP contact firing scheme. RTP contact firing improved the performance of ribbon solar cells by 1.3–1.5% absolute when compared to slow, belt furnace contact firing. This enhancement was due to improved back surface recombination velocity, fill factor, and bulk lifetime. Enhanced hydrogenation and rapid heating and cooling resulted in screen-printed Si ribbon cell efficiencies approaching 15%. 相似文献
16.
A novel contacting technique has been demonstrated that involves low-temperature sinter of aluminium to form localised pinhole ohmic contacts through a silicon dioxide layer to the silicon substrate. A subsequent deposition of amorphous silicon and another low-temperature sinter allows solid-phase epitaxial growth of p+ silicon (Si) in the pinholes to achieve lower effective surface recombination velocities than the localised Al/Si interface. The technique has been demonstrated to allow ohmic contacts to be formed through oxide as thick as 3000 Å. This paper presents further developments of the contacting technique when applied on the back of buried contact solar cells. Higher fill factors (as high as 80%), improved open-circuit voltages (by 20–28 mV) and an increase of 7–12% in short-circuit currents have been achieved as a result. Initial analysis has revealed that heat treatment required for the formation of pinhole contacts or the epitaxial growth of p+ Si has a detrimental effect on the passivation quality of the oxide layer even in regions where no spiking has occurred. These findings indicate further improvement and optimisation of the contacting technique are possible. 相似文献
17.
Yasushi Sobajima Kunihiro Mori Masahiro Tsukamoto Norimitsu Yoshida Masao Takahashi Hikaru Kobayashi Shuichi Nonomura 《Solar Energy Materials & Solar Cells》2005,85(2):240-187
Effects of cyanide (CN) treatment with hydrogenated amorphous silicon (a-Si:H) films have been investigated. The decrease of ΔV/V was observed in cyanide treated a-Si:H films and the successive thermal annealing at 200°C after CN treatment induced the further reduction of the ΔV/V. XPS spectra show the indirect evidence that the cyanide species is present within 10 nm from the hydrogenated amorphous silicon surface. The results of CN treatment with a-Si:H solar cells are demonstrated. 相似文献
18.
We report fabrication and characterization of solar cells based on vapor-liquid-solid (VLS) grown silicon nanowires (NWs) that form core-shell radial p-n junction structures. We observe efficiency enhancement due to the presence of the NWs that increase the light trapping within the device, while the use of gold as VLS catalyst results in increased carrier recombination within the wires. From the spectral efficiency data, we identify that the surface recombination effect becomes more significant in the large surface area NW cells. To remedy this issue we demonstrate the efficacy of a highly conformal Al2O3 film grown by atomic layer deposition to serve as surface passivation layer. This work highlights the key issues confronted by NW-based solar cells grown by VLS technique. 相似文献
19.
R. W. Collins A. S. Ferlauto G. M. Ferreira Chi Chen Joohyun Koh R. J. Koval Yeeheng Lee J. M. Pearce C. R. Wronski 《Solar Energy Materials & Solar Cells》2003,78(1-4):143
Real time spectroscopic ellipsometry has been applied to develop deposition phase diagrams that can guide the fabrication of hydrogenated silicon (Si:H) thin films at low temperatures (<300°C) for highest performance electronic devices such as solar cells. The simplest phase diagrams incorporate a single transition from the amorphous growth regime to the mixed-phase (amorphous+microcrystalline) growth regime versus accumulated film thickness [the a→(a+μc) transition]. These phase diagrams have shown that optimization of amorphous silicon (a-Si:H) intrinsic layers by RF plasma-enhanced chemical vapor deposition (PECVD) at low rates is achieved using the maximum possible flow ratio of H2 to SiH4 that can be sustained while avoiding the a→(a+μc) transition. More recent studies have suggested that a similar strategy is appropriate for optimization of p-type Si:H thin films. The simple phase diagrams can be extended to include in addition the thickness at which a roughening transition is detected in the amorphous film growth regime. It is proposed that optimization of a-Si:H in higher rate RF PECVD processes further requires the maximum possible thickness onset for this roughening transition. 相似文献
20.
A. Focsa I. Gordon J.M. Auger A. Slaoui G. Beaucarne J. Poortmans C. Maurice 《Renewable Energy》2008,33(2):267
In this work, we present the structural quality of polycrystalline silicon films formed by high-temperature chemical vapor deposition (CVD) on mullite ceramics coated with spin-on flowable oxides (FOx) serving as intermediate layers (ILs). The average grain size and the size distribution were investigated by optical microscopy. It is found that more than 65% of the surface of polysilicon films grown on boron-doped FOx is covered by large grains of 5–10 μm. The intra-grain and inner-grain defects as well as the grain orientation were analyzed with the electron backscattering diffraction (EBSD) technique. Twin-type defects such as Σ3 and Σ9 are frequently present in these silicon layers, which are slightly (1 1 0) preferentially oriented. Finally, we present the photovoltaic data on test solar cells made on these CVD polysilicon films. An efficiency of about 3.3% is reported. The limiting factors, as well as possible improvements, are discussed. 相似文献