Efficiency Improvement of Silicon Solar Cells by Nitric Acid Oxidization
TL;DR: In this article, the oxide layer on the surface of a p-type silicon substrate was grown under various growth times and temperatures while under nitric acid treatment, and an efficiency improvement of absolute 2% was obtained using their laboratory fabrication process.
Abstract: In this study, we investigate the effect of nitric acid oxidation on p-type silicon solar cells. The oxide layer on the surface of a p-type silicon substrate was grown under various growth times and temperatures while under nitric acid treatment. After 30 min of growth at 23 °C, an efficiency improvement of absolute 2% was obtained using our laboratory fabrication process.
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Patent•
23 Apr 2011
TL;DR: In this article, a method and structure for obtaining ultra-low surface recombination velocities from highly efficient surface passivation in crystalline silicon substrate-based solar cells by utilizing a bi-layer passivation scheme which also works as an efficient ARC.
Abstract: The disclosed subject matter provides a method and structure for obtaining ultra-low surface recombination velocities from highly efficient surface passivation in crystalline silicon substrate- based solar cells by utilizing a bi-layer passivation scheme which also works as an efficient ARC. The bi-layer passivation consists of a first thin layer of wet chemical oxide or a thin hydrogenated amorphous silicon layer. A second layer of amorphous hydrogenated silicon nitride film is deposited on top of the wet chemical oxide or amorphous silicon film. This deposition is then followed by annealing to further enhance the surface passivation.
32 citations
TL;DR: In this paper, a boron-inkjet printing method was used to create high efficiency n-type Si cells with a Voc of 644 mV, a Jsc of 38.6 mA/cm2, and a fill factor of 76.3%.
Abstract: Formation of a well-passivated boron emitter for mass production of low-cost and high-efficiency n-type silicon solar cells is a major challenge in the photovoltaic industry. In this letter, we report on a novel and commercially viable method, inkjet printing, to create boron emitters. Phosphorus diffusion was used on the rear to form a back-surface held in conjunction with chemically grown oxide/silicon nitride (SiNx) stack on the front and back for surface passivation. Finally, front and back screen-printed contacts were formed through the dielectric stacks to fabricate large-area (239 cm2) n-type cells. This technology resulted in 19.0%-efficient p+-n-n+ cells with a Voc of 644 mV, a Jsc of 38.6 mA/cm2, and a fill factor of 76.3%. This demonstrates for the hrst time the promise of boron-inkjet-printing technology for low-cost and high-performance n-type Si cells.
14 citations
Cites background from "Efficiency Improvement of Silicon S..."
...5 nm) oxide layer on both sides of the wafers followed by PECVD SiNx AR-coating layer deposition on both sides of the cells [13]....
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TL;DR: In this article, the root cause of variation in surface recombination for Si wafers after different cleaning processes and for different passivation layers was investigated using a combination of calibrated photoluminescence (PL) imaging and transmission electron microscopy (TEM).
Abstract: In this work, the root cause of variation in surface recombination for Si wafers after different cleaning processes and for different passivation layers is investigated using a combination of calibrated photoluminescence (PL) imaging and transmission electron microscopy (TEM). The use of a HF-last or oxide-last cleaning and/or conditioning process is shown to have a strong impact on surface recombination for SiNx passivated surfaces, but little impact for Al2O3/SiNx stacks. For a SiNx passivation layer, cross-sectional TEM imaging revealed the formation of a ≈1–2 nm SiOx interlayer resulting from a controlled oxidation during the last cleaning/conditioning step. The presence of the SiOx layer reduces the interface defect density (Dit,midgap) by an order of magnitude and dramatically increases the effective carrier lifetime. However, for Al2O3/SiNx passivated surfaces, TEM studies revealed that a SiOx layer is formed at the interface between the c-Si and AlOx even for cleaning processes ending with HF-last treatment due to which the cleaning sequence has minimal impact on the effective carrier lifetime.
12 citations
Cites background from "Efficiency Improvement of Silicon S..."
...It has previously been reported that a wet-chemically grownSiOx interlayer leads tohigher effectivecarrier lifetimes due to a significant reduction inDit,midgap [3, 5, 15]....
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TL;DR: In this paper, the influence of surface cleaning on the quality of surface passivation achievable for boron-doped emitters was investigated, including the use of different combinations of HCl, HF, HNO3, and ozonated deionized water (DIO3).
Abstract: The use of proper surface preparation and cleaning methods for Si wafers prior to the deposition of passivation layers is essential to minimize surface recombination and realize high efficiencies (> 20%) in crystalline Si photovoltaic cells. In this work, the influence of wafer cleaning on the quality of surface passivation achievable for boron-doped emitters was investigated, including the use of different combinations of HCl, HF, HNO3, and ozonated deionized water (DIO3). These different surface preparations and cleaning sequences were performed on undiffused and boron diffused n-type Cz Si wafers, followed by the deposition of either silicon nitride (SiNx) or an aluminum oxide film capped with SiNx (Al2O3/SiNx stack). Additionally, both planar and anisotropically textured wafers were used. Injection-level dependent photoconductance measurements and calibrated photoluminescence imaging were performed on symmetrical boron diffused samples based on the different cleaning processes and passivation materials described above. Additionally, non-contact corona-Kelvin measurements were used to extract the total charge and interface defect density at the Si surfaces. We found that cleaning variations strongly influence carrier lifetime for SiNx passivated Si, but the effect is less pronounced in the case of Al2O3/SiNx stacks. It was further observed that DIO3-last treatment resulted in higher lifetimes for the SiNx stacks. Overall, it emerged that the (DIO3 + HF + HCl → HF → DIO3) clean is a promising and potentially low cost cleaning sequence for the photovoltaics industry.
10 citations
01 Jan 2017
3 citations
Cites background from "Efficiency Improvement of Silicon S..."
...As shown via simulation in the subsequent section, the large positive Qtot for the SiNx passivation means a very low Dit,midgap is needed to achieve a low J0E, whereas the large negative Qtot of the Al2O3/SiNx passivation stack is less sensitive to variations in Dit,midgap....
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...It has previously been reported that a wet-chemically grown SiOx interlayer leads to higher effective carrier lifetimes due to a significant reduction in Dit,midgap.[56, 58, 59] Therefore, we can conclude that the higher lifetimes obtained for DIO3+HF+HCl→HF→DIO3 and HNO3→HF→HNO3 cleans is due to the chemical passivation exhibited by the 1-2 nm SiOx layer formed as a result of oxide-last step during wafer cleaning process....
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...[53, 54] Not only can DIO3 be used to form very clean Si surfaces, but DIO3 can be used to form very thin SiOx layers that further reduce surface recombination.[55-60]...
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...It has previously been reported that a wet-chemically grown SiOx interlayer leads to higher effective carrier lifetimes due to a significant reduction in Dit,midgap....
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References
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TL;DR: In this paper, the surface passivation of low resistivity singlecrystalline p-silicon wafers is reported using silicon nitride fabricated at low temperature (375 °C) in a remote plasmaenhanced chemical vapor deposition system.
Abstract: Outstanding surface passivation of low‐resistivity single‐crystalline p‐silicon is reported using silicon nitride fabricated at low temperature (375 °C) in a remote plasma‐enhanced chemical vapor deposition system. The effective surface recombination velocity Seff is determined as a function of the bulk injection level from light‐biased photoconductance decay measurements. On polished as well as chemically textured silicon wafers we find that our remote plasma silicon nitride provides better surface passivation than the best high‐temperature thermal oxides ever reported. For polished 1.5 and 0.7 Ω cm p‐silicon wafers, record low Seff values of 4 and 20 cm/s, respectively, are presented.
304 citations
TL;DR: In this article, a remote-plasma SiN film is applied to the rear surface of the low-resistivity p-type substrates to achieve a surface recombination velocities as low as 4 cm s−1.
Abstract: Using a remote-plasma technique as opposed to the conventional direct-plasma technique, significant progress has been obtained at ISFH in the area of low-temperature surface passivation of p-type crystalline silicon solar cells by means of silicon nitride (SiN) films fabricated at 350–400°C in a plasma-enhanced chemical vapour deposition system. If applied to the rear surface of the low-resistivity p-type substrates, the remote-plasma SiN films provide outstanding surface recombination velocities (SRVs) as low as 4 cm s−1, which is by a clear margin the lowest value ever obtained on a low-resistivity p-Si wafer passivated by a solid film, including highest quality thermal oxides. Compared to direct-plasma SiN films or thermally grown oxides, the remote-plasma films not only provide significantly better SRVs on low-resistivity p-silicon wafers, but also an enormously improved stability against ultraviolet (UV) light. The potential of these remote-plasma silicon nitride films for silicon solar cell applications is further increased by the fact that they provide a surface passivation on phosphorus-diffused emitters which is comparable to high-quality thermal oxides. Furthermore, if combined with a thermal oxide and a caesium treatment, the films induce a UV-stable inversion-layer emitter of outstanding electronic quality.
Due to the low deposition temperature and the high refraction index, these remote-plasma SiN films act as highly efficient surface-passivating antireflection coatings. Application of these films to cost-effective silicon solar cell designs presently under development at ISFH turned out to be most successful, as demonstrated by diffused p-n junction cells with efficiencies above 19%, by bifacial p-n junction cells with front and rear efficiencies above 18%, by mask-free evaporated p-n junction cells with efficiencies above 18% and by MIS inversion-layer cells with a new record efficiency of above 17%. All cells are found to be stable during a UV test corresponding to more than 4 years of glass-encapsulated outdoor operation. © 1997 John Wiley & Sons, Ltd.
171 citations
TL;DR: In this article, excellent passivation properties of intrinsic amorphous silicon carbide (a-SiCx:H) films deposited by plasma enhanced chemical vapor deposition on single-crystalline silicon (c-Si) wafers have been obtained.
Abstract: Excellent passivation properties of intrinsic amorphous silicon carbide (a-SiCx:H) films deposited by plasma enhanced chemical vapor deposition on single-crystalline silicon (c-Si) wafers have been obtained. The dependence of the effective surface recombination velocity, Seff, on deposition temperature, total pressure and methane (CH4) to silane (SiH4) ratio has been studied for these films using lifetime measurements made with the quasi-steady-state photoconductance technique. The dependence of the effective lifetime, τeff, on the excess carrier density, Δn, has been measured and also simulated through a physical model based on Shockley–Read–Hall statistics and an insulator/semiconductor structure with fixed charges and band bending. A Seff at the a-SiCx:H/c-Si interface lower than 30 cm s−1 was achieved with optimized deposition conditions. This passivation quality was found to be three times better than that of noncarbonated amorphous silicon (a-Si:H) films deposited under equivalent conditions.
152 citations
TL;DR: In this paper, an ultrathin oxide is grown at room temperature by soaking the silicon wafers in a solution of nitric acid prior to the deposition of the silicon nitride antireflection coating film.
Abstract: We have developed a simple method to passivate industrially produced boron-doped emitters for n-type base silicon solar cells using an ultrathin (∼1.5nm) silicon dioxide layer between the silicon emitter and the silicon nitride antireflection coating film. This ultrathin oxide is grown at room temperature by soaking the silicon wafers in a solution of nitric acid prior to the deposition of the silicon nitride antireflection coating film. The n-type solar cells processed in such a way demonstrate a conversion efficiency enhancement of more than 2% absolute over the solar cells passivated without the silicon dioxide layer.
99 citations
TL;DR: In this paper, it was shown that poly-SiO2 layers with a uniform thickness can be formed even on a rough surface of polycrystalline Si thin film by direct Si oxidation with nitric acid (HNO3).
Abstract: Silicon dioxide (SiO2) layers with a thickness more than 10 nm can be formed at ∼120 °C by direct Si oxidation with nitric acid (HNO3). Si is initially immersed in 40 wt.% HNO3 at the boiling temperature of 108 °C, which forms a ∼1 nm SiO2 layer, and the immersion is continued after reaching the azeotropic point (i.e., 68 wt.% HNO3 at 121 °C), resulting in an increase in the SiO2 thickness. The nitric acid oxidation rates are the same for (1 1 1) and (1 0 0) orientations, and n-type and p-type Si wafers. The oxidation rate is constant at least up to 15 nm SiO2 thickness (i.e., 1.5 nm/h for single crystalline Si and 3.4 nm/h for polycrystalline Si (poly-Si)), indicating that the interfacial reaction is the rate-determining step. SiO2 layers with a uniform thickness are formed even on a rough surface of poly-Si thin film.
54 citations