High-rate deposition of a-SiNx:H for photovoltaic applications by the expanding thermal plasma

Abstract

General rightsCopyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.• Users may download and print one copy of any publication from the public portal for the purpose of private study or research.• You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal ? Take down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. Driven by the need for improvement of the economical competitiveness of photovoltaic energy, the feasibility of high-rate ͑Ͼ1 nm/s͒ amorphous silicon nitride (a-SiN x :H) deposited by the expanding thermal plasma ͑ETP͒ technique has been explored with respect to the application of the a-SiN x :H as functional antireflection coating on crystalline silicon solar cells. First, the deposition rate and the a-SiN x :H film properties, such as refractive index, Si, N, and H atomic density, and hydrogen bonding configurations, have been mapped for various operating conditions. From ellipsometry, elastic recoil detection, and infrared spectroscopy, it has been shown that deposition rates up to 20 nm/s can be reached with a fair film homogeneity and that the refractive index and the N/Si ratio can fully be tuned by the plasma composition while the hydrogen content can be controlled by the substrate temperature. Good antireflection coating performance of the a-SiN x :H has therefore been observed for monocrystalline silicon solar cells. These cells with ETP a-SiN x :H yielded only slightly lower conversion efficiencies than high-quality reference cells due to a much lower degree of surface passivation. This lack of surface passivation has also been shown in a separate study on the surface recombination velocity. Furthermore, it has been tested whether the a-SiN x :H films lead to silicon bulk passivation, which is essential for solar cells based on cheaper, defective silicon stock material such as multicrystalline silicon. It has been proven that bulk passivation of the cells is indeed induced by the high-rate ETP deposited a-SiN x :H after a high-temperature step in which the metal contacts of the cells are processed. These results make the ETP technique an interesting candidate for high-throughput processing of competitive silicon solar cells.

Structure and optical properties of TiO2 thin films deposited by ALD method

“…The effect of minimizing the reflectance of light is achieved, among others, by depositing an antireflection coating. The most popular antireflection coating used in photovoltaics are: SiO 2 , a-SiNx:H, TiO 2 , a-Si:C:H, ZnS, Ta 2 O 5 , SnxOx, SiNx, MgF 2 [1][2][3][4][5][6][7][8][9][10][11][12]. Titanium dioxide 4 and Ti(OCH(CH 3 ) 2 ) 4 , which react with H 2 O.…”

High-Quality Surface Passivation Obtained by High-Rate Deposited Silicon Nitride, Silicon Dioxide and Amorphous Silicon using the Versatile Expanding Thermal Plasma Technique

“…The ETP technique is renowned for the high deposition rates that can be achieved for various materials including a-SiNx:H [4,5]. The reason that these high deposition rates can be achieved is due to the fact that plasma production takes place in an upstream plasma source operated at sub atmospheric pressure.…”

Industrial high-rate (∼5 nm/s) deposited silicon nitride yielding high-quality bulk and surface passivation under optimum anti-reflection coating conditions

“…13 Interestingly, the lowest S eff values are reached for the refractive index range of n ¼ 1Á95-2Á4 in which S eff is basically constant. This range is the most appropriate for solar cell applications while for the widely applied refractive index of n ¼ 2Á1 S eff is comparable to the state-of-the-art S eff values obtained in other industrial-type reactors for somewhat lower resistivity wafers.…”

“…The expanding thermal plasma (ETP) technique is renowned for the high deposition rates that can be achieved for films of various materials, including a-SiN x :H. 13,14 The reason that these high deposition rates can be achieved is due to the fact that plasma production takes place in an upstream plasma source operated at subatmospheric pressure. At this high pressure, plasma production is very effective (with ionization degrees up to 10% and dissociation degrees up to 100% when molecular gases are used).…”

“…Initial studies revealed that the technique was capable of reducing reflection losses 13 and inducing bulk passivation. 14 Evidence for bulk passivation was obtained by local internal quantum efficiency (IQE) measurements, however, the level of bulk passivation still lagged behind compared to state-of-the-art a-SiN x :H films used as a reference.…”