Surface Passivation

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Wmm Erwin Kessels - One of the best experts on this subject based on the ideXlab platform.

  • status and prospects of al2o3 based Surface Passivation schemes for silicon solar cells
    Journal of Vacuum Science and Technology, 2012
    Co-Authors: Gijs G Dingemans, Wmm Erwin Kessels
    Abstract:

    The reduction in electronic recombination losses by the Passivation of silicon Surfaces is a critical enabler for high-efficiency solar cells. In 2006, aluminum oxide (Al2O3) nanolayers synthesized by atomic layer deposition (ALD) emerged as a novel solution for the Passivation of p- and n-type crystalline Si (c-Si) Surfaces. Today, high efficiencies have been realized by the implementation of ultrathin Al2O3 films in laboratory-type and industrial solar cells. This article reviews and summarizes recent work concerning Al2O3 thin films in the context of Si photovoltaics. Topics range from fundamental aspects related to material, interface, and Passivation properties to synthesis methods and the implementation of the films in solar cells. Al2O3 uniquely features a combination of field-effect Passivation by negative fixed charges, a low interface defect density, an adequate stability during processing, and the ability to use ultrathin films down to a few nanometers in thickness. Although various methods can be used to synthesize Al2O3, this review focuses on ALD—a new technology in the field of c-Si photovoltaics. The authors discuss how the unique features of ALD can be exploited for interface engineering and tailoring the properties of nanolayer Surface Passivation schemes while also addressing its compatibility with high-throughput manufacturing. The recent progress achieved in the field of Surface Passivation allows for higher efficiencies of industrial solar cells, which is critical for realizing lower-cost solar electricity in the near future.

  • Surface Passivation of phosphorus diffused n type emitters by plasma assisted atomic layer deposited al2o3
    Physica Status Solidi-rapid Research Letters, 2012
    Co-Authors: Bram Hoex, Van De Mcm Richard Sanden, Jan Schmidt, Rolf Brendel, Wmm Erwin Kessels
    Abstract:

    In recent years Al2O3 has received tremendous interest in the photovoltaic community for the application as Surface Passivation layer for crystalline silicon. Especially p-type c-Si Surfaces are very effectively passivated by Al2O3, including p-type emitters, due to the high fixed negative charge in the Al2O3 film. In this Letter we show that Al2O3 prepared by plasma-assisted atomic layer deposition (ALD) can actually provide a good level of Surface Passivation for highly doped n-type emitters in the range of 10-100 Omega/sq with implied-V-oc values up to 680 mV. For n-type emitters in the range of 100-200 Omega/sq the implied-V-oc drops to a value of 600 mV for a 200 Omega/sq emitter, indicating a decreased level of Surface Passivation. For even lighter doped n-type Surfaces the Passivation quality increases again to implied-V-oc values well above 700 mV. Hence, the results presented here indicate that within a certain doping range, highly doped n- and p-type Surfaces can be passivated simultaneously by Al2O3. (C) 2011 WILEY-VCH Verlag GmbH a Co. KGaA, Weinheim

  • excellent si Surface Passivation by low temperature sio2 using an ultrathin al2o3 capping film
    Physica Status Solidi-rapid Research Letters, 2011
    Co-Authors: Gijs G Dingemans, Van De Mcm Richard Sanden, Wmm Erwin Kessels
    Abstract:

    It is demonstrated that the application of an ultrathin aluminum oxide (Al2O3) capping film can improve the level of silicon Surface Passivation obtained by low-temperature synthesized SiO2 profoundly. For such stacks, a very high level of Surface Passivation was achieved after annealing, with Seff < 2 cm/s for 3.5 Ω cm n-type c-Si. This can be attributed primarily to a low interface defect density (Dit < 1011 eV–1 cm–2). Consequently, the Al2O3 capping layer induced a high level of chemical Passivation at the Si/SiO2 interface. Moreover, the stacks showed an exceptional stability during high-temperature firing processes and therefore provide a low temperature (≤400 °C) alternative to thermally-grown SiO2. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

  • influence of the deposition temperature on the c si Surface Passivation by al2o3 films synthesized by ald and pecvd
    Electrochemical and Solid State Letters, 2010
    Co-Authors: Gijs G Dingemans, Van De Mcm Richard Sanden, Wmm Erwin Kessels
    Abstract:

    The material properties and c-Si Surface Passivation have been investigated for Al 2 O 3 films deposited using thermal and plasma atomic layer deposition (ALD) and plasma-enhanced chemical vapor deposition (PECVD) for temperatures (T dep ) between 25 and 400°C. Optimal Surface Passivation by ALD Al 2 O 3 was achieved at T dep = 150-250°C with S eff < 3 cm/s for ∼2 Ω cm p-type c-Si. PECVD Al 2 O 3 provided a comparable high level of Passivation for T dep = 150-300°C and contained a high fixed negative charge density of ∼6 x 10 12 cm -2 . Outstanding Surface Passivation performance was therefore obtained for thermal ALD, plasma ALD, and PECVD for a relatively wide range of Al 2 O 3 material properties.

  • silicon Surface Passivation by ultrathin al2o3 films synthesized by thermal and plasma atomic layer deposition
    Physica Status Solidi-rapid Research Letters, 2010
    Co-Authors: Gijs G Dingemans, Van De Mcm Richard Sanden, Peter Engelhart, Robert Seguin, Wmm Erwin Kessels
    Abstract:

    In this Letter, we report that both thermal atomic layer deposition (ALD) with H2O, and plasma ALD with an O2 plasma, can be used to deposit Al2O3 for a high level of Surface Passivation of crystalline silicon (c-Si). For 3.5 Ω cm n-type c-Si, plasma ALD Al2O3 resulted in ultralow Surface recombination velocities of Seff 10 nm were required. Thermal stability against a high temperature firing step was demonstrated for ultrathin thermal and plasma ALD Al2O3 films of 5 nm by Seff < 9.2 and < 6.5 cm/s, respectively. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Bart Vermang - One of the best experts on this subject based on the ideXlab platform.

  • addressing the impact of rear Surface Passivation mechanisms on ultra thin cu in ga se2 solar cell performances using scaps 1 d model
    Solar Energy, 2017
    Co-Authors: Raja Venkata Ratan Kotipalli, Bart Vermang, Olivier Poncelet, Yun Zeng, Laurent Francis, Denis Flandre
    Abstract:

    We present a (1-D) SCAPS device model to address the following: (i) the Surface Passivation mechanisms (i.e.field-effect and chemical), (ii) their impact on the CIGS solar cell performance for vary ...

  • improved rear Surface Passivation of cu in ga se _ bf 2 solar cells a combination of an al _ bf 2 o _ bf 3 rear Surface Passivation layer and nanosized local rear point contacts
    IEEE Journal of Photovoltaics, 2014
    Co-Authors: Bart Vermang, Viktor Fjallstrom, Marika Edoff
    Abstract:

    An innovative rear contacting structure for copper indium gallium (di) selenide (CIGS) thin-film solar cells is developed in an industrially viable way and demonstrated in tangible devices. The idea stems from the silicon (Si) industry, where rear Surface Passivation layers are combined with micron-sized local point contacts to boost the open-circuit voltage (VOC) and, hence, cell efficiency. However, compared with Si solar cells, CIGS solar cell minority carrier diffusion lengths are several orders lower in magnitude. Therefore, the proposed CIGS cell design reduces rear Surface recombination by combining a rear Surface Passivation layer and nanosized local point contacts. Atomic layer deposition of Al2O3 is used to passivate the CIGS Surface and the formation of nanosphere-shaped precipitates in chemical bath deposition of CdS to generate nanosized point contact openings. The manufactured Al2O3 rear Surface passivated CIGS solar cells with nanosized local rear point contacts show a significant improvement in VOC compared with unpassivated reference cells.

  • approach for al2o3 rear Surface Passivation of industrial p type si perc above 19
    Progress in Photovoltaics, 2012
    Co-Authors: Bart Vermang, Hans Goverde, Loic Tous, A Lorenz, Patrick Choulat, Jorg Horzel, J John
    Abstract:

    Atomic layer deposition (ALD) of thin Al2O3 (≤10 nm) films is used to improve the rear Surface Passivation of large-area screen-printed p-type Si passivated emitter and rear cells (PERC). A blister-free stack of Al2O3/SiOx/SiNx is developed, leading to an improved back reflection and a rear recombination current (J0,rear) of 92 ± 6 fA/cm2. The Al2O3/SiOx/SiNx stack is blister-free if a 700°C anneal in N2 is performed after the Al2O3 deposition and prior to the SiOx/SiNx capping. A clear relationship between blistering density and lower open-circuit voltage (VOC) due to increased rear contacting area is shown. In case of the blister-free Al2O3/SiOx/SiNx rear Surface Passivation stack, an average cell efficiency of 19.0% is reached and independently confirmed by FhG-ISE CalLab. Compared with SiOx/SiNx-passivated PERC, there is an obvious gain in VOC and short-circuit current (JSC) of 5 mV and 0.2 mA/cm2, respectively, thanks to improved rear Surface Passivation and rear internal reflection. Copyright © 2012 John Wiley & Sons, Ltd.

  • approach for al2o3 rear Surface Passivation of industrial p type si perc above 19
    Progress in Photovoltaics, 2012
    Co-Authors: Bart Vermang, Hans Goverde, Loic Tous, A Lorenz, Patrick Choulat, Jorg Horzel, J John
    Abstract:

    Atomic layer deposition (ALD) of thin Al2O3 (≤10 nm) films is used to improve the rear Surface Passivation of large-area screen-printed p-type Si passivated emitter and rear cells (PERC). A blister-free stack of Al2O3/SiOx/SiNx is developed, leading to an improved back reflection and a rear recombination current (J0,rear) of 92 ± 6 fA/cm2. The Al2O3/SiOx/SiNx stack is blister-free if a 700°C anneal in N2 is performed after the Al2O3 deposition and prior to the SiOx/SiNx capping. A clear relationship between blistering density and lower open-circuit voltage (VOC) due to increased rear contacting area is shown. In case of the blister-free Al2O3/SiOx/SiNx rear Surface Passivation stack, an average cell efficiency of 19.0% is reached and independently confirmed by FhG-ISE CalLab. Compared with SiOx/SiNx-passivated PERC, there is an obvious gain in VOC and short-circuit current (JSC) of 5 mV and 0.2 mA/cm2, respectively, thanks to improved rear Surface Passivation and rear internal reflection. Copyright © 2012 John Wiley & Sons, Ltd.

  • Surface Passivation for si solar cells a combination of advanced Surface cleaning and thermal atomic layer deposition of al2o3
    Solid State Phenomena, 2012
    Co-Authors: Bart Vermang, A Rothschild, A Racz, Xavier Loozen, Joachim John, Karine Kenis, Kurt Wostyn, Twan Bearda, Paul Mertens, Jef Poortmans
    Abstract:

    Thermal atomic layer deposition (ALD) of Al2O3 provides an adequate level of Surface Passivation for both p-type and n-type Si solar cells. To obtain the most qualitative and uniform Surface Passivation advanced cleaning development is required. The studied pre-deposition treatments include an HF (Si-H) or oxidizing (Si-OH) last step and finish with simple hot-air drying or more sophisticated Marangoni drying. To examine the quality and uniformity of Surface Passivation - after cleaning and Al2O3 deposition - carrier density imaging (CDI) and quasi-steady-state photo-conductance (QSSPC) are applied. A hydrophilic Surface clean that leads to improved Surface Passivation level is found. Si-H starting Surfaces lead to equivalent Passivation quality but worse Passivation uniformity. The hydrophilic Surface clean is preferred because it is thermodynamically stable, enables higher and more uniform ALD growth and consequently exhibits better Surface Passivation uniformity.

Jan Schmidt - One of the best experts on this subject based on the ideXlab platform.

  • Surface Passivation of phosphorus diffused n type emitters by plasma assisted atomic layer deposited al2o3
    Physica Status Solidi-rapid Research Letters, 2012
    Co-Authors: Bram Hoex, Van De Mcm Richard Sanden, Jan Schmidt, Rolf Brendel, Wmm Erwin Kessels
    Abstract:

    In recent years Al2O3 has received tremendous interest in the photovoltaic community for the application as Surface Passivation layer for crystalline silicon. Especially p-type c-Si Surfaces are very effectively passivated by Al2O3, including p-type emitters, due to the high fixed negative charge in the Al2O3 film. In this Letter we show that Al2O3 prepared by plasma-assisted atomic layer deposition (ALD) can actually provide a good level of Surface Passivation for highly doped n-type emitters in the range of 10-100 Omega/sq with implied-V-oc values up to 680 mV. For n-type emitters in the range of 100-200 Omega/sq the implied-V-oc drops to a value of 600 mV for a 200 Omega/sq emitter, indicating a decreased level of Surface Passivation. For even lighter doped n-type Surfaces the Passivation quality increases again to implied-V-oc values well above 700 mV. Hence, the results presented here indicate that within a certain doping range, highly doped n- and p-type Surfaces can be passivated simultaneously by Al2O3. (C) 2011 WILEY-VCH Verlag GmbH a Co. KGaA, Weinheim

  • high rate atomic layer deposition of al2o3 for the Surface Passivation of si solar cells
    Energy Procedia, 2011
    Co-Authors: Florian Werner, Walter Stals, Roger Gortzen, Boris Veith, Rolf Brendel, Jan Schmidt
    Abstract:

    Abstract High-rate spatial atomic layer deposition (ALD) enables an industrially relevant deposition of high-quality aluminum oxide (Al2O3) films for the Surface Passivation of silicon solar cells. We demonstrate a homogeneous Surface Passivation at a deposition rate of ∼30 nm/min on 15.6 × 15.6 cm2 silicon wafers of 10 nm thick Al2O3 layers deposited in a novel inline spatial ALD system. The effective Surface recombination velocity on n-type Czochralski-grown (Cz) silicon wafers is shown to be virtually independent of injection level. Surface recombination velocities below 2.9 cm/s and an extremely low interface state density below 8 × 1010 eV 1 cm 2 are achieved. We demonstrate that the novel inline spatial ALD system provides the means to integrate Al2O3 Passivation layers into industrial solar cells.

  • silicon Surface Passivation by atomic layer deposited al2o3
    Journal of Applied Physics, 2008
    Co-Authors: Bram Hoex, Van De Mcm Richard Sanden, Jan Schmidt, Peter Pohl, Wmm Erwin Kessels
    Abstract:

    Thin Al2O3 films with a thickness of 7–30 nm synthesized by plasma-assisted atomic layer deposition (ALD) were used for Surface Passivation of crystalline silicon (c-Si) of different doping concentrations. The level of Surface Passivation in this study was determined by techniques based on photoconductance, photoluminescence, and infrared emission. Effective Surface recombination velocities of 2 and 6 cm/s were obtained on 1.9 Ω cm n-type and 2.0 Ω cm p-type c-Si, respectively. An effective Surface recombination velocity below 1 cm/s was unambiguously obtained for nearly intrinsic c-Si passivated by Al2O3. A high density of negative fixed charges was detected in the Al2O3 films and its impact on the level of Surface Passivation was demonstrated experimentally. The negative fixed charge density results in a flat injection level dependence of the effective lifetime on p-type c-Si and explains the excellent Passivation of highly B-doped c-Si by Al2O3. Furthermore, a brief comparison is presented between the ...

  • 20 1 efficient crystalline silicon solar cell with amorphous silicon rear Surface Passivation
    Progress in Photovoltaics, 2005
    Co-Authors: Martin Schaper, Jan Schmidt, Heiko Plagwitz, Rolf Brendel
    Abstract:

    We have developed a crystalline silicon solar cell with amorphous silicon (a-Si:H) rear-Surface Passivation based on a simple process. The a-Si:H layer is deposited at 225°C by plasma-enhanced chemical vapor deposition. An aluminum grid is evaporated onto the a-Si:H-passivated rear. The base contacts are formed by COSIMA (contact formation to a-Si:H passivated wafers by means of annealing) when subsequently depositing the front silicon nitride layer at 325°C. The a-Si:H underneath the aluminum fingers dissolves completely within the aluminum and an ohmic contact to the base is formed. This contacting scheme results in a very low contact resistance of 3.5 ±0.2 mΩ cm2 on low-resistivity (0.5 Ω cm) p-type silicon, which is below that obtained for conventional Al/Si contacts. We achieve an independently confirmed energy conversion efficiency of 20.1% under one-sun standard testing conditions for a 4 cm2 large cell. Measurements of the internal quantum efficiency show an improved rear Surface Passivation compared with reference cells with a silicon nitride rear Passivation. Copyright © 2005 John Wiley & Sons, Ltd.

Bram Hoex - One of the best experts on this subject based on the ideXlab platform.

  • dielectric Surface Passivation for silicon solar cells a review
    Physica Status Solidi (a), 2017
    Co-Authors: Ruy S Bonilla, Bram Hoex, Phillip Hamer, Pr Wilshaw
    Abstract:

    Silicon wafer solar cells continue to be the leading photovoltaic technology, and in many places are now providing a substantial portion of electricity generation. Further adoption of this technology will require processing that minimises losses in device performance. A fundamental mechanism for efficiency loss is the recombination of photo-generated charge carriers at the unavoidable cell Surfaces. Dielectric coatings have been shown to largely prevent these losses through a combination of different Passivation mechanisms. This review aims to provide an overview of the dielectric Passivation coatings developed in the past two decades using a standardised methodology to characterise the metrics of Surface recombination across all techniques and materials. The efficacy of a large set of materials and methods has been evaluated using such metrics and a discussion on the current state and prospects for further Surface Passivation improvements is provided.

  • excellent c si Surface Passivation by low temperature atomic layer deposited titanium oxide
    Applied Physics Letters, 2014
    Co-Authors: Baochen Liao, Bram Hoex, Armin G. Aberle, C S Bhatia
    Abstract:

    In this work, we demonstrate that thermal atomic layer deposited (ALD) titanium oxide (TiOx) films are able to provide a—up to now unprecedented—level of Surface Passivation on undiffused low-resistivity crystalline silicon (c-Si). The Surface Passivation provided by the ALD TiOx films is activated by a post-deposition anneal and subsequent light soaking treatment. Ultralow effective Surface recombination velocities down to 2.8 cm/s and 8.3 cm/s, respectively, are achieved on n-type and p-type float-zone c-Si wafers. Detailed analysis confirms that the TiOx films are nearly stoichiometric, have no significant level of contaminants, and are of amorphous nature. The Passivation is found to be stable after storage in the dark for eight months. These results demonstrate that TiOx films are also capable of providing excellent Passivation of undiffused c-Si Surfaces on a comparable level to thermal silicon oxide, silicon nitride, and aluminum oxide. In addition, it is well known that TiOx has an optimal refractive index of 2.4 in the visible range for glass encapsulated solar cells, as well as a low extinction coefficient. Thus, the results presented in this work could facilitate the re-emergence of TiOx in the field of high-efficiency silicon wafer solar cells.

  • Surface Passivation of phosphorus diffused n type emitters by plasma assisted atomic layer deposited al2o3
    Physica Status Solidi-rapid Research Letters, 2012
    Co-Authors: Bram Hoex, Van De Mcm Richard Sanden, Jan Schmidt, Rolf Brendel, Wmm Erwin Kessels
    Abstract:

    In recent years Al2O3 has received tremendous interest in the photovoltaic community for the application as Surface Passivation layer for crystalline silicon. Especially p-type c-Si Surfaces are very effectively passivated by Al2O3, including p-type emitters, due to the high fixed negative charge in the Al2O3 film. In this Letter we show that Al2O3 prepared by plasma-assisted atomic layer deposition (ALD) can actually provide a good level of Surface Passivation for highly doped n-type emitters in the range of 10-100 Omega/sq with implied-V-oc values up to 680 mV. For n-type emitters in the range of 100-200 Omega/sq the implied-V-oc drops to a value of 600 mV for a 200 Omega/sq emitter, indicating a decreased level of Surface Passivation. For even lighter doped n-type Surfaces the Passivation quality increases again to implied-V-oc values well above 700 mV. Hence, the results presented here indicate that within a certain doping range, highly doped n- and p-type Surfaces can be passivated simultaneously by Al2O3. (C) 2011 WILEY-VCH Verlag GmbH a Co. KGaA, Weinheim

  • stability of al2o3 and al2o3 a sinx h stacks for Surface Passivation of crystalline silicon
    Journal of Applied Physics, 2009
    Co-Authors: Gijs G Dingemans, Bram Hoex, Van De Mcm Richard Sanden, Peter Engelhart, Robert Seguin, F Einsele, Wmm Erwin Kessels
    Abstract:

    The thermal and ultraviolet (UV) stability of crystalline silicon (c-Si) Surface Passivation provided by atomic layer deposited Al2O3 was compared with results for thermal SiO2. For Al2O3 and Al2O3/a-SiNx:H stacks on 2 Ω cm n-type c-Si, ultralow Surface recombination velocities of Seff 800 °C) used for screen printed c-Si solar cells. Effusion measurements revealed the loss of hydrogen and oxygen during firing through the detection of H2 and H2O. Al2O3 also demonstrated UV stability with the Surface Passivation improving during UV irradiation.

  • on the c si Surface Passivation mechanism by the negative charge dielectric al2o3
    Journal of Applied Physics, 2008
    Co-Authors: Bram Hoex, J. J.h. Gielis, Van De Mcm Richard Sanden, Wilhelmus M. M. Kessels
    Abstract:

    Al2O3 is a versatile high-κ dielectric that has excellent Surface Passivation properties on crystalline Si (c-Si), which are of vital importance for devices such as light emitting diodes and high-efficiency solar cells. We demonstrate both experimentally and by simulations that the Surface Passivation can be related to a satisfactory low interface defect density in combination with a strong field-effect Passivation induced by a negative fixed charge density Qf of up to 1013 cm−2 present in the Al2O3 film at the interface with the underlying Si substrate. The negative polarity of Qf in Al2O3 is especially beneficial for the Passivation of p-type c-Si as the bulk minority carriers are shielded from the c-Si Surface. As the level of field-effect Passivation is shown to scale with Qf2, the high Qf in Al2O3 tolerates a higher interface defect density on c-Si compared to alternative Surface Passivation schemes.

Rolf Brendel - One of the best experts on this subject based on the ideXlab platform.

  • Surface Passivation of phosphorus diffused n type emitters by plasma assisted atomic layer deposited al2o3
    Physica Status Solidi-rapid Research Letters, 2012
    Co-Authors: Bram Hoex, Van De Mcm Richard Sanden, Jan Schmidt, Rolf Brendel, Wmm Erwin Kessels
    Abstract:

    In recent years Al2O3 has received tremendous interest in the photovoltaic community for the application as Surface Passivation layer for crystalline silicon. Especially p-type c-Si Surfaces are very effectively passivated by Al2O3, including p-type emitters, due to the high fixed negative charge in the Al2O3 film. In this Letter we show that Al2O3 prepared by plasma-assisted atomic layer deposition (ALD) can actually provide a good level of Surface Passivation for highly doped n-type emitters in the range of 10-100 Omega/sq with implied-V-oc values up to 680 mV. For n-type emitters in the range of 100-200 Omega/sq the implied-V-oc drops to a value of 600 mV for a 200 Omega/sq emitter, indicating a decreased level of Surface Passivation. For even lighter doped n-type Surfaces the Passivation quality increases again to implied-V-oc values well above 700 mV. Hence, the results presented here indicate that within a certain doping range, highly doped n- and p-type Surfaces can be passivated simultaneously by Al2O3. (C) 2011 WILEY-VCH Verlag GmbH a Co. KGaA, Weinheim

  • high rate atomic layer deposition of al2o3 for the Surface Passivation of si solar cells
    Energy Procedia, 2011
    Co-Authors: Florian Werner, Walter Stals, Roger Gortzen, Boris Veith, Rolf Brendel, Jan Schmidt
    Abstract:

    Abstract High-rate spatial atomic layer deposition (ALD) enables an industrially relevant deposition of high-quality aluminum oxide (Al2O3) films for the Surface Passivation of silicon solar cells. We demonstrate a homogeneous Surface Passivation at a deposition rate of ∼30 nm/min on 15.6 × 15.6 cm2 silicon wafers of 10 nm thick Al2O3 layers deposited in a novel inline spatial ALD system. The effective Surface recombination velocity on n-type Czochralski-grown (Cz) silicon wafers is shown to be virtually independent of injection level. Surface recombination velocities below 2.9 cm/s and an extremely low interface state density below 8 × 1010 eV 1 cm 2 are achieved. We demonstrate that the novel inline spatial ALD system provides the means to integrate Al2O3 Passivation layers into industrial solar cells.

  • 20 1 efficient crystalline silicon solar cell with amorphous silicon rear Surface Passivation
    Progress in Photovoltaics, 2005
    Co-Authors: Martin Schaper, Jan Schmidt, Heiko Plagwitz, Rolf Brendel
    Abstract:

    We have developed a crystalline silicon solar cell with amorphous silicon (a-Si:H) rear-Surface Passivation based on a simple process. The a-Si:H layer is deposited at 225°C by plasma-enhanced chemical vapor deposition. An aluminum grid is evaporated onto the a-Si:H-passivated rear. The base contacts are formed by COSIMA (contact formation to a-Si:H passivated wafers by means of annealing) when subsequently depositing the front silicon nitride layer at 325°C. The a-Si:H underneath the aluminum fingers dissolves completely within the aluminum and an ohmic contact to the base is formed. This contacting scheme results in a very low contact resistance of 3.5 ±0.2 mΩ cm2 on low-resistivity (0.5 Ω cm) p-type silicon, which is below that obtained for conventional Al/Si contacts. We achieve an independently confirmed energy conversion efficiency of 20.1% under one-sun standard testing conditions for a 4 cm2 large cell. Measurements of the internal quantum efficiency show an improved rear Surface Passivation compared with reference cells with a silicon nitride rear Passivation. Copyright © 2005 John Wiley & Sons, Ltd.

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