scholarly journals Understanding of Passivation Mechanism in Heterojunction c-Si Solar Cells

2008 ◽  
Vol 1066 ◽  
Author(s):  
Michio Kondo ◽  
Stefaan De Wolf ◽  
Hiroyuki Fujiwara
Keyword(s):  
Solar Cells ◽  
Epitaxial Layer ◽  
Surface Passivation ◽  
Crystalline Silicon ◽  
Amorphous Layer ◽  
Growth Direction ◽  
Boron Doped ◽  
Junction Structure ◽  
Hydrogenated Amorphous

ABSTRACTIntrinsic hydrogenated amorphous silicon (a-Si:H) films can yield in outstanding electronic surface passivation of crystalline silicon (c-Si) wafers as utilized in the HIT (heterojunction with intrinsic thin layer) solar cells. We have studied the correlation between the passivation quality and the interface nature between thin amorphous layers and an underlying c-Si substrate for understanding the passivation mechanism. We found that a thin (∼5nm) intrinsic layer is inhomogeneous along the growth direction with the presence of a hydrogen rich layer at the interface and that completely amorphous films result in better passivation quality and device performance than an epitaxial layer. Post annealing improves carrier lifetime for the amorphous layer, whereas the annealing is detrimental for the epitaxial layer. We have also found that the passivation quality of intrinsic a Si:H(i) film deteriorates severely by the presence of a boron-doped a-Si:H(p+) overlayer due to Si-H rupture in the a-Si:H(i) film. Finally, for a passivation layer in the hetero-junction structure, a-Si1−xOx will be demonstrated in comparison with a-Si:H.

scholarly journals Light trapping in hydrogenated amorphous and nano-crystalline silicon thin film solar cells

2009 ◽  
Vol 1153 ◽  
Author(s):  
Jeffrey Yang ◽  
Baojie Yan ◽  
Guozhen Yue ◽  
Subhendu Guha
Keyword(s):  
Stainless Steel ◽  
Solar Cells ◽  
Triple Junction ◽  
Crystalline Silicon ◽  
Light Trapping ◽  
Nano Crystalline ◽  
Back Reflectors ◽  
Back Reflector ◽  
Junction Structure ◽  
Hydrogenated Amorphous

AbstractLight trapping effect in hydrogenated amorphous silicon-germanium alloy (a-SiGe:H) and nano-crystalline silicon (nc-Si:H) thin film solar cells deposited on stainless steel substrates with various back reflectors is reviewed. Structural and optical properties of the Ag/ZnO back reflectors are systematically characterized and correlated to solar cell performance, especially the enhancement in photocurrent. The light trapping method used in our current production lines employing an a-Si:H/a-SiGe:H/a-SiGe:H triple-junction structure consists of a bi-layer of Al/ZnO back reflector with relatively thin Al and ZnO layers. Such Al/ZnO back reflectors enhance the short-circuit current density, Jsc, by ˜20% compared to bare stainless steel. In the laboratory, we use Ag/ZnO back reflector for higher Jsc and efficiency. The gain in Jsc is about ˜30% for an a-SiGe:H single-junction cell used in the bottom cell of a multi-junction structure. In recent years, we have also worked on the optimization of Ag/ZnO back reflectors for nano-crystalline silicon (nc-Si:H) solar cells. We have carried out a systematic study on the effect of texture for Ag and ZnO. We found that for a thin ZnO layer, a textured Ag layer is necessary to increase Jsc, even though the parasitic loss is higher at the Ag and ZnO interface due to the textured Ag. However, a flat Ag can be used for a thick ZnO to reduce the parasitic loss, while the light scattering is provided by the textured ZnO. The gain in Jsc for nc-Si:H solar cells on Ag/ZnO back reflectors is in the range of ˜60-75% compared to cells deposited on bare stainless steel, which is much larger than the enhancement observed for a-SiGe:H cells. The highest total current density achieved in an a-Si:H/a-SiGe:H/nc-Si:H triple-junction structure on Ag/ZnO back reflector is 28.6 mA/cm2, while it is 26.9 mA/cm2 for a high efficiency a-Si:H/a-SiGe:H/a-SiGe:H triple-junction cell.

Crystalline Silicon Surface Passivation by Pecv-Deposited Hydrogenated Amorphous Silicon Oxide Films [a-SiOx:H]

2007 ◽  
Vol 989 ◽  
Author(s):  
Thomas Mueller ◽  
Wolfgang Duengen ◽  
Reinhart Job ◽  
Maximilian Scherff ◽  
Wolfgang Fahrner
Keyword(s):  
Solar Cells ◽  
Amorphous Silicon ◽  
Thermal Annealing ◽  
Surface Passivation ◽  
Crystalline Silicon ◽  
Hydrogenated Amorphous Silicon ◽  
Window Layer ◽  
Effective Lifetime ◽  
Si Solar Cells ◽  
Hydrogenated Amorphous

AbstractIn the research field of crystalline silicon (c-Si) solar cells, electronic surface passivation has been recognized as a crucial step to achieve high conversion efficiencies. The main issue of this article is to analyze the surface passivation properties of both, n-type and p-type crystalline silicon wafers by hydrogenated amorphous silicon sub oxide [a-SiOx:H] films the for use in hetero-junction (a-Si/c-Si) solar cells. A window layer is obtained with a certain fraction of oxygen in the a-SiOx:H layers.The a-SiOx:H films were deposited by decomposition of silane, carbon dioxide and hydrogen as source gases using plasma enhanced chemical vapor deposition (PECVD). Films with varying deposition parameters such as gas flow ratio (oxygen fraction) and plasma frequency (13.56, 70.0 and 110.0 MHz) are compared.To determine the passivation quality of the a-SiOx:H films, microwave-detected photo conductance decay (µ-PCD) provides a contactless measurement of the effective recombination lifetime of free carriers. The film compositions and also the changes in the microscopic structure of the amorphous network upon thermal annealing are studied using Raman spectroscopy and optical profiling techniques.The Raman spectra reveal the generation of Si-(OH)x and Si-O-Si bonds after thermal annealing in the layers, leading to a higher effective lifetime, as it reduces the defect absorption of the sub oxides.For n-type FZ material, lifetime values as high as 1650 µs are obtained, resulting in a surface recombination velocity Seff < 9.5 cm/s.

scholarly journals The Role of Silicon Heterojunction and TCO Barriers on the Operation of Silicon Heterojunction Solar Cells: Comparison between Theory and Experiment

2021 ◽  
Vol 2021 ◽  
pp. 1-12
Author(s):  
Yaser Abdulraheem ◽  
Moustafa Ghannam ◽  
Hariharsudan Sivaramakrishnan Radhakrishnan ◽  
Ivan Gordon
Keyword(s):  
Solar Cells ◽  
Large Scale ◽  
Surface Passivation ◽  
Series Resistance ◽  
Crystalline Silicon ◽  
Thermionic Emission ◽  
Analytical Description ◽  
Theoretical Explanation ◽  
The Impact

Photovoltaic devices based on amorphous silicon/crystalline silicon (a-Si:H/c-Si) heterojunction interfaces hold the highest efficiency as of date in the class of silicon-based devices with efficiencies exceeding 26% and are regarded as a promising technology for large-scale terrestrial PV applications. The detailed understanding behind the operation of this type of device is crucial to improving and optimizing its performance. SHJ solar cells have primarily two main interfaces that play a major role in their operation: the transparent conductive oxide (TCO)/a-Si:H interface and the a-Si:H/c-Si heterojunction interface. In the work presented here, a detailed analytical description is provided for the impact of both interfaces on the performance of such devices and especially on the device fill factor ( FF ). It has been found that the TCO work function can dramatically impact the FF by introducing a series resistance element in addition to limiting the forward biased current under illumination causing the well-known S-shape characteristic in the I-V curve of such devices. On the other hand, it is shown that the thermionic emission barrier at the heterojunction interface can play a major role in introducing an added series resistance factor due to the intrinsic a-Si:H buffer layer that is usually introduced to improve surface passivation. Theoretical explanation on the role of both interfaces on device operation based on 1D device simulation is experimentally verified. The I-V characteristics of fabricated devices were compared to the curves produced by simulation, and the observed degradation in the FF of fabricated devices was explained in light of analytical findings from simulation.

scholarly journals High quality crystalline silicon surface passivation by combined intrinsic and n-type hydrogenated amorphous silicon

2011 ◽  
Vol 99 (20) ◽  
pp. 203503 ◽  
Author(s):  
Jan-Willem A. Schüttauf ◽  
Karine H. M. van der Werf ◽  
Inge M. Kielen ◽  
Wilfried G. J. H. M. van Sark ◽  
Jatindra K. Rath ◽  
...  
Keyword(s):  
Amorphous Silicon ◽  
Silicon Surface ◽  
Surface Passivation ◽  
Crystalline Silicon ◽  
Hydrogenated Amorphous Silicon ◽  
High Quality ◽  
Hydrogenated Amorphous ◽  
Silicon Surface Passivation

Improved Passivation of a-Si:H / c-Si Interfaces Through Film Restructuring

2008 ◽  
Vol 1066 ◽  
Author(s):  
Michael Zanoni Burrows ◽  
U. K. Das ◽  
S. Bowden ◽  
S. S. Hegedus ◽  
R. L. Opila ◽  
...  
Keyword(s):  
Hydrogen Bonding ◽  
Surface Passivation ◽  
Crystalline Silicon ◽  
Silicon Surfaces ◽  
Initial Surface ◽  
Effective Lifetime ◽  
Bonding Structure ◽  
First Time ◽  
Post Deposition

ABSTRACTThe as-deposited passivation quality of amorphous silicon films on crystalline silicon surfaces is dependent on deposition conditions and resulting hydrogen bonding structure. However the initial surface passivation can be significantly improved by low temperature post-deposition anneal. For example an improvement in effective lifetime from 780 μsec as-deposited to 2080 μsec post-anneal is reported in the present work. This work probes the hydrogen bonding environment using monolayer resolution Brewster angle transmission Fourier transform infrared spectroscopy of 100 Å thick films. It is found that there is significant restructuring at the a-Si:H / c-Si interface upon annealing and a gain of mono-hydride bonding at the c-Si surface is detected. Calculations show an additional 3.56 − 4.50 × 1014 cm−2 mono-hydride bonding at c-Si surface due to annealing. The estimation of the surface hydride oscillator strength in transmission mode is reported for the first time to be 7.2 × 10−18 cm on Si (100) surface and 7.5 × 10−18 cm on Si (111).

scholarly journals Effect of Hydrogen Content in Intrinsic a-Si:H on Performances of Heterojunction Solar Cells

2013 ◽  
Vol 2013 ◽  
pp. 1-6 ◽  
Author(s):  
Yun-Shao Cho ◽  
Chia-Hsun Hsu ◽  
Shui-Yang Lien ◽  
Dong-Sing Wuu ◽  
In-Cha Hsieh
Keyword(s):  
Solar Cells ◽  
Hydrogen Content ◽  
Crystalline Silicon ◽  
Phase Particle ◽  
Optical Emission ◽  
Point Of View ◽  
Experimental Result ◽  
Heterojunction Solar Cells ◽  
Hydrogenated Amorphous ◽  
Silane Plasma

Influences of hydrogen content in intrinsic hydrogenated amorphous silicon (i-a-Si:H) on performances of heterojunction (HJ) solar cells are investigated. The simulation result shows that in the range of 0–18% of the i-layer hydrogen content, solar cells with higher i-layer hydrogen content can have higher degree of dangling bond passivation on single crystalline silicon (c-Si) surface. In addition, the experimental result shows that HJ solar cells with a low hydrogen content have a poor a-Si:H/c-Si interface. The deteriorate interface is assumed to be attributed to (i) voids created by insufficiently passivated c-Si surface dangling bonds, (ii) voids formed by SiH2clusters, and (iii) Si particles caused by gas phase particle formation in silane plasma. The proposed assumption is well supported and explained from the plasma point of view using optical emission spectroscopy.

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