Abstract In this work, by exploiting two-dimensional (2-D) TCAD numerical simulations, we performed a study of optimum emitter coverage ratio (R opt ) to reach maximum performance on back contact-back junction (BC-BJ) solar cells. R opt exhibits a strong dependence on pitch, emitter and back surface field (BSF) doping and bulk resistivity, ranging between 0.6 and 0.95. By fixing BSF doping, emitter doping and bulk resistivity, BSF and emitter width can be optimized independently one another. The optimum BSF width and the optimum emitter width are given by a trade-off between series resistance and electrical shading losses. From the design perspective, focusing on optimizing the BSF and emitter width is more effective than optimizing R at fixed pitch or BSF width

Cocorullo, Giuseppe

Crupi, Felice

Guerra, Noemi

Guevara, Marco

Maccaronio, Vincenzo

Procel, Paul

English

Open Access Repository

1876-6102 © 2015 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).Peer review by the scientific conference committee of SiliconPV 2015 under responsibility of PSE AGdoi: 10.1016/j.egypro.2015.07.022  Energy Procedia  77 ( 2015 )  149 – 152 ScienceDirect5th International Conference on Silicon Photovoltaics, SiliconPV 2015 Understanding the optimization of the emitter coverage in BC-BJ solar cells Paul Procel, Marco Guevara, Vincenzo Maccaronio, Noemi Guerra, Felice Crupi, Giuseppe Cocorullo DIMES, University of Calabria, 87036 Rende (CS), Italy Abstract In this work, by exploiting two-dimensional (2-D) TCAD numerical simulations, we performed a study of optimum emitter coverage ratio (Ropt) to reach maximum performance on back contact-back junction (BC-BJ) solar cells. Ropt exhibits a strong dependence on pitch, emitter and back surface field (BSF) doping and bulk resistivity, ranging between 0.6 and 0.95. By fixing BSF doping, emitter doping and bulk resistivity, BSF and emitter width can be optimized independently one another. The optimum BSF width and the optimum emitter width are given by a trade-off between series resistance and electrical shading losses. From the design perspective, focusing on optimizing the BSF and emitter width is more effective than optimizing R at fixed pitch or BSF width.  © 2015 The Authors. Published by Elsevier Ltd. Peer review by the scientific conference committee of SiliconPV 2015 under responsibility of PSE AG. Keywords: back contact; back junction; solar cells; BC-BJ; TCAD;   1. Introduction Silicon-based back contact-back junction (BC-BJ) solar cell has been demonstrated particularly promising concept in order to improve the conversion efficiency (currently more than 24% [1],[2]) because of its evident advantages, such as the absence of front contact, elimination of shadowing losses and the simplification of cell interconnection at module level. An important design parameter of BC-BJ solar cell is the emitter coverage R, defined as the pitch fraction occupied by the emitter width. Several works have suggested different optimum values of emitter coverage ratio (Ropt) to reach maximum efficiencies [3], [4], ranging between 0.7 and 0.8. This optimum value is explained by electrical shadow and series resistance losses balance [5]. The aim of this work is to Available online at www.sciencedirect.com© 2015 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).Peer review by the scientific conference committee of SiliconPV 2015 under responsibility of PSE AG150   Paul Procel et al. /  Energy Procedia  77 ( 2015 )  149 – 152 understand the dependence of Ropt on the main physical and geometrical parameters of BC-BJ solar cells by exploiting TCAD simulations.  2. Simulation methodology  Fig. 1 illustrates the simulated symmetry element used in this work calibrated as 200 μm-thick floating zone (FZ) cSi n-type substrate. The doping profiles in back surface field (BSF), front surface field (FSF) and emitter are Gaussian functions of the spatial coordinate featuring the peak located at the edge of the interface and a junction depth of 2 μm for BSF and emitter and of 1μm for FSF region. The front and back surfaces are coated by a double-layer anti-reflective coating (ARC) composed by Si3N4 and SiO2. Front interface is texturized by regular upright pyramids featuring a 10 μm base, while back interface is planar. The physical models have been calibrated by using the state-of-the-art parameterizations in [6] described on [7]. For all the simulations we used the standard AM1.5G spectrum (1000 W/m2), FSF peak doping concentration equal to 2.51x1018 cm-3, and a gap of 5 μm. A set of experiments was performed considering the following parameter ranges: emitter and BSF doping peak from 1x1018 to 1x1021 cm-3, BSF width from 55 μm to 300 μm, emitter width from 90 μm to 1600 μm, two different bulk resistivity values of 1 -cm and 10 -cm. The main investigated parameter is Ropt, which represents the value of R required to maximize the efficiency for each analysis, performed by fixing some parameters and varying the others. Therefore, Ropt is a relative optimum and not the absolute optimum.                Fig. 1. Sketch of the symmetry element of BC-BJ solar cell used in the simulations. 3. Results and discussion    Fig. 2 illustrates Ropt as a function of emitter and BSF doping keeping constant pitch and emitter width, for different values of BSF width and bulk resistivity. Ropt ranges in a wide interval between 0.6 and 0.95. According to [7], in terms of efficiency, there are optimum values of BSF and emitter doping levels, which do not depend one another and are quite insensitive to the cell geometrical parameters and to the bulk resistivity.  In the rest of this paper, in the case of a bulk resistivity of 1 -cm (10 -cm) we used the optimum BSF doping of 2.51x1020 cm-3 (6.31x1019 cm-3) and the optimum emitter doping of 1.58x1019 cm-3.         Paul Procel et al. /  Energy Procedia  77 ( 2015 )  149 – 152 151                Fig. 2. (a) Simulated Ropt dependence from BSF and emitter doping; (b) dotted lines illustrate calculated efficiencies.                 Fig. 3. Calculated Ropt for different values of pitch (left), emitter width (middle) and BSF width (right).  Numbers above points are calculated efficiencies. Fig. 3 illustrates results from simulations that were performed to analyze Ropt as a function of pitch, BSF and emitter width for fixed doping levels on emitter and BSF and for two different values of bulk resistivity. Ropt significantly increases with pitch and emitter width, while it significantly decreases with BSF width, ranging again in a wide interval between 0.6 and 0.95. In the case of a bulk resistivity of 1 -cm (10 -cm), the absolute maximum efficiency is 23.08 (22.96) corresponding to Ropt of 0.91 (0.81).  Fig. 4 illustrates efficiency as a function of BSF and emitter width keeping constant BSF and emitter doping levels for different values of bulk resistivity. It is worth noting that the BSF and the emitter width can be optimized independently one another. In the case of a bulk resistivity of 1 -cm (10 -cm), the optimum BSF width is 55 μm (100 μm) and the optimum emitter width is 646 μm (448 μm). These optimum values are obtained as a trade-off between electrical shading and series resistance effects. The electrical shading losses decrease by increasing the emitter width and by reducing the BSF width, while the series resistance losses increase by increasing the emitter width and by reducing the BSF width. By comparing Fig. 4a and 4b, it is evident that by increasing the bulk resistivity, the optimum BSF width increases due to the stronger contribution of bulk to total series resistance losses. b) a) 152   Paul Procel et al. /  Energy Procedia  77 ( 2015 )  149 – 152          Fig. 4. Simulated efficiency dependence from BSF and emitter width for a bulk resistivity of 1 -cm (a) and 10 -cm (b). In both cases, the BSF and the emitter width can be optimized independently one another. 4. Conclusions    In this study, we reported that Ropt exhibits a strong dependence on emitter and BSF doping levels, pitch, emitter and BSF width, and bulk resistivity, ranging between 0.6 and 0.95. From the geometry design perspective, it is more effective optimizing independently the BSF and emitter width than optimizing R at fixed pitch or BSF width. In the case of a bulk resistivity of 1 -cm (10 -cm), we obtained an absolute maximum efficiency of 23.08 (22.96) for BSF width of 55 μm (100 μm) and emitter width of 646 μm (448 μm), which give a pitch of 706 μm (553 μm) and Ropt of 0.91 (0.81). Ackowledgments This work has been partially supported by the Ecuadorian National Department of Science and Technology (SENESCYT). References [1] Cousins P., Smith D., Luan H.-C., Maning J., Dennis T., Walhauer A., Wilson K., Harley G., Mulligan W.: Generation 3: Improved performance at lower cost, Proc. 35th IEEE Photovoltaic Specialist Conference PVSC. Honolulu, Hawaii, USA; 2010. p. 275-278. [2] Franklin E. et al Design, fabrication and characterization of a 24.4% efficient interdigitated back contact solar cell, Progress in Photovoltaics, 29th EU PVSEC, Amsterdam, 2014 DOI: 10.1002/pip.2556 [3] Renshaw J., Rohatgi A., Device optimization for screen printed interdigitated back contact solar cells. Photovoltaic Specialists Conference (PVSC); 2011. 37th IEEE. [4] Renshaw J., Kang M.H., Meernonqkolkiar V., Rohatgi A., Carlson O.,Bennett M., 34th IEEE Photovoltaic Specialists Conference (PVSC). Philadelphia; 7-12 June 2009. p. 375 -379. [5] Kluska S., Ganek F., Rudiger M., Hermle M., Glunz S., Modeling and optimization study of industrial n-type high-efficiency back-contact back-junction silicon solar cells. Solar Energy Materials & Solar Cells, 94, 568, 2010. p. 568-577 [6] Synopsis, Sentaurus device user guide, Version G-2012.06; June 2012. [7] Procel P., Maccaronio V., Crupi F., Cocorullo G., Zanuccoli M., Magnone P., Fiegna C. Analysis of the Impact of Doping Levels on Performance of Back Contact - Back Junction Solar Cells, in Proc. of 4rd SiliconPV, Energy Procedia, 's-Hertogenbosch; 2014. p. 128 - 132.  a) b) 

Understanding the Optimization of the Emitter Coverage in BC-BJ Solar Cells☆

AbstractIn this work, by exploiting two-dimensional (2-D) TCAD numerical simulations, we performed a study of optimum emitter coverage ratio (Ropt) to reach maximum performance on back contact-back junction (BC-BJ) solar cells. Ropt exhibits a strong dependence on pitch, emitter and back surface field (BSF) doping and bulk resistivity, ranging between 0.6 and 0.95. By fixing BSF doping, emitter doping and bulk resistivity, BSF and emitter width can be optimized independently one another. The optimum BSF width and the optimum emitter width are given by a trade-off between series resistance and electrical shading losses. From the design perspective, focusing on optimizing the BSF and emitter width is more effective than optimizing R at fixed pitch or BSF width

Elsevier - Publisher Connector 

1876-6102 © 2015 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license 
(http://creativecommons.org/licenses/by-nc-nd/4.0/).
Peer review by the scientific conference committee of SiliconPV 2015 under responsibility of PSE AG
doi: 10.1016/j.egypro.2015.07.022 
 Energy Procedia  77 ( 2015 )  149 – 152 
ScienceDirect
5th International Conference on Silicon Photovoltaics, SiliconPV 2015 
Understanding the optimization of the emitter coverage in 
BC-BJ solar cells 
Paul Procel, Marco Guevara, Vincenzo Maccaronio, Noemi Guerra, Felice Crupi, 
Giuseppe Cocorullo 
DIMES, University of Calabria, 87036 Rende (CS), Italy 
Abstract 
In this work, by exploiting two-dimensional (2-D) TCAD numerical simulations, we performed a study of optimum emitter 
coverage ratio (Ropt) to reach maximum performance on back contact-back junction (BC-BJ) solar cells. Ropt exhibits a strong 
dependence on pitch, emitter and back surface field (BSF) doping and bulk resistivity, ranging between 0.6 and 0.95. By fixing 
BSF doping, emitter doping and bulk resistivity, BSF and emitter width can be optimized independently one another. The 
optimum BSF width and the optimum emitter width are given by a trade-off between series resistance and electrical shading 
losses. From the design perspective, focusing on optimizing the BSF and emitter width is more effective than optimizing R at 
fixed pitch or BSF width. 
 
© 2015 The Authors. Published by Elsevier Ltd. 
Peer review by the scientific conference committee of SiliconPV 2015 under responsibility of PSE AG. 
Keywords: back contact; back junction; solar cells; BC-BJ; TCAD;   
1. Introduction 
Silicon-based back contact-back junction (BC-BJ) solar cell has been demonstrated particularly promising 
concept in order to improve the conversion efficiency (currently more than 24% [1],[2]) because of its evident 
advantages, such as the absence of front contact, elimination of shadowing losses and the simplification of cell 
interconnection at module level. An important design parameter of BC-BJ solar cell is the emitter coverage R, 
defined as the pitch fraction occupied by the emitter width. Several works have suggested different optimum values 
of emitter coverage ratio (Ropt) to reach maximum efficiencies [3], [4], ranging between 0.7 and 0.8. This optimum 
value is explained by electrical shadow and series resistance losses balance [5]. The aim of this work is to 
Available online at www.sciencedirect.com
© 2015 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license 
(http://creativecommons.org/licenses/by-nc-nd/4.0/).
Peer review by the scientific conference committee of SiliconPV 2015 under responsibility of PSE AG
150   Paul Procel et al. /  Energy Procedia  77 ( 2015 )  149 – 152 
understand the dependence of Ropt on the main physical and geometrical parameters of BC-BJ solar cells by 
exploiting TCAD simulations.  
2. Simulation methodology  
Fig. 1 illustrates the simulated symmetry element used in this work calibrated as 200 μm-thick floating zone (FZ) 
cSi n-type substrate. The doping profiles in back surface field (BSF), front surface field (FSF) and emitter are 
Gaussian functions of the spatial coordinate featuring the peak located at the edge of the interface and a junction 
depth of 2 μm for BSF and emitter and of 1μm for FSF region. The front and back surfaces are coated by a double-
layer anti-reflective coating (ARC) composed by Si3N4 and SiO2. Front interface is texturized by regular upright 
pyramids featuring a 10 μm base, while back interface is planar. 
The physical models have been calibrated by using the state-of-the-art parameterizations in [6] described on [7]. 
For all the simulations we used the standard AM1.5G spectrum (1000 W/m2), FSF peak doping concentration equal 
to 2.51x1018 cm-3, and a gap of 5 μm. A set of experiments was performed considering the following parameter 
ranges: emitter and BSF doping peak from 1x1018 to 1x1021 cm-3, BSF width from 55 μm to 300 μm, emitter width 
from 90 μm to 1600 μm, two different bulk resistivity values of 1 ȍ-cm and 10 ȍ-cm. The main investigated 
parameter is Ropt, which represents the value of R required to maximize the efficiency for each analysis, performed 
by fixing some parameters and varying the others. Therefore, Ropt is a relative optimum and not the absolute 
optimum. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Fig. 1. Sketch of the symmetry element of BC-BJ solar cell used in the simulations. 
3. Results and discussion    
Fig. 2 illustrates Ropt as a function of emitter and BSF doping keeping constant pitch and emitter width, for 
different values of BSF width and bulk resistivity. Ropt ranges in a wide interval between 0.6 and 0.95. According to 
[7], in terms of efficiency, there are optimum values of BSF and emitter doping levels, which do not depend one 
another and are quite insensitive to the cell geometrical parameters and to the bulk resistivity.  In the rest of this 
paper, in the case of a bulk resistivity of 1 ȍ-cm (10 ȍ-cm) we used the optimum BSF doping of 2.51x1020 cm-3 
(6.31x1019 cm-3) and the optimum emitter doping of 1.58x1019 cm-3. 
 
 
 
 
 
 
 
 Paul Procel et al. /  Energy Procedia  77 ( 2015 )  149 – 152 151
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Fig. 2. (a) Simulated Ropt dependence from BSF and emitter doping; (b) dotted lines illustrate calculated efficiencies. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Fig. 3. Calculated Ropt for different values of pitch (left), emitter width (middle) and BSF width (right).  Numbers above points are calculated 
efficiencies. 
Fig. 3 illustrates results from simulations that were performed to analyze Ropt as a function of pitch, BSF and 
emitter width for fixed doping levels on emitter and BSF and for two different values of bulk resistivity. Ropt 
significantly increases with pitch and emitter width, while it significantly decreases with BSF width, ranging again 
in a wide interval between 0.6 and 0.95. In the case of a bulk resistivity of 1 ȍ-cm (10 ȍ-cm), the absolute 
maximum efficiency is 23.08 (22.96) corresponding to Ropt of 0.91 (0.81). 
 
Fig. 4 illustrates efficiency as a function of BSF and emitter width keeping constant BSF and emitter doping 
levels for different values of bulk resistivity. It is worth noting that the BSF and the emitter width can be optimized 
independently one another. In the case of a bulk resistivity of 1 ȍ-cm (10 ȍ-cm), the optimum BSF width is 55 μm 
(100 μm) and the optimum emitter width is 646 μm (448 μm). These optimum values are obtained as a trade-off 
between electrical shading and series resistance effects. The electrical shading losses decrease by increasing the 
emitter width and by reducing the BSF width, while the series resistance losses increase by increasing the emitter 
width and by reducing the BSF width. By comparing Fig. 4a and 4b, it is evident that by increasing the bulk 
resistivity, the optimum BSF width increases due to the stronger contribution of bulk to total series resistance losses. 
b) a) 
152   Paul Procel et al. /  Energy Procedia  77 ( 2015 )  149 – 152 
 
 
 
 
 
 
 
 
 
Fig. 4. Simulated efficiency dependence from BSF and emitter width for a bulk resistivity of 1 ȍ-cm (a) and 10 ȍ-cm (b). In both cases, the BSF 
and the emitter width can be optimized independently one another. 
4. Conclusions    
In this study, we reported that Ropt exhibits a strong dependence on emitter and BSF doping levels, pitch, emitter 
and BSF width, and bulk resistivity, ranging between 0.6 and 0.95. From the geometry design perspective, it is more 
effective optimizing independently the BSF and emitter width than optimizing R at fixed pitch or BSF width. In the 
case of a bulk resistivity of 1 ȍ-cm (10 ȍ-cm), we obtained an absolute maximum efficiency of 23.08 (22.96) for 
BSF width of 55 μm (100 μm) and emitter width of 646 μm (448 μm), which give a pitch of 706 μm (553 μm) and 
Ropt of 0.91 (0.81). 
Ackowledgments 
This work has been partially supported by the Ecuadorian National Department of Science and Technology 
(SENESCYT). 
References 
[1] Cousins P., Smith D., Luan H.-C., Maning J., Dennis T., Walhauer A., Wilson K., Harley G., Mulligan W.: Generation 3: Improved 
performance at lower cost, Proc. 35th IEEE Photovoltaic Specialist Conference PVSC. Honolulu, Hawaii, USA; 2010. p. 275-278. 
[2] Franklin E. et al Design, fabrication and characterization of a 24.4% efficient interdigitated back contact solar cell, Progress in Photovoltaics, 
29th EU PVSEC, Amsterdam, 2014 DOI: 10.1002/pip.2556 
[3] Renshaw J., Rohatgi A., Device optimization for screen printed interdigitated back contact solar cells. Photovoltaic Specialists Conference 
(PVSC); 2011. 37th IEEE. 
[4] Renshaw J., Kang M.H., Meernonqkolkiar V., Rohatgi A., Carlson O.,Bennett M., 34th IEEE Photovoltaic Specialists Conference (PVSC). 
Philadelphia; 7-12 June 2009. p. 375 -379. 
[5] Kluska S., Ganek F., Rudiger M., Hermle M., Glunz S., Modeling and optimization study of industrial n-type high-efficiency back-contact 
back-junction silicon solar cells. Solar Energy Materials & Solar Cells, 94, 568, 2010. p. 568-577 
[6] Synopsis, Sentaurus device user guide, Version G-2012.06; June 2012. 
[7] Procel P., Maccaronio V., Crupi F., Cocorullo G., Zanuccoli M., Magnone P., Fiegna C. Analysis of the Impact of Doping Levels on 
Performance of Back Contact - Back Junction Solar Cells, in Proc. of 4rd SiliconPV, Energy Procedia, 's-Hertogenbosch; 2014. p. 128 - 132.  
a) b) 


Understanding the Optimization of the Emitter Coverage in BC-BJ Solar Cells 

https://www.openaccessrepository.it/record/34160/files/fulltext.pdf

Understanding the Optimization of the Emitter Coverage in BC-BJ Solar Cells☆

Abstract

Similar works

Full text

Available Versions

Open Access Repository

Elsevier - Publisher Connector