TY - JOUR
T1 - Understanding Transport in Hole Contacts of Silicon Heterojunction Solar Cells by Simulating TLM Structures
AU - Muralidharan, Pradyumna
AU - Leilaeioun, Mehdi Ashling
AU - Weigand, William
AU - Holman, Zachary C.
AU - Goodnick, Stephen M.
AU - Vasileska, Dragica
N1 - Funding Information:
Manuscript received August 1, 2019; revised October 4, 2019 and November 10, 2019; accepted November 28, 2019. Date of publication December 19, 2019; date of current version February 19, 2020. This work was supported in part by the Engineering Research Center Program of the National Science Foundation and in part by the Office of Energy Efficiency and Renewable Energy of the Department of Energy under NSF Cooperative Agreement EEC-1041895. (Corresponding author: Pradyumna Muralidharan.) P. Muralidharan, M. Leilaeioun, Z. C. Holman, and S. M. Goodnick are with the School of Electrical, Computer and Energy Engineering, Arizona State University, Tempe, AZ 85287 USA (e-mail: pmuralid@asu.edu; ashling@asu.edu; zachary.holman@asu.edu; stephen.goodnick@asu.edu).
Publisher Copyright:
© 2011-2012 IEEE.
PY - 2020/3
Y1 - 2020/3
N2 - Silicon heterojunction (SHJ) solar cell device structures use carrier-selective contacts that enable efficient collection of majority carriers while impeding the collection of minority carriers. However, these contacts can also be a source of resistive losses that degrade the performance of the solar cell. In this article, we evaluate the performance of the carrier-selective hole contact - hydrogenated amorphous silicon (a-Si:H)(i)/a-Si:H(p)/indium tin oxide (ITO)/Ag - by simulating transport in SHJ solar cell transfer length method structures. We study contact resistivity behavior by varying the a-Si:H(i) layer thickness, ITO(n+) and a-Si:H(p) layer doping, temperature, and interface defect density at the a-Si:H(i)/ crystalline silicon (c-Si) interface. In particular, we consider the effect of ITO/a-Si:H(p) and the a-Si:H(i)/c-Si heterointerfaces on contact resistivity as they play a crucial role in modulating transport through the hole contact structure. Transport models such as band-to-band tunneling, and thermionic emission models were added to describe transport across the heterointerfaces. Until now, most simulation studies have treated the ITO as a Schottky contact; in this article, we treat the ITO as an n-type semiconductor. Our simulations match well with corresponding experiments conducted to determine contact resistivity. As the a-Si:H(i) layer thickness is increased from 4 to 16 nm, the simulated contact resistivity increases from 0.50 to 2.1 Ωcm2, which deviates a maximum of 8% from the experimental measurements. It should be noted that we calculate the contact resistivity for the entire hole contact stack, which takes into account transport across the a-Si:H(p)/c-Si and ITO/a-Si:H(p) heterointerface. Corresponding experiments on cell structures showed a fill factor degradation from 77% to 70%. Our simulations indicate that a highly doped n-type ITO layer facilitates tunneling at the ITO/a-Si:H(p) heterointerface, which leads to low contact resistivities.
AB - Silicon heterojunction (SHJ) solar cell device structures use carrier-selective contacts that enable efficient collection of majority carriers while impeding the collection of minority carriers. However, these contacts can also be a source of resistive losses that degrade the performance of the solar cell. In this article, we evaluate the performance of the carrier-selective hole contact - hydrogenated amorphous silicon (a-Si:H)(i)/a-Si:H(p)/indium tin oxide (ITO)/Ag - by simulating transport in SHJ solar cell transfer length method structures. We study contact resistivity behavior by varying the a-Si:H(i) layer thickness, ITO(n+) and a-Si:H(p) layer doping, temperature, and interface defect density at the a-Si:H(i)/ crystalline silicon (c-Si) interface. In particular, we consider the effect of ITO/a-Si:H(p) and the a-Si:H(i)/c-Si heterointerfaces on contact resistivity as they play a crucial role in modulating transport through the hole contact structure. Transport models such as band-to-band tunneling, and thermionic emission models were added to describe transport across the heterointerfaces. Until now, most simulation studies have treated the ITO as a Schottky contact; in this article, we treat the ITO as an n-type semiconductor. Our simulations match well with corresponding experiments conducted to determine contact resistivity. As the a-Si:H(i) layer thickness is increased from 4 to 16 nm, the simulated contact resistivity increases from 0.50 to 2.1 Ωcm2, which deviates a maximum of 8% from the experimental measurements. It should be noted that we calculate the contact resistivity for the entire hole contact stack, which takes into account transport across the a-Si:H(p)/c-Si and ITO/a-Si:H(p) heterointerface. Corresponding experiments on cell structures showed a fill factor degradation from 77% to 70%. Our simulations indicate that a highly doped n-type ITO layer facilitates tunneling at the ITO/a-Si:H(p) heterointerface, which leads to low contact resistivities.
KW - Amorphous semiconductors
KW - Contact resistance
KW - Heterojunctions
KW - Silicon
KW - Simulation
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U2 - 10.1109/JPHOTOV.2019.2957655
DO - 10.1109/JPHOTOV.2019.2957655
M3 - Article
AN - SCOPUS:85081106794
SN - 2156-3381
VL - 10
SP - 363
EP - 371
JO - IEEE Journal of Photovoltaics
JF - IEEE Journal of Photovoltaics
IS - 2
M1 - 8936950
ER -