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Solar Energy
journal homepage: www.elsevier.com/locate/solener
Computational analysis of a high-efficiency tunnel oxide passivated contact
(TOPCon) solar cell with a low-work-function electron-selective-collection
layer
Cheng Quan
a,b,
⁎
,1
, Yuheng Zeng
b,1
, Dan Wang
b
, Mingdun Liao
b
, Hui Tong
b,c
, Zhenhai Yang
b
,
Zhizhong Yuan
a
, Pingqi Gao
b
, Baojie Yan
b
, Kangmin Chen
a
, Jichun Ye
b
a
School of Material Science & Engineering, Jiangsu University, Zhenjiang City 212013, PR China
b
Ningbo Institute of Material Technology and Engineering, Chinese Academy of Sciences (CAS), Ningbo City 315201, PR China
c
University of Chinese Academy of Sciences, Beijing City 100049, PR China
ARTICLE INFO
Keywords:
Passivated contact
Low work-function metal
Tunnel oxide
Silicon solar cell
ABSTRACT
In this work, the tunnel oxide passivated contact (TOPCon) with a low-work-function electron-selective-col-
lection (ESC) layer is studied using a numerical simulation method. An exhaustive comparison between the low-
work-function ESC TOPCon and the heavily-doped-Si TOPCon solar cell is carried out to find out the differences
between these two kinds of devices. The work function modulated ESC TOPCon with a work function of
typically < 3.6 eV and a low defect-density oxide layer of 1.2–1.4 nm displays an maximum implied open circuit
voltage (iV
oc
) of 742 mV and a superior fill factor (FF) of 86%, which is competitive with a regular heavily-
doped-Si ESC TOPCon solar cell. Noted that a defective transition layer (DTL) between the low-work-function
layer and the oxide layer is studied herein, in which enhanced recombination decays not only the surface
passivation but also the carrier transport. Also, the practical problems that might impede the development of a
high-efficiency low-work-function ESC TOPCon solar cell are discussed. In summary, this work presents an
overall computational analysis of the low-work-function ESC layer, tunnel oxide, defective transition layer and
their combined effects on device performances, which provides a pathway towards fabricating a high-efficiency
low-work-function ESC TOPCon solar cell.
1. Introduction
Silicon heterojunction solar cell with the interdigitated back-con-
tacted structure has created the new world’s record of 26.6%
(Yoshikawa et al., 2017a, 2017b). Inspired by the concept of silicon
heterojunction solar cell, to develop high-efficiency silicon hetero-
junction solar cells with new materials for carrier-selection collection
has become a hot topic in the photovoltaic field. In general, various new
materials with a low or high work function (metal, metal oxide, or
metal fluoride) can play as the role for carrier-selective collection, ex-
hibiting the potential to compete with the traditional heavily-doped Si
layer. Some pioneering works have proved that the new-concept solar
cells with various carrier-selective collection layers exhibit excellent
performances with the power conversion efficiency approaching 20%
(Allen et al., 2017, Wan et al., 2016a, 2016b, Allen et al., 2016, Yang
et al., 2016a, 2016b, Wan et al., 2016a, 2016b, Bullock et al., 2016).
Noted that in the existing publications, most work used the intrinsic
hydrogenated amorphous Si as the tunnel layer to passivate contact.
However, to deposit an intrinsic hydrogenated amorphous Si film needs
a high-quality plasma-enhanced chemical-vaper-deposition system that
is typically expensive. To overcome this issue, using SiO
2
to replace
hydrogenated amorphous Si as the tunnel layer to passivate contact is a
possible option, as its growth is much simpler and cheaper (Asuha et al.,
2003, Moldovan et al., 2014, Barnett et al., 2003) due to the avoidance
of the plasma-enhanced chemical-vaper-deposition system. More im-
portant, an optimized SiO
2
layer has exhibited excellent passivation and
tunnel properties in high-efficiency tunnel oxide passivated contact
(TOPCon) solar cells (Richter et al., 2017, Feldmann et al., 2014a,
2014b, Tao et al., 2016, Yan et al., 2015). Using tunnel oxide with a
low-work-function capping layer is a promising option for the electron-
selective-collection (ESC) structure, because the electron tunnel barrier
(∼3.05 eV) is much lower than the hole barrier ( ∼4.73 eV) in oxide.
Several important scientific issues have to be classi fied before the
application of the tunnel oxide/low-work-function ESC structure in
https://doi.org/10.1016/j.solener.2018.06.008
Received 10 November 2017; Received in revised form 7 May 2018; Accepted 1 June 2018
⁎
Corresponding author at: School of Material Science & Engineering, Jiangsu University, Zhenjiang City 212013, PR China.
1
Represent as co-first authors.
E-mail addresses: quancheng@nimte.ac.cn (C. Quan), kmchen@ujs.edu.cn (K. Chen), jichun.ye@nimte.ac.cn (J. Ye).
Solar Energy 170 (2018) 780–787
0038-092X/ © 2018 Elsevier Ltd. All rights reserved.
T