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Current Applied Physics
journal homepage: www.elsevier.com/locate/cap
Characterization of tunnel oxide passivated contact with n-type poly-Si on p-
type c-Si wafer substrate
Xueqi Guo
a,b,1
, Yuheng Zeng
b,1
, Zhi Zhang
b
, Yuqing Huang
b
, Mingdun Liao
b
, Qing Yang
b
,
Zhixue Wang
b
, Minyong Du
c
, Denggao Guan
a,∗∗
, Baojie Yan
b,∗
, Jichun Ye
b,∗∗∗
a
College of Materials and Chemistry & Chemical Engineering, Chengdu University of Technology, 1# Dongsanlu, Erxiangqiao, Chengdu, Sichuan Province 610059, PR
China
b
Ningbo Materials Institute of Technology and Engineering, CAS, Ningbo City, Zhejiang Province 315201, PR China
c
Dalian Institute of Chemical Physics, CAS, Dalian, Liaoning Province, PR China
ARTICLE INFO
Keywords:
Solar cell
C-V measurement
Built-in potential
poly-Si
TOPCon
p-n junction
ABSTRACT
The junction properties of tunnel silicon oxide (SiO
x
) passivated contact (TOPCon) with n-type poly-Si on p-type
c-Si wafer are characterized using current-voltage (J-V) and capacitance-voltage (C-V) measurements. The dark
J-V curves show a standard diode characteristic with a turn-on voltage of ∼0.63 V, indicating a p-n junction is
formed. While the C-V curve displays an irregular shape with features of 1) a slow C increase with the decrease of
the magnitude of reverse bias voltage, being used to estimate the built-in potential (V
bi
), 2) a significant increase
at a given positive bias voltage, corresponding to the geometric capacitance crossing the ultrathin SiO
x
, and 3) a
sharp decrease to negative values, resulting from the charge tunneling through the SiO
x
layer. The C of depleting
layer deviates from the normal linear curve in the 1/C
2
-V plot, which is caused by the diffusion of P dopants from
the n-type poly-Si into the p-type c-Si wafer as confirmed by the electrochemical capacitance-voltage mea-
surements. However, the 1/C
2+γ
-V plots with γ > 0 leads to linear curves with a proper γ and the V
bi
can still be
estimated. We find that the V
bi
is the range of 0.75–0.85 V, increases with the increase of the doping ratio during
the poly-Si fabrication process, and correlates with the passivation quality as measured by the reverse saturated
current and implied open circuit voltage extracted from transient photoconductivity decay.
Surface passivation has become one of the most important techni-
ques for improving the efficiency of c-Si solar cells. Currently, two
major materials have been used for the passivation, namely thin
(∼5 nm) intrinsic hydrogenated amorphous silicon (a-Si:H) and ultra-
thin (∼1.5 nm) silicon oxide (SiO
x
), where the former is used in a-Si/c-
Si hetero-junction (SHJ or HIT) solar cells [1–3] and the later in tunnel
oxide passivated contact (TOPCon) c-Si solar cells [4–6]. These two cell
structures have been well developed in recent years and have shown the
record energy conversion efficiencies [3,5]. Although the TOPCon solar
cell [4] has been invented much later than the HIT solar cell [1], it has
attracted a significant attention because of the compatibility with the
current main stream c-Si solar panel production technology and the
record efficiency of 25.7% [5] has exceeded the highest efficiency
achieved by HIT solar cell without interdigitized back contact (IBC) [7].
On one hand, the common TOPCon solar cell structure is built on n-type
c-Si wafer with a front B-diffused emitter and an ultrathin SiO
x
/n-type
poly-Si TOPCon back field contact, while on the other hand, the ma-
jority of current c-Si solar panels are made with p-type c-Si wafers.
From the technology continuity and cost effective point of view, the
TOPCon solar cell structure on p-type c-Si wafer is desirable for solar
panel production and could be easily adapted into the current p-PERC
lines. Therefore, the study of TOPCon solar cell on p-type c-Si is
meaningful for the photovoltaic industry at least in the present or very
near future.
TOPCon solar cell on p-type wafer has two structures, one is with a
P-diffused front emitter and a B-doped poly-Si back field contact (BFC)
p-TOPCon structure [8] and one is opposite with a B-doped front field
contact (FFC) and a P-doped poly-Si n-TOPCon emitter [6]. Experi-
mentally, it has demonstrated a 24.4% efficiency with an n-type poly-Si
back emitter solar cell [6], and it has the potential to increase the
https://doi.org/10.1016/j.cap.2019.04.014
Received 12 November 2018; Received in revised form 1 March 2019; Accepted 21 April 2019
∗
Corresponding author.
∗∗
Corresponding author.
∗∗∗
Corresponding author.
E-mail addresses: gdg@cdut.edu.cn (D. Guan), yanbaojie@nimte.ac.cn (B. Yan), jichun.ye@nimte.ac.cn (J. Ye).
1
Equal contribution as first authors.
Current Applied Physics 19 (2019) 811–816
Available online 22 April 2019
1567-1739/ © 2019 Korean Physical Society. Published by Elsevier B.V. All rights reserved.
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