24P016-O
Deposition of highly stable cluster-free a-Si:H films using a fast gas flow
multi-hollow discharge plasma CVD method
高速ガス流マルチホロープラズマCVD法を用いた
高光安定クラスタフリーa-Si:H膜の作製
Kosuke Hatozaki1, Kenta Nakahara1, Yuuji Hashimoto1, Takeaki Matsunaga1,
Daisuke Yamashita1, Hidefumi Matsuzaki1, Hyunwoong Seo1, Kunihiro Kamataki2,
Giichiro Uchida1, Naho Itagaki1, Kazunori Koga1 and Masaharu Shiratani1
波戸﨑浩介，中原賢太1，橋本優史1，松永剛明1，山下大輔1，松崎秀文1，徐鉉雄1，鎌滝晋礼2，内田儀一郎1，板垣奈穂1,3，古閑一憲1，白谷正治11Graduate School of Information Science and Electrical Engineering, Kyushu University
2Center for Research and Advancement in Higher Education Kyushu University
1,2744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan
3
PRESTO, Japan Science and Technology Agency, 5 Sanbancho, Chiyoda-ku, Tokyo 102-0075, Japan
1,2
九州大学大学院システム情報科学府 〒819-0395 福岡市西区元岡744
3JSTさきがけ 〒102-0075 東京都千代田区三番町5
We have deposited cluster-free a-Si:H films using a fast gas flow multi-hollow discharge plasma CVD
method. To evaluate their quality as an I layer of PIN solar cells, we have measured Fill Factor (FF) of
N-type c-Si/a-Si:H/Ni Schottky cells of such cluster-free a-Si:H films. Our films deposited at a rate of 0.51
nm/s show high initial FF of 0.556, high stable FF of 0.523, and quite low light induced degradation ratioof 5.93 %.

1. Introduction
Light-induced degradation of hydrogenatedamorphous silicon (a-Si:H) has been an important
issue for a-Si:H solar cells, because light
exposure initially causes a reduction of theconversion efficiency of the cells due to thedegradation [1]. During the deposition,amorphous silicon particles (clusters) in a size
range below 10 nm are generated in the plasmas
and they deposit into the films [2]. For
conventional plasma CVD of a-Si:H films,
clusters are generated in discharges and deposit
into the films, and degrade efficiency andstability of the cells using such films. Reducing
incorporation of the clusters is important forrealizing highly stable a-Si:H solar cells of highefficiency [3]. It motivated us to deposit
cluster-free a-Si:H films to realize stable a-Si:H
solar cells of a high efficiency.
Recently, we have deposited highly stablea-Si:H films of 4.7x10 15 cm-3 in stabilized defectdensity at a rate of 3 nm/s at substratetemperature Ts= 250°C by suppressing
incorporation of clusters into the films [4,5]. Thefilms show high stability against light exposure.
In this study, we have deposited cluster-free
a-Si:H films using the SiH 4 multi-hollow
discharge plasma CVD method [4]. We report
performance of Schottky solar cells using suchcluster-free a-Si:H films.
2. Experimental
Experiments were carried out using a
multi-hollow discharge plasma CVD reactor asshown in Fig. 1. Multi-hollow powered and two
grounded electrodes had holes of 5mm in diameter
were placed in a stainless-steel vessel. SiH4 gas was
fed from a gas inlet at a flow rate of 150 sccm andwas pumped out through the electrodes. The gaspressure was 0.5 Torr. The discharge frequency andpower were 60 MHz and 40 W, respectively.
Cluster-free a-Si:H films were deposited on a
N-type c-Si substrate set in the upstream region

Fig.1. Multi-hollow discharge plasma CVD
reactor.

from the discharges, because clusters generated in
the discharges were driven toward the downstream
region by gas flow. We deposited 605 nm films ofa-Si:H at Ts= 250°C. The deposition rate was 0.51
nm/s.
FF
wasevaluatedirradiating
N-typec-Si/a-Si:H/Ni Schottky cells by irradiation of an
AM 1.5 solar spectrum light of 100 mW/cm2 (1SUN) at Ts=30 °C. The stabilized FF was measured
after 6 hours 40 min light soaking under conditionsof 2.7 SUN irradiation and Ts=50°C.

of Schottky cell are 0.556 and 0.523, respectively.
This degradation ratio is 5.93%. Initial Pmax of thecell was 0.859 mW/cm2. Stabilized Pmax was 0.797
mW/cm2 which was 7.21% lower than the initialone. Light soaking has little influence on Voc andthe initial and stabilized Voc are 0.37 V. The initialand stabilized Jsc were 4.21 mA/cm2 and 4.17
mA/cm2, respectively. These results suggest thata-Si:H films with little light induced degradation
can be deposited by suppressing the cluster
incorporation.

3. Results and Discussion
Initial and stabilized J-V and P-V characteristicof the Schottky cell are shown in Fig. 2 and Table I.
The fill factor (FF), maximum power (Pmax), open
circuit voltage (Voc), short circuit current density(Jsc), series resistance (Rs), and parallelresistance(Rsh) are obtained from J-V curves of theSchottky cells. The initial and stabilized FF values

4. Conclusions
We have examined characteristics of N-type
c-Si/a-Si:H/Ni Schottky cells using cluster-free
a-Si:H films deposited by the multi-hollow
discharge plasma CVD method. Our films
deposited at a rate of 0.51 nm/s show high initial FFof 0.556, high stable FF of 0.523, and quite low
light induced degradation ratio of 5.93%. Theseresults indicate that our method is useful tofabricate highly stable a-Si:H solar cells.

51
InitialStabilized
InitialStabilized

0.8

3

0.6

20.4

10.2

00

0.1

0.2

0.3

0.4

P (mW/cm2)

J (mA/cm2)

400.5

V (V)
Fig. 2 Initial and stabilized J-V characteristic ofSchottky solar cell. Conditions: SiH4 150sccm,0.5Torr, Frequency 60MHz, Ts 250°C, Electrodepower 40W, 6h40min light soaking underconditions of 2.7 SUN and Ts 50°C.

Table I. Initial and stabilized characteristics of Schottkycell (FF, Pmax, Voc, Jsc, Rs, and Rsh) and degradation
ratios of FFand Pmax values
Characteristicsof Schottky cell
FFPmax (mW/cm2)
Voc (V)Jsc (mA/cm2)
Rs ( cm2)
Rsh ( cm2) Initial

Stabilized

0.556
0.859
0.37
4.21
15.5
524

0.523
0.797
0.37
4.17
19.6
466

Degradation
ratio
5.93%
7.21%

Acknowledgements
This work was partly supported by the New Energy
andIndustrialTechnologyDevelopment
Organization (NEDO) and Photovoltaic Power
Generation Technology Research Association(PVTEC).
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