−報3文−

新規アルミニウム添加酸化亜鉛系材料の開発と太陽電池への応用
倉持豪人＊ 1
秋池良＊ 1飯草仁志＊ 1
玉野公章＊ 1
内海健 太 郎＊ 1
渋 田 見哲夫＊ 1
Porponth Sichanugrist ＊ 2
小 長 井誠＊ 2

Development of Novel Aluminum − Doped Zinc Oxide Material and Its
Application to Solar Cells
Hideto KURAMOCHIRyo AKIIKE
Hitoshi IIGUSA
Kimiaki TAMANO
Kentaro UTSUMI
Tetsuo SHIBUTAMI
Porponth SICHANUGRIST
Makoto KONAGAI

This study addresses the electrical and optical properties, durability under high-humidity condition, and surface
morphology of the novel aluminum-doped zinc oxide (AZO) films formed by DC magnetron sputtering. These novel
AZO films showed higher transmittance in the near-infrared area and good durability under 85℃-85%RH condition.
These novel films also had a higher haze value after wet chemical etching than normal AZO films. The haze value ofthe novel AZO films was higher than that of the normal AZO films; their values are 90% at 550 nm and 60% at 800 nm.
Furthermore, the novel AZO films were applied in amorphous Si (a-Si) single-type solar cells as the front electrode.
The short-circuit current of the solar cell using the novel AZO films was higher than that of the solar cell using thenormal AZO films. As an optimization-based result, an efficiency as high as 10.2% was obtained, showing that thenovel AZO films are a promising material for the front electrode of a-Si solar cells.

1．Introduction

cells. They provide low electrical and optical losses,
and fulfil in most cases additional optical function such

Transparent conductive oxide (TCO) films areas light scattering to improve the performance of thesenecessary as front electrode for most thin film solarsolar cells1). Additionally, the durability of TCO films is＊1
＊2

東京研究所
東京工業大

important for stabilizing the performance of such cells.
It is known that TCO films with a textured surface

TOSOH Research & Technology Review Vol.57（2013）4

can scatter light at the interface between TCO and Si

high durability for AZO films16,17). A film with a lower

layers2). The degree of light scattering property can bealuminum doping level has good transmittance, but its

represented by haze value, which should be increased

durability is poor.

to further enhance the light scattering property. It is

In this work, we have developed novel AZO films,

well known that the haze value of TCO films is strongly

named AZO-X and AZO-HX films, formed by DC

3)

magnetron sputtering. After film deposition, wetaffected by their surface morphology .
Typically, fluorine-doped tin oxide (FTO) films 4)5)chemical etching using HCl was employed to modify

and aluminum-doped zinc oxide (AZO) films formed

the surface morphology of the films. As the results, weby magnetron sputtering, gallium-doped zinc oxide

have achieved such films formed on a flat substrate(GZO) films6)

formed by magnetron sputtering or7)

with a higher haze value than AZO film for excellent

boron-doped zinc oxide (BZO) films formed by low-light scattering. And then we have applied these films

pressure chemical vapour deposition (LPCVD) areto the front electrodes of amorphous Si solar cells andused as thin-film Si solar cells. Conductive zinc oxide

achieved high cell performance.

films such as AZO films and BZO films have attracted
attention as front TCO films because it is easy to modify
their surface morphology by selecting their deposition
technique and conditions, and by using post-treatment
conditions

8-10)

2．Experimental Procedure［1］Preparation of TCO films. Furthermore, AZO, GZO or BZO films

The AZO films were deposited on the glass substrate

are high stability against hydrogen plasma as compared(Corning EAGLE XG) by DC magnetron sputtering11)

with FTO films . However, the stability of AZO, GZO

using AZO targets. The alumina content was 1.0 or 2.0or BZO film properties under 85℃ -85%RH condition iswt%. The novel AZO films were also deposited by DC12)

inferior to that of FTO film properties .
Some deposition techniques for preparing conductive
zinc oxide films have been reported. Among the various

magnetron sputtering using the novel AZO targets.
These targets are ZnO targets doped with Al and otherelements.

deposition techniques, the main process is sputtering

The deposition was carried out at a substrateusing ceramic targets because it has an advantage of thetemperature of 200℃ , a discharge power density of 3.7

reliable control of film properties and film thickness.

W/cm2, and an argon deposition pressure of 0.4 Pa. The

Berginski et al.13) have reported the effect of substratetemperature during RF magnetron sputteringbase pressure just before sputtering was about 1.0×-510 Pa.

deposition, the aluminum content of AZO targets,

The thickness, resistivity, and optical transmittance ofand film surface morphology after wet etching.

the films were measured using a surface profiler, a Hall

According to their report, the substrate temperature ineffect measurement system at room temperature, and a

sputtering should be over 300 ℃ for a high haze value

spectrophotometer in air, respectively. The rate of theof approximately 5% at 1000 nm. However, a substrate

resistivity change of these films was evaluated undertemperature of more than 300 ℃ is very high because

85 ℃ -85%RH condition. By wet chemical etching using

it is difficult to select the materials for the sputtering

diluted HCl (0.5%), the surface morphology of the films

system. Therefore, it is necessary to satisfy the highwas modulated into a textured surface structure.

haze value at a substrate temperature below 200℃ .
14,15)

Jorj and coworkers

After wet chemical etching, the surface morphology,

have prepared an AZO film byfilm thickness, and roughness of these films were

RF sputtering using a ZnO target doped with 0.5 or 1.0

evaluated using scanning electron microscopy

wt% Al2O3. The AZO film with a HCl etching time of 50(SEM), surface profilometry, and atomic forces has a high haze value of approximately 60% at 550 nm.

microscopy (AFM), respectively. The total and diffuse

Furthermore, a higher haze value of approximately 70%

transmittances of the textured films were measured

has been obtained with additional HF etching.

with a spectrophotometer in air. The haze value is

In contrast, it is known that it is difficult to achievea good balance between high transmittance anddefined as the ratio of diffuse transmittance to totaltransmittance.

東ソー研究・技術報告

第 57 巻（2013）［2］Preparation of amorphous Si solar cellsolar cells were fabricated using the etched films as
the front TCO films. The structure of these solar cells
was glass substrate/textured TCO films/p-i-n typeamorphous Si:H/B-doped ZnO/Ag/Al. The test cells
had an area of 0.09 cm 2. The photocurrent density voltage (J-V) characteristics of the fabricated cells were50
Change in resistivity after test［%］p-i-n-type amorphous Si:H single-junction thin-film

30⑵
2010⑶

⑴

0solar simulator radiation. The spectral response of these0200

4006008001000Time［h］cells was evaluated using quantum efficiency (QE)
Fig.２

3．Result and Discussion⑴AZO−X⑵AZO（Al2O3：1wt％）⑶AZO（Al2O3：2wt％）

40

measured at 25 ℃ under 1 sun (AM 1.5, 100 mW/cm2)

measurement.

5

Durability for formed AZO films.
（Film thickness：1000nm）

is attributable to grain boundary scattering, on the［1］Resistances, transmittances, and durabilities ofbasis of experimental and theoretical considerations22)

the formed AZO films

concerning the relationship between carrier

The transmittance spectra of formed AZO films areconcentration and Hall mobility. Thus, the durability-shown in Fig. １. The transmittance in the near-infraredenhancing effect of AZO-X film is thought to be due

areas was decreased with increasing alumina contents.

to the crystallinity improvement of as-deposited films

Fig. 2 shows the durability test result of AZO films underachieved by doping with Al and other elements.

85℃ - 85%RH condition. The rate of resistivity change
was increased with decreasing alumina contents. That［2］Resistances, transmittances, and durabilities ofphenomenon means that the durability was inferior.

the texture-etched AZO films

Thus, it is difficult to achieve a good balance between

The resistances and transmittances of the texture-transmittance in the near-infrared areas and durability.

etched AZO films and FTO film (CVD) are shown in

However, our developed material, novel AZO (AZO-X)

Table 1 and Fig. 3. With increasing alumina content,film, achieved a good balance between transmittance inthe sheet resistance decreased, and the transmittancethe near-infrared areas and durability.

in near-infrared areas also decreased. In this case,18-21)

have reported

increasing alumina content leads to a higher carrierthat improving the crystallinity of as-depositedconcentration and the carrier concentration of thepolycrystalline AZO films is important for improving

films affects sheet resistance and transmittance23). Thatthe resistivity stability, and that their resistivity increase

is, increasing carrier concentration results in a lower

with exposure time in a high-humidity environment

sheet resistance and a lower transmittance in near-

Minami and coworkers

infrared areas. The novel texture-etched AZO films,
named AZO-X and AZO-HX films, have resistances andTransmittance［％］100transmittances that are approximately the same as those80⑴

60of the AZO (Al2O3: 1 wt%) film and FTO film (CVD).

⑵

40Rs［ohm/sq.］
8⑴AZO−X⑵AZO（Al2O3：1wt％） 6⑶AZO（Al2O3：2wt％） 2

20
0200

400

600

800

1000

Table１

⑶

1200

1400

Wavelength［nm］

Fig.１

Transmittance spectra of formed AZO films.
（Film thickness：1000nm）

Resistivity of texture−etched AZO films.

RsFilm thickness［ohm ／ sq.］
［nm］
⑴AZO
（Al2O3：1wt％）
9700⑵AZO（Al2O3：2wt％）
4700
11700⑶AZO−X
11⑷AZO−HX700
101000⑸SnO2：F（CVD）

TOSOH Research & Technology Review Vol.57（2013）

6Transmittance［％］10080⑴⑸60⑴AZO（Al2O3：1wt％）⑵⑵AZO（Al2O3：2wt％）40⑶⑷

Rms 172nm
AZO−HX⑶AZO−X

Rms 60nm
AZO（Al2O3：1wt％）⑷AZO−HX

20（CVD）⑸SnO2：F
0400

600

800

1000

1200

1400

Rms 125nm

Wavelength［nm］

Fig.３

AZO−X

Rms 21nm
AZO（Al2O3：2wt％）

Transmittance of texture−etched AZO films.

Fig. 4 shows the relationship between theRms 39nm

transmittance at 1000nm and the durability test result

SnO2：F（CVD）

of the textured films under 85℃ -85%RH condition at1000h. After wet chemical etching, the novel texture-

SEM image of texture−etched AZO films.

Fig.５

etched AZO films, named AZO-X and AZO-HX films,
achieved good balance between transmittance in near-

the novel AZO films were higher than that of the otherinfrared areas and durability. The durability of thesefilms; their values of the AZO-HX film are 90% at 550 nm

films was comparable to that of the FTO film (CVD).

and 60% at 800 nm. As shown in Fig. 5, the high rms

As described above, the novel texture-etched AZO

contributed to the high haze value.

films showed the excellent properties of transmittanceand durability after wet chemical etching.

［4］Performance of amorphous Si solar cell
The novel films have been applied as the front［3］Surface morphology of the textured AZO films

electrode of a-Si single-type solar cells. Fig. 7 shows

The surface of the fabricated AZO films was

the relationship between the haze value at 800 nm

modulated into a textured surface structure by wet

and the typical parameters of a-Si single cells. As canchemical etching using diluted HCl.

be seen in this figure, the open-circuit voltages (Voc)
were approximately the same for all the cells, and thefilms measured by SEM. The rms roughness of each

short-circuit current (Jsc) increased with increasing

film is shown in Fig. 5. The surface morphology of thehaze value, as expected. There is a positive correlationnovel AZO films showed a larger crater than the otherbetween Jsc and the haze value at 800 nm. Masumo etfilms. Furthermore, the rms roughness of the AZO-HX

al. reported that the short-circuit current of the cells

film increased up to 172 nm. Figure 6 shows the hazepeaks at approximately 40% haze value at 800 nm24).

value spectra of the various films. The haze value ofHowever, that result was based on a tandem-type solar

10040.0
AZO（Al2O3：1wt％）

30.0
20.0

AZO
（Al2O3：2wt％）

10.0

SnO2：F（CVD）

AZO−HXAZO−XHaze value［%］

Change in resistivity after test［%］Fig. 5 shows the surface morphology of the various

80

Relationship between the transmittance at 1000nm
and the durability test result.

60

AZO（Al2O3：1wt％）

40

AZO（Al2O3：2wt％）

090

400

Transmittance at 1000nm［%］

Fig.４

AZO−X
SnO2：F（CVD）

80

200.070

AZO−HX600

800

1000 1200 1400

Wavelength［nm］

Fig.６

Haze value spectra of texture−etched AZO films.

141.0121080.5
020406080

Haze value at 800nm

Fig.７7AZO
AZO（Al2O3：2wt％） （Al2O3：1wt％） AZO−HX
SnO2：F
AZO−X
1.012（CVD）
100.8860.64

Efficiency［％］

Voltage［V］

16

第 57 巻（2013）

FFAZO
AZO
（Al2O3：2wt％） （Al2O3：1wt％） AZO−HX
SnO2：F
AZO−X
1.518（CVD）

Current density［mA／cm2］

東ソー研究・技術報告

20.4

0020

40

60

80

Haze value at 800nm

Relationship between the haze value at 800nm and the typical parameter of a−Si single cells.

cell that required the current balance of each cell.
In contrast, as shown in Fig. 7, our results showed

Referencesthat Jsc could be increased even when the haze value at１）A. V. Shah, J. Meier, F. Meillaud, J. Guillet, D.

800 nm increased up to 60% when AZO-HX was appliedFischer, C. Droz, X. Niquille, S. Faye, and M.

as the front electrode.

Vanecek, J. Non-Cryst. Solids , 338-340, 639（2004）

Fig. 7 shows these efficiencies of a-Si single cells. A２）J. Muller, B. Rech, J. Springer, and M. Vanecek,

high efficiency of 10.2% was achieved in the AZO-HXSol. Energy Mater. Sol. Cells , 77, 917（2004）

film. A higher efficiency with better FF can be achieved

３）L. Yang and L. F. Chen, MRS Proc ., 336, 669（1994）

by optimizing the nature of contact between the AZO-

４）K. Sato, Y. Gotoh, Y. Hayashi, K. Adachi, and H.

HX film and the p-layer of the cell.

Nishimura, Rep. Res. Lab. Asahi Glass Co., Ltd ., 40,233（1990）

4．Conclusions

５）O. Kluth, B. Rech, L. Houben, S. Wieder, G.
Schope, C. Beneking, H. Wagner, A. Loffl, and H. W.

We have developed the novel AZO films for solar cell.

Schock, Thin Solid Films , 351, 247（1999）

The novel AZO films achieved good balance between

６）M. Miyazaki, K.Sato, A.Mitsui, and H. Nishimura, J.

transmittance in near-infrared areas and durability
under 85℃ -85%RH condition. After wet chemical

Non-Cryst. Solids , 218, 323（1997）７）S. Fay, S. Dubail, U. Kroll, J. Meier, Y. Ziegler, andetching, the surface of the novel AZO films showed aA. Shah, Proc. 16th EU-PVSEC , p. 361（2000）

larger crater than the other films. The haze value of the８）K. Tabuchi, W. W. Wenas, A. Yamada, M. Konagai,

novel AZO films were higher than that of the other films

and K. Takahashi, Jpn. J. Appl. Phys ., 32, 3764

fabricated with an additional wet etching process.

（1993）

Furthermore, the novel AZO films were appliedin amorphous Si single-type solar cells as the front９）Y. Nasuno, M. Kondo, and A. Matsuda, Jpn. J. Appl.

Phys ., 40, L303（2001）

electrode. The short-circuit current of the solar cell10）J. Bailat, D. Domine, R. Schluchter, J. Steinhauser,

using the novel AZO films were higher than that of theS. Fay, F. Freitas, C. Bucher, L. Feitknecht, X.

solar cell using the other films.

Niquille, T. Tscharner, A. Shsh, and C. Ballif, Proc.

Finally, as an optimization-based result, an efficiency
as high as 10.2% was obtained, showing that thenovel AZO films are a promising material for the front
electrode of a-Si solar cells.
These features of the novel AZO films are suitable forthe application to other-type solar cells.

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