> home > Feature Articles
 
Recent Progress of Cu(In,Ga)Se2 and Cu(In,Ga)(S,Se)2-based Solar Cells
Jakapan Chantana, Takashi Mine
File 1 : Vol27_No2_Feature Articles-2.pdf (0 byte)

Recent Progress of Cu(In,Ga)Se2
and Cu(In,Ga)(S,Se)2-based Solar Cells

JAKAPAN CHANTANA AND TAKASHI MINEMOTO*)
DEPARTMENT OF ELECTRICAL AND ELECTRONIC ENGINEERING, RITSUMEIKAN UNIVERSITY, JAPAN

*) Corresponding author: minemoto@se.ritsumei.ac.jp

ABSTRACT

Recent progress of Cu(In,Ga)Se2 (CIGSe) and Cu(In,Ga)(S,Se)2 (CIGSSe) based solar cells as a result of the effects of alkali elements and device structures is reviewed. CIGSe and CIGSSe-based solar cells with high conversion efficiency (η) above 20% have been reported. The small amount of alkali elements in CIGSe and CIGSSe absorbers leads to the improvement of photovoltaic performance. Alkali element Na introduction causes an increase in the carrier concentration in the absorbers. Alkali element K incorporation leads to a Cu-depleted absorber surface composition. Therefore, the high density of CdCu donors near the absorber surface with a very thin CdS buffer is achieved, resulting in electronic inversion near the absorber surface, thus forming a p-n homojunction and increasing open-circuit voltage. Furthermore, to enhance short-circuit current density of CIGSe and CIGSSe-based solar cells, conventional CdS/ZnO buffer layers in the solar cells were replaced by more transparent materials for the development of the device structure to reduce optical losses in short wavelengths less than 520 nm. It is revealed that the CdS/ZnO buffer layers are promisingly substituted by the alternative ZnS(O,OH)/Zn1-xMgxO buffer layers, which possess large bandgap-energies. Ultimately, η (> 22%) is achieved through solar cells with alternative buffer layers.

INTRODUCTION

Electrical energy, a useful form of energy, is normally generated from fossil fuels, which have an adverse impact on the environment and will be depleted. Sustainable energies such as hydroelectricity energy, solar energy, wind energy, and geothermal energy are considered to solve the foreseeable energy crisis. One intriguing and sustainable energy source is solar energy, generated by solar cells using the photovoltaic (PV) effect [1,2]. Currently, crystalline silicon (Si)-based solar cells are dominating the PV market; however, their production costs are still high. Thin-film solar cells are a promising candidate for cost reduction [1,2]. One of the most interesting thin-film solar cells is the chalcopyrite I-III-VI2 solar cell, which was first developed in the 1970s with a Ga-free absorber [3]. The important chalcopyrite compounds for photovoltaic application are CuInSe2, CuInS2, and CuGaSe2 with bandgap-energies (Eg) of 1.0, 1.5, and 1.7 eV, respectively. The Eg can be varied by alloying the compounds. Chalcopyrite Cu(In,Ga)Se2 (CIGSe) and Cu(In,Ga)(S,Se)2 (CIGSSe)-based thin-film solar cells have been reported with conversion efficiencies (η) above 20% [4-7].

The introduction of alkali elements plays an important part in the high η of the CIGSe and CIGSSe-based solar cells [4-6]. The influence of alkali element sodium (Na) on photovoltaic performances of the CIGSe solar cells has been examined since the 1990s [8], and a number of publications reported on this topic regarding the improvement of solar cell performance [9-12]. It was demonstrated that the introduction of Na into CIGSe absorbers effectively enhances the η of CIGSe solar cells [13]. The utilization of alkali element potassium (K) as a dopant was published and led to the considerable increase in η by post deposition treatments (PDT) [4-6,14,15]. In addition to Na and K, heavier alkali elements rubidium (Rb) and caesium (Cs) were investigated [5]. Subsequently, CIGSe solar cells with η of 22.6% were achieved using alkali element Rb in place of Na and K in the alkali PDT [5].

The conventional structure of the CIGSe and CIGSSe-based solar cells is Glass/Mo/CIGSe or CIGSSe/CdS (buffer 1)/ZnO (buffer 2)/ZnO:Al/Ni-Al as shown in Fig. 1. To further enhance the η of the CIGSe and CIGSSe-based solar cells, the device structure has been developed. The CdS buffer (buffer 1) in the solar cells absorbs light with short wavelengths (λ) of below 520 nm owing to its Eg of about 2.4 eV, thus limiting short-circuit current density (JSC). Alternative materials for buffer 1 with larger Eg, such as ZnS, ZnS(O,OH), (Cd,Zn)S, ZnSe, In2S3, In2Se3 and In(OH,S), have been intensively investigated in the replacement of traditional CdS buffers [6,16-19]. In addition, Zn1-xMgxO has been demonstrated as an appropriate buffer layer (buffer 2) in solar cells instead of the ZnO buffer layer (buffer 2) [18,20-22], where Eg of Zn1-xMgxO is larger than that of ZnO. Consequently, the development of solar cell structure by the optimization of ZnS(O,OH) (buffer 1)/Zn1-xMgxO (buffer 2) buffer layers in the CIGSSe solar cell results in an increase in the in-house η of 22.8% [6].

In this literature, the recent progress of CIGSe and CIGSSe-based solar cells with high η is discussed with a focus on the impact of alkali elements as the dopant, and on the device structure (buffer 1 and buffer 2).

CIGSe AND CIGSSe-BASED SOLAR CELLS

Figure 1 demonstrates the traditional structure of the CIGSe and CIGSSe-based solar cells (Glass/Mo/CIGSe or CIGSSe/CdS (buffer 1)/ZnO (buffer 2)/ZnO:Al/Ni-Al). In the structure, the back contact (nontransparent back-contact) is molybdenum (Mo), normally deposited by a sputtering process. This layer needs to have high conductivity to avoid ohmic losses. The CIGSe and CIGSSe-based absorbers are p-type film absorbers (2-3 μm). The layers absorb most of the sun light and generate the photocurrent, and thus are called absorbers. The CIGSe absorber is generally fabricated by a three-stage deposition process [23], and the CIGSSe absorber can be prepared using a two-step process, whereby a sputter-deposited Cu-In-Ga precursor is prepared and followed by a selenizanition and sulfurization (SAS) process [24]. For the improvement of cell performance, PDT of alkali elements is performed after the fabrication of the absorber layers [4-6], and/or the absorber surface treatment, such as KCN etching, is conducted [25,26].

 



Fig. 1: Structure of CIGSe and CIGSSe-based solar cells.

CdS layers (about 50 nm), deposited by chemical bath deposition (CBD), are normally utilized as buffer 1 because the conduction band offset of CdS/CIGSe interface is appropriate [27], and/or CdS can form a high-quality-p-n junction owing to the prevention of sputtering damage on the absorber surface during fabrication of successive layers by the sputtering process. A very thin and highly-resistive ZnO layer (50-80 nm) as buffer 2 is generally prepared by sputtering. The ZnO (buffer 2) is used to prevent direct contact of ZnO:Al (transparent conductive oxide, TCO) and the absorbers since the rough surface of the absorber layers may not be covered completely with a CBD-CdS buffer layer with a typical thickness of about 50 nm [28]. The TCO layer (about 300 nm) is n-type wide gap TCO, having high transparent and conductivity to avoid ohmic losses. The TCO can be ZnO:Al, ZnO:B (heavily doped ZnO) or In2O3:Sn (ITO). ZnO:Al and ITO are normally fabricated by a sputtering method, whereas ZnO:B is generally prepared by a metal-organic chemical vapor deposition method. Finally, the front contact of the solar cells is an Al layer or Al/Ni layers, which are deposited using thermal evaporation or electron beam evaporation.

EFFECT OF ALKALI ELEMENTS

First, the impact of alkali element Na is discussed. Soda-lime glass (SLG) is generally utilized as the substrate for CIGSe and CIGSSe-based solar cells since it can provide the appropriate amount of Na in the absorbers for high solar cell performance during their growth. For Na-free substrates such as stainless foil and polyimide film, Na introduction into the absorbers can be achieved by NaF-PDT [4,29]. Though the detailed mechanism of the impact of Na is still open for discussion, the role of Na in a CuInSe2 structure was theoretically reported by Wei et al., who wrote that Na with the right concentration replaces InCu antisite defects, thus increasing carrier concentration [30]. Moreover, the increased p-type conductivity of CIGSe absorbers induced by Na introduction to enhance open-circuit voltage (VOC) is feasibly attributed to the formation of a shallow acceptor state several tens of meV above the valance band maximum [11,31]. It was reported that the enhancement of the Na concentration from 5.3×1018 to 7.9×1018 atoms/cm3 gives rise to the increase in VOC [32], thereby increasing the η.

Next, the effect of alkali element K is discussed. The introduction of K into CIGSe can be attained by KF-PDT [4,5]. It was reported that the absorber surface treatments with KF produce the increase in VOC [4,5]. It was shown by Chirila et al. that KF-PDT after CIGSe fabrication not only results in the partial ion exchange of Na with K within the CIGSe film, thereby decreasing amount of Na, but also leads to the modification of the chemical composition profile near the CIGSe surface (below 30 nm), thus depleting mostly Cu and Ga [4]. Normally, the CdS layer requires a thickness of about 50 nm or thicker for high cell performance in CIGSe solar cells with a non-alkali K treated absorber [33]. However, Chirila et al. reported that KF-PDT allows the decrease in CdS thickness below 50 nm without the deterioration of photovoltaic performance, thus increasing the η up to 20.4% [4]. This is because KF-PDT changes the surface chemical composition near the CIGSe surface, especially the Cu deficiency. Therefore, in the short duration of CdS deposition for very thin layers (below 50 nm), a high density of the CdCu donor near the CIGSSe surface, producing electronic inversion of the surface, is attained by diffusion of Cd into the Cu vacancies, thanks to the Cu-depleted CIGSe surface composition induced by KF-PDT, forming a p-n homojunction.

Moreover, the influences of heavier alkali element Rb and Cs are discussed. It was reported that the Rb and Cs introductions into CIGSe can be performed by RbF-PDT and CsF-PDT, respectively [5]. The RbF-PDT and CsF-PDT lead to the decreases in Na and K in CIGSe absorbers [5]. However, it is still unclear whether Rb and Cs push away Na and K only along the grain boundaries or also in the bulk of the grain, and it is an area for further examination. The η of the CIGSe solar cell is enhanced by K-PDT, Rb-PDT, and Cs-PDT because of the gain in VOC [5]. Moreover, the gain in VOC for KF-PDT is greater than for RbF-PDT or CsF-PDT; however, the CIGSe solar cells with RbF-PDT or CsF-PDT still demonstrate higher η owing to the accompanying loss JSC for KF-PDT.

It is seen that the introduction of alkali elements plays an important role in the enhancement of η of CIGSe-based solar cells. The introduction of alkali element K into CIGSSe absorbers was additionally performed by K treatment, thus increasing the η of CIGSSe-based solar cells to 22.3% [6]. Table 1 provides a summary of the high photovoltaic performance (> 20%) of CIGSe and CIGSSe solar cells with different PDT-methods applied, where their buffer 1 is a CdS layer. It is found that the CIGSe solar cell with η of 22.6% was achieved by alkali element Rb [5].

 

Absorber

PDT

JSC (mA/cm2)

VOC (mV)

FF (%)

η (%)

Ref.

CIGSe
CIGSe
CIGSe
CIGSSe
CIGSe
CIGSe

N/A
NaF+KF
KF
K
RbF
RbF

35.4
35.1
34.8
39.4
36.6
37.8

740
736
757
721
746
741

77.5
78.9
79.1
78.2
79.3
80.6

20.3*
20.4*
20.8*
22.3*
21.7*
22.6*

[34]
[4]
[15]
[6]
[35]
[5]


Table 1: Summary of high solar cell performances (> 20%) of CIGSe and CIGSSe solar cells with different PDT-method applied.
The buffer 1 of the solar cells is CdS layer.
*Certified solar cell efficiency.

INFLUENCE OF DEVICE STRUCTURE

To further enhance solar cell performance, especially the JSC, beyond that of the CIGSe and CIGSSe solar cells with a traditional CdS (buffer 1)/ZnO (buffer 2) layers as seen in Fig. 1, the device structure of the solar cells is developed and discussed. The traditional CdS (buffer 1) and ZnO (buffer 2) layers were replaced by more transparent materials to reduce to the optical losses in the short λ less than 520 nm as shown in Fig. 1.

It is known that the introduction of Zn into CdS to form (Cd,Zn)S leads to the enhancement of Eg. Here, the beneficial effect of bandgap widening of buffer layers is explained by our recent work. (Cd,Zn)S was prepared by a CBD process and its properties were investigated for possibly replacing the CdS (buffer 1) to enhance the JSC. The solution for (Cd,Zn)S growth consisted of CdSO4 (1.5 mmol/L), ZnSO4 (7 mmol/L), ammonia (0.37 mol/L), and thiourea (50 mmol/L). It was revealed that [Zn]/([Zn]+[Cd]) of the resulting (Cd,Zn)S film on SLG substrate, investigated by energy dispersive spectroscopy (EDS) operated at 4 kV, is approximately 0.25. The Eg of this Cd0.75Zn0.25S film on SLG substrate, obtained from its (αhν)2 plot as a function of photon energy (hν), is about 2.6 eV, higher than that of CdS, where the α denotes the absorption coefficient of the Cd0.75Zn0.25S film. We consequently replaced the traditional CdS (buffer 1) by Cd0.75Zn0.25S (buffer 1) in the CIGSe solar cell. Figure 2 demonstrates (a) external quantum efficiencies (EQE) and integrated photocurrent densities of CIGSe solar cells and (b) their first derivations of the EQE spectra. The structure of the solar cells is SLG/Mo/CIGSe/buffer 1/ZnO/ITO/Ni-Al. The buffer 1 layers are Cd0.75Zn0.25S and CdS for reference. The Egs of ZnO, Cd0.75Zn0.25S, CdS, and CIGSe layers in the structures of the solar cells were obtained from the first derivation of the EQE spectra of the solar cells seen in Fig. 2(b). It is disclosed that the Cd0.75Zn0.25S in the structure of the solar cell has a larger Eg of 2.69 eV than that of CdS (2.47 eV). As a result, in Fig. 2(a) the EQE of the solar cell with the Cd0.75Zn0.25S as buffer 1 is improved in short λ (below 520 nm), there by increasing the integrated photocurrent density from 34.82 (CdS) to 36.49 mA/cm2 (Cd0.75Zn0.25S). According to our recent results, a CIGSSe solar cell with η of 19.7% was reported with the replacement of the CdS layer by Cd0.75Zn0.25S [36]. It is suggested that a conventional CdS (buffer 1) can be replaced by the materials with larger Eg such as (Cd,Zn)S to improve JSC, thus enhancing the η.

 

Fig. 2: (a) External quantum efficiencies (EQE) and integrated photocurrent densities of CIGSe solar cells and (b) their first derivations of the EQE spectra. The structure of the solar cells is SLG/Mo/CIGSe/buffer 1/ZnO/ITO/Ni-Al. The buffer 1 layers are Cd0.75Zn0.25S and CdS for reference.

It was recently published that the CIGSSe solar cells with alternative ZnS(O,OH) (buffer 1)/Zn1-xMgxO (buffer 2) layers in replacements of traditional CdS/ZnO layers gives rise to the highest η of 22.8% (in-house) [6], where Zn1-xMgxO was prepared by atomic layer deposition (ALD). This is because the larger Eg of ZnS(O,OH) than that of CdS increases the JSC, and the band alignment at the p-n junction should be optimized by tuning the composition of Zn1-xMgxO, which should contribute to the increase in VOC.

 

MgO power density
(W/cm2)

ZnO power density
(W/cm2)

[Mg]/([Mg]+[Zn])
(x)

Eg (eV)

Urbach energy (meV)

Resistivity
(Ω.cm)

0
1.28
1.86
3.16

2.13
1.95
1.81
1.5

0
0.112
0.211
0.4

3.3
3.53
3.73
4.1

88.9
93.6
98.4
162.5

3.13×10-2
1.04×10-1
1.34×102
N/A


Table 2: Zn1-xMgxO films on SLG substrates with different [Mg]/([Mg]+[Zn]) ratios, x, with their optical and electrical properties. The material compositions in Zn1-xMgxO films were measured by energy dispersive spectroscopy (EDS) operated at 4 kV.

In addition, it is known that Zn1-xMgxO layers could be prepared by radio frequency (RF) magnetron co-sputtering. In our recent work, Zn1-xMgxO layers were thus deposited to examine their optical and electrical properties for feasibly replacing ZnO (buffer 2). We prepared Zn1-xMgxO layers with different Mg contents by RF magnetron co-sputtering from ZnO (99.99%) and MgO (99.99%) targets. The sputtering power densities for ZnO and MgO targets were varied to change Mg contents (x), expressed as [Mg]/([Mg]+[Zn]), in the resulting Zn1-xMgxO films on SLG substrates as shown in Table 2. Figure 3 shows the corresponding transmittance spectra of Zn1-xMgxO films on SLG substrates with different x (0-0.4), investigated by EDS. The absorption coefficient (α) of Zn1-xMgxO films was derived from their transmittance and reflectance spectra, thus resulting to the (αhν)2 plots as a function of photon energy (hν) to estimate the optical Eg of Zn1-xMgxO films as demonstrated in Table 2. The absorption edge makes a blue shift as x increases from 0 to 0.4 in Fig 3, thus increasing the Eg of Zn1-xMgxO from 3.3 to 4.1 eV in Table 2. Moreover, the resistivity of Zn1-xMgxO is significantly increased with increasing x from 0 to 0.4 in Table 2. It is notable that the basic crystal structure of the Zn1-xMgxO in the x range of 0-0.4 is that of ZnO, observed by X-ray diffraction [20].

 

Fig. 3: Optical transmittance spectra of Zn1-xMgxo films on SLG substrates with different [Mg]/([Mg]+[Zn]) ratios, x, (0-0.4). The optical transmittances of the films were measured by uv-vIS-nIR spectrophotometer (uv-3600, Shimadzu).

When the hν is near or less than the optical Eg of the Zn1-xMgxO films, their absorption coefficient (α) shows the exponential dependence on the hν [37]:

(1)

where α0 is a constant. Eu is Urbach energy, correlating to the width of the band tail, and can be utilized to investigate the impact of defects in the Zn1-xMgxO films. According to Equation (1), the plot of ln α as a function of hν should give the linear relation and Eu is obtained from the slope. The ln α versus hν for the Zn1-xMgxO films with different x is shown in Fig. 4, where the Eu was estimated from the reciprocal gradient of the linear portions of the curves as shown in Table 2. Eu is increased from 88.9 meV for pure ZnO (x=0) to 162.5 meV for Zn0.6Mg0.4O (x=0.4) in Table 2 and Fig. 4, where Eu is over 100 meV, when x is greater than or equal to 0.4, indicating that the film quality is severely deteriorated. According to the results, Zn1-xMgxO film can be used as buffer 2 in the replacement of traditional ZnO since Eg and resistivity of Zn1-xMgxO films are larger than those of ZnO, feasibly decreasing optical losses for the enhanced JSC [18], and reducing the shunt path for improved VOC [28], respectively. It was already reported that ZnO (buffer 2) was replaced by Zn1-xMgxO film for the improvement of cell performance [5,6].

 

Fig. 4: Plots of ln α of Zn1-xMgxO films on SLG substrates with different [Mg]/([Mg]+[Zn]) ratios, x, on SLG substrates as a function of photon energy (hν).

Consequently, the alternative materials for buffer 1 and buffer 2 in Fig. 1 have been intensively investigated by several research groups in the replacement of traditional CdS/ZnO buffers so far [6,16-19]. Table 3 illustrates a summary of the CIGSe and CIGSSe solar cells with different buffer layers (buffer 1 and buffer 2) for various device structures. Up to now, 22.8%-efficient CIGSSe solar cells (in-house) have been achieved [6], where the CIGSSe absorber was subjected to K treatment, and the alternative ZnS(O,OH) (buffer 1)/Zn1-xMgxO (buffer 2) replaced the traditional CdS/ZnO layer to reduce the optical losses in short λ below 520 nm.

 

Absorber

PDT

Buffer 1 / Buffer 2

JSC (mA/cm2)

VOC (mV)

FF (%)

η (%)

Ref.

CIGSe
CIGSSe
CIGSSe
CIGSSe
CIGSSe
CIGSe
CIGSe
CIGSe
CIGSe
CIGSSe
CIGSSe
CIGSSe
CIGSSe
CIGSSe

RbF
K
N/A
N/A
N/A
N/A
N/A
N/A
N/A
K
N/A
K
K
N/A

CdS/ZnO (Traditional)
CdS/ZnO (Traditional)
CdS/ZnO (Traditional)
Thin-CdS/ZnS(O,OH)/ZnO
(Cd,Zn)S/ZnO
ZnSe/ZnO
(Zn,In)Se/ZnO
In(OH,S)/ZnO
In2S3/ZnO
CdS/(Zn,Mg)O
ZnS(O,OH)/ZnO
ZnS(O,OH)/(Zn,Mg)O
ZnS(O,OH)/(Zn,Mg)O
(Cd,Zn)S/(Zn,Mg)O

37.8
39.4
36.6
37.7
38.5
34.4
30.4
35.5
16.4
41.6
39.9
39.4
41.4
38.1

741
721
692
654
684
554
652
594
665
704
685
717
711
683

80.6
78.2
75.7
75.2
74.2
73
76
75
78
77.4
76.5
77.9
77.5
74.9

22.6*
22.3*
19.2**
18.6**
19.7**
13.6**
15.1**
15.7**
16.4**
22.7**
20.9*
22.0*
22.8**
19.6**

[5]
[6]
[36]
[36]
[36]
[38]
[39]
[40]
[41]
[6]
[42]
[6]
[6]
[43]


Table 3: Summary of the CIGSe and CIGSSe solar cells with different buffer layers.
*Certified solar cell efficiency **in-house solar cell efficiency

CONCLUSION

CIGSe and CIGSSe-based solar cells with η above 20% have been reported. Alkali elements (Na, K, Rb, and Cs) were discussed. The role of Na was theoretically predicted; in particular, that the right amount of Na would lead to the increase in carrier concentration of the absorber, thus enhancing VOC. The KF-PDT for K introduction in the absorbers changes their surface chemical composition, especially the Cu deficiency. Consequently, in the short duration of CdS deposition for very thin layers (below 50 nm), a high density of CdCu donors near absorber surface, resulting in electronic inversion of the surface, is accomplished by the diffusion of Cd into the Cu vacancies due to the Cu-depleted absorber surface composition induced by KF-PDT, forming a p-n homojunction.

A 20.4%-efficient CIGSe solar cell on a polyimide substrate with very thin CdS thickness (below 50 nm) was reported by NaF- and KF-PDT in the CIGSe absorber [4]. Moreover, it was found that the CIGSe solar cell with η of 22.6% was achieved by incorporation of the heavier alkali element Rb [5].

To further increase photovoltaic performance beyond those of solar cells with traditional CdS/ZnO buffer layers, these traditional buffer layers were replaced with more transparent materials. Consequently, 22.8%-efficient CIGSSe solar cells (in-house) were achieved [6], where the CIGSSe absorber was subjected to K treatment, and the alternative ZnS(O,OH) (buffer 1)/Zn1-xMgxO (buffer 2) buffer layers were used to replace the traditional CdS/ZnO buffer layers to reduce the optical losses in short λ below 520 nm.

Acknowledgements: This work is partly supported by NEDO (the New Energy and Industrial Technology Development Organization) in Japan. The authors would like to thank Dr. Takuya Kato and Dr. Hiroki Sugimoto from Atsugi Research Center, Solar Frontier K. K., Japan, for their valuable discussions.

References

[1] Y. Hamakawa, Thin-Film Solar Cells Next Generation Photovoltaics and Its Applications, Springer: Heidelberg, 2004.
[2] E. Vallat-Sauvain, A. Shah, and J. Bailat, Thin Film Solar Cells, Fabrication, Characterization and Applications, Wiley: Chichester, 2006.
[3] J. L. Shay, S. Wagner, and H. M. Kasper, Appl. Phys. Lett. 27, 89 (1975).
[4] A.Chirila, P. Reinhard, F. Pianezzi, P. Bloesh, A. R. Uhl, C. Fella, L. Kranz, D. Keller, C. Gretener, H. Hagendorfer, D. Jaeger, R. Erni, S. Nishiwaki, S. Buecheler, and A. N. Tiwari, Nat. Mater. 12, 1107 (2013).
[5] P. Jackson, R. Wuerz, D. Hariskos, E. Lotter, W. Witte, and M. Powalla, Phys. Status Solidi RRL 10, 583 (2016).
[6] R. Kamada, T. Yagioka, S. Adachi, A. Handa, K. F. Tai, T. Kato, and H. Sugimoto, The 43rd IEEE Photovoltaic Specialists Conference, 2016, pp. 1287-1291.
[7] M. Powalla, P. Jackson, D. Hariskos, S. Paetel, W. Witte, R. Wuerz, E. Lotter, R Menner, and W. Wischmann, The 29th European Photovoltaic Solar Energy Conference, 2014, 3AO.4.2.
[8] J. Hedstrom, H. Ohlsen, M. Bodegard, A. Kylner, L. Stolt, D. Hariskos, M. Ruckh, and H. W. Schock, The 23rd IEEE Photovoltaic Specialists Conference, 1993, pp. 364-371.
[9] T. Nakada, D. Iga, H. Ohbo, and A. Kunioka, Jpn. J. Appl. Phys. 36, 732 (1997).
[10] D. Braunger, D. Hariskos, G. Bilger, U. Rau, and H. W. Schock, Thin Solid Films 361, 161 (2000).
[11] S. Ishizuka, A. Yamada, K. Matsubara, P. Fons, K. Sakurai, and S. Niki, Appl. Phys. Lett. 93, 124105 (2008).
[12] P. T. Erslev, J. W. Lee, W. N. Shafarman, and J. D. Cohen, Thin Solid Films 517, 2277 (2009).
[13] M. A. Contreras, B. Egaas, P. Dippo, J. Webb, J. Granata, K. Ramanathan, S. Asher, A. Swartzlander, and R. Noufi, The 26th IEEE Photovoltaic Specialists Conference, 1997, pp. 359-362.
[14] R. Wuerz, A. Eicke, F. Kessler, S. Paetel, S. Efimenko, and C. Schlegel, Sol. Energy Mater. Sol. Cells 100, 132 (2012).
[15] P. Jackson, D. Hariskos, R. Wuerz, W. Wischmann, and M. Powella, Phys. Status Solidi RRL 8, 219 (2014).
[16] S. Siebentritt, Solar Energy 77, 767 (2004).
[17] D. Hariskos, S. Spiering, and M. Powalla, Thin Solid Films 480-481, 99 (2005).
[18] D. Hariskos, B. Fuchs, R. Menner, N. Naghavi, C. Hubert, D. Lincot, and M. Powalla, Prog. Photovol. Res. Appl. 17, 479 (2009).
[19] J. Song, S. S. Li, L. Chen, R. Noufi, T. J. Anderson, and O. D. Crisalle, The 4th World Conference on Photovoltaic Energy Conversion, 2006, pp. 534-537.
[20] T. Minemoto, T. Negami, S. Nishiwaki, H. Takakura, and Y. Hamakawa, Thin Solid Films 372, 173 (2000).
[21] T. Minemoto, Y. Hashimoto, T. Satoh, T. Negami, H. Takakura, and Y. Hamakawa, J. Appl. Phys. 89, 8327 (2001).
[22] K. Tanaka, T. Minemoto, and H. Takakura, Solar Energy 83, 477 (2009).
[23] A. M. Gabor, J. R. Tuttle, M. H. Bode, A. Franz, A. L. Tennant, M. A. Contreras, R. Noufi, D. G. Jensen, and A. M. Hermann, Sol. Energy Mater. Sol. Cells 41-42, 247 (1996).
[24] K. Kushiya, Solar Energy 77, 717 (2004).
[25] Y. Ogawa, A. J. Waldau, T. H. Hua, Y. Hashimoto, and K. Ito, Appl. Surf. Sci. 92, 232 (1996).
[26] J. Chantana, T. Kato, H. Sugimoto, and T. Minemoto, Curr. Appl. Phys. 17, 461(2017).
[27] T. Minemoto, T. Matsui, H. Takakura, Y. Hamakawa, T. Negami, Y. Hashimoto, T. Uenoyama, and M. Kitagawa, Sol. Energy Mater. Sol. Cells 67, 83 (2001).
[28] S. Ishizuka, K. Sakurai, A. Yamada, K. Matsubara, P. Fons, K. Iwata, S. Nakamura, Y. Kimura, T. Baba, N. Nakanishi, T. Kojima, and S. Niki, Sol. Energy Mater. Sol. Cells 87, 541 (2005).
[29] A. Chirila, S. Buecheler, F. Pianezzi, P. Bloesh, C. Gretener, A. R. Uhl, C. Fella, L. Kranz, J. Perrenoud, S. Seyrling, S. NiShiwaki, Y. E. Bilger, and A. N. Tiwari, Nat. Mater. 10, 857 (2011).
[30] S. Wei, S. B. Zhang, and A. Zunger, J. Appl. Phys. 85, 7214 (1999).
[31] U. Rau, M. Schmitt, D. Hilburger, F. Engelhardt, O. Seifert, and J. Parisi, The 25th IEEE Photovoltaic Specialists Conference, 1997, pp. 1005.
[32] J. Chantana, T. Watanabe, S. Teraji, K. Kawamura, and T. Minemoto, Appl. Surf. Sci. 314, 845 (2014).
[33] P. Jackson, R. Wurz, U. Rau, J. Mattheis, M. Kurth, T. Schlotzer, G. Bilger, and J. Werner, Prog. Photovol. Res. Appl. 15, 507 (2007).
[34] P. Jackson, D. Hariskos, E. Lotte, S. Paetel, R. Wuerz, R. Menner, W. Wischmann, and M. Powalla, Prog. Photovol. Res. Appl. 19, 894 (2011).
[35] P. Jackson, D. Hariskos, R. Wuerz, O. Kiowski, A. Bauer, T. M. Friedlmeier, and M. powalla, Phys. Status Solidi RRL 9, 28 (2015).
[36] J. Chantana, T. Suwansichon, K. Kawabata, T. Kato, H. Sugimoto, and T. Minemoto, The 26th International Photovoltaic Science and Engineering Conference (PVSEC-26), Singapore, 3.2.6f (October 24-28, 2016).
[37] V. Srikant, and D. R. Clarke, J. Appl. Phys. 81, 6357 (1997).
[38] A. Ennaoui, W. Esele, M. C. Lux-Steiner, T. P. Niesen, and F. Karg, Thin Solid Films 431-432, 335 (2003).
[39] A. Yamada, S. Chaisitsak, Y. Ohtake, and M. Konagai, The 2nd World Conference and Exhibition on Photovoltaic Solar Energy Conversion, Vienna, pp. 1177-1180.
[40] D. Hariskos, M. Ruckh, U. Ruhle, T. Walter, H. W. Schock, J. Hedstrom, and L. Stolt, Sol. Energy Mater. Sol. Cells 41-42, 345 (1996).
[41] N. Naghvi, S. Spiering, M. Powalla, B. Canava, A. Taisme, J. -F. Guillemoles, S. Taunier, A. Etcheberry, and D. Lincot, Mater. Res. Soc. Symp. Proc. 763, 465 (2003).
[42] M. Nakamura, N. Yoneyama, K. Horiguchi, Y. Iwata, K. Yamaguchi, H. Sugimoto, and T. Kato, The 40th IEEE Photovoltaic Specialists Conference, 2014, pp. 0107-0110.
[43] J. Chantana, T. Kato, H. Sugimoto, and T. Minemoto, Prog. Photovol. Res. Appl. (2017). DOI: 10.1002/pip.2879.

 

Jakapan Chantana was born in Surat Thani, Thailand in July 1978. He received his PhD from Osaka University, Japan in March 2012. He is an associate professor of the Department of Electrical and Electronic Engineering, Ritsumeikan University, Japan (April 2016 - present). He was also an assistant professor (October 2015 - March 2016), and senior researcher (April 2012 - September 2015) at Ritsumeikan University. His current research works are device fabrication and characterization of compound semiconductor thin-film solar cells.

Takashi Minemoto is a professor of the Department of Electrical and Electronic Engineering at Ritsumeikan University, Japan (2015 - present). He was an associate professor (2009 - 2015), lecturer (2004 - 2009) and post-doctoral fellow (2003 - 2004) at Ritsumeikan University, and was a limited term researcher (2001 - 2002) at the Institute of Energy Conversion at the University of Delaware, USA. He earned his PhD degree at Ritsumeikan University in 2001. His current research works are device fabrication and characterization of compound semiconductor thin-film solar cells and the analysis of outdoor field tests of photovoltaic modules.