Increase in conversion efficiency of above 14% in Cu(In,Ga)₃Se₅ (β-CIGS) solar cells by Na₂S incorporation through the surface of β –CIGS film

Kim, Ji Hye,Kim, Seung Tae,Larina, Liudmila,Ahn, Byung Tae,Kim, KiHwan,Yun, Jae Ho Elsevier 2018 Solar energy materials and solar cells Vol.179 No.-

<P><B>Abstract</B></P> <P>Little work has been reported on the performance improvement of the β-CIGS solar cell itself even though the β-CIGS phase can have an ideal band gap for high-conversion efficiency solar cells. We incorporated Na<SUB>2</SUB>S to β-CIGS film by supplying Na<SUB>2</SUB>S to three different stages: on the (In,Ga)<SUB>2</SUB>Se<SUB>3</SUB> layer, on the α-CIGS layer, and on the β -CIGS layer in the three-stage co-evaporation process. The purpose of Na<SUB>2</SUB>S incorporation was to control the carrier concentration and passivate grain boundaries in β–CIGS film. With Na<SUB>2</SUB>S incorporation on the β–CIGS surface, both the Cu and Se concentrations at the β–CIGS surface were greatly reduced and the Na-depleted subsurface area that existed in the referenced β–CIGS film without Na<SUB>2</SUB>S was eliminated. The carrier concentration determined at 100kHz was lowest with Na<SUB>2</SUB>S incorporation on the β–CIGS surface, while that determined at 1MHz was similar with various Na<SUB>2</SUB>S supply stages. The open-circuit voltage and fill factor greatly increased in the β–CIGS solar cell with the Na<SUB>2</SUB>S incorporation. The cell conversion efficiency with Na<SUB>2</SUB>S incorporation on the β-CIGS layer improved from 10.3% to 14.2% without AR coating, which is a record efficiency in β-CIGS solar cells at this time.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The performance of Cu(In,Ga)<SUB>3</SUB>Se<SUB>5</SUB> (β-CIGS) solar cell was improved by Na<SUB>2</SUB>S doping. </LI> <LI> Na<SUB>2</SUB>S was supplied on the surfaces of (In,Ga)<SUB>2</SUB>Se<SUB>3</SUB>, α-CIGS layer, and β -CIGS layers. </LI> <LI> Na<SUB>2</SUB>S on the β–CIGS surface reduced both the Cu and Se concentrations at the surface. </LI> <LI> Na<SUB>2</SUB>S on the β–CIGS surface eliminated the Na depletion zone in the CIGS film. </LI> <LI> The cell conversion efficiency improved from 10.3% to 14.2% without AR coating. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>(a) A schematic three-stage co-evaporation process for Cu(In,Ga)<SUB>3</SUB>Se<SUB>5</SUB> (β-CIGS) film with Na<SUB>2</SUB>S incorporation at various stages and (b) J-V curves of the β–CIGS solar cell with the best efficiency of 14.2% without antireflective coating by Na<SUB>2</SUB>S incorporation on the β–CIGS layer (③).</P> <P>[DISPLAY OMISSION]</P>

Cu(In,Ga)Se2 superstrate-type solar cells with Zn1−xMgxO buffer layers

Takashi Minemoto,Shinya Harada,Hideyuki Takakura 한국물리학회 2012 Current Applied Physics Vol.12 No.1

Superstrate-type Cu(In,Ga)Se2 (CIGS) thin film solar cells were fabricated using Zn1-xMgxO buffer layers. Due to the diffusion of Cd into CIGS during the growth of the CIGS layer, the conventional buffer material of CdS is not suitable. ZnO is a good candidate because of higher thermal tolerance but the conduction band offset (CBO) of ZnO/CIGS is not appropriate. In this study, the Zn1-xMgxO buffer layers were used to fulfill both the requirements. The superstrate-type solar cells with a soda-lime glass/In2O3:Sn/Zn1-xMgxO/CIGS/Au structure were fabricated with different band gap energies of the Zn1-xMgxO layer. The CIGS layers [Ga/(In + Ga)~0.25] were deposited by co-evaporation method. The substrate temperature during the CIGS deposition of 450 ℃ did not cause the intermixing of the Zn1-xMgxO and CIGS layers. The conversion efficiency of the cell with Zn1-xMgxO was higher than that with ZnO due to the improvement of open-circuit voltage and shunt resistance. The results well corresponded to the behavior of the adjustment of CBO, demonstrating that the usefulness of the Zn1-xMgxO layer for the CBO control in the superstrate-type CIGS solar cells. Superstrate-type Cu(In,Ga)Se2 (CIGS) thin film solar cells were fabricated using Zn1-xMgxO buffer layers. Due to the diffusion of Cd into CIGS during the growth of the CIGS layer, the conventional buffer material of CdS is not suitable. ZnO is a good candidate because of higher thermal tolerance but the conduction band offset (CBO) of ZnO/CIGS is not appropriate. In this study, the Zn1-xMgxO buffer layers were used to fulfill both the requirements. The superstrate-type solar cells with a soda-lime glass/In2O3:Sn/Zn1-xMgxO/CIGS/Au structure were fabricated with different band gap energies of the Zn1-xMgxO layer. The CIGS layers [Ga/(In + Ga)~0.25] were deposited by co-evaporation method. The substrate temperature during the CIGS deposition of 450 ℃ did not cause the intermixing of the Zn1-xMgxO and CIGS layers. The conversion efficiency of the cell with Zn1-xMgxO was higher than that with ZnO due to the improvement of open-circuit voltage and shunt resistance. The results well corresponded to the behavior of the adjustment of CBO, demonstrating that the usefulness of the Zn1-xMgxO layer for the CBO control in the superstrate-type CIGS solar cells.

Analysis of photovoltaic cell parameters of non-vacuum solution processed Cu(In, Ga)Se₂ thin film based solar cells

Khan, F.,Lee, H.J.,Oh, M.,Kim, J.H. Association for Applied Solar Energy ; Elsevier Sc 2014 SOLAR ENERGY -PHOENIX ARIZONA THEN NEW YORK- Vol.108 No.-

The losses in Cu(In, Ga)Se<SUB>2</SUB> (CIGS) solar cells due to photovoltaic (PV) cell parameters, namely the shunt resistance R<SUB>sh</SUB>, series resistance R<SUB>s</SUB>, diode ideality factor n, and reverse saturation current density J<SUB>0</SUB>, were analyzed in this study. The PV cell parameters of the solar cells were analytically determined for various doping concentrations of Cu and In in CIGS films. The CIGS films were deposited using a low cost non-toxic solvent (deionized) by a non-vacuum process (spray pyrolysis technique). They were subsequently characterized using XRD, FE-SEM, I-V and UV-Vis techniques to correlate the structural, electrical, and optical properties of the films with solar cell performance. Maximum short circuit current density of 0.0218A/cm<SUP>2</SUP> is achieved for Cu/Se and In/Se molar ratios of 0.131 and 0.318, respectively. However, the maximum obtained V<SUB>oc</SUB> value is 0.431V for Cu/Se and In/Se molar ratios of 0.105 and 0.191, respectively. The maximum achieved efficiency was ~4.38% for Cu/Se and In/Se molar ratios of 0.105 and 0.191, respectively. Analytically predicted values of R<SUB>sh</SUB>, R<SUB>s</SUB>, n, and J<SUB>0</SUB> were 116.82Ωcm<SUP>2</SUP>, 4.64Ωcm<SUP>2</SUP>, 1.8016, and 1.4952x10<SUP>-6</SUP>A/cm<SUP>2</SUP>, respectively.

Determination of the lateral collection length of charge carriers for silver-nanowire-electrode-based Cu(In,Ga)Se₂ thin-film solar cells

Lee, Sangyeob,Jang, Jiseong,Cho, Kyung Soo,Oh, Yong-Jun,Hong, Ki-Ha,Song, Soomin,Kim, Kihwan,Eo, Young-Joo,Ho Yun, Jae,Gwak, Jihye,Chung, Choong-Heui Elsevier 2019 Solar energy Vol.180 No.-

<P><B>Abstract</B></P> <P>Silver nanowire (AgNW) electrodes have been employed in solar cells as transparent conducting electrodes (TCEs). When a AgNW electrode is used as a network-type TCE in solar cells, photogenerated charge carriers must laterally travel to reach AgNW networks. If the empty space of the network is larger than the lateral collection length of the charge carriers ( <SUB> L lc </SUB> ), a significant fraction of the charge carriers will be lost. Therefore, determination of <SUB> L lc </SUB> is essential for choosing and/or designing a suitable network for solar cells. Here, we develop a method to relate the lateral photocurrent measured from a specially designed pattern to the <SUB> L lc </SUB> value. We apply this method to Cu(In,Ga)Se<SUB>2</SUB> thin-film solar cells with AgNW TCEs. The <SUB> L lc </SUB> value was determined to be ≈ 26 μm in the CdS/CIGS/Mo structure under 1-sun illumination. The measured lateral collection length is much larger than the normal spacing between AgNWs, indicating a high lateral collection efficiency in AgNW TCE-based CIGS thin-film solar cells.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Lateral collection length is important for network-electrode-based solar cells. </LI> <LI> A method to determine the lateral collection length is developed. </LI> <LI> The lateral collection length for Cu(In,Ga)Se<SUB>2</SUB> solar cells was 26 μm under 1-sun. </LI> <LI> The method can be aaplied to other solar cells with network-transparent-electrodes. </LI> </UL> </P>

Fabrication of Cu(In, Ga)Se2 thin film solar cell absorbers from electrodeposited bilayers

Yusuke Oda,Masakazu Matsubayashi,Takashi Minemoto,Hideyuki Takakura 한국물리학회 2010 Current Applied Physics Vol.10 No.2

CuInSe2 (CIS) and Cu(In, Ga)Se2 (CIGS) films as solar cell absorbers have been fabricated from electrodeposited (ED) In–Se/CIS and CIS/CuGaSe2 (CGS) bilayers, respectively. Firstly, In–Se/CIS bilayers were intermixed by annealing at 600 ℃ for 10 min and it followed that CIS films with large grains and controlled compositional ratios were realized. CIS solar cells using these films showed around 2.2% efficiency. Next,CIS/CGS bilayers were annealed at 600 ℃ for 60 min for intermixing. Here, oxygen-free CGS films prepared from Cu–Ga–Se solution added Li2SO4 as the supporting electrolyte were used because Ga–O compound formed in ED-CGS films worked as the defects. As the results, around 2.9% efficiency CIGS solar cell using the films was realized. Especially, 29.7 mA/㎠ and 36.1 mA/㎠ high short-circuit current density were obtained in the CIS and CIGS solar cells, respectively. These results indicate that ED-bilayers technique is useful to realize low-cost and high efficiency solar cell.

Na₂S 하부층을 이용한 Cu(In,Ga)Se₂ 광흡수층의 저온증착 및 Cu(In,Ga)Se₂ 박막태양전지에의 응용

신해나라,신영민,김지혜,윤재호,박병국,안병태,Shin, Hae Na Ra,Shin, Young Min,Kim, Ji Hye,Yun, Jae Ho,Park, Byung Kook,Ahn, Byung Tae 한국태양광발전학회 2014 Current Photovoltaic Research Vol.2 No.1

High-efficiency in $Cu(In,Ga)Se_2$ (CIGS) solar cells were usually achieved on soda-lime glass substrates due to Na incorporation that reduces deep-level defects. However, this supply of sodium from sodalime glass to CIGS through Mo back electrode could be limited at low deposition temperature. Na content could be more precisely controlled by supplying Na from known amount of an outside source. For the purpose, an $Na_2S$ layer was deposited on Mo electrode prior to CIGS film deposition and supplied to CIGS during CIGS film. With the $Na_2S$ underlayer a more uniform component distribution was possible at $350^{\circ}C$ and efficiency was improved compared to the cell without $Na_2S$ layer. With more precise control of bulk and surface component profile, CIGS film can be deposited at low temperature and could be useful for flexible CIGS solar cells.

Growth of Sn(O,S)2 buffer layers and its application to Cu(In,Ga)Se2 solar cells

김지혜,신동협,권혁상,안병태 한국물리학회 2014 Current Applied Physics Vol.14 No.12

Sn-based thin films as new buffer layer for Cd-free Cu(In,Ga)Se2 (CIGS) solar cells were developed. The Sn(O,S)2 films were formed on CIGS substrates by chemical bath deposition from an alkaline ammonia solution by reacting tin(IV) chloride with thiourea. Optimization of the growth process allowed the smooth and conformal coverage of the films on the CIGS substrates with a thickness of 20 nm that was a self-limited thickness in the chemical bath deposition process. XPS analysis revealed that the asdeposited films contained SneO, SneOH, and SneS bondings and the ratio of SneS bonding to SneO bonding was 0.3. The CIGS solar cell fabricated with a 20-nm thick Sn(O,S)2 buffer layer had the best efficiency of 11.5% without AR coating. The open circuit voltage, short circuit current, and fill factor were 0.55 V, 34.4 mA/cm2, and FF ¼ 0.61, respectively. The open circuit voltage and fill factor were low compared to the conventional CIGS solar cell with a 50-nm thick CdS buffer due to too thin Sn(O,S)2 buffer layer.

Growth of Sn(O,S)₂ buffer layers and its application to Cu(In,Ga)Se₂ solar cells

Kim, J.H.,Shin, D.H.,Kwon, H.S.,Ahn, B.T. Elsevier 2014 CURRENT APPLIED PHYSICS Vol.14 No.12

Sn-based thin films as new buffer layer for Cd-free Cu(In,Ga)Se<SUB>2</SUB> (CIGS) solar cells were developed. The Sn(O,S)<SUB>2</SUB> films were formed on CIGS substrates by chemical bath deposition from an alkaline ammonia solution by reacting tin(IV) chloride with thiourea. Optimization of the growth process allowed the smooth and conformal coverage of the films on the CIGS substrates with a thickness of 20 nm that was a self-limited thickness in the chemical bath deposition process. XPS analysis revealed that the as-deposited films contained Sn-O, Sn-OH, and Sn-S bondings and the ratio of Sn-S bonding to Sn-O bonding was 0.3. The CIGS solar cell fabricated with a 20-nm thick Sn(O,S)<SUB>2</SUB> buffer layer had the best efficiency of 11.5% without AR coating. The open circuit voltage, short circuit current, and fill factor were 0.55 V, 34.4 mA/cm<SUP>2</SUP>, and FF = 0.61, respectively. The open circuit voltage and fill factor were low compared to the conventional CIGS solar cell with a 50-nm thick CdS buffer due to too thin Sn(O,S)<SUB>2</SUB> buffer layer.

Time-resolved photoluminescence of Cu(In,Ga)(Se,S)2 thin films and temperature dependent current density-voltage characteristics of their solar cells on surface treatment effect

Jakapan Chantana,Takuya Kato,Hiroki Sugimoto,Takashi Minemoto 한국물리학회 2017 Current Applied Physics Vol.17 No.4

Influences of the surface treatments of Cu(In,Ga)(Se,S)2 (CIGSSe) thin films, which are KCN, HCl, or thiuorea treatments, were investigated by time-resolved photoluminescence (TRPL) and temperature dependent current density-voltage (J-V) characteristics of their solar cells. It is demonstrated that the KCN treatment optimized under 1 wt% leads to the significant increase in conversion efficiency (h) up to 19.21%. On the other hand, the h of the CIGSSe solar cells is in ranges of 13.70e15.51% and 9.86e10.70% with the HCl treatments (0.3e0.7 mol/L), and thiuorea treatments (0.5e1.5 mol/L), respectively, which are lower than 16.66% that of the reference solar cell without the surface treatment. According to TRPL measurements, the quality of near-surface CIGSSe is improved with the KCN treatment (1 wt%) owing to enhanced TRPL lifetimes, whereas that is deteriorated with the HCl and thiuorea treatments due to decreased TRPL lifetimes. In addition, according to the temperature-dependent J-V measurement, the interface recombination of the CIGSSe solar cell is decreased with the KCN treatment, while that of the CIGSSe solar cells is increased with the HCl and thiuorea treatments. Ultimately, 19.21%-efficient CIGSSe solar cell with the KCN treatment (1 wt%) at room temperature with the increased VOC of 0.692 V was obtained, which is around 15.3% relatively higher h than that of the solar cell without the surface treatment.

Properties of the Cu(In,Ga)Se_2 absorbers deposited by electron-beam evaporation method for solar cells

Zhao-Hui Li,조의식,권상직 한국물리학회 2011 Current Applied Physics Vol.11 No.1

Cu(In,Ga)Se_2 thin films were formed using the commercial Cu(In,Ga)Se_2 bulk by electron-beam evaporation method with the various beam current of the irradiated electrons. The experimental results showed that the Cu-rich Cu(In_(1-x)Ga_x)Se_2 films could be deposited successfully when the electron-beam current increased up to 90 mA. After the annealing process at 550℃ for 1 h in the vacuum of 3 × 10^6torr, the as-deposited amorphous Cu(In,Ga)Se_2 thin film was crystallized and the Cu-rich CIGS film was converted to Cu-poor film. The chemical composition the morphology and the band gap of the annealed Cu(In,Ga)Se_2 films were also analyzed.