• Korean Journal of Materials Research
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• v.22 no.5
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• pp.259-273
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• 2012

Chalcogenide-based semiconductors, such as $CuInSe_2$, $CuGaSe_2$, Cu(In,Ga)$Se_2$ (CIGS), and CdTe have attracted considerable interest as efficient materials in thin film solar cells (TFSCs). Currently, CIGS and CdTe TFSCs have demonstrated the highest power conversion efficiency (PCE) of over 11% in module production. However, commercialized CIGS and CdTe TFSCs have some limitations due to the scarcity of In, Ga, and Te and the environmental issues associated with Cd and Se. Recently, kesterite CZTS, which is one of the In- and Ga- free absorber materials, has been attracted considerable attention as a new candidate for use as an absorber material in thin film solar cells. The CZTS-based absorber material has outstanding characteristics such as band gap energy of 1.0 eV to 1.5 eV, high absorption coefficient on the order of $10^4cm^{-1}$, and high theoretical conversion efficiency of 32.2% in thin film solar cells. Despite these promising characteristics, research into CZTS-based thin film solar cells is still incomprehensive and related reports are quite few compared to those for CIGS thin film solar cells, which show high efficiency of over 20%. The recent development of kesterite-based CZTS thin film solar cells is summarized in this work. The new challenges for enhanced performance in CZTS thin films are examined and prospective issues are addressed as well.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.15 no.6
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• pp.252-259
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• 2005

Single crystal $CuGaSe_2$ layers were grown on thoroughly etched semi-insulating CaAs(100) substrate at $450^{\circ}C$ with hot wall epitaxy (HWE) system by evaporating $CuGaSe_2$ source at $610^{\circ}C$. The crystalline structure of the single crystal thin films was investigated by the photoluminescence (PL) and double crystal X-ray diffraction (DCXD). The carrier density and mobility of single crystal $CuGaSe_2$ thin films measured with Hall effect by Van der Pauw method are $4.87{\times}10^{17}cm^{-3}$ and $129cm^2/V{\cdot}s$ at 293 K, respectively. The temperature dependence of the energy band gap of the $CuGaSe_2$ obtained from the absorption spectra was well described by the Varshni's relation, $E_g(T)=1.7998eV-(8.7489{\times}10^{-4}eV/K)T^2/(T+335K)$. The voltage, current density of maxiumun power, fill factor, and conversion, efficiency of $n-CdS/p-CuGaSe_2$, heterojunction solar cells under $80mW/cm^2$ illumination were found to be 0.41 V, $21.8mA/cm^2$, 0.75 and 11.17%, respectively.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.585-585
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• 2012

$Cu(In_{1-x}Ga_x)Se_2$(CIGS) 박막 태양전지는 Chalcopyrite 계 박막 태양전지로 Cu, In, Ga, Se 각 원소의 조성을 적절히 조절하여 박막을 성장시킨다. 성장시킨 CIGS 박막은 광흡수계수가 $10^5cm^{-1}$로 다른 물질보다 뛰어나고 직접 천이형 반도체로서 얇은 두께로도 고효율의 박막 제작이 가능하다. CIGS 태양전지를 제조하는 방법은 3-stage 동시 증착법, 금속 전구체의 셀렌화 공정법, 전기 증착법 등이 있다. 그 중에 금속 전구체의 셀렌화 공정법은 다른 제조 방법에 비해 대면적 생산에 유리한 장점이 있다. 하지만 아직 상대적으로 3-stage 동시 증착법에 비해 낮은 에너지 변환 효율이 보고된다. 본 실험에서는 기존의 금속 전구체의 셀렌화 공정법과는 달리 전구체 증착과 셀렌화 공정을 동시에 하고, Se cracker를 통하여 Se 원료를 주입하는 방식인 반응성 스퍼터링 공정에서 reservoir zone의 온도 변화에 따른 특성을 분석하였다. Se cracker의 reservoir zone 온도가 증가할수록 Cu/(In+Ga) 비가 증가한다. CIGS 박막 태양전지의 구조는 Al/Ni/ITO/i-ZnO/CdS/CIGS/Mo/Soda lime glass이다. CIGS 박막의 조성비가 Cu/(In+Ga)=0.89, Ga/(In+Ga)=0.17인 박막 태양전지에서 개방전압 0.34 V, 단락전류밀도 $32.61mA/cm^2$, 충실도 56.2% 그리고 변환 효율 6.19%를 얻었다. 본 연구는 2011년도 지식경제부의 재원으로 한국에너지 기술평가원(KTEP)의 지원을 받아 수행한 연구 과제입니다(No.20093020010030).

• Proceedings of the Materials Research Society of Korea Conference
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• 2003.03a
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• pp.83-83
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• 2003

The stochiometric mix of evaporating materials for the CuInSe$_2$ single crystal thin films was prepared from horizontal furnace. To obtain the single crystal thin films, CuInSe$_2$ mixed crystal was deposited on thoroughly etched semi-insulating GaAs(100) substrate by the Hot Wall Epitaxy (HWE) system. The source and substrate temperature were 62$0^{\circ}C$ and 41$0^{\circ}C$, respectively. The crystalline structure of single crystal thin films was investigated by the photoluminescence and double crystal X-ray diffraction (DCXD). The carrier density and mobility of CuInSe$_2$ single crystal thin films measured from Hall effect by van der Pauw method are 9.62$\times$10$^{16}$ cm$^{-3}$ , 296 $\textrm{cm}^2$/V.s at 293 K, respectively From the photocurrent spectrum by illumination of perpendicular light on the c-axis of the CuInSe$_2$ single crystal thin film, we have found that the values of spin orbit splitting ΔSo and the crystal field splitting ΔCr were 6.1 meV and 175.2 meV at 10 K, respectively. From the photoluminescence measurement on CuInSe$_2$ single crystal thin film, we observed free excition (Ex) existing only high quality crystal and neutral bound exiciton (D$^{\circ}$,X) having very strong peak intensity. Then, the full-width-at -half-maximum(FWHM) and binding energy of neutral donor bound excition were 7 meV and 5.9 meV, respectivity. By Haynes rule, an activation energy of impurity was 59 meV.

• Korean Journal of Materials Research
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• v.21 no.8
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• pp.461-467
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• 2011

Cu(In, Ga)$Se_2$ (CIGS) precursor films were electrodeposited on Mo/glass substrates in acidic solutions containing $Cu^{2+}$, $In^{3+}$, $Ga^{3+}$, and $Se^{4+}$ ions at -0.6 V (SCE) and pH. 1.8. In order to induce recrystallization, the electrodeposited $Cu_{1.00}In_{0.81}Ga_{0.09}Se_{2.08}$ (25.0 at.% Cu + 20.2 at.% In + 2.2 at.% Ga + 52.0 at.% Se) precursor films were annealed under a high Se gas atmosphere for 15, 30, 45, and 60 min, respectively, at $500^{\circ}C$. The Se amount in the film increased from 52 at.% to 62 at.%, whereas the In amount in the film decreased from 20.8 at.% to 9.1 at.% as the annealing time increased from 0 (asdeposited state) to 60 min. These results were attributed to the Se introduced from the furnace atmosphere and reacted with the In present in the precursor films, resulting in the formation of the volatile $In_2Se$. CIGS precursor grains with a cauliflower shape grew as larger grains with the $CuSe_2$ and/or $Cu_{2-x}Se$ faceted phases as the annealing times increased. These faceted phases resulted in rough surface morphologies of the CIGS films. Furthermore, the CIGS layers were not dense because the empty spaces between the grains were not removed via annealing. Uniform thicknesses of the $MoSe_2$ layers occurred at the 45 and 60 min annealing time. This implies that there was a stable reaction between the Mo back electrode and the Se diffused through the CIGS film. The results obtained in the present research were sufficiently different from comparable studies where the recrystallization annealing was performed under an atmosphere of Ar gas only or a low Se gas pressure.

• 한국태양에너지학회:학술대회논문집
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• 2012.03a
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• pp.149-152
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• 2012

$Cu(In,Ga)Se_2$ (CIGS) is one of the most promising photovoltaic materials because of large conversion efficiency which has been achieved with an optimum Ga/(In+Ga) composition in $CuIn_{1-x}Ga_xSe_2$ (X~0.3). The Ga/(In+Ga) content is important to determine band gap, solar cell performances and carrier behaviors at grain boundary (GB). Effects of Ga/(In+Ga) content on physical properties of the CIGS layers have been extensively studied. In previous research, it is reported that GB is not recombination center of CIGS thin-film solar cells. However, GB recombination and electron-hole pair behavior studies are still lacking, especially influence of with different X on CIGS thin-films. We obtained the GB surface potential, local current and I-V characteristic of different X (00.7 while X~0.3 showed higher potential than 100 mV on GBs. Higher potential on GBs appears positive band bending. It can decrease recombination loss because of carrier separation. Therefore, we suggest recombination and electron-hole behaviors at GBs depending on composition of X.

• Journal of the Korean Chemical Society
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• v.48 no.5
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• pp.504-509
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• 2004

The reaction of Cu metal with mixed alkali metal polyselenide flux ($KNaSe_x$) produced large plate-like crystals of $KCu_4Se_3$. The structure of $KCu_4Se_3$, determined with X-ray single crystal diffraction techniques, is tetragonal (P4/mmm, a=4.013(1))${\AA}$, c=9.712(1))${\AA}$, z=1, R=6.7%). The structure is composed $[Cu_4Se_3]_n^{n-}$double layers which are made of fused anti PbO-type Cu2Se2 layers. Temperature variable resistivity measurement on single crystal of $KCu_4Se_3$ shows metallic behavior ranging from $1.8{\times}10^{-4}{\Omega}{\cdot}cm$ (at 300 K) to $1.0{\times}10^{-6}{\Omega}{\cdot}cm$ (at 20 K).

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.314.2-314.2
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• 2013

CIGS 박막의 물성은 조성에 크게 영향을 받으며, 특히 박막 내 Cu/(In+Ga) 비는 매우 중요한 변수로서 태양전지 특성에 영향을 주게 된다. Cu(In1-xGax)Se2 박막의 전하농도 및 반도체로의 성격을 가장 명확하게 결정하는 조성비는 Cu/(In+Ga) 비이다. 태양전지와 같은 소자로 작용하기 위해서는 Cu/(In+Ga) 비가 1보다 작아야 한다. 고효율의 태양전지는 Cu/(In+Ga)조성이 0.85~0.95로 slightly Cu-poor가 되어야 만들어진다. 본 연구에서는 Cu조성에 따른 CIGS 박막의 구조적, 전기적 특성과 CIGS 태양전지 효율 특성에 관하여 연구하였다. 미세구조 분석결과 Cu 조성이 증가함에 따라 큰 결정립을 가지며 결정립의 성장이 고르게 되어 접합 형성을 좋게 하는 경향을 보였다. X선 회절 분석결과, Cu 함유량 비율이 증가하면서 <112>의 우선배향성에서 <220/204>으로 변화하였다. 그러나, Cu/(In+Ga) 비율이 1이상이 첨가됨에 따라 우선배향은 다시 <112>로 변화함을 알 수 있었다. EDX 분석결과 Ga/(In+Ga) 0.31, Cu/(In+Ga) 0.86의 비율일 때, Carrier density $1.49{\times}1016$ cm-3을 나타내었다. CIGS의 태양전지의 효율 측정결과 Voc=596mV, Jsc=37.84mA/cm2, FF=72.96%로 ${\eta}$=16.47%를 달성하였다.

• Current Photovoltaic Research
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• v.1 no.1
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• pp.38-43
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• 2013

$Cu(In,Ga)_3Se_5$ is a candidate material for the top cell of $Cu(In,Ga)Se_2$ tandem cells. This phase is often found at the surface of the $Cu(In,Ga)Se_2$ film during $Cu(In,Ga)Se_2$ cell fabrication, and plays a positive role in $Cu(In,Ga)Se_2$ cell performance. However, the exact properties of the $Cu(In,Ga)_3Se_5$ film have not been extensively studied yet. In this work, $Cu(In,Ga)_3Se_5$ films were fabricated on Mo-coated soda-lime glass substrates by a three-stage co-evaporation process. The Cu content in the film was controlled by varying the deposition time of each stage. X-ray diffraction and Raman spectroscopy analyses showed that, even though the stoichiometric Cu/(In+Ga) ratio is 0.25, $Cu(In,Ga)_3Se_5$ is easily formed in a wide range of Cu content as long as the Cu/(In+Ga) ratio is held below 0.5. The optical band gap of $Cu_{0.3}(In_{0.65}Ga_{0.35})_3Se_5$ composition was found to be 1.35eV. As the Cu/(In+Ga) ratio was decreased further below 0.5, the grain size became smaller and the band gap increased. Unlike the $Cu(In,Ga)Se_2$ solar cell, an external supply of Na with $Na_2S$ deposition further increased the cell efficiency of the $Cu(In,Ga)_3Se_5$ solar cell, indicating that more Na is necessary, in addition to the Na supply from the soda lime glass, to suppress deep level defects in the $Cu(In,Ga)_3Se_5$ film. The cell efficiency of $CdS/Cu(In,Ga)_3Se_5$ was improved from 8.8 to 11.2% by incorporating Na with $Na_2S$ deposition on the CIGS film. The fill factor was significantly improved by the Na incorporation, due to a decrease of deep-level defects.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.06a
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• pp.121-122
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• 2007

Single crystal $CuAlSe_2$ layers were grown on thoroughly etched sem-insulating GaAs(l00) substrate at $410^{\circ}C$ with hot wall epitaxy (HWE) system by evaporating $CuAlSe_2$ source at $680^{\circ}C$. The crystalline structure of the single crystal thin films was investigated by the photoluminescence and double crystal X-ray diffraction (DCXD). The carrier density and mobility of single crystal $CuAlSe_2$ thin films measured with Hall effect by van der Pauw method are $9.24{\times}l0^{16}\;cm^{-3}$ and $295\;cm^2/V{\cdot}s$ at 293K, respectively. The temperature dependence of the energy band gap of the $CuAlSe_2$ obtained from the absorption spectra was well described by the Varshni's relation, $E_g(T)\;=\;2.8382\;eV\;-\;(8.68\;{\times}\;10^{-4}\;eV/K)T^2/(T\;+\;155\;K)$.