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Development of a New Double Buffer Layer for Cu(In, Ga) Se₂ Solar Cells
Larina, Liudmila,Kim, Ki-Hwan,Yoon, Kyung-Hoon,Ahn, Byung-Tae 한국신재생에너지학회 2006 한국신재생에너지학회 학술대회논문집 Vol.2006 No.06
The new approach to buffer layer design for CIGS solar cells that permitted to reduce the buffer absorption losses in the short wavelength range and to overcome the disadvantages inherent to Cd-free CIGS solar cells was proposed. A chemical bath deposition method has been used to produce a high duality buffer layer that comprises thin film of CdS and Zn-based film. The double layer was grown on either ITO or CIGS substrates and its morphological, structural and optical properties were characterized. The Zn-based film was described as the ternary compound ZnS_x(OH)_y. The composition of the ZnS_x(OH)_y layer was not uniform throughout its thickness. ZnS_x(OH)_y/CdS/substrate region was a highly intermixed region with gradually changing composition. The short wavelength cut-off of double layer was shifted to shorter wavelength (400nm) compared to that (520 nm) for the standard CdS by optimization of the double buffer design. The results show the way to improve the light energy collection efficiency of the nearly cadmium-free CIGS-based solar cells.
Alignment of energy levels at the ZnS/Cu(In,Ga)Se<sub>2</sub> interface
Larina, Liudmila,Shin, Donghyeop,Kim, Ji Hye,Ahn, Byung Tae Royal Society of Chemistry 2011 ENERGY AND ENVIRONMENTAL SCIENCE Vol.4 No.9
<P>Further understanding of the electronic structure at the ZnS/Cu(In,Ga)Se<SUB>2</SUB> interface is necessary to enhance the electron injection across the interface in Cu(In,Ga)Se<SUB>2</SUB> solar cells. The valence band structure and shallow core levels were investigated by ultraviolet photoelectron spectroscopy depth profile analysis with He II line excitation. ZnS film was grown by a chemical bath deposition on a Cu(In,Ga)Se<SUB>2</SUB> absorber deposited by the co-evaporation of Cu, In, Ga, and Se elemental sources. The discontinuity of 2.0 eV in the valence band edge at the ZnS/Cu(In<SUB>0.7</SUB>Ga<SUB>0.3</SUB>)Se<SUB>2</SUB> interface was directly determined. This type of valence band offset yields a spike conduction band alignment of 0.25 eV. The positions of the VBM and the Zn 3d core-level emission of the buffer underwent the substantial shifts of 0.36 eV and 0.64 eV to a lower binding energy levels during the etching process. The shifts are ascribed to the contribution of the band bending in the ZnS buffer layer and its graded chemical composition. This study is the first to determine the small conduction band offset at the interface formed by the chemical bath deposited ZnS layer and the Cu(In<SUB>0.7</SUB>Ga<SUB>0.3</SUB>)Se<SUB>2</SUB> absorber. Our results also provide information toward the design optimization of the optoelectronic properties of the ZnS/Cu(In<SUB>0.7</SUB>Ga<SUB>0.3</SUB>)Se<SUB>2</SUB> interface. To enhance the electron injection from Cu(In<SUB>0.7</SUB>Ga<SUB>0.3</SUB>)Se<SUB>2</SUB> absorber to ZnS layer further lowering of the energy barrier is required. For this purpose, the bandgap of ZnS should be reduced by controlling the crystal structure and composition or its Fermi level should be upward shifted by appropriate doping.</P> <P>Graphic Abstract</P><P>For the first time a small conduction band offset at the ZnS/Cu(In<SUB>0.7</SUB>Ga<SUB>0.3</SUB>)Se<SUB>2</SUB> interface was found. The spike conduction band alignment of 0.25 eV is consistent with the efficiency of CIGS cell based on CBD ZnS buffer. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c1ee01292d'> </P>
Kim, Jekyung,Larina, Liudmila,Chung, Sung-Yoon,Shin, Donghyeop,Shin, Byungha Published for the Materials Research Society by th 2018 Journal of materials research Vol.33 No.23
<▼1><B>Abstract</B><P/></▼1><▼2><P>Despite the potential as a promising alternative to CdTe and Cu(In,Ga)Se2, the kesterite compound Cu2ZnSn(S,Se)4 (CZTSSe) presents a critical challenge mainly from its high open-circuit voltage (<I>V</I>oc) deficit. Indeed, the <I>V</I>oc of the record CZTSSe solar cell to date has accounted for only 61% of that calculated by the Shockley-Queisser limit, whose origin can be ascribed to nonradiative recombination from a high density of defects and secondary phases. Therefore, an atomistic understanding and characterization of CZTSSe is highly essential to overcoming the current shortcomings in kesterite. This review discusses the advanced characterization techniques for studying the intrinsic properties of kesterite at a nanometer scale. Moreover, a cation substitution with an ionic mismatch around constituents is recognized as an effective route to address the fundamental limit (i.e., the cationic disorder) in CZTSSe. Here, we review recent studies on a novel chalcogenide Cu2BaSn(S,Se)4 that substitutes Zn with Ba and results in less cationic disordering.</P></▼2>
Nikolay, Tsvetkov,Larina, Liudmila,Shevaleevskiy, Oleg,Ahn, Byung Tae Royal Society of Chemistry 2011 ENERGY AND ENVIRONMENTAL SCIENCE Vol.4 No.4
<P>To improve the conversion efficiency of dye-sensitized solar cells (DSSCs) it is necessary to understand the electronic structure of the TiO<SUB>2</SUB>–dye–electrolyte interface in detail. A sturdy junction at the interface can be provided by modifying the electronic structure of the TiO<SUB>2</SUB> electrode with Nb doping. The Nb-doped TiO<SUB>2</SUB> was prepared by a sol–gel method followed by a hydrothermal treatment; the Nb content was varied from 0.5 to 3.0 mol%. The X-ray photoelectron spectroscopy showed that the Fermi level of TiO<SUB>2</SUB> electrode shifted away from the conduction band minimum (CBM) when the Nb content is low (≤1.5 mol%) and shifted toward the CBM when the Nb content is high (≥2.5 mol%). The shift of Fermi level with low Nb doping was due to the passivation of the oxygen vacancies at the TiO<SUB>2</SUB> nanoparticle surface. Intraband states were formed when dopant content was 1.5 and 2.5 mol%. We have found that the photovoltaic parameters of DSSCs based on doped TiO<SUB>2</SUB> sensitized with a <I>cis</I>-[Ru(dcbpyH)<SUB>2</SUB>(NCS)<SUB>2</SUB>](NBu<SUB>4</SUB>)<SUB>2</SUB>, N719 dye, are closely related to the electronic structure of the Nb-doped TiO<SUB>2</SUB> electrode. The changes of short circuit current and open circuit voltage of DSSCs were explained in relation to the electronic structure of the TiO<SUB>2</SUB> electrode. The best efficiency of 8.0% was demonstrated by DSSCs with 2.5 mol% Nb-doped TiO<SUB>2</SUB>.</P> <P>Graphic Abstract</P><P>Lightly Nb-doped TiO<SUB>2</SUB> electrodes with improved electronic structure were fabricated and used as photoanodes for dye sensitized solar cells with increased performance. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c0ee00678e'> </P>
Cd-free CIGS solar cells with buffer layer based on the In<sub>2</sub>S<sub>3</sub> derivatives
Kim, Kihwan,Larina, Liudmila,Yun, Jae Ho,Yoon, Kyung Hoon,Kwon, HyukSang,Ahn, Byung Tae The Royal Society of Chemistry 2013 Physical chemistry chemical physics Vol.15 No.23
<P>This study guided by device evaluations was conducted to reveal the reasons for the loss of the photo-generated carriers in CIGS cells with the buffer based on In<SUB>2</SUB>S<SUB>3</SUB> derivatives. Chemical bath deposited In<SUB><I>x</I></SUB>(OOH,S)<SUB><I>y</I></SUB> films have been employed as a Cd-free buffer layers. When compared to solar cells with CdS buffer layer, the Cu<SUB>0.9</SUB>(In<SUB>0.7</SUB>,Ga<SUB>0.3</SUB>)Se<SUB>2.1</SUB> (<I>E</I><SUB>g</SUB> = 1.18 eV) cells with the In<SUB><I>x</I></SUB>(OOH,S)<SUB><I>y</I></SUB> buffer exhibited strong voltage-dependent carrier collection and poor spectral response above 500 nm, presumably, due to energy barrier at the junction. In order to improve the charge collection by upward shift of the conduction band minimum of CIGS absorber, In<SUB><I>x</I></SUB>(OOH,S)<SUB><I>y</I></SUB>/Cu<SUB>0.9</SUB>(In<SUB>0.55</SUB>,Ga<SUB>0.45</SUB>)Se<SUB>2.1</SUB> (<I>E</I><SUB>g</SUB> = 1.30 eV) solar cells were also fabricated and their spectral responses were examined. When compared to the Cu<SUB>0.9</SUB>(In<SUB>0.7</SUB>,Ga<SUB>0.3</SUB>)Se<SUB>2.1</SUB> cells, the improved spectral response and voltage dependent carrier collection were obtained. Nevertheless, considerable loss in charge collection above 500 nm was still observed. The efficiency reached 9.3% while the Cu<SUB>0.9</SUB>(In<SUB>0.7</SUB>,Ga<SUB>0.3</SUB>)Se<SUB>2.1</SUB> cell exhibited only the efficiency of 3.4%. Finally, CIGS (<I>E</I><SUB>g</SUB> = 1.18 eV) solar cells with n-ZnO/i-ZnO/In<SUB><I>x</I></SUB>(OOH,S)<SUB><I>y</I></SUB>/CdS/CIGS and n-ZnO/i-ZnO/CdS/In<SUB><I>x</I></SUB>(OOH,S)<SUB><I>y</I></SUB>/CIGS configurations were fabricated. The influence of the TCO/buffer interface on the device characteristics was also addressed by means of comparison between the characteristics of two cells employing different interfaces. A 13.0% efficient cell has been achieved from n-ZnO/i-ZnO/CdS/In<SUB><I>x</I></SUB>(OOH,S)<SUB><I>y</I></SUB>/CIGS configuration. The obtained data suggested that the limitation of the device efficiency was mainly related to the i-ZnO/In<SUB><I>x</I></SUB>(OOH,S)<SUB><I>y</I></SUB> interface. The experimental results provide the knowledge base for further optimization of the interface properties to form high-quality p–n junction in the CIGS solar cells employing the CBD In<SUB>2</SUB>S<SUB>3</SUB> buffer layer.</P> <P>Graphic Abstract</P><P>Our research on chemical bath deposited In<SUB>2</SUB>S<SUB>3</SUB> buffer layer for Cd-free CIGS solar cell reveals that the optoelectronic properties of the TCO/buffer interface require such close control as the properties of the buffer/CIGS interface. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c3cp50324k'> </P>