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Rehan, Shanza,Moon, Jihyun,Kim, Tae Gun,Gwak, Jihye,Kim, Juran,Kim, Jeong Won,Jo, William,Ahn, Seung Kyu,Ahn, SeJin unknown 2018 Nano energy Vol.48 No.-
<P><B>Abstract</B></P> <P>Na has been believed to improve the device parameters of open circuit voltage (V<SUB>OC</SUB>) and fill factor (FF) presumably by increasing the carrier concentration (N<SUB>A</SUB>) of vacuum-processed Cu(In,Ga)Se<SUB>2</SUB> films. In solution-processed CI(G)Se devices as well, Na reportedly increases V<SUB>OC</SUB> and FF but this improvement is not correlated with the increase in N<SUB>A,</SUB> suggesting a different physical mechanism associated with Na in solution-based routes. In this contribution, experimental results on the role of Na addition in solution-processed CISe films and devices were reported, in which Na addition had no influence on N<SUB>A</SUB> nor on film composition in spite of the notable increase in the device efficiency. On the contrary, Na was found to mitigate the interfacial recombination by reducing the undesirable surface defects. Along with this understanding, Na addition in our air-processable route resulted in a CISe device with 12.83% efficiency, which is comparable to the current world record efficiency of solution-processed CISe devices.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Air-processable, nanoparticle-based approach yields 12.8% efficient CISe device. </LI> <LI> A new role of Na addition was revealed. </LI> <LI> The position of dominant recombination was shifted from interface to bulk by Na. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Rehan, Shanza,Kim, Ka Young,Han, Jeonghyeob,Eo, Young-Joo,Gwak, Jihye,Ahn, Seung Kyu,Yun, Jae Ho,Yoon, KyungHoon,Cho, Ara,Ahn, SeJin American Chemical Society 2016 ACS APPLIED MATERIALS & INTERFACES Vol.8 No.8
<P>A common feature of the inorganic thin films including Cu(In,Ga)(S,Se)(2) fabricated by nonvacuum solution based approaches is the doubled-layered structure, with a top dense inorganic film and a bottom carbon-containing residual layer. Although the latter has-been considered to be the main efficiency limiting factor, (as a source of high series resistance); the exact influence of this layer is still not clear, and contradictory views are present. In this study, using a CISe as a model system, we report experimental evidence indicating that the carbon residual layer itself is electrically benign to the device performance. Conversely, carbon was found to play a significant role in determining the depth elemental distribution of final film, in which carbon selectively hinders the diffusion of Cu during selenization, resulting in significantly Cu-deficient top CISe layer while improving the film morphology. This carbon-affected compositional and morphological, impact on the top CISe films is a determining factor for the device efficiency, which was supported by the finding that CISe solar cells processed from the precursor film containing intermediate amount of carbon demonstrated high efficiencies of up to 9.15% whereas the performances of the devices prepared from the precursor films with very high and very low carbon were notably poor.</P>
직접 용액 코팅법에 의해 제조한 CuInSe₂에 잔존하는 탄소 불순물층 형성에 관한 연구
안세진(SeJin Ahn),Shanza Rehan,어영주(Young-Joo Eo),곽지혜(Jihye Gwak),윤경훈(Kyunghoon Yoon),조아라(Ara Cho) 한국태양광발전학회 2014 Current Photovoltaic Research Vol.2 No.1
Formation mechanism of residual carbon layer, frequently observed in the CuInSe₂ (CIS) thin film prepared by direct solution coating routes, was investigated in order to find a way to eliminate it. As a model system, a methanol solution with dissolved Cu and In salts, whose viscosity was adjusted by adding ethylcellulose (EC), was chosen. It was found that a double layer, a top metal ion-derived film and bottom EC-derived layer, formed during an air drying step presumably due to different solubility between metal salts and EC in methanol. Consequently, the top metal ion-derived film acts as a barrier layer inhibiting further thermal decomposition of underlying EC, resulting a formation of bottom carbon residue layer.
Structural, optical and electrical impacts of marcasite in pyrite thin films
Moon, Dong Gwon,Rehan, Shanza,Lim, Soo Yeon,Nam, Dahyun,Seo, Ilwan,Gwak, Jihye,Cheong, Hyeonsik,Cho, Yong Soo,Lee, Yunsang,Ahn, SeJin Elsevier 2018 Solar energy Vol.159 No.-
<P><B>Abstract</B></P> <P>The structural and electro-optical influence of marcasite on the properties of solution-processed iron pyrite thin films was investigated. Marcasite has a strong tendency to form simultaneously with pyrite upon sulfurization of amorphous iron-oxide precursor films, leading to a mixed-phase structure in which pyrite grains are surrounded by nanocrystalline marcasite boundaries. The optical analysis in combination with spectroscopic ellipsometry revealed that marcasite should have a bandgap of approximately 0.85–0.88 eV with a higher absorption coefficient than pyrite, differing strongly from the prior belief that marcasite has a bandgap of less than 0.4 eV. In addition, the pyrite/marcasite film has been found to have a larger diffusion coefficient for photogenerated minority carriers than the phase-pure pyrite film from electrochemical impedance analyses, resulting in a higher photocurrent density, as determined through photoelectrochemical measurement. The facile transport of a minority carrier along the marcasite boundaries is the putative origin of the observed improvement in the photoactivity of the pyrite/marcasite mixture films.</P> <P><B>Highlights</B></P> <P> <UL> <LI> In the mixture film, pyrite is surrounded by nanocrystalline marcasite. </LI> <LI> Marcasite has a bandgap of 0.85 to 0.88 eV, which is not as small as 0.4 eV. </LI> <LI> Marcasite phase provids an efficient path for diffusion of photogenerated holes. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>