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Fabrication of Robust Nanoscale Contact between a Silver Nanowire Electrode and CdS Buffer Layer in Cu(In,Ga)Se<sub>2</sub> Thin-film Solar Cells

Silver nanowire transparent electrodes have been employed as window layers for Cu(In,Ga)Se2 thin-film solar cells. Bare silver nanowire electrodes ...

Korea Institute of Energy Research

University of Science and Technology, Daejeon

CuInSe(2) (CIS) absorber layers for thin film solar cells were formed via a nonvacuum route using nanoparticle precursors. A low-temperature colloidal process was used to prepare nanoparticles by which amorphous Cu-In-Se nanoparticles were formed within 1 min of reaction without any external heating. Raman spectra of the particles revealed that they were presumably mixtures of amorphous Cu-Se and In-Se binaries. Selenization of the precursor film prepared by doctor blade coating of the Cu-In-Se nanoparticles resulted in a facile growth of the particles up to micrometer scale. However, it also left large voids in the final film, which acted as short circuiting paths in completed solar cells. To solve this problem, we applied a solution-filling treatment in which a solution containing Cu and In ions was additionally coated onto the precoated nanoparticles, resulting in a complete infiltration of the filler solution into the pores in the nanoparticles based film. By this approach, short circuiting of the device was significantly mitigated and a conversion efficiency of up to 1.98% was obtained.

CuInSe2 (CIS) thin films prepared from amorphous Cu-In-Se nanoparticle precursors for solar cell application.

 Using thermal evaporation, we fabricated five uniform and regular arrays of Ag nanostructures with different shapes that were based on an anodized aluminum oxide template and analyzed their optical properties. Round-top-shaped structures are obtained readily, whereas to obtain needle-on-round-top-shaped and needle-shaped structures, control of the directionality of evaporation, pore size, length, temperature of the substrate, etc., was required. We then observed optical sensitivity of the nanostructures by using surface-enhanced Raman scattering, and we preliminarily investigated the dependency of Raman signal to the roughness and shape of the nanostructures.

Microfabrication and optical properties of highly ordered silver nanostructures.

A simple direct solution coating process for forming CuInSe₂ (CIS) thin films was described, employing a low-cost and environmentally friendly precursor solution. The precursor solution was prepared by mixing metal acetates, ethanol, and ethanolamine. The facile formation of a precursor solution without the need to prefabricate nanoparticles enables a rapid and easy processing, and the high stability of the solution in air further ensures the precursor preparation and the film deposition in ambient conditions without a glove box. The thin film solar cell fabricated with the absorber film prepared by this route showed an initial conversion efficiency of as high as 7.72 %.

CuInSe₂ thin-film solar cells with 7.72 % efficiency prepared via direct coating of a metal salts/alcohol-based precursor solution.

CuInSe2 (CISe) absorber layers for thin-film solar cells were fabricated through the selenization of amorphous Cu-In-S nanoparticles, which were prepared by using a low-temperature colloidal process within one minute without any external heating. Two strategies for obtaining highly dense CISe absorber films were used in this work; the first was the modification of nanoparticle surface through chelate complexation with ethanolamine, and the second strategy utilized the lattice expansion that occurred when S atoms in the precursor particles were replaced with Se during selenization. The synergy of these two strategies allowed formation of highly dense CISe thin films, and devices fabricated using the absorber layer demonstrated efficiencies of up to 7.94% under AM 1.5G illumination without an anti-reflection coating.

Amorphous Cu-In-S nanoparticles as precursors for CuInSe2 thin-film solar cells with a high efficiency.

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. 

Jihye Gwak

Photovoltaics Laboratory

Korea Institute of Energy Research

Fabrication of Robust Nanoscale Contact between a Silver Nanowire Electrode and CdS Buffer Layer in Cu(In,Ga)Se₂ Thin-film Solar Cells

Jihye Gwak

.css-o250i3{font-size:18px;font-family:Open Sans,sans-serif;line-height:21.6px;}Photovoltaics Laboratory

Korea Institute of Energy Research

Fabrication of Robust Nanoscale Contact between a Silver Nanowire Electrode and CdS Buffer Layer in Cu(In,Ga)Se2 Thin-film Solar Cells

Photovoltaics Laboratory

Fabrication of Robust Nanoscale Contact between a Silver Nanowire Electrode and CdS Buffer Layer in Cu(In,Ga)Se₂ Thin-film Solar Cells