ITO 투명 전극 필름은 디스플레이, 전기 자동차 등 산업 전 범위에서 널리 사용되는 전자 재료이다. 본 연구에서는 이러한 indium tin oxide (ITO) 필름의 열성형 안정성을 향상시키기 위하여 Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) 전도성 고분자 코팅 용액 조성을 결정하였다. 1000 S/cm의 고 전도성을 보이는 PEDOT:PSS 용액에 끓는점이 각기 다른 4가지 종류의 용매를 희석하였고, 코팅 전 후 면저항 변화를 분석하였다. 또한 380~800 nm 영역의 광 투과율 분 석 및 Raman 스펙트럼 분석을 통하여 PEDOT:PSS 박막이 코팅된 ITO 투명 전극의 전기적 특성 결정 메커니즘을 규명하였 다. 230°C 열성형 공정 결과 ITO 필름은 113% 연신 상태에서 이미 전기 전도성을 읽었지만, ethylene glycol을 희석 용매로 사용하여 얻어진 전도성 고분자 박막이 적용된 ITO 필름은 126% 고 연신 상태에서도 초기 60 Ω/sq 면저항을 246 Ω/sq로 유지하는 우수한 전기 전도성을 보였다.

Silver nanowire (AgNW) networks have been adopted as a front electrode in Cu(In,Ga)Se2 (CIGS) thin film solar cells due to their low cost and compatibility with the solution process. When an AgNW network is applied to a CIGS thin film solar cell, reflection loss can increase because the CdS layer, with a relatively high refractive index (n ~ 2.5 at 550 nm), is exposed to air. To resolve the issue, we apply solution-processed ZnO nanorods to the AgNW network as an anti-reflective coating. To obtain high performance of the optical and electrical properties of the ZnO nanorod and AgNW network composite, we optimize the process parameters – the spin coating of AgNWs and the concentration of zinc nitrate and hexamethylene tetramine (HMT – to fabricate ZnO nanorods. We verify that 10 mM of zinc nitrate and HMT show the lowest reflectance and 10% cell efficiency increase when applied to CIGS thin film solar cells.

Flexible transparent conducting films (TCFs) were fabricated by dip-coating single-wall carbon nanotubes (SWCNTs) onto a flexible polyethylene terephthalate (PET) film. The amount of coated SWCNTs was controlled simply by dipping number. Because the performance of SWCNT-based TCFs is influenced by both electrical conductance and optical transmittance, we evaluated the film performance by introducing a film property factor using both the number of interconnected SWCNT bundles at intersection points, and the coverage of SWCNTs on the PET substrate, in field emission scanning electron microscopic images. The microscopic film property factor was in an excellent agreement with the macroscopic one determined from electrical conductance and optical transmittance measurements, especially for a small number of dippings. Therefore, the most crucial factor governing the performance of the SWCNT-based TCFs is a SWCNT-network structure with a large number of intersection points for a minimum amount of deposited SWCNTs.

We have investigated the structural and electrical properties of Ga-doped ZnO (GZO) thin films deposited by anRF magnetron sputtering at various RF powers from 50 to 90W. All the GZO thin films are grown as a hexagonal wurtzitephase with highly c-axis preferred parameters. The structural and electrical properties are strongly related to the RF power. Thegrain size increases as the RF power increases since the columnar growth of GZO thin film is enhanced at an elevated RFpower. This result means that the crystallinity of GZO is improved as the RF power increases. The resistivity of GZO rapidlydecreases as the RF power increases up to 70W and saturates to 90W. In contrast, the electron concentration of GZO increasesas the RF power increases up to 70W and saturates to 90W. GZO thin film shows the lowest resistivity of 2.2×10−4Ωcmand the highest electron concentration of 1.7×1021cm−3 at 90W. The mobility of GZO increases as the RF power increasessince the grain boundary scattering decreases due to the reduced density of the grain boundary at a high RF power. Thetransmittance of GZO thin films in the visible range is above 90%. GZO is a feasible transparent electrode for application asa transparent electrode for thin film solar cells.

We have investigated the structural and optical properties of Ga-doped ZnO (GZO) thin films deposited by RFmagnetron sputtering at various deposition temperatures from 100 to 500oC. All the GZO thin films are grown as a hexagonalwurtzite phase with highly c-axis preferred parameter. The structural and electrical properties are strongly related to depositiontemperature. The grain size increases with the increasing deposition temperature up to 400oC and then decreases at 500oC. Thedependence of grain size on the deposition temperature results from the variation of thermal activation energy. The resistivityof GZO thin film decreases with the increasing deposition temperature up to 300oC and then decreases up to 500oC. GZO thinfilm shows the lowest resistivity of 4.3×10−4Ωcm and highest electron concentration of 1.0×1021cm−3 at 300oC. The mobilityof GZO thin films increases with the increasing deposition temperature up to 400oC and then decreases at 500oC. GZO thinfilm shows the highest resistivity of 14.1cm2/Vs. The transmittance of GZO thin films in the visible range is above 87% atall the deposition temperatures. GZO is a feasible transparent electrode for the application to the transparent electrode of thinfilm solar cells.

Transparent conducting oxide (TCO) films are widely used for optoelectronic applications. Among TCO materials,zinc oxide (ZnO) has been studied extensively for its high optical transmission and electrical conduction. In this study, the effectsof O2 plasma pretreatment on the properties of Ga-doped ZnO films (GZO) on polyethylene naphthalate (PEN) substrate werestudied. The O2 plasma pretreatment process was used instead of conventional oxide buffer layers. The O2 plasma treatmentprocess has several merits compared with the oxide buffer layer treatment, especially on a mass production scale. In this process,an additional sputtering system for oxide composition is not needed and the plasma treatment process is easily adopted as anin-line process. GZO films were fabricated by RF magnetron sputtering process. To improve surface energy and adhesionbetween the PEN substrate and the GZO film, the O2 plasma pre-treatment process was used prior to GZO sputtering. As theRF power and the treatment time increased, the contact angle decreased and the RMS surface roughness increased significantly.It is believed that the surface energy and adhesive force of the polymer surfaces increased with the O2 plasma treatment andthat the crystallinity and grain size of the GZO films increased. When the RF power was 100W and the treatment time was120 sec in the O2 plasma pretreatment process, the resistivity of the GZO films on the PEN substrate was 1.05×10-3Ω-cm,which is an appropriate range for most optoelectronic applications.

Changes in the surface morphology and light scattering of textured Al doped ZnO thin films on glasssubstrates prepared by rf magnetron sputtering were investigated. As-deposited ZnO:Al films show a hightransmittance of above 80% in the visible range and a low electrical resistivity of 4.5×10-4Ω·cm. The surfacemorphology of textured ZnO:Al films are closely dependent on the deposition parameters of heater temperature,working pressure, and etching time in the etching process. The optimized surface morphology with a cratershape is obtained at a heater temperature of 350oC, working pressure of 0.5 mtorr, and etching time of 45seconds. The optical properties of light transmittance, haze, and angular distribution function (ADF) aresignificantly affected by the resulting surface morphologies of textured films. The film surfaces, havinguniformly size-distributed craters, represent good light scattering properties of high haze and ADF values.Compared with commercial Asahi U (SnO2:F) substrates, the suitability of textured ZnO:Al films as frontelectrode material for amorphous silicon thin film solar cells is also estimated with respect to electrical andoptical properties.