To establish low-temperature process conditions, process-property correlation has been investigated for Ga-doped ZnO (GZO) thin films deposited by pulsed DC magnetron sputtering. Thickness of GZO films and deposition temperature were varied from 50 to 500 nm and from room temperature to 250 oC, respectively. Electrical properties of the GZO films initially improved with increase of temperature to 150 oC, but deteriorated subsequently with further increase of the temperature. At lower temperatures, the electrical properties improved with increasing thickness; however, at higher temperatures, increasing thickness resulted in deteriorated electrical properties. Such changes in electrical properties were correlated to the microstructural evolution, which is dependent on the deposition temperature and the film thickness. While the GZO films had c-axis preferred orientation due to preferred nucleation, structural disordering with increasing deposition temperature and film thickness promoted grain growth with a-axis orientation. Consequently, it was possible to obtain a good electrical property at relatively low deposition temperature with small thickness.

고성능 투명 전극의 개발은 유기 태양 전지, 유기 발광 다이오드와 같은 저가형 유연 유기 광전자 소자의 개발에 매우 중요하다. 가장 널리 쓰이고 있는 투명전극인 indium tin oxide (ITO)는 비싼 가격과 잘 깨어지는 특성 을 가지고 있어서 저가형 유연 전자 소자의 개발에 많은 제한을 주고 있으며, 이를 극복하기 위한 대체 투명 전극의 개발에 대한 연구가 활발히 진행되고 있다. 은 나노와이어(silver nanowire, AgNW)는 우수한 전기 전도도와 광 투과 도를 가지고 저렴하며 뛰어난 유연성 때문에 ITO의 대체 투명전극으로서 큰 각광을 받고 있다. 그러나 AgNW의 거 친 표면은 유기 광전자 소자의 누설전류를 크게 증가시켜서 소자의 효율을 떨어뜨리기 때문에 이를 극복하는 기술의 개발이 시급한 실정이다. 본 연구에서는 UV 광 경화성 접착제를 이용하여 AgNW를 PET기판으로 transfer 시키는 방법으로 AgNW가 매몰된 유연 전도성 투명 기판을 제작하였으며, 이 기판은 낮은 표면 거칠기, 낮은 면저항과 높은 광투과도를 보여준다. 본 연구에서 개발된 AgNW가 매몰된 유연 전도성 투명 기판은 유기전자소자의 대체투명전극 으로 활용될 수 있는 가능성을 보여준다.

One-dimensional (1D) silver nanostructures, which possess the highest conductivity among all room-temperature materials, moderate flexibility and high transmittance, are one of the most promising candidate materials to replace conventional indium tin oxide transparent electrodes. However, the short length and large diameter of 1D silver nanostructures cause a substantial decrease in the optical transparency or an increase in the sheet resistance. In this work, ultra-long silver nanofiber networks were synthesized with a low-cost and scalable electrospinning process, and the diameter of the nanofibers were finetuned to achieve a higher aspect ratio. The decrease in the diameter of the nanofibers resulted in a higher optical transparency at a lower sheet resistance: 87 % at 300 Ω/sq, respectively. It is expected that an electrospun silver nanofiber based transparent electrode can be used as a key component in various optoelectronic applications.

유기태양전지의 투명전극으로서 기존의 값비싸고 깨지기 쉬운 Indium Tin Oxide (ITO) 전극을 대체하고자, 전도성 고분자인 poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)를 적용하였다. 솔벤트의 도핑 농도에 따른 PEDOT:PSS 박막의 전기 전도도와 표면 거칠기의 특성 변화를 관찰하고, 그 결과가 PEDOT:PSS를 투명전극으로 사용한 유기태양전지의 특성에 미치는 영향을 연구하였다. PEDOT:PSS의 솔벤트 농도가 증가함에 따라, 박막의 표면 거칠기가 증가하고, 이는 유기태양전지의 단락전류의 변화를 야기했다. 또한, 소자의 홀 이동층이 얇아짐에 따라 광활성층의 단파장영역의 광흡수가 증가하는 것을 관찰할 수 있었다.

Metal nanowires can be coated on various substrates to create transparent conducting films that can potentially replace the dominant transparent conductor, indium tin oxide, in displays, solar cells, organic light-emitting diodes, and electrochromic windows. One issue with these metal nanowire based transparent conductive films is that the resistance between the nanowires is still high because of their low aspect ratio. Here, we demonstrate high-performance transparent conductive films with silver nanofiber networks synthesized by a low-cost and scalable electrospinning process followed by two-step sequential thermal treatments. First, the PVP/AgNO3 precursor nanofibers, which have an average diameter of 208 nm and are several thousands of micrometers in length, were synthesized by the electrospinning process. The thermal behavior and the phase and morphology evolution in the thermal treatment processes were systematically investigated to determine the thermal treatment atmosphere and temperature. PVP/AgNO3 nanofibers were transformed stepwise into PVP/Ag and Ag nanofibers by two-step sequential thermal treatments (i.e., 150˚C in H2 for 0.5 h and 300˚C in Ar for 3 h); however, the fibrous shape was perfectly maintained. The silver nanofibers have ultrahigh aspect ratios of up to 10000 and a small average diameter of 142 nm; they also have fused crossing points with ultra-low junction resistances, which result in high transmittance at low sheet resistance.