= 아 래 =
1. 일 시 : 2013. 6. 11 (화), 16:00 ~
2. 장 소 : 응용공학동 1층 영상강의실
3. 연 사 : 문주호 교수 (연세대학교 신소재공학과)
4. 제 목 : Printable Conductive Materials for Displays and Photovoltaics
In recent years, increasing attention has been devoted to the development of convenient and low-cost printing techniques to fabricate conductive features using liquid-phase materials for use in various electronic applications such as displays, solar cells, radio frequency identification tags, and electroluminescence devices.1-3 To date, noble metals such as gold and silver have mainly been utilized in printing highly conductive elements in electronic devices, but the high cost of these metals has hindered their use in this appealing approach.4-6 As a result, copper is a promising alternative material as it is highly conductive and significantly cheaper than Au and Ag. However, the formation of a surface oxide layer on Cu is inevitable in an ambient atmosphere because the oxide phases are thermodynamically more stable. From the point of view of printed conductor applications, the presence of surface copper oxides has two negative consequences: it increases the required annealing temperature and it reduces the electrical conductivity. Here, we present an approach that prevents surface oxidation of Cu nanoparticles through the formation of copper carboxylate shells. In particular, it is imperative to develop a low cost transparent electrode with low resistivity and high transparency to fabricate cost-effective solar cells. Although crystalline indium tin oxide (ITO) has been widely adopted as a transparent electrode in solar cells, it is an undesirable material for use in low cost solar cells because of the scarcity of indium and its high deposition cost. Silver nanowires (AgNWs) network films have recently attracted substantial interest as a transparent conducting material. Transparent electrodes composed of random AgNW networks can be readily achieved by simple and scalable solution processing such as spin coating, rod coating,drop casting, and air-spraying from AgNWs dispersion. However, the AgNWs film is easy to undergo local oxidation and melting on a heated substrate in the atmosphere, which adversely affects the conductivity of the AgNWs film. In addition, the low carrier collecting efficiency of AgNW films could pose another hurdle. The limited contact area of AgNWs with n-type or buffer layers is incapable of effectively collecting the charge carrier generated at the p-n junction. Here, we propose a sandwich composite electrode structure of Al doped ZnO (AZO)/AgNWs/AZO fabricated by all solution processes. The AZO/AgNW/AZO composite structure is suitable for cost-effective large area fabrication, because it involves relatively low-cost materials, and it is prepared by scalable solution processes instead of high-vacuum process. The AgNWs inserted in AZO layers reduced sheet resistance dramatically of a solution processed AZO layer, and the density of AgNWs plays an important role in determining the film conductivity and optical transparency. The AZO underlayer acts as an n-type buffer layer as well as a surface flattener against the absorber layer, while the upper layer prevents the AgNWs from local melting-induced disconnection. As a result, the thermal stability of the AgNWs was enhanced and the adhesion of AgNWs to the substrate was improved. We applied the AZO/AgNW/AZO composite electrode on the CIGS thin film solar cells and observed the power conversion efficiency of 11% comparable to reference ITO used solar cells. We also demonstrated the similar approach involvingcopper nanowire (CuNW) in form of AZO/CuNW/AZO. Our low temperature processed AZO/CuNW/AZO composite electrode at 70oC exhibited highly transparency (> 88%) and low sheet resistance (< 25 ohm sq-1) as well as good thermal oxidation stability against the exposure to air and flexibility.