Realization of ZnO/PVK transparent heterojunction by solution processing routes

International Nano Letters, Aug 2013

In this work, transparent heterojunction between zinc oxide (ZnO) and poly(N-vinyl carbazole) (PVK) was fabricated by solution processing techniques such as spin-coating and dip-coating techniques; then, its performance was studied using current (I)-voltage (V) measurement at room temperature. Before fabricating the heterojunction, initially, the growth characteristics of both thin films were independently optimized on a well-cleaned glass substrate, then its structural properties, optical properties, and surface topography were characterized using an X-ray diffractometer, UV-VIS-NIR spectrophotometer, and atomic force microscope, respectively. The structural analysis confirms the existence of a PVK thin film in amorphous nature and ZnO thin film in hexagonal crystal structure. The transparent nature of the heterojunction was found to be more than 85% in the visible and NIR regions with the absorption onset in the ultraviolet region. The observed experimental results explored the possibilities of fabricating ZnO/PVK transparent heterojunction by solution-based routes on a transparent fluorine-doped tin oxide substrate for transparent electronics applications.

A PDF file should load here. If you do not see its contents the file may be temporarily unavailable at the journal website or you do not have a PDF plug-in installed and enabled in your browser.

Alternatively, you can download the file locally and open with any standalone PDF reader:

https://link.springer.com/content/pdf/10.1186%2F2228-5326-3-9.pdf

Realization of ZnO/PVK transparent heterojunction by solution processing routes

Prakash Thanigainathan 0 Chandrasekar Paramasivan 1 0 Department of Medical Bionanotechnology, Chettinad Hospital and Research Institute , Kelambakkam, Tamilnadu 603103, India 1 Department of Physics, Saveetha Engineering College , Saveetha Nagar, Thandalam, Chennai, Tamil Nadu 602 105, India In this work, transparent heterojunction between zinc oxide (ZnO) and poly(N-vinyl carbazole) (PVK) was fabricated by solution processing techniques such as spin-coating and dip-coating techniques; then, its performance was studied using current (I)-voltage (V) measurement at room temperature. Before fabricating the heterojunction, initially, the growth characteristics of both thin films were independently optimized on a well-cleaned glass substrate, then its structural properties, optical properties, and surface topography were characterized using an Xray diffractometer, UV-VIS-NIR spectrophotometer, and atomic force microscope, respectively. The structural analysis confirms the existence of a PVK thin film in amorphous nature and ZnO thin film in hexagonal crystal structure. The transparent nature of the heterojunction was found to be more than 85% in the visible and NIR regions with the absorption onset in the ultraviolet region. The observed experimental results explored the possibilities of fabricating ZnO/PVK transparent heterojunction by solution-based routes on a transparent fluorine-doped tin oxide substrate for transparent electronics applications. - Background Materials which are displaying the remarkable combination of high electrical conductivity and optical transparency already form the basis of many important technological applications including flat panel displays, solar energy capture, and other optoelectronic devices [1]. Transparent electronic devices such as bipolar transistors and diodes can be fabricated with the help of p-n transparent junction. After the discovery of the first transparent semiconductor delafossite CuAlO2 in 1997 by Kawazoe et al. [2], the development of a series of ptype transparent materials and transparent p-n junction devices such as UV-light-emitting diodes was triggered. Very recently, Snure et al. [3] discovered another p-type transparent oxide (CuBO2) that also belongs to the delafossite family but exhibits better room-temperature electrical conductivity (1.65 S/cm). Zinc oxide (ZnO) is a transparent n-type semiconductor material having a wide bandgap (e.g., approximately 3.37 eV at room temperature) with large exciton binding energy of approximately 60 meV [4]. Such properties make them well suited for the realization of many optoelectronic applications. Poly(N-vinyl carbazole) (PVK) is one of the famous holes conducting polymeric material with amorphous nature and widely utilized in the fabrication of blue light-emitting diodes [5]. It has, by linear chains of repeated molecular groups (H2CHC)n with pendant carbazole side groups [(C6H4)2NH], arranged randomly around the same chain. Since the electrical and optical properties of films strongly depend on their microstructure, stoichiometric nature, and impurities present, each deposition technique with its associated parameters yields films of different properties. Depending on the deposition method, the substrate can have a significant influence on the properties of the films. Particularly, the thermal expansion coefficient of the substrate affects the orientation of crystallites in the films and its electrical properties. Solution processing is envisioned as a key technology in the low-cost production of electronic devices on both conducting and non-conducting substrates. In this report, the formation of transparent heterojunction between ZnO and PVK thin films by solution processing routes and their performance were discussed. Methods All the precursor and solvent materials were used in asreceived condition without any further purification. Transparent PVK solution was prepared in dichloromethane (DCM) by dissolving 0.5 g of PVK in 20 ml of DCM at room temperature. The well-cleaned substrates (glass or fluorine-doped tin oxide (FTO)) were dip-coated using freshly prepared polymer sol and then baked at 80C for 15 min to get the PVK films. In the case of ZnO thin films, the sol was prepared [6] using the following procedure: isopropyl alcohol (136.4 ml) and diethanolamine (5.2 ml) were stirred for 15 min at room temperature; then, zinc acetate dehydrate (13.38 g) was added and stirred once again for 60 min then refluxed at 70C for 30 min, cooled, and aged for 6 h. The use of metal acetate instead of the commonly used alkoxides will reduce the problem of moisture sensitivity like significant factors in assessing the effectiveness of a process. A commercially available flat motor with a fan which is able to rotate at 2,000 rpm on 12 V DC supply was used to spin coat the ZnO sol on the substrates. After deposition, the films were baked in a box furnace at 450C for 10 min and allowed to reach room temperature before int (...truncated)


This is a preview of a remote PDF: https://link.springer.com/content/pdf/10.1186%2F2228-5326-3-9.pdf

Prakash Thanigainathan, Chandrasekar Paramasivan. Realization of ZnO/PVK transparent heterojunction by solution processing routes, International Nano Letters, 2013, pp. 9, Volume 3, Issue 1, DOI: 10.1186/2228-5326-3-9