Ion-beam-deposited ultrathin transparent metal contacts

Using ion-beam sputtering we have prepared ultrathin transparent metal contacts with large broad-band optical transmittance and low electrical sheet resistance. Metal films deposited by ion-beam sputtering have exceptionally small surface roughness, and films as thin as about 20 Angstrom are continuous and conductive, and provide optical transmittance as large as 80%. Ultrathin transparent metal contacts provide a number of advantages over more commonly used conductive transparent metal oxides such as indium tin oxide. Unlike indium tin oxide, ultrathin metal contacts can he deposited at room temperature and require no post-deposition anneal, allowing thin film optoelectronic devices such as organic light-emitting diodes and photovoltaic cells to be fabricated on low-cost, lightweight, flexible polymeric substrates. Transparent metal contacts may also eliminate the oxygen-related degradation of organic thin film devices associated with indium tin oxide contacts. Using 30-Angstrom thick ion-beam-deposited transparent palladium contacts we have fabricated organic light-emitting diodes on inexpensive, flexible plastic substrates and obtained devices with good injection and emission characteristics. Finally, unlike indium tin oxide, ultrathin metal contacts provide large optical transmittance in the ultraviolet part of the spectrum, making them useful for ultraviolet photodetectors and providing the potential for increased conversion efficiency for photovoltaic cells, especially for space applications. (C) 2000 Elsevier Science S.A. All rights reserved.