Ion-beam-deposited ultrathin transparent metal contacts

Using ion-beam sputtering we have prepared ultrathin transparent metal cont acts with large broad-band optical transmittance and low electrical sheet r esistance. Metal films deposited by ion-beam sputtering have exceptionally small surface roughness, and films as thin as about 20 Angstrom are continu ous and conductive, and provide optical transmittance as large as 80%. Ultr athin transparent metal contacts provide a number of advantages over more c ommonly 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 optoe lectronic devices such as organic light-emitting diodes and photovoltaic ce lls to be fabricated on low-cost, lightweight, flexible polymeric substrate s. Transparent metal contacts may also eliminate the oxygen-related degrada tion 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 ch aracteristics. Finally, unlike indium tin oxide, ultrathin metal contacts p rovide large optical transmittance in the ultraviolet part of the spectrum, making them useful for ultraviolet photodetectors and providing the potent ial for increased conversion efficiency for photovoltaic cells, especially for space applications. (C) 2000 Elsevier Science S.A. All rights reserved.