INTERFACE FORMATION BETWEEN POLY(2,5-DIHEPTYL-P-PHENYLENEVINYLENE) AND CALCIUM - IMPLICATIONS FOR LIGHT-EMITTING-DIODES

The early stages of metal/polymer interface formation between calcium and poly(2,5-diheptyl-p-phenylenevinylene) (PDHPV) have been studied using both X-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy. Charge transfer is observed from the metal atoms to the polymer; as a result the calcium atoms at the interface are ionic, and negative bipolarons appear as the charge-carrying species on the polymer chains. This n-type doping of PDHPV by calcium leads to the appearance of new electronic states in the polymer bandgap. The calcium atoms appear to diffuse into the near surface region of the polymer, rather than forming a well-defined overlayer on the organic films.