Electrical treeing and luminescence in a polymer p-n junction under extreme reverse bias

Abstract

A polymer p-n junction was subjected to an extreme reverse bias, up to 1000 V, to investigate its reverse bias characteristics and possible breakdown. A full breakdown did not take place even after more than 2 h of continuous stress. Electrical treeing, a pre-breakdown phenomenon commonly encountered in insulating polymers, was instead observed. The electrical treeing was accompanied by intense light emission, and incurred significant material loss in the polymer film, the latter which was attributed to hot electron bombardment. The impact by hot electrons also caused light emission from the luminescent conjugated polymer. The polymer junction was realized via in situ redox doping reactions in a planar solid-state light-emitting electrochemical cell made from a polymer mixed conductor. The cell was activated with a forward bias and subsequently cooled to freeze the p-n junction. The reverse bias of a doped polymer junction brings interesting opportunities to study the electrical treeing phenomenon, the luminescent conjugated polymer and the still lacking reverse-bias characteristics of an organic p-n junction.