Field-activated structural traps at organic pigment/metal interfaces causing photocurrent multiplication phenomena

Carrier traps at the perylene pigment/metal interface, which give rise to a large photocurrent multiplication phenomenon showing a gain of more than 104-fold, were investigated. The energetic depth of these traps increased with applied electric field, contrary to the behavior of usual electronic traps. To explain this, a model of field-activated structural traps was proposed; that is, dead ends at an imperfect organic/metal contact capture holes more tightly under a stronger electric field. Estimated values of five trapped holes per 10 nm2 and dead ends of the order of 1 nm long suggest that the proposed structural traps are closely related to the molecular-sized roughness at the pigment surface.