The stability of normal vs. inverted organic solar cells under highly damp conditions: Comparison with the same interfacial layers

Abstract

The stability of normal and inverted organic solar cells is investigated under a highly damp condition (90% relative humidity) in air. For fair comparison, both cells are fabricated not only with the same active layers but also with the same interfacial and electrode layers. The experimental results indicate that the inverted cells do outlive the normal cells and that the top electrode/interfacial layer is a vulnerable component that affects the life time most significantly. Furthermore, inverted cells are shown to have a degradation trend that differs significantly from that of the normal cells: the former have a voltage-dominant degradation due to the change in the work function of the metal oxide-based anodic interfacial layers; and the latter have a current-dominant degradation associated with the formation of bubble-like features. Based on the causes of degradation, methods for avoiding or delaying the observed degradations are proposed and tested for each type of cells. 28 (1.4) fold enhancement in T-80-lifetime is achieved for inverted (normal) cells with the proposed method.