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

• Stability of normal and inverted organic solar cells (OSCs) with the same layers were compared.
• Under the specified damp condition (27 °C, 90% humidity), inverted was superior to normal OSCs.
• Normal formed bubble-like features, decreasing mainly in Jsc while inverted showed loss in Voc.
• The cause of aging is thoroughly analyzed and simple method to improve the stability is proposed.
• The stability (T80) of unencapsulated inverted (normal) OSCs improved by a factor of 28 (1.4).

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 T80-lifetime is achieved for inverted (normal) cells with the proposed method.

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