The effect of charge extraction layers on the photo-stability of vacuum-deposited versus solution-coated organic solar cells

• We study photo-stability of ClInPc:C60 versus P3HT:PCBM OSCs.
• Contact photo-degradation affects vacuum-deposited and solution-coated solar cells.
• Interfacial extraction layers are necessary to avoid contact photo-degradation.
• The presence of excitons at organic-electrode interface is critical for degradation.
• Physical separation of photo-active layer and electrode enhances stability.

Organic solar cells (OSCs) are studied for their photo-stability in inert atmosphere. Polymer solar cells with a bulk heterojunction (BHJ) of poly(3-hexylthiophene) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM) are contrasted with small molecule solar cells with a BHJ of chloroindium phthalocyanine (ClInPc) and C60-fullerene. A series of charge extraction layers at the hole and electron collecting contacts are examined for their role in OSC performance and stability. The inter-compatibilities of these extraction layers in vacuum-deposited small molecule OSCs (SM-OSCs) versus solution-coated polymer OSCs (P-OSCs) are explored. Through photo-stability studies, we show that interfacial extraction layers are necessary to avoid contact photo-degradation, which otherwise leads to strong reductions in OSC efficiencies. We also highlight certain extraction layer combinations that result in strong inter-electrode degradation, and we discuss incompatibilities in extraction layers among SM-OSCs versus P-OSCs. Our results suggest that the presence of excitons at the organic-electrode interface likely plays a critical role in contact photo-degradation. By minimizing contact photo-degradation, which dominates the majority of short-term OSC degradation, a new avenue for studying OSC stability behavior and opportunities to focus on other losses in OSCs become possible.

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