Cesium carbonate-doped 1,4,5,8-naphthalene-tetracarboxylic-dianhydride used as efficient electron transport material in polymer solar cells

• We demonstrate that NTCDA can be n-type doped efficiently by cesium carbonate.
• The conductivity increases up to a dopant ratio of 50%.
• Highly doped NTCDA shows morphology changes which affect the mobility.
• Cs2CO3 doped NTCDA is an efficient electron transport layer for polymer solar cells.

The use of appropriate charge carrier transport materials in organic solar cells strongly influences the device performance. In this work, we focused on the molecular electron transport material 1,4,5,8-naphthalene-tetracarboxylic-dianhydride (NTCDA) doped by cesium carbonate (Cs2CO3). We first investigated the electrical properties of such n-type doped material as a function of the doping concentration before using it as electron transport layer (ETL) in polymer solar cells. The doped transparent ETL reduces the series resistance leading to an increased open circuit voltage. A power conversion efficiency of 3.8% was finally achieved in a device with a blend of poly(3-hexylthiophene-2,5-diyl):phenyl-C61-butyric acid methyl ester (P3HT:PCBM) as the active layer and a 5 nm-thick NTCDA:Cs2CO3 film with a molar ratio of 30% as ETL.

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