Enhancement in performance of polymer solar cells by introducing solution-processed dipole interlayer

• Inverted-structure device with a double interlayer (sol–gel zinc oxide (ZnO) layer + CsF layer formed through solution process) was fabricated.
• The power conversion efficiency was enhanced from 7.5% to 8.2% by a 9.3% increase in the fill factor (FF).
• We demonstrated the enhancement of the FF by atomic force microscopy, space charge limited current, and photoluminescence.

Metal fluorides (e.g., LiF and BaF2) are usually introduced as an electron transport layer in conventional polymer solar cells (PSCs). However, because they are insoluble, vacuum deposition is inevitable, resulting in a high process cost and the difficulty of introduction in PSCs. In this study, we fabricated inverted PSCs with a double interlayer by using solution-processable cesium fluoride and ZnO to improve the electron extraction. The power conversion efficiency was enhanced from 7.5% to 8.2% by a 9.3% increase in the fill factor. In addition, we demonstrated the enhancement of the FF by atomic force microscopy, space charge limited current, and photoluminescence.

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