Charge selectivity in polymer:Fullerene-based organic solar cells with a chemically linked polyethylenimine interlayer

Fu Chiao Wu, Kuo Cheng Tung, Wei Yang Chou, Fu Ching Tang, Horng Long Cheng

Research output: Contribution to journalArticlepeer-review

11 Citations (Scopus)


The power conversion efficiency of solar cells can be optimized via an efficient charge collection by electrodes. In this study, a simple linear polyethylenimine (LPEI), which is an insulating polymer, was adopted as the cathode interfacial layer of poly(3-hexylthiophene) (P3HT):[6,6]-phenyl-C61-butyric acid methyl ester (PCBM)-based bulk-heterojunction organic solar cells (OSCs) with a non-inverted configuration. All photovoltaic parameters of the OSCs were significantly enhanced by depositing LPEI onto the oxygen plasma-treated P3HT:PCBM active layers. The causes of performance enhancement in OSCs were studied. Results revealed that the microstructure and morphology of the P3HT:PCBM layer were almost unaffected by the oxygen plasma treatment and the subsequent LPEI deposition. The X-ray photoelectron spectra of the specimens demonstrated that with the aid of oxygen plasma treatment, the linked LPEI molecules formed a well-aligned dipole layer on top of the P3HT:PCBM layer through the bonding of nitrogen (N) with oxygen (O). The results from quantum chemical calculations showed that the LPEI molecule with an N-O bond had a larger dipole moment at an appropriate direction than that without an N-O bond. By contrast, the LPEI molecules can form a dipole layer with a random orientation in the absence of N-O bonds. The conductive atomic force microscopy images of the specimens showed that the well-aligned dipole layer could facilitate electron transfer and could block hole transfer from the P3HT:PCBM to the cathodes. The well-aligned and augmented interface dipoles improved the charge selectivity at the cathodes and the photovoltaic performance of the devices.

Original languageEnglish
Pages (from-to)120-126
Number of pages7
JournalOrganic Electronics
Publication statusPublished - 2016 Feb

All Science Journal Classification (ASJC) codes

  • Electronic, Optical and Magnetic Materials
  • Biomaterials
  • General Chemistry
  • Condensed Matter Physics
  • Materials Chemistry
  • Electrical and Electronic Engineering


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