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Self-doping n-type Polymer as Cathode Interface Layer Enables Efficient Organic Solar Cells by Increasing Built-in Electric Field and Boosting Interface Contact

Abstract

The self-doped polymer cathode interface materials for organic solar cells have been widely investigated to enhance the ohmic contact between the electrode and the photosensitive active layer. Here, a novel polymer named PBTA-FN with self-doping effect was successfully synthesized by incorporating benzotriazole (BTA) as an electron-deficient group and a fluorene containing an amino group. In favor of the n-type backbone and amine-based groups, an obvious n-type doping was obtained, resulting in the dramatically improved conductivity of the PBTA-FN. Subsequently, the PBTA-FN and PFN as cathode interface layers (CILs) have been successfully applied in the organic solar cells based on PBDB-T-2F:IT-4F. A notable power conversion efficiency of 12.18% and 11.03% can be achieved with PBTA-FN and PFN as CILs, respectively. The PBTA-FN shows a better planarity than PFN from the results by density functional theory. The self-doping behaviour of PBTA-FN was determined by electron paramagnetic resonance, which exhibits a higher mobility and carrier density. The water contact angle results on surface of active-layer/ PBTA-FN bilayer suggest the PBTA-FN surface polarity is improved, which is attributed to a larger interface dipole. Thus, the PBTA-FN can reduce the work function of Al electrode and enhance the built-in electric potential, which further confirmed by ultraviolet photoelectron spectroscopy and Mott Schottky curves, and the related device produce a higher Voc (0.88 V) than that of PFN (0.86 V). This work provides a deeper understanding of the PBTA-FN interlayer mechanism and has potential application in optoelectronic devices.

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Publication details

The article was received on 29 Jun 2019, accepted on 08 Aug 2019 and first published on 12 Aug 2019


Article type: Paper
DOI: 10.1039/C9TC03506K
J. Mater. Chem. C, 2019, Accepted Manuscript

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    Self-doping n-type Polymer as Cathode Interface Layer Enables Efficient Organic Solar Cells by Increasing Built-in Electric Field and Boosting Interface Contact

    Y. Wang, Z. Liang, X. Li, J. Qin, M. Ren, C. Yang, X. Bao, Y. Xia and J. Li, J. Mater. Chem. C, 2019, Accepted Manuscript , DOI: 10.1039/C9TC03506K

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