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Issue 7, 2020
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Steering the electron transport properties of pyridine-functionalized fullerene derivatives in inverted perovskite solar cells: the nitrogen site matters

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Abstract

Fullerene derivatives with strong electron-accepting abilities have been extensively used as electron transport layers (ETLs) of inverted (p–i–n) planar heterojunction perovskite solar cells (iPSCs); however the effect of a specific heteroatom site within the fullerene derivative on its electron transport properties has scarcely been studied. Herein, by employing pyridinecarboxaldehydes bearing different nitrogen sites within the pyridine moiety as a reactant, three novel pyridine-functionalized fullerene derivatives with variable nitrogen sites (abbreviated as C60-n-Py, where n is the relative position of pyridine nitrogen with the site of pyridine moieties linked to the pyrrolidine ring of fullerene derivatives, n = 2, 3, 4) were synthesized facilely via a one-step 1,3-dipolar cycloaddition reaction, and their molecular structures as well as molecular packing were unambiguously determined by X-ray single crystal diffraction. Despite that C60-n-Py (n = 2, 3, 4) exhibit negligible difference in the molecular energy level and optical absorption, when using C60-n-Py as a novel ETL in CH3NH3PbI3 (MAPbI3) iPSC devices, their electron transport properties are found to sensitively depend on the nitrogen site within the pyridine moiety, and the C60-3-Py-based device shows the highest power conversion efficiency (PCE) of 17.57%, surpassing those of C60-2-Py- and C60-4-Py-based devices (12.79% and 16.51%, respectively). The discrepancy of the electron transport properties of C60-n-Py is primarily due to the difference in the coordination interaction between the pyridine moiety and the Pb2+ ion of the MAPbI3 perovskite layer, which is determined by the nitrogen site according to X-ray photoelectron spectroscopic (XPS) characterization and theoretical studies. The stronger coordination interaction between the pyridine moiety and the Pb2+ ion for the C60-3-Py-based device leads to reinforced passivation of the trap state within the MAPbI3 perovskite film, affording improved device performance and ambient stability of the C60-3-Py device. Moreover, C60-n-Py (n = 2, 3, 4) were further used as ETLs of Cs0.05FA0.83MA0.12PbI2.55Br0.45 (abbreviated as CsFAMA) iPSC devices, and C60-3-Py shows the best ETL performance as well, confirming the universality of our approach in steering the electron transport properties of C60-n-Py.

Graphical abstract: Steering the electron transport properties of pyridine-functionalized fullerene derivatives in inverted perovskite solar cells: the nitrogen site matters

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Supplementary files

Article information


Submitted
06 Nov 2019
Accepted
13 Jan 2020
First published
15 Jan 2020

J. Mater. Chem. A, 2020,8, 3872-3881
Article type
Paper

Steering the electron transport properties of pyridine-functionalized fullerene derivatives in inverted perovskite solar cells: the nitrogen site matters

B. Li, J. Zhen, Y. Wan, X. Lei, L. Jia, X. Wu, H. Zeng, M. Chen, G. Wang and S. Yang, J. Mater. Chem. A, 2020, 8, 3872
DOI: 10.1039/C9TA12188A

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