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Simple mono-halogenated perylene diimides as non-fullerene electron transporting materials in inverted perovskite solar cells with ZnO nanoparticle cathode buffer layers

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Abstract

We have synthesized and characterized three perylene diimides, X-PDI, where X = H, F, or Br. These three compounds have been tested for the substitution of [6,6]-phenyl C61 butyric acid methyl ester (PC61BM) in inverted perovskite solar cells (PVSCs). Although the efficiency of PDI derivative-based conventional PVSCs is as high as 17.6% (J. Mater. Chem. A, 2016, 4, 8724), the corresponding performance of inverted PVSCs is still lagging behind and improvement is necessary. For electron accepting (from CH3NH3PbI3 perovskite) and electron transporting properties of the materials, UV-visible absorption spectroscopy, electrochemical cyclic voltammetry, direct current conductivity, space-charge limited current (SCLC) electron mobility, atomic force microscopy (AFM) surface morphology, and photoluminescence (PL) spectroscopy gauging charge-trapping have been studied. The HOMO/LUMO energy levels are 5.94/4.00, 5.83/3.96, 6.00/3.97, and 5.48/3.73 eV for H-PDI, F-PDI, Br-PDI, and PC61BM, respectively. Direct current conductivities of H-PDI, F-PDI, Br-PDI, and PC61BM are 8.71 × 10−8, 1.18 × 10−9, 2.2 × 10−6, and 8.42 × 10−6 S cm−1, respectively. The SCLC electron mobility of H-PDI, F-PDI, Br-PDI, and PC61BM are 1.12 × 10−4, 8.31 × 10−6, 1.08 × 10−3, and 5.00 × 10−3 S cm−1, respectively. PL spectroscopy of CH3NH3PbI3 perovskite provides emission at wavelength of 781 nm, which is the same as for the perovskite layer covered with a thin film of H-PDI or F-PDI. However, the emission wavelength was blue-shifted to 773–774 nm when the perovskite layer was covered with a thin film of Br-PDI or PC61BM. Using UV-visible absorption spectroscopy, the solubility (in chloroform) was determined as 1.2 × 10−2, 8.7 × 10−2 and >10−1 mol L−1 for F-PDI, H-PDI, and Br-PDI, respectively. In thin film state, UV-visible absorption spectroscopy indicated that the extent of molecular aggregation was F-PDIH-PDI > Br-PDI, which is consistent with the AFM-estimated root-mean-square roughness of F-PDI > H-PDI > Br-PDI ∼ PC61BM. Without the solution processed ZnO NP cathode buffer layer (CBL), the power conversion efficiency (PCE) of H-PDI, F-PDI, Br-PDI, and PC61BM PVSCs is ∼1%, ∼0%, 3.2%, and 4.1%, respectively. With the ZnO NP CBL, PCE is ∼7.8%, ∼0%, 10.5%, and 11.1% for H-PDI, F-PDI, Br-PDI, and PC61BM PVSCs, respectively. Through this study, we have demonstrated that the simple mono-bromine substituted perylene diimide (Br-PDI), is solution processable and has potential for use as a non-fullerene electron accepting and electron transporting material in inverted PVSCs.

Graphical abstract: Simple mono-halogenated perylene diimides as non-fullerene electron transporting materials in inverted perovskite solar cells with ZnO nanoparticle cathode buffer layers

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Publication details

The article was received on 25 Mar 2017, accepted on 06 May 2017 and first published on 08 May 2017


Article type: Paper
DOI: 10.1039/C7TA02617J
Citation: J. Mater. Chem. A, 2017, Advance Article
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    Simple mono-halogenated perylene diimides as non-fullerene electron transporting materials in inverted perovskite solar cells with ZnO nanoparticle cathode buffer layers

    J. Wu, W. Huang, Y. Chang, B. Tsai, Y. Hsiao, C. Chang, C. Chen and C. Chen, J. Mater. Chem. A, 2017, Advance Article , DOI: 10.1039/C7TA02617J

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