title: Impact of molecular solvophobicity vs. solvophilicity on device performances of dimeric perylene diimide based solution-processed non-fullerene organic solar cells.
abstract: Because of their outstanding molecular optoelectronic properties, perylene diimides (PDIs) are promising alternatives to the commonly used PCBM. However, the overly strong aggregation ability, poor solution-processability and compatibility of PDIs severely limit their photovoltaic applications. We turned to borrowing the amphiphile concept to improve these supramolecular properties. Practically, we fine-tuned the molecular solvophobicity with respect to the molecular solvophilicity, e.g. F(solvophob/solvophil), by changing the number of the weakly solvophobic 2-methoxyethoxyl (EG) groups in the bay-region of the thienyl-bridged dimeric PDI backbone, forming three PDI dimers of Bis-PDI-T (0 EG), Bis-PDI-T-EG (2 EG) and Bis-PDI-T-di-EG (4 EG) (Scheme 1). The photovoltaic properties using these dimers as the solution-processed non-fullerene electron-acceptor and P3HT as the electron-donor were investigated via the device configuration of ITO/PEDOT:PSS/P3HT:PDI dimer/Ca/Al. Bis-PDI-T exhibited overly strong aggregation ability and very poor solution-processability, which severely limited compatibility, giving a very poor power conversion efficiency (PCE) of 0.007%. When two EG groups were attached at the 1,1'-positions, the resulted Bis-PDI-T-EG showed dramatically reduced aggregation ability, improved solution-processability, compatibility and proper phase separation. Small sized phases (∼20 nm) dominated in the active layer and the best PCE was increased to 0.39%. When four solvophobic EG functions were introduced, affording Bis-PDI-T-di-EG with excellent supramolecular properties, particularly, the improvement of the phase separation with an increased phase size of 24 nm and the enhanced electron and hole mobilities, by 2-4 times, with respect to that of Bis-PDI-T-EG. The best PCE was further enhanced to 0.88%. After using 1-chloronaphthalene as the co-solvent of 1,2-dichlorobenzene to further improve the compatibility, the PCE was improved further up to 0.41% for Bis-PDI-T, 0.76% for Bis-PDI-T-EG and 1.54% for Bis-PDI-T-di-EG.
authors.affiliation: Beijing National Laboratory of Molecular Science, Institute of Chemistry, Chinese Academy of Sciences, Beijing, 100190, PR China.
authors.forename: Zhenhuan
authors.initials: Z
authors.lastname: Lu
authors.forename: Xin
authors.initials: X
authors.lastname: Zhang
authors.forename: Chuanlang
authors.initials: C
authors.lastname: Zhan
authors.forename: Bo
authors.initials: B
authors.lastname: Jiang
authors.forename: Xinliang
authors.initials: X
authors.lastname: Zhang
authors.forename: Lili
authors.initials: L
authors.lastname: Chen
authors.forename: Jiannian
authors.initials: J
authors.lastname: Yao
mesh_terms: D019281:Dimerization; D057927:Hydrophobic and Hydrophilic Interactions; D007094:Imides / Q000737:chemistry*; D015394:Molecular Structure; D010569:Perylene / Q000031:analogs & derivatives / Q000737:chemistry*; D011789:Quantum Theory; D012993:Solar Energy; D012996:Solutions
chemical_list: D007094:Imides; D012996:Solutions; D010569:Perylene