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Small-molecule heterojunctions: Stability to ageing under sunlight
Applied Surface Science  (IF6.707),  Pub Date : 2021-12-01, DOI: 10.1016/j.apsusc.2021.152084
Georgy L. Pakhomov, Vlad V. Travkin, Mikhail N. Drozdov, Yury I. Sachkov, Pavel A. Yunin

We report a study on two types of the model thin-film systems: a bilayer SubPc/C60 film and variously mixed (co-deposited) SubPc:C60 films, where SubPc is boron chloride subphthalocyanine, C60 is buckminsterfullerene, both materials are small molecule semiconductors widely known in photovoltaics. These systems were subjected to a full-day exposure (13 h) to a simulated sunlight in air, which was expected to cause either photodestruction or soft annealing of molecular materials, or both. The morphology of the films in the aged and pristine states was assessed and compared using four methods: ToF-SIMS, optical spectroscopy, surface relief analysis and XRD. Based on the findings, the following conclusions can be made: 1) Neither interlayer mixing in the bilayer nor any noticeable phase delamination occur in the mixed systems; 2) Ageing affects the film morphology rather than depth distribution of its components; 3) SubPc component gets strongly oxidized/destroyed with ageing; 4) In a gradient mixed film the concentration of the components tends to equalize through the ageing process; 5) Fullerene may demonstrate some features of ordering, whereas SubPc remains X-ray amorphous.