Abstract
Polymer solar cells have gained great attention due to their tremendous potential for applications in lightâweight, largeâarea, and flexible photovoltaic modules fabricated via continuous rollâtoâroll processes. Despite the significant progress, however, their efficiency and operating stability are still inadequate for commercial applications. Interfacial engineering of the electronâcollecting buffer layer and the organic photoactive layer through the use of organic dipole interlayers, has been proposed as a simple and scalable way to improve the overall solar cell performance. Here, highly efficient inverted polymer:fullerene solar cells have been successfully developed with a power conversion efficiency of over 10%. The bulk heterojunction layer consists of the poly[4,8âbis(5â(2âethylhexyl)thiophenâ2âyl)benzo[1,2âb:4,5âb]dithiopheneâaltâ3âfluorothieno[3,4âb]thiopheneâ2âcarboxylate] (PTB7âTh) and the [6,6]âphenylâC71âbutyric acid methyl ester (PC71BM), as the electron donor and electron acceptor, respectively. Key to this success is the insertion of the ionic polyacetyleneâbased conjugated polymer, poly(Nâdodecylâ2âethynylpyridinium bromide), as an interfacial dipole layer. The latter is shown to lower the work function of the electron transporting zinc oxide layer and increase the builtâin potential, consequently facilitating efficient charge transport/extraction. Optimized solar cells exhibit power conversion efficiency values exceeding 10% while their operating stability under continuous solarâsimulated illumination is significantly enhanced when ultraviolet light is effectively blocked using a suitable optical filter.
The polyacetyleneâbased polyelectrolyte interlayers significantly enhance the efficiency and stability of polymer:fullerene solar cells due to their conformal coatings on the metal oxide electronâcollecting buffer layers.