>10% Efficiency Polymer:Fullerene Solar Cells with Polyacetylene-Based Polyelectrolyte Interlayers

Polymer solar cells have gained great attention due to their tremendous potential for applications in light-weight, large-area, and flexible photovoltaic modules fabricated via continuous roll-to-roll processes. Despite the significant progress, however, their efficiency and operating stability are still inadequate for commercial applications. Interfacial engineering of the electron-collecting 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[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b]dithiophene-alt-3-fluorothieno[3,4-b]thiophene-2-carboxylate] (PTB7-Th) and the [6,6]-phenyl-C₇₁-butyric acid methyl ester (PC₇₁BM), as the electron donor and electron acceptor, respectively. Key to this success is the insertion of the ionic polyacetylene-based conjugated polymer, poly(N-dodecyl-2-ethynylpyridinium 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 built-in potential, consequently facilitating efficient charge transport/extraction. Optimized solar cells exhibit power conversion efficiency values exceeding 10% while their operating stability under continuous solar-simulated illumination is significantly enhanced when ultraviolet light is effectively blocked using a suitable optical filter.