Suppressing pre-aggregation to increase polymer solar cell ink shelf life

Abstract

Chemical degradation and morphology failure of ink-processed organic solar cells are now extensively studied. In contrast, the general problem that inks prepared via thermal and mechanical agitation degrade and age rapidly at room temperature has yet to be delineated as a commercialization bottleneck and resolved. This study unveils the intrinsic aging of common polymer:nonfullerene acceptor (NFA) binary inks and the impact of electro-optically active component additives on ink shelf life. As a result, we developed an effective approach to slow down the ink aging by employing an additive (i.e. PCBM variants) with high miscibility with the polymer and NFA. It is inferred that the PCBMs in the inks acts as a co-solvent and slows down the polymer and possibly the NFA pre-aggregation, preventing the formation of large domains in the films. At the same time, the PCBMs dissolved in the polymer-rich phase of the devices can maintain the electron percolations and hence benefit charge creation and collection. The method of introducing a hyper-miscible third component, that is, with concentration above the percolation threshold, to improve ink shelf life and maintain the percolation is delineated for the first time. It represents a synergistic approach to promote the scale-up of ink-processed organic solar cells.