Control of solvent aggregation to impact active layer morphology and enhance performance in non-fullerene organic solar cells

The use of solvent additives in the active layer casting solution has proved to be an effective strategy to enhance the performance of solar cells. Solvent additives often have high boiling points, can enhance or reduce solubility, and thereby promote polymer aggregation in solution prior to spin-coating. As a consequence, the use of solvent additives can facilitate the crystallization process. The resulting ordered structure can remarkably increase charge photogeneration, carrier lifetime, and carrier mobility.
Recently, we have found that volatile solvent additives can also improve the performance of organic solar cell fabricated with solution-processed non-fullerene acceptors, including Y6 to achieve device efficiencies in excess of 10%. We examined the effects of solvent quality on the structure in solution of both the donor and acceptor, and the resulting effects on film morphology and performance in solar cell devices. A combination of resonant soft X-ray scattering, grazing-incidence wide-angle X-ray scattering, energy-filtered TEM, and ultrafast spectroscopy reveal the complex interplay between solution structure and subsequent film structure through perturbations induced by solvent additives.