No abstract

Nonfullerene acceptors are being actively explored for polymer solar cells (PSCs) with their advantages in extending the absorption range, reducing the energy loss, and therefore enhancing the power conversion efficiency (PCE). But to boost the PCE further, mobilities of these nonfullerene acceptors should be improved. For nonfullerene acceptors, the π-π stacking distance between cofacially stacked molecules significantly affects their mobility. Here, we demonstrate a strategy to increase the mobility of heteroheptacene-based nonfullerene acceptors by reducing their π-π stacking distances via control over the bulkiness of lateral side-chains. The incorporation of 2-butyloctyl substituents into the nonfullerene acceptor (M36) leads to its increased mobility with a reduced π-π stacking distance of 3.45 Å. Consequently, M36 affords an enhanced PCE of 16% which is the highest among all acceptor-donor-acceptor-type nonfullerene acceptors to date. The strategy of control over the bulkiness of side-chains on nonfullerene acceptors should aid the development of more efficient PSCs.

With the aid of a suitable third component acceptor material, the best-performance semitransparent organic solar cell shows an outstanding efficiency of 13.49% at an average visible transmittance of 22.58%.