Structure–property relationships for bis-diketopyrrolopyrrole molecules in organic photovoltaics

Abstract

The design of small organic molecules for efficient solution-processed organic solar cells is hampered by the absence of relationships that connect molecular structure via processing to blend morphology and power conversion efficiency. Here we study a series of bis-diketopyrrolopyrrole molecules in which we systematically vary the aromatic core, the solubilizing side chains, and the end groups to achieve power conversion efficiencies of 4.4%. By comparing the morphology and performance we attempt to identify and rationalize the structure–property relationships. We find that the tendency to aggregate or crystallize are important factors to control and that these require a subtle balance.