Mixed C60/C70 based fullerene acceptors in polymer bulk-heterojunction solar cells

► Identically substituted C60 and C70 mixtures are investigated as acceptors in polymer solar cells. ► No negative effects are observed on the charge transport. ► C60/C70 mixtures can have a very different morphology compared to either pure fullerene. ► Evidence of different quantum efficiencies for polymer and fullerene excitations is presented.