Composition

A composition comprising an electron donor, a fullerene electron acceptor and a non-fullerene electron acceptor wherein the non-fullerene electron acceptor is a compound of formula (I):

• wherein each EAG is an electron accepting group;
• and EDG is an electron-donating group of formula (II) or (III):
• wherein:
• each X is independently O or S;
• Ar3 and Ar4 independently in each occurrence is a monocyclic or polycyclic aromatic or heteroaromatic group;
• Ar5 is selected from the group consisting of thiophene, furan and benzene which is unsubstituted or substituted with one or two substituents;
• R1 and R2 independently in each occurrence is a substituent;
• R4 and R5 are each independently H or a substituent;
• R3 and R6 are each independently H, a substituent or a divalent group bound to EAG;
• Z1 is a direct bond or Z1 together with the substituent R4 forms Ar1 wherein Ar1 is a monocyclic or polycyclic aromatic or heteroaromatic group;
• Z2 is a direct bond or Z2 together with the substituent R5 forms Ar2 wherein Ar2 is a monocyclic or polycyclic aromatic or heteroaromatic group;
• p is 1, 2 or 3;
• q is 1, 2 or 3;
• and
• ---- is a point of attachment to EAG.