Diketopyrrolopyrrole polymers for use in organic field effect transistors

A polymer comprising one or more repeating unit(s) of the formula

• wherein
• a is an integer of 1 to 5,
• b is an integer of 1 to 3,
• c is an integer of 1 to 3,
• d is an integer 2 or 3,
• e is an integer 2 or 3,
• the sum of a, b and c is equal to or smaller than 7,
• Ar1, Ar1′, Ar3 and Ar3′ are independently of each other a group of formula
• or a group —Ar4—Ar5—[Ar6]f—,
• Ar4 is a group of formula
• Ar5 and Ar6 have independently of each other the meaning of Ar1, f is 0, or an integer 1,
• Ar2 is a group of formula
• one of X1 and X2 is N and the other is CH, and
• R1, R2, R1′ and R2′ may be the same or different and are selected from hydrogen, a C1-C100alkyl group, a C6-C24aryl, which can be substituted one to three times with C1-C8alkyl, C1-C8thioalkoxy, and/or C1-C8alkoxy, or pentafluorophenyl;
• wherein the polymers have a weight average molecular weight of 4,000 Daltons or greater;
• with the proviso that polymers of formula
• having a molecular weight below 10000 are excluded, and with the further proviso that polymers of formula
• having a molecular weight below 10000 are excluded;
• and
• with the further proviso that the following polymer
• having a molecular weight of 28589 g/mol and a λ onset of 904 (film) is excluded.