Ghani, F.; Opitz, A.; Pingel, P.; Heimel, G.; Salzmann, I.; Frisch, J.; Neher, D.; Tsami, A.; Scherf, U.; Koch, N.: Charge Transfer in and Conductivity of Molecularly Doped Thiophene-Based Copolymers. Journal of Polymer Science B: Polymer Physics 53 (2015), p. 58-63

The electrical conductivity of organic semiconductors can be enhanced by orders of magnitude via doping with strong molecular electron acceptors or donors. Ground-state integer charge transfer and charge-transfer complex formation between organic semiconductors and molecular dopants have been suggested as the microscopic mechanisms causing these profound changes in electrical materials properties. Here, we study charge-transfer interactions between the common molecular p-dopant 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane and a systematic series of thiophene-based copolymers by a combination of spectroscopic techniques and electrical measurements. Subtle variations in chemical structure are seen to significantly impact the nature of the charge-transfer species and the efficiency of the doping process, underlining the need for a more detailed understanding of the microscopic doping mechanism in organic semiconductors to reliably guide targeted chemical design.