TY  - JOUR
A1  - Shivhare, Rishi
A1  - Erdmann, Tim
A1  - Hoermann, Ulrich
A1  - Collado-Fregoso, Elisa
A1  - Zeiske, Stefan
A1  - Benduhn, Johannes
A1  - Ullbrich, Sascha
A1  - Huebner, Rene
A1  - Hambsch, Mike
A1  - Kiriy, Anton
A1  - Voit, Brigitte
A1  - Neher, Dieter
A1  - Vandewal, Koen
A1  - Mannsfeld, Stefan C. B.
T1  - Alkyl Branching Position in Diketopyrrolopyrrole Polymers
T2  - Chemistry of materials : a publication of the American Chemical Society
N2  - Diketopyrrolopyrrole (DPP)-based donor acceptor copolymers have gained a significant amount of research interest in the organic electronics community because of their high charge carrier mobilities in organic field-effect transistors (OFETs) and their ability to harvest near-infrared (NIR) photons in solar cells. In this study, we have synthesized four DPP based donor-acceptor copolymers with variations in the donor unit and the branching point of the solubilizing alkyl chains (at the second or sixth carbon position). Grazing incidence wide-angle X-ray scattering (GIWAXS) results suggest that moving the branching point further away from the polymer backbone increases the tendency for aggregation and yields polymer phases with a higher degree of crystallinity (DoC). The polymers were blended with PC70BM and used as active layers in solar cells. A careful analysis of the energetics of the neat polymer and blend films reveals that the charge-transfer state energy (E-CT) of the blend films lies exceptionally close to the singlet energy of the donor (E-D*), indicating near zero electron transfer losses. The difference between the optical gap and open-circuit voltage (V-OC) is therefore determined to be due to rather high nonradiative 418 +/- 13 mV) and unavoidable radiative voltage losses (approximate to 255 +/- 8 mV). Even though the four materials have similar optical gaps, the short-circuit current density (J(SC)) covers a vast span from 7 to 18 mA cm(-2) for the best performing system. Using photoluminescence (PL) quenching and transient charge extraction techniques, we quantify geminate and nongeminate losses and find that fewer excitons reach the donor-acceptor interface in polymers with further away branching points due to larger aggregate sizes. In these material systems, the photogeneration is therefore mainly limited by exciton harvesting efficiency.
Y1  - 2018
UR  - https://publishup.uni-potsdam.de/frontdoor/index/index/docId/51612
SN  - 0897-4756
SN  - 1520-5002
VL  - 30
IS  - 19
SP  - 6801
EP  - 6809
PB  - American Chemical Society
CY  - Washington
ER  -