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
BT  - Interplay between Fibrillar Morphology and Crystallinity and Their Effect on Photogeneration and Recombination in Bulk-Heterojunction Solar Cells
JF  - 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
U6  - https://doi.org/10.1021/acs.chemmater.8b02739
SN  - 0897-4756
SN  - 1520-5002
VL  - 30
IS  - 19
SP  - 6801
EP  - 6809
PB  - American Chemical Society
CY  - Washington
ER  - 
TY  - JOUR
A1  - Di Pietro, Riccardo
A1  - Erdmann, Tim
A1  - Carpenter, Joshua H.
A1  - Wang, Naixiang
A1  - Shivhare, Rishi Ramdas
A1  - Formanek, Petr
A1  - Heintze, Cornelia
A1  - Voit, Brigitte
A1  - Neher, Dieter
A1  - Ade, Harald W.
A1  - Kiriy, Anton
T1  - Synthesis of High-Crystallinity DPP Polymers with Balanced Electron and Hole Mobility
JF  - Chemistry of materials : a publication of the American Chemical Society
Y1  - 2017
U6  - https://doi.org/10.1021/acs.chemmater.7b04423
SN  - 0897-4756
SN  - 1520-5002
VL  - 29
SP  - 10220
EP  - 10232
PB  - American Chemical Society
CY  - Washington
ER  - 
TY  - JOUR
A1  - Li, Tian-yi
A1  - Benduhn, Johannes
A1  - Qiao, Zhi
A1  - Liu, Yuan
A1  - Li, Yue
A1  - Shivhare, Rishi
A1  - Jaiser, Frank
A1  - Wang, Pei
A1  - Ma, Jie
A1  - Zeika, Olaf
A1  - Neher, Dieter
A1  - Mannsfeld, Stefan C. B.
A1  - Ma, Zaifei
A1  - Vandewal, Koen
A1  - Leo, Karl
T1  - Effect of H- and J-Aggregation on the Photophysical and Voltage Loss of Boron Dipyrromethene Small Molecules in Vacuum-Deposited Organic Solar Cells
JF  - The journal of physical chemistry letters
N2  - An understanding of the factors limiting the open-circuit voltage (V-oc) and related photon energy loss mechanisms is critical to increase the power conversion efficiency (PCE) of small-molecule organic solar cells (OSCs), especially those with near-infrared (NIR) absorbers. In this work, two NIR boron dipyrromethene (BODIPY) molecules are characterized for application in planar (PHJ) and bulk (BHJ) heterojunction OSCs. When two H atoms are substituted by F atoms on the peripheral phenyl rings of the molecules, the molecular aggregation type in the thin film changes from the H-type to J-type. For PHJ devices, the nonradiative voltage loss of 0.35 V in the J-aggregated BODIPY is lower than that of 0.49 V in the H-aggregated device. In BHJ devices with a nonradiative voltage loss of 0.35 V, a PCE of 5.5% is achieved with an external quantum efficiency (EQE) maximum of 68% at 700 nm.
Y1  - 2019
U6  - https://doi.org/10.1021/acs.jpclett.9b01222
SN  - 1948-7185
VL  - 10
IS  - 11
SP  - 2684
EP  - 2691
PB  - American Chemical Society
CY  - Washington
ER  -