TY - JOUR
T1 - All-Polymer Solar Cells
T2 - Impact of the Length of the Branched Alkyl Side Chains on the Polymer Acceptors on the Interchain Packing and Electronic Properties in Amorphous Blends
AU - Wang, Tonghui
AU - Coropceanu, Veaceslav
AU - Brédas, Jean Luc
N1 - Funding Information: This work has been supported by the Office of Naval Research in the framework of award no. N00014-17-1-2208, as well as by the Georgia Institute of Technology. Publisher Copyright: © 2019 American Chemical Society.
PY - 2019
Y1 - 2019
N2 - All-polymer solar cells are attracting increasing attention because polymer acceptors present specific advantages, especially over fullerene derivatives. The length of the branched alkyl side chains on the polymer acceptors has been reported to have different impacts in the crystalline versus amorphous domains of donor/acceptor blends. Given that amorphous domains are difficult to characterize experimentally, here, molecular dynamics simulations are combined with density functional theory calculations to examine at the molecular scale the role that the side-chain length plays on the interchain packing and electronic properties. As representative examples, blends of the poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b;4,5-b′]dithiophene-2,6-diyl-alt-(4-(2-ethylhexyl)-3-fluorothieno[3,4-b]thiophene)-2-carboxylate-2-6-diyl)] (PCE10) donor with the poly(thieno[3,4-c]1-dione-alt-3,4-difluorothiophene) (PTPD[2F]T) acceptor are discussed; two different branched side chains on the thieno[3,4-c]pyrrole-4,6-dione (TPD) moieties of the acceptor polymer are considered, that is, 2-hexyldecyl and 2-decyltetradecyl. Increasing the side-chain length is found to decrease the PTPD[2F]T backbone planarity and importantly to bring a higher extent of interactions between the side chains and their own TPD moieties, which plays a critical role in determining the interchain packings. The nature of these packings are then correlated with the following: (i) the electron-transfer rates between neighboring PTPD[2F]T chains; (ii) the energetic distribution of the interfacial charge-transfer states; and (iii) the nonradiative recombination processes from the charge-transfer states to the ground state and the associated voltage losses. Overall, our findings point to a higher electron mobility and a lower nonradiative voltage loss in the PCE10/PTPD[2F]T blends where the polymer acceptor has shorter side chains.
AB - All-polymer solar cells are attracting increasing attention because polymer acceptors present specific advantages, especially over fullerene derivatives. The length of the branched alkyl side chains on the polymer acceptors has been reported to have different impacts in the crystalline versus amorphous domains of donor/acceptor blends. Given that amorphous domains are difficult to characterize experimentally, here, molecular dynamics simulations are combined with density functional theory calculations to examine at the molecular scale the role that the side-chain length plays on the interchain packing and electronic properties. As representative examples, blends of the poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b;4,5-b′]dithiophene-2,6-diyl-alt-(4-(2-ethylhexyl)-3-fluorothieno[3,4-b]thiophene)-2-carboxylate-2-6-diyl)] (PCE10) donor with the poly(thieno[3,4-c]1-dione-alt-3,4-difluorothiophene) (PTPD[2F]T) acceptor are discussed; two different branched side chains on the thieno[3,4-c]pyrrole-4,6-dione (TPD) moieties of the acceptor polymer are considered, that is, 2-hexyldecyl and 2-decyltetradecyl. Increasing the side-chain length is found to decrease the PTPD[2F]T backbone planarity and importantly to bring a higher extent of interactions between the side chains and their own TPD moieties, which plays a critical role in determining the interchain packings. The nature of these packings are then correlated with the following: (i) the electron-transfer rates between neighboring PTPD[2F]T chains; (ii) the energetic distribution of the interfacial charge-transfer states; and (iii) the nonradiative recombination processes from the charge-transfer states to the ground state and the associated voltage losses. Overall, our findings point to a higher electron mobility and a lower nonradiative voltage loss in the PCE10/PTPD[2F]T blends where the polymer acceptor has shorter side chains.
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U2 - 10.1021/acs.chemmater.9b02284
DO - 10.1021/acs.chemmater.9b02284
M3 - Article
SN - 0897-4756
SP - 6239
EP - 6248
JO - Chemistry of Materials
JF - Chemistry of Materials
ER -