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Ultrafast Charge Generation Pathways in Photovoltaic Blends Based on Novel Star‐Shaped Conjugated Molecules
Author(s) -
Kozlov Oleg V.,
Luponosov Yuriy N.,
Ponomarenko Sergei A.,
KauschBusies Nina,
Paraschuk Dmitry Yu,
Olivier Yoann,
Beljonne David,
Cornil Jérôme,
Pshenichnikov Maxim S.
Publication year - 2015
Publication title -
advanced energy materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 10.08
H-Index - 220
eISSN - 1614-6840
pISSN - 1614-6832
DOI - 10.1002/aenm.201401657
Subject(s) - materials science , homo/lumo , organic solar cell , intramolecular force , ultrafast laser spectroscopy , photochemistry , molecule , acceptor , absorption (acoustics) , chemical physics , density functional theory , spectroscopy , computational chemistry , organic chemistry , chemistry , polymer , physics , quantum mechanics , composite material , condensed matter physics
The quest for new materials is one of the main factors propelling recent advances in organic photovoltaics. Star‐shaped small molecules (SSMs) have been proven promising candidates as perspective donor material due to the increase in numbers of excitation pathways caused by the degeneracy of the lowest unoccupied molecular orbital (LUMO) level. In order to unravel the pathways of the initial photon‐to‐charge conversion, the photovoltaic blends based on three different SSMs with a generic structure of N(phenylene‐ nt hiophene‐dicyanovinyl‐alkyl) 3 ( n = 1–3), and [6,6]‐phenyl‐C 71 ‐butyric acid methyl ester (PC 71 BM) acceptor are investigated by ultrafast photoinduced absorption spectroscopy assisted by density functional theory calculations. It is shown that both electron transfer from SSMs to PC 71 BM and hole transfer from PC 71 BM to SSMs are equally significant for generation of long‐lived charges. In contrast, intramolecular (intra‐SSM) charge separation results in geminate recombination and therefore constitutes a loss channel. Overall, up to 60% of long‐lived separated charges are generated at the optimal PC 71 BM concentrations. The obtained results suggest that further improvement of the SSM‐based solar cells is feasible via optimization of blend morphology and by suppressing the intra‐SSM recombination channel.