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Effects of Alkyl Terminal Chains on Morphology, Charge Generation, Transport, and Recombination Mechanisms in Solution‐Processed Small Molecule Bulk Heterojunction Solar Cells
Author(s) -
Min Jie,
Luponosov Yuriy N.,
Gasparini Nicola,
Richter Moses,
Bakirov Artem V.,
Shcherbina Maxim A.,
Chvalun Sergei N.,
Grodd Linda,
Grigorian Souren,
Ameri Tayebeh,
Ponomarenko Sergei A.,
Brabec Christoph J.
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.201500386
Subject(s) - materials science , alkyl , heterojunction , recombination , organic solar cell , solubility , space charge , photovoltaic system , molecule , charge carrier , optoelectronics , analytical chemistry (journal) , chemical physics , chemistry , physics , electron , organic chemistry , polymer , ecology , biochemistry , quantum mechanics , biology , composite material , gene
Length of the terminal alkyl chains at dicyanovinyl (DCV) groups of two dithienosilole (DTS) containing small molecules ( DTS(Oct) 2 ‐(2T‐DCV‐Me) 2 and DTS(Oct) 2 ‐(2T‐DCV‐Hex) 2 ) is investigated to evaluate how this affects the molecular solubility and blend morphology as well as their performance in bulk heterojunction organic solar cells (OSCs). While the DTS(Oct) 2 ‐(2T‐DCV‐Me) 2 (a solubility of 5 mg mL −1 ) system exhibits both high short circuit current density ( J sc ) and high fill factor, the DTS(Oct) 2 ‐(2T‐DCV‐Hex) 2 (a solubility of 24 mg mL −1 ) system in contrast suffers from a poor blend morphology as examined by atomic force morphology and grazing incidence X‐ray scattering measurements, which limit the photovoltaic properties. The charge generation, transport, and recombination dynamics associated with the limited device performance are investigated for both systems. Nongeminate recombination losses in DTS(Oct) 2 ‐(2T‐DCV‐Hex) 2 system are demonstrated to be significant by combining space charge limited current analysis and light intensity dependence of current–voltage characteristics in combination with photogenerated charge carrier extraction by linearly increasing voltage and transient photovoltage measurements. DTS(Oct) 2 ‐(2T‐DCV‐Me) 2 in contrast performs nearly ideal with no evidence of nongeminate recombination, space charge effects, or mobility limitation. These results demonstrate the importance of alkyl chain engineering for solution‐processed OSCs based on small molecules as an essential design tool to overcome transport limitations.