1 research outputs found
Following the TRMC Trail: Optimization of Photovoltaic Efficiency and Structure–Property Correlation of Thiophene Oligomers
Semiconducting
conjugated oligomers having same end group (<i>N</i>-ethylrhodanine)
but different central core (thiophene: <b>OT–T</b>, bithiophene: <b>OT–BT</b>, thienothiophene: <b>OT–TT</b>)
connected through thiophene pi-linker (alkylated terthiophene) were
synthesized for solution processable bulk-heterojunction solar cells.
The effect of the incorporation of an extra thiophene to the central
thiophene unit either through C–C bond linkage to form bithiophene
or by fusing two thiophenes together to form thienothiophene on the
optoelectronic properties and photovoltaic performances of the oligomers
were studied in detail. Flash photolysis time-resolved microwave conductivity
(FP–TRMC) technique shows <b>OT–TT</b> has significantly
higher photoconductivity than <b>OT–T</b> and <b>OT–BT</b> implying that the former can outperform the latter two derivatives
by a wide margin under identical conditions in a bulk-heterojunction
solar cell device. However, the initial photovoltaic devices fabricated
from all three oligomers (with PC<sub>71</sub>BM as the acceptor)
gave power conversion efficiencies (PCEs) of about 0.7%, which was
counterintuitive to the TRMC observation. By using TRMC results as
a guiding tool, solution engineering was carried out; no remarkable
changes were seen in the PCE of <b>OT–T</b> and <b>OT–BT</b>. On the other hand, 5-fold enhancement in the
device efficiency was achieved in <b>OT–TT</b> (PCE:
3.52%, <i>V</i><sub>OC</sub>: 0.80 V, <i>J</i><sub>SC</sub>: 8.74 mA cm<sup>–2</sup>, FF: 0.50), which was
in correlation with the TRMC results. The structure–property
correlation and the fundamental reasons for the improvement in device
performance upon solvent engineering were deduced through UV–vis
absorption, atomic force microscopy, bright-field transmission electron
microscopy, photoluminescence quenching analysis and two-dimensional
grazing incidence X-ray diffraction studies