2 research outputs found
Computer-Aided Screening of Conjugated Polymers for Organic Solar Cell: Classification by Random Forest
Owing to the diverse
chemical structures, organic photovoltaic
(OPV) applications with a bulk heterojunction framework have greatly
evolved over the last two decades, which has produced numerous organic
semiconductors exhibiting improved power conversion efficiencies (PCEs).
Despite the recent fast progress in materials informatics and data
science, data-driven molecular design of OPV materials remains challenging.
We report a screening of conjugated molecules for polymer–fullerene
OPV applications by supervised learning methods (artificial neural
network (ANN) and random forest (RF)). Approximately 1000 experimental
parameters including PCE, molecular weight, and electronic properties
are manually collected from the literature and subjected to machine
learning with digitized chemical structures. Contrary to the low correlation
coefficient in ANN, RF yields an acceptable accuracy, which is twice
that of random classification. We demonstrate the application of RF
screening for the design, synthesis, and characterization of a conjugated
polymer, which facilitates a rapid development of optoelectronic materials
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