Alkoxyphenylthiophene Linked Benzodithiophene Based
Medium Band Gap Polymers for Organic Photovoltaics: Efficiency Improvement
upon Methanol Treatment Depends on the Planarity of Backbone
Kakaraparthi Kranthiraja
Kumarasamy Gunasekar
Woosum Cho
Myungkwan Song
Young Geun Park
Jin Yong Lee
Yurim Shin
In-Nam Kang
Ajeong Kim
Hyunjung Kim
BongSoo Kim
Sung-Ho Jin
10.1021/ma5010875.s001
https://acs.figshare.com/articles/journal_contribution/Alkoxyphenylthiophene_Linked_Benzodithiophene_Based_Medium_Band_Gap_Polymers_for_Organic_Photovoltaics_Efficiency_Improvement_upon_Methanol_Treatment_Depends_on_the_Planarity_of_Backbone/2241154
Two donor–acceptor (D–A)
medium band gap polymers, <b>P1</b> and <b>P2</b>, alkoxyphenylthiophene
(APTh) linked benzodithiophene (BDT) as an electron-rich unit and
1,3-di(2′-bromothien-5′-yl)-5-(2-ethylhexyl)thieno[3,4-<i>c</i>]pyrrole-4,6-dione (TPD) (<b>A1</b>) or [5,6-bis(octyloxy)-4,7-di(thiophen-2-yl)benzo[<i>c</i>][1,2,5]thiadiazole] (BT) (<b>A2</b>) as an electron-deficient
unit, have successfully been synthesized via microwave-assisted Stille
polymerization and utilized for bulk heterojunction (BHJ) polymer
solar cells (PSCs). <b>P1</b> shows a well-distinguished absorption
shoulder between 590 and 620 nm attributed to the π–π
stacking of a polymer backbone; such kind of absorption shoulder is
not observed in <b>P2</b>, indicating that the <b>P1</b> has more planar structure than that of <b>P2</b>. This is
due to the fact that the sulfur atom of thiophene spacer and the oxygen
atom of carbonyl groups in TPD have more pronounced intramolecular
noncovalent interactions (INCI) in <b>P1</b> than that of the
sulfur atom of thiophene spacer and the oxygen atom of alkoxy groups
of BT in <b>P2</b>. The bulk heterojunction polymer solar cells
(BHJ PSCs) were fabricated with the configuration of ITO/PEDOT:PSS/polymer
(<b>P1</b> or <b>P2</b>):PC<sub>71</sub>BM/LiF/Al. The <b>P1</b> device shows better photovoltaic performance with open-circuit
voltage (<i>V</i><sub>oc</sub>) of 0.91 V and the power
conversion efficiency (PCE) of 4.19% than the <b>P2</b> device
(<i>V</i><sub>oc</sub>: 0.71 V; PCE: 1.88%) in neat blend
films under the illumination of AM 1.5G (100 mW/cm<sup>2</sup>). Upon
treating the active layers containing <b>P1</b> and <b>P2</b> with methanol, the PCE of the <b>P1</b> device is increased
from 4.19 to 7.14%. In contrast, the PCE of the <b>P2</b> device
is decreased from 1.88 to 1.82%. Space charge limited current mobility,
atomic force microscopy, transmission electron microscopy, time-of-flight
secondary ion mass spectrometry, and impedance spectroscopy studies
strongly support the enhanced PCE for the <b>P1</b> device is
attributed to the increased mobility, nanoscale morphology, and reduced
resistance upon methanol treatment; these favorable properties for
the <b>P1</b> polymer are highly correlated with the planarity
of the backbone.
2014-10-28 00:00:00
BT
bulk heterojunction polymer
absorption
mobility
P 1
TPD
INCI
sulfur atom
Voc
impedance spectroscopy studies
power conversion efficiency
PCE
Methanol Treatment Depends
P 1 device
Medium Band Gap Polymers
ion mass spectrometry
BDT
PSC
transmission electron microscopy
ITO
P 2.
thiophene spacer
intramolecular noncovalent interactions
P 1 polymer
P 2 device
methanol
AM
oxygen atom
BHJ