10 research outputs found
Thickness Effect of Bulk Heterojunction Layers on the Performance and Stability of Polymer:Fullerene Solar Cells with Alkylthiothiophene-Containing Polymer
We
report a pronounced thickness effect of bulk heterojunction
(BHJ) layers on the performance and stability of inverted polymer
solar cells with the BHJ layers of poly[(4,8-bis(5-(octylthio)thiophen-2-yl)benzo[1,2-b:4,5-b′]dithiophene-<i>co</i>-3-fluorothieno[3,4- b]thiophene-2-carboxylate]
(PBDT-TS1) and [6,6]-phenyl-C<sub>71</sub>-butyric acid methyl ester
(PC<sub>71</sub>BM). The thickness of the BHJ layers was varied from
40 to 120 nm by changing solution concentrations and spin-coating
speeds. The results showed that the film thickness considerably affected
the performance and stability of devices. The power conversion efficiency
reached ca. 9% at the thickness of 80 nm by the optimized nanoscale
phase separation between donor and acceptor components. However, the
devices with 120 nm-thick BHJ layers showed better device stability
under continuous illumination with a simulated solar light due to
the well-maintained surface morphology and nanostructure in addition
to the improved morphological volume stability
A Pronounced Dispersion Effect of Crystalline Silicon Nanoparticles on the Performance and Stability of Polymer:Fullerene Solar Cells
We investigated the dispersion effect of crystalline
silicon nanoparticles
(SiNP) on the performance and stability of organic solar cells with
the bulk heterojunction (BHJ) films of poly(3-hexylthiophene) (P3HT)
and [6,6]-phenyl-C<sub>61</sub>-butyric acid methyl ester (PC<sub>61</sub>BM). To improve the dispersion of SiNP in the BHJ films,
we attached octanoic acid (OA) to the SiNP surface via esterification
reaction and characterized it with Raman spectroscopy and high-resolution
transmission electron microscopy. The OA-attached SiNP (SiNP-OA) showed
improved dispersion in chlorobenzene without change of optical absorption,
ionization potential and crystal nanostructure of SiNP. The device
performance was significantly deteriorated upon high loading of SiNP
(10 wt %), whereas relatively good performance was maintained without
large degradation in the case of SiNP-OA. Compared to the control
device (P3HT:PC<sub>61</sub>BM), the device performance was improved
by adding 2 wt % SiNP-OA, but it was degraded by adding 2 wt % SiNP.
In particular, the device stability (lifetime under short time exposure
to 1 sun condition) was improved by adding 2 wt % SiNP-OA even though
it became significantly decreased by adding 2 wt % SiNP. This result
suggests that the dispersion of nanoparticles greatly affects the
device performance and stability (lifetime)
Liquid Crystal-Gated-Organic Field-Effect Transistors with In-Plane Drain–Source–Gate Electrode Structure
We report planar liquid crystal-gated-organic
field-effect transistors (LC-<i>g</i>-OFETs) with a simple
in-plane drain–source–gate electrode structure, which
can be cost-effectively prepared by typical photolithography/etching
processes. The LC-<i>g</i>-OFET devices were fabricated
by forming the LC layer (4-cyano-4′-pentylbiphenyl, 5CB) on
top of the channel layer (poly(3-hexylthiophene), P3HT) that was spin-coated
on the patterned indium–tin oxide (ITO)-coated glass substrates.
The LC-<i>g</i>-OFET devices showed p-type transistor characteristics,
while a current saturation behavior in the output curves was achieved
for the 50–150 nm-thick P3HT (channel) layers. A prospective
on/off ratio (>1 × 10<sup>3</sup>) was obtained regardless
of the P3HT thickness, whereas the resulting hole mobility (0.5–1.1
cm<sup>2</sup>/(V s)) at a linear regime was dependent on the P3HT
thickness. The tilted ordering of 5CB at the LC-P3HT interfaces, which
is induced by the gate electric field, has been proposed as a core
point of working mechanism for the present LC-<i>g</i>-OFETs
Doping Effect of Organosulfonic Acid in Poly(3-hexylthiophene) Films for Organic Field-Effect Transistors
We attempted to dope poly(3-hexylthiophene) (P3HT) with
2-ethylbenzenesulfonic
acid (EBSA), which has good solubility in organic solvents, in order
to improve the performance of organic field effect transistors (OFET).
The EBSA doping ratio was varied up to 1.0 wt % because the semiconducting
property of P3HT could be lost by higher level doping. The doping
reaction was confirmed by the emerged absorption peak at the wavelength
of ∼970 nm and the shifted S2p peak (X-ray photoelectron spectroscopy),
while the ionization potential and nanostructure of P3HT films was
slightly affected by the EBSA doping. Interestingly, the EBSA doping
delivered significantly improved hole mobility because of the greatly
enhanced drain current of OFETs by the presence of the permanently
charged parts in the P3HT chains. The hole mobility after the EBSA
doping was increased by the factor of 55–86 times depending
on the regioregularity at the expense of low on/off ratio in the case
of unoptimized devices, while the optimized devices showed ∼10
times increased hole mobility by the 1.0 wt % EBSA doping with the
greatly improved on/off ratio even though the source and drain electrodes
were made using relatively cheaper silver instead of gold
Efficient Deep Red Light-Sensing All-Polymer Phototransistors with <i>p</i>‑type/<i>n</i>-type Conjugated Polymer Bulk Heterojunction Layers
Here
we demonstrate deep red light-sensing all-polymer phototransistors
with bulk heterojunction layers of poly[4,8-bis[(2-ethylhexyl)-oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-<i>b</i>]-thiophenediyl] (PTB7) and poly[[<i>N</i>,<i>N</i>′-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-<i>alt</i>-5,5′-(2,2′-bithiophene)] (P(NDI2OD-T2)).
The device performances were investigated by varying the incident
light intensity of the deep red light (675 nm), while the signal amplification
capability was examined by changing the gate and drain voltages. The
result showed that the present all-polymer phototransistors exhibited
higher photoresponsivity (∼14 A/W) and better on/off photoswitching
characteristics than the devices with the pristine polymers under
illumination with the deep red light. The enhanced phototransistor
performances were attributed to the well-aligned nanofiber-like morphology
and nanocrystalline P(NDI2OD-T2) domains in the blend films, which
are beneficial for charge separation and charge transport in the in-plane
direction
Strong Composition Effects in All-Polymer Phototransistors with Bulk Heterojunction Layers of p‑type and n‑type Conjugated Polymers
We
report the composition effect of polymeric sensing channel layers
on the performance of all-polymer phototransistors featuring bulk
heterojunction (BHJ) structure of electron-donating (p-type) and electron-accepting
(n-type) polymers. As an n-type component, poly(3-hexylthiopehe-<i>co</i>-benzothiadiazole) end-capped with 4-hexylthiophene (THBT-4ht)
was synthesized via two-step reactions. A well-studied conjugated
polymer, poly(3-hexylthiophene) (P3HT), was employed as a p-type polymer.
The composition of BHJ (P3HT:THBT-4ht) films was studied in detail
by varying the THBT-4ht contents (0, 1, 3, 5, 10, 20, 30, 40, and
100 wt %). The best charge separation in the P3HT:THBT-4ht films was
measured at 30 wt % by the photoluminescence (PL) study, while the
charge transport characteristics of devices were improved at the low
THBT-4ht contents (<10 wt %). The photosensing experiments revealed
that the photosensivity of all-polymer phototransistors was higher
than that of the phototransistors with the pristine P3HT layers and
strongly dependent on the BHJ composition. The highest (corrected)
responsivity (<i>R</i><sub>C</sub>) was achieved at 20 wt
%, which can be attributable to the balance between the best charge
separation and transport states, as investigated for crystal nanostructures
and surface morphology by employing synchrotron-radiation grazing-incidence
wide-angle X-ray scattering, high-resolution/scanning transmission
electron microscopy, and atomic force microscopy
Light-Induced Open Circuit Voltage Increase in Polymer Solar Cells with Ternary Bulk Heterojunction Nanolayers
We
report a light-induced open circuit voltage (<i>V</i><sub>OC</sub>) increase in polymer solar cells with ternary bulk
heterojunction (BHJ) layers that are composed of poly(3-hexylthiophene)
(P3HT), poly[(4,8-bis(2-ethylhexyloxy)-benzo[1,2-b:4,5-b′]dithiophene)-2,6-diyl-<i>alt</i>-(N-2-ethylhexylthieno[3,4-<i>c</i>]pyrrole-4,6-dione)-2,6-diyl]]
(PBDTTPD), and [6,6]-phenyl-C<sub>61</sub>-butyric acid methyl ester
(PC<sub>61</sub>BM). The ternary BHJ layers were prepared by varying
the composition of donor polymers at a fixed ratio (1:1 by weight)
of donor (P3HT + PBDTTPD) to acceptor (PC<sub>61</sub>BM). Results
showed that <i>V</i><sub>OC</sub> was gradually increased
under continuous illumination of solar light (100 mW/cm<sup>2</sup>) for ternary solar cells, whereas no <i>V</i><sub>OC</sub> increase was measured for binary solar cells without PBDTTPD. As
a consequence, the power conversion efficiency (PCE) of ternary solar
cells (except the highest PBDTTPD content) was rather higher after
solar light illumination for 10 h, even though the binary solar cell
exhibited significantly lowered PCE after 10 h illumination. The <i>V</i><sub>OC</sub> increase has been attributed to the lateral
phase segregation between P3HT and PBDTTPD domains in the ternary
BHJ layers under continuous illumination of solar light, as evidenced
from the analysis result by Raman spectroscopy, atomic force microscopy,
transmission electron microscopy, and synchrotron radiation grazing-incidence angle X-ray diffraction measurements
Hybrid Phototransistors Based on Bulk Heterojunction Films of Poly(3-hexylthiophene) and Zinc Oxide Nanoparticle
Hybrid phototransistors (HPTRs) were fabricated on glass
substrates using organic/inorganic hybrid bulk heterojunction films
of p-type poly(3-hexylthiophene) (P3HT) and n-type zinc oxide nanoparticles
(ZnO<sub><i>NP</i></sub>). The content of ZnO<sub><i>NP</i></sub> was varied up to 50 wt % in order to understand
the composition effect of ZnO<sub><i>NP</i></sub> on the
performance of HPTRs. The morphology and nanostructure of the P3HT:ZnO<sub><i>NP</i></sub> films was examined by employing high resolution
electron microscopes and synchrotron radiation grazing angle X-ray
diffraction system. The incident light intensity (<i>P</i><sub>IN</sub>) was varied up to 43.6 μW/cm<sup>2</sup>, whereas
three major wavelengths (525 nm, 555 nm, 605 nm) corresponded to the
optical absorption of P3HT were applied. Results showed that the present
HPTRs showed typical p-type transistor performance even though the
n-type ZnO<sub><i>NP</i></sub> content increased up to 50
wt %. The highest transistor performance was obtained at 50 wt %,
whereas the lowest performance was measured at 23 wt % because of
the immature bulk heterojunction morphology. The drain current (<i>I</i><sub>D</sub>) was proportionally increased with <i>P</i><sub>IN</sub> due to the photocurrent generation in addition
to the field-effect current. The highest apparent and corrected responsivities
(<i>R</i><sub>A</sub> = 4.7 A/W and <i>R</i><sub>C</sub> = 2.07 A/W) were achieved for the HPTR with the P3HT:ZnO<sub><i>NP</i></sub> film (50 wt % ZnO<sub><i>NP</i></sub>) at <i>P</i><sub>IN</sub> = 0.27 μW/cm<sup>2</sup> (555 nm)
All-Polymer Solar Cells with Bulk Heterojunction Films Containing Electron-Accepting Triple Bond-Conjugated Perylene Diimide Polymer
A triple
bond-linked perylene diimide (PDI) conjugated polymer,
poly{[<i>N</i>,<i>N</i>′-dioctylperylene-3,4,9,10-bis(dicarboximide)-1,7(6)-diyl]-<i>alt</i>-[(2,5-bis(2-ethylhexyl)-1,4-phenylene)bis(ethyn-2,1-diyl]}
(PDIC8-EB), was examined as an electron-accepting component in all-polymer
solar cells. As an electron-donating component, poly[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-<i>b</i>]-thiophenediyl] (PTB7) and poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b′]dithiophene-<i>alt</i>-3-fluorothieno[3,4-<i>b</i>]thiophene-2-carboxylate]
(PTB7-Th) were introduced in order to investigate the feasibility
of PDIC8-EB because of their similarity. Results showed that the power
conversion efficiency (PCE) was higher for the PTB7-Th:PDIC8-EB solar
cells (PCE = 3.58%) than the PTB7:PDIC8-EB solar cells (PCE = 2.81%).
The better performance of the PTB7-Th:PDIC8-EB solar cells has been
attributed to the formation of a well-defined nanodomain morphology
in the PTB7-Th:PDIC8-EB bulk heterojunction layer, as measured with
transmission electron microscopy (TEM), atomic force microscopy (AFM),
and synchrotron radiation grazing incidence X-ray diffraction (GIXD)
Broadband pH-Sensing Organic Transistors with Polymeric Sensing Layers Featuring Liquid Crystal Microdomains Encapsulated by Di-Block Copolymer Chains
We report broadband pH-sensing organic
field-effect transistors (OFETs) with the polymer-dispersed liquid
crystal (PDLC) sensing layers. The PDLC layers are prepared by spin-coating
using ethanol solutions containing 4-cyano-4′-pentyl-biphenyl
(5CB) and a diblock copolymer (PAA-<i>b</i>-PCBOA) that
consists of LC-philic block [poly(4-cyano-biphenyl-4-oxyundecyl acrylate)
(PCBOA)] and acrylic acid block [poly(acrylic acid) (PAA)]. The spin-coated
sensing layers feature of 5CB microdomains (<5 μm) encapsulated
by the PAA-<i>b</i>-PCBOA polymer chains. The resulting
LC-integrated-OFETs (PDLC-<i>i</i>-OFETs) can detect precisely
and reproducibly a wide range of pH with only small amounts (10–40
μL) of analyte solutions in both static and dynamic perfusion
modes. The positive drain current change is measured for acidic solutions
(pH < 7), whereas basic solutions (pH > 7) result in the negative
change of drain current. The drain current trend in the present PDLC-<i>i</i>-OFET devices is explained by the shrinking-expanding mechanism
of the PAA chains in the diblock copolymer layers