44 research outputs found
Self-Assembled Conjugated Polyelectrolyte–Ionic Liquid Crystal Complex as an Interlayer for Polymer Solar Cells: Achieving Performance Enhancement via Rapid Liquid Crystal-Induced Dipole Orientation
A simple
approach was demonstrated to manipulate dipole moment of interlayer
in polymer solar cells (PSCs). The ionic liquid crystals (ILCs) 3-((2′-(4″-cyanoÂbiphenyl-4-yloxy)Âethyl)ÂdimethylÂammonio)ÂpropaneÂsulfonate
(CbpNSO) with zwitterionic charges were blended with cationic conjugated
polyelectrolyte (CPE) polyÂ[3-(6-trimethylammoniumhexyl)Âthiophene]
(PTNBr) to afford a novel CPE–ILC complex. The water/alcohol
solubility of the CPE–ILC complex enables it to be green solvent
processable. The spontaneous orientation of liquid crystal (LC) favors
more ordered structural arrangement in CPE–ILC complexes. More
importantly, LC-assistant assembly improves the orientation of dipole
at cathode and significantly reduces the work function of ITO. The
power conversion efficiency (PCE) of P3HT:PC<sub>60</sub>BM-based
inverted PSCs with the layer of PTNBr–CbpNSO is increased by
37% with respect to that of the device with pure PTNBr. Incorporation
of PTNBr–CbpNSO into the devices based on PBDTTT-C-T and PC<sub>71</sub>BM affords a notable PCE of 7.49%. It should be noted that
mesogens reduce the activation energy of molecular reorganization
and accelerate dipole orientation in CPE–ILC interlayer under
external electric field, which enables the dipole of this interlayer
can be readily manipulated. Because of the rapid orientation of the
dipole, PTNBr–CbpNSO shows reversible dipole at the active
layer/ITO interface during the reversible bias process
Electrostatic Self-Assembled Metal Oxide/Conjugated Polyelectrolytes as Electron-Transporting Layers for Inverted Solar Cells with High Efficiency
Three
conjugated polyelectrolytes (CPEs) based on polythiophenes
bearing anionic (polyÂ[(3-(4′-sulfonatobutyl)Âoxymethyl-2,5-thiophene)-<i>alt</i>-2,5-thiophene] sodium salt, PTSO-Na), neutral (HT-polyÂ[3-(6′-diethanolamino)-hexylthiophene],
PTNOH) and cationic (HT-polyÂ[3-(6′-<i>N</i>,<i>N</i>,<i>N</i>-trimethylammonium)-hexylthiophene],
PTN-Br) pendant groups were synthesized to improve the power conversion
efficiency (PCE) of inverted polymer solar cells (I-PSCs) by deposition
on the surface of ZnO to form a ZnO/CPE electron-transporting layer
(ETL). Insertion of CPE to ZnO–active layer interfaces effectively
lowered the energy barrier for electron transport and reduced the
inherent incompatibility between the hydrophilic metal oxide and hydrophobic
active layers. The I-PSCs (ITO/ZnO/CPE/P3HT:PCBM/PEDOT:PSS/Ag) incorporating
anionic PTSO-Na achieved a 16% efficiency enhancement (PCE = 3.47%)
over the standard device with a ZnO monolayer ETL (PCE = 2.99%). For
the deposition of neutral PTNOH and cationic PTN-Br on top of ZnO,
we observed strong electrostatic interaction between cationic quaternary
amines of the CPE and anionic oxygen ions of the ZnO surfaces, which
obtained a uniform formation of strong dipoles across the interfaces
and an intimate interfacial contact. The self-assembly formed by partial
protonation in neutral PTNOH increased the PCE of I-PSC to 3.98%,
whereas the stronger electrostatic self-assembly produced in ZnO/PTN-Br
bilayers not only delivered the device with the best PCE (4.08%) among
the three CPEs but also yielded an exceptional device lifetime without
encapsulation. It is worth noting that the performance of the I-PSC
with PTN-Br already surpassed that of conventional ones (ITO/PEDOT:PSS/P3HT:PCBM/PTN-Br/LiF/Al).
Moreover, the PCE of the device based on a ZnO/PTN-Br ETL was further
improved to 4.45% after UV treatment with a 43% enhancement compared
with the monolayer ZnO device, which is due to improved electrostatic
self-assembly. These findings on electrostatic self-assembled metal
oxide/CPE bilayer ETL provide a simple and easy strategy for fabrication
of high-performance and long-term stable I-PSCs
Versatile Electron-Collecting Interfacial Layer by in Situ Growth of Silver Nanoparticles in Nonconjugated Polyelectrolyte Aqueous Solution for Polymer Solar Cells
Novel PEIE-Ag composites by in situ
growth of silver nanoparticles
in polyÂ(ethylenimine)-ethoxylated (PEIE) aqueous solution are explored
as an efficient interfacial layer for improving inverted polymer solar
cells (PSCs) performance. The hybrid PEIE-Ag interfacial material
is simple to fabricate only via ultraviolet irradiation with good
water-solubility and unique film formation. The generated Ag nanoparticles
can anchor in the PEIE polymer chains to form a conductive continuous
interpenetrating network structure. Combining of the advantages of
PEIE and Ag nanoparticles, the PEIE-Ag shows enhanced charge transport,
electron selective and collection, and improved light-harvesting,
mainly due to the surface plasmon resonance effect, better energy
alignment induced by the formation of ideal dipole layer, as well
as the improved conductivity. These distinguished interfacial properties
result in the power conversion efficiency of inverted PSCs based on
polyÂ[4,8-bisÂ(2-ethyl-hexyl-thiophene-5-yl)-benzoÂ[1,2-b:4,5-b]Âdithiophene-2,6-diyl]-<i>alt</i>-[2-(2-ethyl-hexanoyl)-thienoÂ[3,4-<i>b</i>]Âthiophen-4,6-diyl]
(PBDTTT-C-T) and [6,6]-phenyl C<sub>71</sub>-butyric acid methyl ester
(PC<sub>71</sub>BM) photoactive layer substantially improved up to
7.66% from 6.11%. Moreover, the device performance is insensitively
dependent on the thickness of the PEIE-Ag interfacial layer, broadening
the thicknesses selection window for interfacial materials. These
results demonstrate that PEIE-Ag is a potential interfacial material
compatible with roll-to-roll techniques and suitable for printed electronic
devices
Optical Engineering of Uniformly Decorated Graphene Oxide Nanoflakes via in Situ Growth of Silver Nanoparticles with Enhanced Plasmonic Resonance
A nanocomposite of silver-nanoparticle-decorated
graphene oxide
(GO–Ag NPs), enhanced by the surface plasmon resonance (SPR)
effect, improved the performance of polymer solar cells (PSCs). The
GO–Ag NPs were fabricated in situ via ultraviolet (UV) irradiation
(254 nm) of GO and an aqueous solution of AgNO<sub>3</sub>. The photoexcited
GO accelerated reduction of Ag<sup>+</sup> ions into silver nanoparticles
(Ag NPs) upon UV irradiation, and the Ag NPs spontaneously deposited
on the GO nanoflakes because the numerous functional groups on GO
enable efficient adsorption of Ag<sup>+</sup> ions and Ag NPs via
electrostatic interactions. The strong coupling between the SPR effect
of GO–Ag NPs and incident light offers the probability of improved
light absorption and corresponding exciton generation rate with enhanced
charge collection, resulting in significant enhancement in short-circuit
current density and power conversion efficiency (PCE). Therefore,
the PCE of PSCs based on polyÂ[4,8-bisÂ(2-ethylhexylthiophene-5-yl)-benzoÂ[1,2-<i>b</i>:4,5-<i>b</i>]Âdithiophene-2,6-diyl]-<i>alt</i>-[2-(2-ethylhexanoyl)ÂthienoÂ[3,4-<i>b</i>]Âthiophen-4,6-diyl]
and [6,6]-phenyl C<sub>71</sub>-butyric acid methyl ester has been
substantially elevated to 7.54% from 6.58% by introducing GO–Ag
NPs at the indium tin oxide/polyÂ(3,4-ethylenedioxythiophene):polystyrene
sulfonic acid interface. In addition, the excellent properties of
GO–Ag NPs, including its simple preparation, processability
in aqueous solution, cost-effectiveness, and sustainability, make
it suitable for the roll-to-roll manufacturing of PSCs
Universal and Versatile MoO<sub>3</sub>‑Based Hole Transport Layers for Efficient and Stable Polymer Solar Cells
Two
solution-processed and highly dispersed MoO<sub>3</sub> called
d-(MoO<sub>3</sub>)<sub>120</sub> and d-(MoO<sub>3</sub>)<sub>15</sub> with sizes of 120 nm and extremely smaller 15 nm, respectively,
are applied into polymer solar cells, and the evaporated MoO<sub>3</sub> as hole transport layers (HTLs) in devices is also compared. It
is the first time it has been found that the different size of MoO<sub>3</sub> can induce the quite different morphologies of the HTLs and
their upper active layers due to the unexpectedly caused difference
in the surface energy levels. It is worthy to note that the performance
of the device with solution-processed d-(MoO<sub>3</sub>)<sub>15</sub> is higher than that of the device with polyÂ(3,4-ethylenedioxythiophene):ÂpolyÂ(styrenesulfonate)
(PEDOT:PSS) HTLs and even comparable to that of the device with optimized
evaporated-MoO<sub>3</sub>. Simulated by the transfer matrix method,
the light intensity and the exciton generation rate in the active
layer are found to be greatly enhanced by incorporation of an ultrathin
MoO<sub>3</sub> combined with PEDOT:PSS. As a result, by inserting
a layer of evaporated MoO<sub>3</sub> (e-MoO<sub>3</sub>) between
the ITO and PEDOT:PSS, power conversion efficiency (PCE) can be dramatically
improved to 7.10% for PBDTTT-C-T:PC<sub>71</sub>BM. Moreover, the
e-MoO<sub>3</sub>/PEDOT:PSS bilayer also ensures good stability for
the devices, due to the MoO<sub>3</sub> preventing moisture and oxygen
attack and protecting ITO from corrosion caused by the acid PEDOT:PSS
Cooperative Assembly of Pyrene-Functionalized Donor/Acceptor Blend for Ordered Nanomorphology by Intermolecular Noncovalent π–π Interactions
A facile
approach to develop the stable and well-defined bulk heterojunction
(BHJ) nanomorphology has been demonstrated. Novel pyrene (Py)-functionalized
diblock copolymers polyÂ(3-hexylthiophene)-<i>block</i>-polyÂ[3-(10-(pyren-1-yloxy)Âdecyloxy)Âthiophene]
(P3HT-<i>b</i>-P3TPy), and pyrene-functionalized fullerene
[6,6]-phenyl-C<sub>61</sub>-butyric acid 1-pyrene butyl ester (PCBPy),
were successfully synthesized. The π–π interactions
of Py mesogens interdigitated between the functionalized fullerene
and P3TPy segment can allow for the cooperative assembly of P3HT-<i>b</i>-P3TPy and PCBPy. The orientation of the Py mesogens also
can further enhance the molecular arrangement. Compared with the as-cast
and thermal annealing, solvent annealing can promote cooperative assembly
of P3HT-<i>b</i>-P3TPy:PCBPy undergoing the slow film growth.
Note that the assembly microstructure strongly depends on the molar
ratio of P3HT and P3TPy with Py mesogens. Low loading of P3TPy block
in the copolymers blends keeps the same behavior to the P3HT, whereas
relatively high loading of Py mesogens favors the better intermolecular
π–π stacking interactions between P3HT-<i>b</i>-P3TPy and PCBPy. As a result, the P3HT-<i>b</i>-P3TPyÂ(3/1) forms the orientated nanowires with PCBPy in bulk heterojunction,
and the average domain size is estimated to be 10–20 nm, which
is desirable for enlarge surface area for donor/acceptor interfaces
and give a bicontinuous pathway for efficient electron transfer. Furthermore,
the cooperative assembly between P3HT-<i>b</i>-P3TPy and
PCBPy is found to effectively suppress the PCBPy macrophase separation,
and stabilize the blend morphology
Self-Organized Hole Transport Layers Based on Polythiophene Diblock Copolymers for Inverted Organic Solar Cells with High Efficiency
Novel fluoroalkyl side-chain diblock copolymers, polyÂ(3-hexylthiophene)-block-polyÂ[3-(4-(3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluorooctyloxy)Âphenyl)Âdecyloxy)Âthiophene]
(P3HT-b-P3FAT), were successfully synthesized by Grignard metathesis
(GRIM) polymerization. Driven by the low surface energy of fluoroalkyl
side chains, the fluorinated polymers can spontaneously segregate
on the surface of poly-(3-hexylthiophene) (P3HT) during spin-coating
processes. As the P3HT block increases in the copolymer, higher concentrations
of fluoropolymers are required to form the self-assembled monolayer
on the surface. The fluorinated part forms an interfacial dipole that
shifts the work function of the anode metal, while the P3HT block
can interact with the P3HT donor for hole transport. With this self-assembly
hole transport layer to align the energy levels, P3HT:PCBM photovoltaic
devices are easily fabricated to achieve improved performance. Overall,
devices prepared with 1.5 mg mL<sup>–1</sup> copolymer PFT-3HT
with a 3:1 ratio of P3HT to P3FAT block in the active layer solution
displayed PCE values of up to 4.6% (50% PCE increase over a PEDOT:PSS
control device) and showed a significant long-term stability in excess
of 300 h in air
Self-Assembly of Diblock Polythiophenes with Discotic Liquid Crystals on Side Chains for the Formation of a Highly Ordered Nanowire Morphology
Diblock
copolymers bearing a triphenylene (TP) discotic liquid
crystals moiety, polyÂ(3-hexylthiophene)-block-polyÂ[3-(10-(2,3,6,7,10-pentakisÂ(hexyloxy)Âtriphenylen)-decyloxy)Âthiophene]
(P3HT-b-P3TPT), was successfully synthesized by Grignard metathesis
polymerization. The self-assembled nanowire structures of these diblock
copolymers have been investigated by atomic force microscopy and transmission
electron microscopy. The domain size and crystallinity of the nanostructures
can be easily controlled by tuning the P3HT/P3TPT block ratio and
by employing different annealing processes such as thermal and solvent
annealing. The results of X-ray diffraction indicate that both intermolecular
interactions and mesogen packing are essential for the formation of
nanostructures in the diblock copolymers. Although the block ratio
of P3HT and P3TPT comes to 9:1 and the copolymer undergoes solvent
annealing followed by thermal treatment, an optimal crystalline nanowire
with a size of 16.9 nm is formed. In addition, solar cells based on
these copolymers as electron donors in combination with [6,6]-phenyl-C<sub>61</sub>-butyric acid methyl ester (PC<sub>61</sub>BM) or <i>N</i>,<i>N</i>′-diÂ(2-ethylhexyl)Âperylene-3,4,9,10-tetracarboxylbisimide
(PDI) as electron acceptors have been constructed, and the effect
of the nanomorphology on device performance has been investigated
In Situ Fabricating One-Dimensional Donor–Acceptor Core–Shell Hybrid Nanobeams Network Driven by Self-Assembly of Diblock Copolythiophenes
In situ growth of cadmium sulfide
(CdS) quantum dots (QDs) was achieved directly through solvent-assisted
grafting in the self-assembled templates of amphiphilic all conjugated
diblock copolythiophene, polyÂ(3-hexylthiophene)-<i>b</i>-polyÂ(3-(2-(2-(2-methoxyethoxy)Âethoxy)Âethoxy)Âmethylthiophene) (P3HT-<i>b</i>-P3TEGT) and gas–solid reaction. Such diblock polymer
templates allowed a desired amount of cadmium sulfide salt (CdÂ(Ac)<sub>2</sub>) to easily accomplish dispersion and self-assembly via controlled
assembling block copolymers in selective solvents. After P3HT-<i>b</i>-P3TEGT polymer templates grafted with Cd<sup>2+</sup> precursor
(P3HT-<i>b</i>-P3TEGT/Cd<sup>2+</sup>) reacting in hydrogen
sulfide (H<sub>2</sub>S) gas, one-dimensional core–shell nanobeams
network P3HT-<i>b</i>-P3TEG/CdS (donor–acceptor)
was formed with excellent phase separation between P3HT-<i>b</i>-P3TEGT crystalline domains and inorganic CdS QDs domains at nanoscales,
which was driven by the interaction between oxygen atoms of ethylene
oxide side chains and Cd<sup>2+</sup> ions, and the thermodynamic
equilibrium between polymer chains deformation. The one-dimensional
wire-like nanostructure were highly desirable for the active layers
in photovoltaic devices as providing high carrier mobility, large
interfacial area between electron donor and acceptor, and highly efficient
transport pathways to improve the power conversion efficiency (PCE)
of hybrid bulk heterojunction solar cells
Experimental Investigation and Theoretical Calculation of Molecular Architectures on Carbazole for Photovoltaics
A new
conjugated polymer containing 6<i>H</i>-phenanthroÂ[1,10,9,8-cdefg]Âcarbazole
(PC) and 4,7-dithien-2-yl-2,1,3-benzoÂthiadiazole (DTBT) units,
so-called PPCDTBT, is synthesized based on the further modification
of carbazole moieties for polyÂ[<i>N</i>-9″-hepta-decanyl-2,7-carbazole-<i>alt</i>-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzoÂthiadiazole)]
(PCDTBT). The resulting polymer exhibits a narrow band gap with 1.77
eV, resulting from the broader conjugation, while maintaining a low-lying
HOMO energy level. The polymer geometry is severely transformed by
the large fused block phenanthrocarbazole (PC). Through the density
functional theory and time-dependent density functional theory calculations
at the B3LYP/6-31GÂ(d,p) level on the polymer dimer models, a big torsion
angle is the main reason for breaking the backbone coplanarity and,
consequently, the conjugation and organization. Moreover, a different
transition from the HOMO-2 orbital is responsible for the absorption
shoulder at a short wavelength. After ordinary optimization, the best
power conversion efficiency of 2.3% is achieved with a preferable <i>V</i><sub>oc</sub> of 0.80 V and <i>J</i><sub>sc</sub> of 7.9 mA/cm<sup>2</sup>. Additionally, for holding extended conjugation
from the fused carbazole-like unit and suppressing the strong torsion,
naphthocarbazole (NC) and the counterpart alternative polymer of NC
and DTBT (PNCDTBT) are proposed and simulated, which would be more
planar for better intra- and intermolecular interactions