11 research outputs found
Quaternary Organic Solar Cells Enhanced by Cocrystalline Squaraines with Power Conversion Efficiencies >10%
The incorporation of multiple donors into the bulk-heterojunction layer of organic polymer solar cells (PSCs) has been demonstrated as a practical and elegant strategy to improve photovoltaics performance. However, it is challenging to successfully design and blend multiple donors, while minimizing unfavorable interactions (e.g., morphological traps, recombination centers, etc.). Here, a new Förster resonance energy transfer-based design is shown utilizing the synergistic nature of three light active donors (two small molecules and a high-performance donorâacceptor polymer) with a fullerene acceptor to create highly efficient quaternary PSCs with power conversion efficiencies (PCEs) of up to 10.7%. Within this quaternary architecture, it is revealed that the addition of small molecules in low concentrations broadens the absorption bandwidth, induces cocrystalline molecular conformations, and promotes rapid (picosecond) energy transfer processes. These results provide guidance for the design of multiple-donor systems using simple processing techniques to realize single-junction PSC designs with unprecedented PCEs
Quaternary Organic Solar Cells Enhanced by Cocrystalline Squaraines with Power Conversion Efficiencies >10%
The incorporation of multiple donors into the bulk-heterojunction layer of organic polymer solar cells (PSCs) has been demonstrated as a practical and elegant strategy to improve photovoltaics performance. However, it is challenging to successfully design and blend multiple donors, while minimizing unfavorable interactions (e.g., morphological traps, recombination centers, etc.). Here, a new Förster resonance energy transfer-based design is shown utilizing the synergistic nature of three light active donors (two small molecules and a high-performance donorâacceptor polymer) with a fullerene acceptor to create highly efficient quaternary PSCs with power conversion efficiencies (PCEs) of up to 10.7%. Within this quaternary architecture, it is revealed that the addition of small molecules in low concentrations broadens the absorption bandwidth, induces cocrystalline molecular conformations, and promotes rapid (picosecond) energy transfer processes. These results provide guidance for the design of multiple-donor systems using simple processing techniques to realize single-junction PSC designs with unprecedented PCEs
Ultrathin Nanotube/Nanowire Electrodes by SpinâSpray Layer-by-Layer Assembly: A Concept for Transparent Energy Storage
A Mesoporous Catalytic Membrane Architecture for LithiumâOxygen Battery Systems
Controlling
the mesoscale geometric configuration of catalysts
on the oxygen electrode is an effective strategy to achieve high reversibility
and efficiency in Li-O<sub>2</sub> batteries. Here we introduce a
new Li-O<sub>2</sub> cell architecture that employs a catalytic polymer-based
membrane between the oxygen electrode and the separator. The catalytic
membrane was prepared by immobilization of Pd nanoparticles on a polyacrylonitrile
(PAN) nanofiber membrane and is adjacent to a carbon nanotube electrode
loaded with Ru nanoparticles. During oxide product formation, the
insulating PAN polymer scaffold restricts direct electron transfer
to the Pd catalyst particles and prevents the direct blockage of Pd
catalytic sites. The modified Li-O<sub>2</sub> battery with a catalytic
membrane showed a stable cyclability for 60 cycles with a capacity
of 1000 mAh/g and a reduced degree of polarization (âŒ0.3 V)
compared to cells without a catalytic membrane. We demonstrate the
effects of a catalytic membrane on the reaction characteristics associated
with morphological and structural features of the discharge products
via detailed ex situ characterization
Toward Efficient Thick Active PTB7 Photovoltaic Layers Using Diphenyl Ether as a Solvent Additive
The development of
thick organic photovoltaics (OPV) could increase absorption in the
active layer and ease manufacturing constraints in large-scale solar
panel production. However, the efficiencies of most low-bandgap OPVs
decrease substantially when the active layers exceed âŒ100 nm
in thickness (because of low crystallinity and a short exciton diffusion
length). Herein, we report the use of solvent additive diphenyl ether
(DPE) that facilitates the fabrication of thick (180 nm) active layers
and triples the power conversion efficiency (PCE) of conventional
thienothiophene-<i>co</i>-benzodithiophene polymer (PTB7)-based
OPVs from 1.75 to 6.19%. These results demonstrate a PCE 20% higher
than those of conventional (PTB7)-based OPV devices using 1,8-diiodooctane.
Morphology studies reveal that DPE promotes the formation of nanofibrillar
networks and ordered packing of PTB7 in the active layer that facilitate
charge transport over longer distances. We further demonstrate that
DPE improves the fill factor and photocurrent collection by enhancing
the overall optical absorption, reducing the series resistance, and
suppressing bimolecular recombination
Ultrathin Nanotube/Nanowire Electrodes by SpinâSpray Layer-by-Layer Assembly: A Concept for Transparent Energy Storage
Fully integrated transparent devices require versatile architectures for energy storage, yet typical battery electrodes are thick (20â100 ÎŒm) and composed of optically absorbent materials. Reducing the length scale of active materials, assembling them with a controllable method and minimizing electrode thickness should bring transparent batteries closer to reality. In this work, the rapid and controllable spinâspray layer-by-layer (SSLbL) method is used to generate high quality networks of 1D nanomaterials: single-walled carbon nanotubes (SWNT) and vanadium pentoxide (V<sub>2</sub>O<sub>5</sub>) nanowires for anode and cathode electrodes, respectively. These ultrathin films, deposited with âŒ2 nm/bilayer precision are transparent when deposited on a transparent substrate (>87% transmittance) and electrochemically active in Li-ion cells. SSLbL-assembled ultrathin SWNT anodes and V<sub>2</sub>O<sub>5</sub> cathodes exhibit reversible lithiation capacities of 23 and 7 ÎŒAh/cm<sup>2</sup>, respectively at a current density of 5 ÎŒA/cm<sup>2</sup>. When these electrodes are combined in a full cell, they retain âŒ5 ÎŒAh/cm<sup>2</sup> capacity over 100 cycles, equivalent to the prelithiation capacity of the limiting V<sub>2</sub>O<sub>5</sub> cathode. The SSLbL technique employed here to generate functional thin films is uniquely suited to the generation of transparent electrodes and offers a compelling path to realize the potential of fully integrated transparent devices
Coevaporated Bisquaraine Inverted Solar Cells: Enhancement Due to Energy Transfer and Open Circuit Voltage Control
There is currently enormous interest
in the development of small
molecule organic solar cells (SMSC), as in principle, these systems
offer advantages over both conventional Si photovoltaics and organic
polymer solar cells. Here, we report FoÌrster Resonance Energy
Transfer (FRET) enhanced inverted SMSC fabricated by coevaporating
two different squaraine donors, a symmetrical squaraine (SQ, 2,4-bis-4-[(<i>N</i>,<i>N</i>-diisobutylamino)-2,6-dihydroxyphenyl]
squaraine), and an asymmetrical squaraine (ASSQ, 2,4-bis-[(<i>N</i>,<i>N</i>-diisobutylamino)-2,6-dihydroxyphenyl]-4-(4-diphenyliminio)
squaraine). ASSQ absorbs blue light (λ<sub>max</sub> 540 nm)
and emits from 550 nm to the near-infrared region, which overlaps
with SQ absorption (λ<sub>max</sub> 690 nm). Therefore, by utilizing
a thin film containing the two squaraine donors as the active layer
in a SMSC, we can both broaden the photovoltaic absorption spectrum,
and reduce recombination loss as a result of FRET. This strategy has
resulted in SMSC with power conversion efficiencies (PCE) which are
up to 46% greater than those obtained by using a single squaraine
donor. Ultrafast time-resolved photoluminescence and transient absorption
spectroscopy provide clear evidence of FRET between the small molecules,
with a rapid energy transfer time of âŒ1 ps. At optimal blending,
which correlates to the highest PCE measured, the efficiency of energy
transfer is as high as 85%. Furthermore, in the devices containing
two different squaraine molecules, the open circuit voltage (<i>V</i><sub>OC</sub>) is proportional to the fraction of the two
donors in the blend, allowing us to predict the <i>V</i><sub>OC</sub> as the ratio of the two donors is changed. SMSC with
inverted structures also demonstrate long-term stability in ambient
conditions compared to devices employing a conventional architecture
PEOz-PEDOT:PSS Composite Layer: A Route to Suppressed Hysteresis and Enhanced Open-Circuit Voltage in a Planar Perovskite Solar Cell
The
successful commercialization of perovskite solar cells (Pvs-SCs)
calls for the need to find low-temperature processable interlayers
with outstanding charge-transport features. In this work, we strategically
blend polyÂ(2-ethyl-2-oxazoline) (PEOz) with PEDOT:PSS as the modified
hole transport layer (HTL) to achieve high-efficiency PâIâN
CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub> Pvs-SCs. The PEOz-PEDOT:PSS
HTL exhibits enhanced features over the conventional layer including
the following: (1) promoting perovskite with enlarged grain sizes
to decrease the perovskite layerâs recombination, (2) increasing
the work function of the HTL, and (3) decreasing the noncapacitive
current in Pvs-SCs. Remarkably, we demonstrate a 17.39% power conversion
efficiency with very low hysteresis and high <i>V</i><sub>oc</sub> values of 1.075 V for Pvs-SCs with PEOz-PEDOT:PSS
Underwater Organic Solar Cells via Selective Removal of Electron Acceptors near the Top Electrode
Electron acceptor degradation of organic solar cells is considered a main contributor to performance instability and a barrier for the commercialization of organic solar cells. Here, we selectively remove the electron acceptors on the surface of donor:acceptor blend films using a tape stripping technique. The near-edge X-ray absorption fine structure (NEXAFS) spectrum reveals that only 6% of the acceptor component is left on the blend film surface after the tape stripping, creating a polymer-rich surface. The optimized morphology avoids direct contact of electron acceptors with the oxygen and water molecules from the film surface. Moreover, the polymer-rich surface dramatically enhances the adhesion between the photoactive layer and the top metal electrode, which prevents delamination of the electrode. Our results finally demonstrate that the selective removal of electron acceptors near the top electrode facilitates the realization of highly durable organic solar cells that can even function under water without encapsulation