The formation of pinhole-free perovskite photoactive films with full surface coverage has been a tremendous challenge for up-scaling planar perovskite solar cells (PSCs) while maintaining their high power conversion efficiencies (PCEs). Particularly, a significant mismatch between the surface energies of a hydrophilic perovskite precursor solution and a hydrophobic organic charge transport layer (CTL) has been a major cause for the poor and random surface coverage of perovskite photoactive films, which drastically reduces the scalability and reproducibility of PSCs. Here, we report a universal method to create extremely compact perovskite photoactive films on a variety of hydrophobic CTLs. By introducing an amphiphilic conjugated polyelectrolyte as an interfacial compatibilizer, we succeed in improving the wettability of perovskite precursor solutions on hydrophobic CTLs and fabricating perovskite photoactive films over large areas. Our approach enables the scalable fabrication of planar PSCs with large areas (1 cm2, PCE of 17%) while preserving nearly 90% of the PCEs of the corresponding small-area devices (PCE of 19%).
The fabrication of organic photovoltaic modules via printing techniques has been the greatest challenge for their commercial manufacture. Current module architecture, which is based on a monolithic geometry consisting of serially interconnecting stripe-patterned sub-cells with finite widths, requires highly sophisticated patterning processes that significantly increase the complexity of printing production lines and cause serious reductions in module efficiency due to so-called ‘aperture loss’ in series connection regions. In this study, we demonstrate an innovative module structure that can simultaneously reduce both patterning processes and aperture loss. By using a charge recombination feature that occurs at contacts between electron/hole transport layers, we devise a series connection method that facilitates module fabrication without patterning the charge transport layers. With the successive deposition of component layers using slot-die and doctor-blade printing techniques, we achieve a high module efficiency reaching 7.5% with area of 4.15 cm2.
The integration of planar-type perovskite (Eg ~ 1.5 eV) solar cells (PSCs) with a bulk-heterojunction (BHJ) composite comprising a near-infrared (NIR) absorbing conjugated polymer (Eg < 1.4 eV) and a fullerene derivative is a promising approach to overcoming the narrow absorption limit of typical PSCs. Nevertheless, integrated solar cells (ISCs) suffer from low fill factors (FFs) and inefficient NIR harvesting, mainly due to poor charge transport in the BHJ films. Here, we successfully demonstrate highly efficient P-I-N perovskite/BHJ ISCs with an enhanced FF and improved NIR harvesting by introducing a novel n-type semiconducting polymer and a new processing additive into the BHJ films. The optimized ISCs exhibit a power conversion efficiency (PCE) of 16.36%, which far surpasses that of the reference PSCs (~ 14.70%) due to the increased current density (Jsc ~ 20.04 mA cm-2) resulting from the additional NIR harvesting. Meanwhile, the optimized ISCs maintain a high FF of 77% and an open-circuit voltage (Voc) of 1.06 V. These results indicate that this approach is a versatile means of overcoming the absorption and theoretical efficiency limits of state-ofthe- art PSCs.
We report the fabrication and measurement of solar cells with 6% power conversion efficiency using the alternating copolymer,
poly[N-9''-hepta-decanyl-2,7-carbazole-alt-5,5-(4',7'-di-2-thienyl-2',1',3'-benzothiadiazole), PCDTBT, in
bulk heterojunction (BHJ) composites with the fullerene derivative [6,6]-phenyl C70-butyric acid methyl ester (PC70BM).
The PCDTBT/PC70BM solar cells exhibit the best performance of any BHJ system studied to date; Jsc = 10.6 mA/cm2,
Voc = 0.88 V, FF = 0.66 and ηe = 6.1% under air mass 1.5 global (AM 1.5G) irradiation of 100 mW/cm2. The internal
quantum efficiency (IQE) is close to 100%, implying that essentially every absorbed photon results in a separated pair of
charge carriers and that all photogenerated carriers are collected at the electrodes.
Camphor sulfonic acid doped conducting polyaniline (PANI:CSA) was synthesized by self-stabilized dispersion
polymerization (SSDP). Well ordered polymer chains grow at the interface between aqueous and organic phase at low
temperature around -35 °C. Thus, the growing polymer chains act as a stabilizer, producing high quality polyaniline with
high electrical conductivity and with low content of structural defects. Moreover, the PANI:CSA thin film shows an
apparent Drude peak in the infrared region with a high d.c. conductivity of 550 Scm-1, and a high transmittance in the
visible region. Using this highly conducting polyaniline as a transparent electrode, flexible polymer light-emitting diodes
(PLEDs) and flexible polymer solar cells (PSCs) were fabricated on flexible poly(ethersulfone) (PES) substrates. The
flexible PLEDs show high performance with a luminance of 2300 cdm-2 and a luminous efficiency of 1.6 cdA-1. In
addition, flexible PSCs based on composites of regioregular poly
(3-hexylthiophene) (rr-P3HT) as an electron donor and
phenyl-C61-butyric acid methyl ester (PCBM) as an electron acceptor exhibit a reasonable power conversion efficiency
(PCE) of 1.8 %.
We report on the fabrication and characterization of hybrid polymer light emitting device (HPLEDs) with high
brightness and simplicity in design with improved robustness than the conventional polymer light-emitting diodes. We
demonstrate the incorporation of Au capped inorganic titanium oxide TiO2 nanocomposite in electroluminescent polymer
and fabricated HPLED. We achieved enhanced optical properties of the device and the increased performance of the
HPLED is attributed from the electronic charge transport properties of Au capped metal oxide particles in the
electroluminescence polymer. The interfacial contact area of electroluminescence polymer and cathode increased by the
incorporated nanoparticles in the organic polymer phase thereby improved luminescence properties.
New electroluminescent copolymers with fluoro groups in vinylene unit, poly(9,9-di-hexylfluorene-2,
7-vinylene-co-pphenylenedifluorovinylene)
(PFVPDFV), have been synthesized by the GILCH polymerization. The fluoro groups were
introduced on vinylene units to increase the electron affinities of the copolymers. The PFVPDFVs exhibit absorption
spectra with maximum peaks at 371 ~ 413 nm. In the PL spectra of PFVPDFVs, as the PDFV content increases up to
50% in the copolymer system, fwhm was decreased by 4 - 38 nm as compared to PFV. The HOMO energy levels of the
copolymers were about 5.25 - 5.50 eV, and the LUMO energy levels were about 2.67-2.97 eV. The polymer LEDs
(ITO/PEDOT/polymer/Al) of PFVPDFVs showed emission with maximum peaks at around 472 - 538 nm. By adjusting
the feed ratios of PDFV in the copolymers, it was possible to tune the emission colors from greenish yellow to orange
depending on the obtained CIE coordinates. The luminescence efficiencies of the copolymers at room temperature are
about 0.1-1.47 cd/A. The introduction of up to 50 % of PDFV in PFVPDFVS can enhance the device performance to
result in high current density, brightness and efficiency due to the increased electron injection ability caused by the
presence of fluoro groups in the vinylene units.
PPV derivatives, polymers with vinylene units, have their tendency to exhibit degradation, after irradiation with white
light or operation of the device, resulting in the appearance of a shifted absorption and emission band in the short
wavelength regions of the spectra. In order to reduce oxidation of the vinylene group, the vinylene group was cyclized
using two 5-membered rings. In this paper, we report the synthesis and properties of new copolymers utilizing
poly(5,5,10,10-tetrakis(2-ethylhexyl)-5,10-dihydroindeno[2,1-a]indene-2,7-diyl) (PININE) and benzothiadiazole (BT).
PININE copolymers with BT and thiophene units exhibit high PCE for polymer solar cells (PSCs). Under white light
illumination (AM 1.5 G, 100 mW/cm2), the cell based on PININEDTBT/PCBM as the active layer has a short circuit
current density (Isc) of 5.93 mA/cm2, a fill factor (FF) of 43 %, and PCE of 1.88 %. These copolymers have not only
good processability due to indenoindene unit, in which four alkyl groups can be incorporated, but also the strong and
uniform absorbance in the whole visible region.
New light-emitting PCPP derivatives, poly(4,4-bis{4-[(2-ethylhexyl)oxy]phenyl}-4H-cyclopenta[def]phen- anthrene)
(BEHP-PCPP), with stabilized blue emission is reported. The OLED with the configuration of ITO/PEDOT:PSS/BEHPPCPP/
Ca/Al generates EL emission with maximum peak at 430 nm, low turn-on voltage (9V), and CIE coordinates (x
= 0.19, y = 0.15) for the blue color without any filtering. The maximum brightness of the OLEDs using BEHP-PCPP
was 1034 cd/m2 at 15 V. The maximum luminescence efficiency of the polymer LEDs with BEHP-PCPP was 0.21
cd/A at 617 mA/cm2.
New fluorin-containing electroluminescent polymers in vinylene units, poly(2-dimethyldodecylsilyl-p-phenylenedifluorovinylene)
(DMDS-PPDFV), have been synthesized by GILCH polymerization. This polymer has been used
as the electroluminescent layers in light-emitting diodes (LEDs) (ITO/PEDOT/polymer/Al). DMDS-PPDFV shows
PL around λmax = 455 nm (exciting wavelength, 365 nm) and green EL around λmax =489nm. Attachment of two the
fluoro groups were introduced to poly(2-dimethydodecylsilyl-1,4-phenylenevinylene) (DMDS-PPV) to give DMDSPPDFV
in an attempt to increase the electron affinity of the parent polymer.
New electroluminescent polymer with tetrakis-alkoxy group, poly[2,3,5,6-tetrakis(2-ethylhexyloxy)-1,4-
phenylenevinylene] (TEH-PPV), has been synthesized by the Gilch polymerization. TEH-PPV with tetrakisethylhexyloxy
groups in phenylene unit can get shorter conjugation length than MEH-PPV, and had more blue shifted
absorption and emission peaks due to steric hindrance. Tetrakis-ethylhexyloxy groups induced very conjugated
backbone is twisted. And, they can enhance the internal efficiency of the conjugated polymer as emissive layer in
PLED because of the restraint of inter-chain interaction by the avoidance of close packing to give decent device
performance.
By introducing a titanium oxide (TiOx) layer between the active layer and the aluminum cathode in polymer based
electronic devices, we have demonstrated devices with excellent air stability and with enhanced performance. The TiOx
layer acts as a shielding and scavenging layer which prevents the intrusion of oxygen and humidity into the
electronically active polymers, thereby improving the lifetime of unpackaged devices exposed to air by nearly two orders
of magnitude. We have also fabricated polymer tandem solar cells with a power conversion efficiency of 6.5%, with
each layer processed from solution. A transparent TiOx layer is used to separate and connect the front cell and the back
cell. The TiOx layer serves as an electron transport and collecting layer for the first cell and as a stable foundation that
enables the fabrication of the second cell to complete the tandem cell architecture. We use an inverted structure with the
low band-gap polymer/fullerene composite as the charge separating layer in the front cell and the high band-gap polymer
composite as the charge separating layer in the back cell.
Fluorescent conjugated polymers have attracted much attention due to their potential applications in flat panel displays.
There are few studies on the degradation of the PPV film in air when irradiated. The photodegradation reaction is a chain
scission process involving oxygen in air to yield terminal 4-vinylbenzoic acid groups. The photodegradation of
conducting polymer may seriously effect the performance of electroluminescence devices.
In order to reduce oxidation of the vinylene group, the vinylic group was cyclized using carbon-containing 5-membered
rings. In case of PININE, it is possible to introduce four alkyl groups in the sp3 carbons in the bicycle, which will
increase the solubility of the polymer. PININE was used as the electroluminescence layer for the light-emitting diode.
PININE shows turn-on voltage of 6.5 V, and EL with maximum peak at 477 nm, maximum brightness of 2187 cd/m2 at
12 V, and efficiency of 0.34 cd/A at 162 mA/cm2. The change in luminescence following irradiation with white light on
the PININE was not observed. When irradiated with white light, the films of MEH-PPV showed significantly decreased
peaks of UV and PL. As compared to this, the films of PININE showed stable spectra when irradiated over same period of time.
By introducing a solution-based titanium oxide (TiOx) layer between the polymer and Al electrode in polymer lightemitting
diodes, we have demonstrated that the devices exhibit an enhanced efficiency. The TiOx layer reduces the
barrier height between the polymer and Al cathode, thereby facilitating the electron injection in the devices and
enhancing the device performance by achieving a balance of charge injection and transport between the electrons and
holes. Moreover, we also believe that the TiOx layers prevent the diffusion of metal ions into the emitting polymers
during the Al deposition process, and reduce the degree of quenching centers in the active polymers.
One of the problems limiting the device efficiency of polymer light-emitting diodes is the imbalance of charge injection and transport between the electrons and holes. This problem is particularly serious for the case of aluminum (Al) electrode. By introducing solution-based titanium oxide (TiOx) layer between the polymer and Al electrode, we have demonstrated that the devices exhibit an enhanced efficiency. The TiOx layer reduces the barrier height between the polymer and Al cathode, thereby facilitating the electron injection in the devices and enhancing the device performance. Moreover, we also believe that the TiOx layers prevent the diffusion of metal ions into the emitting polymers during the Al deposition process, reducing the degree of quenching centers in the active polymers.
Polymer field-effect transistors with a field-effect mobility of μ ≈0.3 cm2/V.s have been demonstrated using
regioregular poly(3-hexylthiophene) (rr-P3HT). Devices were fabricated by dip-coating the semiconducting polymer
followed by annealing at 150°C for 10 minutes. The heat annealed devices exhibit an increased field-effect mobility
compared with the as-prepared devices. Morphology studies and analysis of the channel resistance demonstrate that the
annealing process increases the crystallinity of rr-P3HT and improves the contact between the electrodes and the P3HT
films, thereby increasing the field effect mobility of the films. Based on the results obtained from unipolar FETs using rr-
P3HT, we have also applied postproduction heat treatment to ambipolar polymer FETs fabricated with rr-P3HT and C61-
butyric acid methyl ester (PCBM). Devices were fabricated using aluminum (Al) source and drain electrodes to achieve
an equivalent injection for the both holes and electrons. As the case of P3HT unipolar FETs, the thermal annealing
method also improves the film morphology, crystallinity, and the contact properties between Al and active layer, thereby
resulting in excellent ambipolar characteristics with the hole mobility of 1.7×10-3 cm2/V.s and the electron mobility of
2.0×10-3 cm2/V.s.
New architectural polymer photovoltaic cells approaching 5% power conversion efficiency have been fabricated using titanium oxide (TiOx) as an optical spacer. Solar cells with a TiOx layer (deposited by a sol-gel process) between the active layer and the electron collecting aluminum electrode exhibit approximately 50% enhancement in power conversion efficiency compared to similar devices without the optical spacer. The TiOx layer increases the efficiency by modifying the spatial distribution of the light intensity inside the device, thereby creating more photogenerated charge carriers in the bulk heterojunction layer.
One of the serious problems in polymer light-emitting diodes (PLEDs) is the difficulty of electron injection in the current PLEDs device of anode/polymer/cathode geometry. This is particularly true for the case of aluminum (Al) electrode. The work function of Al is too high to match with the Lowest Unoccupied Molecular Orbit (LUMO) level of the luminescent polymers, thereby lowering the device efficiency. In this work, by introducing solution-based titanium oxide (TiOx) thin film as an electron injection layer between the polymer and Al electrode, we demonstrate that the devices exhibit an enhanced efficiency. The TiOx layer reduces the barrier height between the polymer and aluminum (Al) cathode, thereby facilitating the electron injection in the devices.
Conjugated polymers with a stabilized blue emission are of importance for the realization of full-color displays using polymer light-emitting diodes. We report a new class of blue-emitting polymers utilizing a new back-bone, poly(2,6-(4,4-bis(2-ethylhexyl)-4H-cyclopenta [def] phenanthrene)) (PCPP). This material emits a stabilized, efficient blueelectroluminescence(EL) without exhibiting any peak in the long wavelength region (green region) even after prolonged annealing for 18 hours at an elevated temperature of 150°C in air. This attributes to the chemical structure of this new polymer. The backbone of PCPP intrinsically inhibits the formation of the keto-defects mainly responsible for the degradation to green color in typical poly(fluorine) type materials, thereby stabilizing the blue EL emission in the devices.
By applying the specific fabrication conditions such as postproduction annealing at 150oC for 30 minutes, polymer solar cells with 5% power conversion efficiency are demonstrated. These devices exhibit remarkable thermal stability. We attribute the improved performance to changes in the bulk heterojunction material induced by thermal annealing. The improved nanoscale morphology, the increased crystallinity of the semiconducting polymer, and the improved contact to the electron collecting electrode facilitate charge generation, charge transport to, and charge collection at the electrodes, thereby enhancing the device efficiency by lowering the series resistance of the polymer solar cells. Also new architectural polymer solar cells with 5% power conversion efficiency have been fabricated using titanium oxide (TiOx) as an optical spacer. Solar cells with a TiOx layer (deposited by a sol-gel process) between the active layer and the electron collecting aluminum electrode exhibit approximately 50% enhancement in power conversion efficiency compared to similar devices without the optical spacer. The TiOx layer increases the efficiency by modifying the spatial distribution of the light intensity inside the device, thereby creating more photogenerated charge carriers in the bulk heterojunction layer.
We fabricated polymer-fullerene photovoltaic (PV) devices using various conjugated polymers, poly[2-methoxy-5-(2’-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV), poly{2-[4-(3,7-dimethyloctyloxy)-phenoxy]-1,4-phenylenevinyl-ene} (p-DMOP-PPV), and their copolymer system, p-DMOP-co-MEH-PPV. By comparing PV characteristics of such devices with a systematic change of the energy levels (ionization potential Ip and electron affinity Ea), we investigated the origin of open circuit voltage (Voc) of the devices. Our results indicate that the magnitude of Voc is governed by the difference between Ea of the fullerene and Ip of the polymer, which is not consistent with previous consideration of the work function difference between electrodes as in conventional metal-insulator-metal type devices.
We present experimental evidence that orientation of the polymer chains in semiconducting polymer films leads to lower thresholds for gain narrowing. Two different materials have been investigated: neat films of poly(p-phenylene vinylene) (PPV) and blends of poly(2-methoxy-5-(2'- ethyl-hexyloxy)-1-4-phenylenevinylene) (MEH-PPV) in polyethylene (PE). Gain narrowing is not observed in non- oriented films in either of the two materials. However, free-standing films of PPV drawn to a ratio of (7:1) showed gain narrowing at threshold one order of magnitude lower than typically found for non-oriented films of soluble PPV derivatives. For the MEH-PPV blends, gain narrowing is observed in diluted films with concentrations of the active polymer of approximately 1 percent. The thresholds for these dilute, but chain extended and highly oriented free standing films are comparable to those obtained in neat thin film waveguides of the same material. These result are correlated with the microstructure of the films, as investigated by x- ray diffraction.
We report steady-state photoinduced absorption (PIA) and photoinduced reflectance (PIR) in films of MEH-PPV and BCHA- PPV blended with fullerene-based acceptors. Absorption from the metastable charge-transferred state is probed by PIA; the modulated absorption spectrum causes changes in the real part of the index of refraction, (Delta) n, which can be measured directly by PIR. The charge transfer gives rise to pronounced features in (Delta) n, including vibrational structure in the mid- and near-IR. Our measurements over a wide spectral range allow quantitative comparison of (Delta) n obtained from PIR with that obtained from Kramers- Kronig transformation of the PIA data. We find good agreement throughout the IR, indicating that our method for measuring (Delta) n is useful as an analytical tool for optical characterization and for prediction of optical spectral ranges for nonlinear optical response.
We report photoinduced absorption and photoinduced reflectance spectra of poly(3-octyl thiophene)- methanofullerene films. The data allow direct evaluation of the corresponding changes in the complex refractive index, (Delta) N equals (Delta) n((omega) )+i(Delta) (kappa) ((omega) ), of the films. As a results of the efficient photoinduced intermolecular charge transfer, the magnitudes of (Delta) n((omega) ) and (Delta) (kappa) ((omega) ) are significantly enhanced over those in either of the component materials, with (Delta) n and (Delta) (kappa) approximately equals 10-2 in the infrared at laser pump intensity of only 50mW/cm2. Moreover, the photoinduced absorption shows new features at 1.2 eV and 1.6 eV, both of which are associated with excited state absorptions of the methanofullerene anion. The implications of these photoinduced changes in the index resulting from photoexcitations are discussed in terms of potential optoelectronic and nonlinear optical applications of these materials, indicating that conducting polymer/methanofullerene films are promising as high- performance nonlinear optical materials.
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