High-efficiency Polymer Research Articles

High-Efficiency Polymer:Nonfullerene Solar Cells with Quaterthiophene-Containing Polyimide Interlayers.

Interfacial layers (interlayers) are one of the emerging approaches in organic solar cells with bulk heterojunction (BHJ) layers because the solar cell efficiency can be additionally improved by their presence. However, less attention is paid to the use of interlayers for polymer:nonfullerene solar cells, which have strong advantages over polymer:fullerene solar cells. In addition, most polymers used for the interlayers possess a low glass transition temperature (T g). Here, it is demonstrated that two types of quarterthiophene‐containing polyimides (PIs) with high T g (>198 °C), which are synthesized using pyromellitic dianhydride (PMDA) and cyclobutane‐1,2,3,4‐tetracarboxylic dianhydride (CTCDA), can act as an interfacial layer in the polymer:nonfullerene solar cells with the BHJ layers of poly[(2,6‐(4,8‐bis(5‐(2‐ethylhexyl)thiophen‐2‐yl)‐benzo[1,2‐b:4,5‐b′]dithiophene))‐alt‐(5,5‐(1′,3′‐di‐2‐thienyl‐5′,7′‐bis(2‐ethylhexyl)benzo[1′,2′‐c:4′,5′‐c′]dithiophene‐4,8‐dione))] (PBDB‐T) and 3,9‐bis(2‐methylene(3‐(1,1‐dicyanomethylene)‐indanone))‐5,5,11,11‐tetrakis(4‐hexylphenyl)‐dithieno[2,3‐d:2′,3′‐d′]‐s‐indaceno[1,2‐b:5,6‐b′]dithiophene) (ITIC), or (3‐(1,1‐dicyanomethylene)‐1‐methyl‐indanone)‐5,5,11,11‐tetrakis(4‐hexylphenyl)‐dithieno[2,3‐d:2′,3′‐d′]‐s‐indaceno[1,2‐b:5,6‐b′]‐dithiophene) (IT‐M). Interestingly, the efficiency and stability of devices are improved by the PMDA‐based PI interlayers with a stretched chain structure but degraded by the CTCDA‐based PI interlayers with a bended chain structure.

3D printing individualized triboelectric nanogenerator with macro-pattern

Triboelectric nanogenerator (TENG) is one of the most attractive candidates for providing a green energy source capable of satisfying the world's energy consumption. 3D printing is a promising route to satisfy the demands of various self-powered devices with individualized design in practical applications such as signal processing, precisely tuning circuits, active sensor networks, remote controls, and flexible electronics. This work reports an approach of fused deposition modeling (FDM), one of 3D printing methods, which enables the creation of optimized digital designs for TENG devices for the purpose of efficiently harvesting ambient vibration energy. To obtain satisfying output power and high mechanical energy conversion efficiency, various positive and negative polymers were chosen as friction layers, such as polylactic acid (PLA), nylon (PA), a mixture of polypropylene and polyethylene (PP/PE), and poly(ethylene terephthalateco-1,4-cylclohexylenedimethylene terephthalate) (PETG). By increasing the vibrational frequency from 5 Hz to 20 Hz, the output voltage of the TENG device increased from 50 V to 241 V in a TENG device using nylon (PA) and a mixture of polypropylene and polyethylene (PP/PE). The TENG device had a 0° contact angle between the two films, which also had some macroscopic patterns on their surfaces. Simultaneously, a decrease in the filling rate (from 100% to 20%) and thickness (from 0.4 to 0.2 mm) resulted in an increase in the output voltage from 57 V to 176 V and from 50 V to 241 V, respectively. To better understand the effects of the printing parameters on the output performance, we studied the factors of the filling rate, thickness, contact angle and the width of the zigzag pattern. From these results, we conclude that 3D printing based on the FDM strategy to fabricate TENG outstandingly improves the output performance by decreasing the effective Young's modulus. Additionally, the peak of the current reaches 1.52 mA in ultrashort time. The triboelectrification efficiency in this vertical contact-separation mode reaches 63.9%. Our concept of 3D printing based on FDM will stimulate further fundamental work in fabricating approaches to harvesting environmental energy.

Effect of Fluorination on the Photovoltaic Properties of Medium Bandgap Polymers for Polymer Solar Cells

AbstractFluorination of conjugated polymers is one of the effective strategies to tune the molecular energy levels and morphology for high efficient polymer solar cells (PSCs). Herein, two novel donor‐acceptor conjugated polymers, PffBT and PBT, based on bis(3,5‐bis(hexyloxy)phenyl)benzo[1,2‐ b:4,5‐b']dithiophene and benzo[c][1,2,5]thiadiazole (BT) with or without fluorination, respectively, were synthesized, and their photovoltaic properties were compared. The polymer PffBT based on fluorinated BT showed lower frontier energy levels, improved polymer ordering, and a well‐developed fibril structure in the blend with PC71BM. As a result, the PSCs based on PffBT/PC71BM exhibit a superior power conversion efficiency (PCE) of 8.6% versus 4.4% for PBT‐based devices, due to a high space charge limit current (SCLC) hole mobility, mixed orientation of polymer crystals in the active layer, and low bimolecular recombination.

High-Efficiency Polymer Solar Cells by Using Co-solvents 1-Chloronaphthalene and 1,8-Octanedithiol as Processing Additives

The copolymer poly-BDT-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione (PC20BDTDPP) with the bulkier alkoxy on BDT and alkyl on DPP is widely used in organic photovoltaic cells as a potential donor material. Power conversion efficiency (PCE) of polymer solar cells fabricated withPC20BDTDPP as the electron donor blended with [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) as the electron acceptor was improved from 4.90% to 9.10% by adding 1–5% of the co-solvents (1-chloronaphthalene and 1,8-octanedithiol) as processing additives. The enhanced PCE was attributed to optimized surface morphology and packed polymer chains leading to better phase separation morphology by the solvent additive. Furthermore, owing to its very narrow band gap, the synthesized polymer demonstrates a great potential for tandem or parallel-like solar cells.

Crystalline defect formation on aluminum bond pads during CMOS wafer storage and process strategies for defect elimination

Crystalline aluminum fluoride defects were observed on aluminum bond pads of wafers from a complementary metal oxide semiconductor process in a wafer fab after less than a month of storage. These defects were formed by reaction of moisture in the front opening unified pod wafer storage container with residual bond pad sidewall fluorocarbon etch polymer releasing gaseous HF which further reacted with nucleation sites on the bond pad aluminum surface, resulting in crystalline aluminum fluoride defects. Elimination of the residual bond pad fluorocarbon polymer using a polymer free etch process or high-efficiency postetch polymer solvent strip resulted in a significant improvement in crystalline defect-free storage time (6 months). However, 12 month storage of sidewall polymer-free wafers showed reappearance of crystalline aluminum fluoride defects. The fluorine source contributing to the appearance of long-term aluminum fluoride crystalline defects was surface fluorine in the top 50 Ǻ of the aluminum bond pad. Lowering the surface fluorine levels from 3%–4% to 1.5% (by Auger electron spectroscopy) resulted in up to 36 months defect-free wafer storage. Incorporating O2/H2 plasma resist strip and high-temperature polymer solvent strip into postetch processing were found to be effective surface fluorine reducing process strategies.

Facile Synthesis of the O-Functionalized Ladder-Type Dipyran Building Block and Its Application in Polymer Solar Cells.

A new centrosymmetrical dipyran unit (DTDP) is successfully prepared by means of an efficient and universal way, and a series of PDTDP polymers have been prepared so as to assess their potential application in organic photovoltaic. The function of pyran moiety is not merely limited to tune the electron-donating roles and energy levels but it also contributes to solubility improvement. Interestingly, all pyran-based polymers displayed wide absorption ranging from 350 to 780 nm, but varied aggregation phenomena are observed. Furthermore, the quantum chemistry calculations for dimers, morphology study and grazing-incidence wide-angle X-ray scattering analysis for blend films have been utilized to understand the variations at photovoltaic performances. Finally, PDTDP-4 achieved the highest power conversion efficiency of 7.26% ( Voc = 0.72 V, FF = 0.66, and Jsc = 15.30 mA/cm2), demonstrating promising usage for high-efficiency polymer donors in polymer solar cells. In all, not only a promising dipyran building block is provided by this study, more dipyran derivatives and polymers could be prepared via this facile synthetic route.

Enhancement of uranium recovery from seawater using amidoximated polymer gel synthesized from radiation-polymerization and crosslinking of acrylonitrile and methacrylic acid monomers

The amidoximated polymer gel for uranium recovery from natural seawater was successfully synthesized from radiation-polymerization and crosslinking of acrylonitrile (AN) and methacrylic acid (MAA) monomers with N,N’-Methylene bisacrylamide (MBA) as the crosslink agent. The optimum condition to prepare the polymer gel is: the gamma ray dose of 40 kGy, the AN:MAA ratio of 80:20, and the crosslink agent concentration of 8 g/L. The polymer gel can be reused for at least 8 times without significant performance decrease. The kinetic of seawater absorption by the adsorbent was quite rapid, reaching the equilibrium swelling ratio of approximately 250% in about 30 min. By submersion of this polymer gel in the seawater sample with only 300 and 840 ppb of added uranium for 4 weeks, the adsorption capacity reached as much as 6.96 and 9.64 mg/g, respectively. By submersion of this polymer gel in the seawater sample with 30 and 2140 ppm of added uranium for 1 week, the adsorption capacity reached as much as 334 and 409 mg/g, respectively. This high-efficiency amidoxime polymer gel offers a possibility of being utilized as a seawater uranium recovery agent on an industrial scale. Suitable elution conditions to minimize mass loss as well as suitable locations with clear seawater and no algae growth will need to be identified. Moreover, the research outcome presents a novel environmental remediation process to adsorb uranium ions released into seawater following a nuclear accident.

Controlling Molecular Conformation for Highly Efficient and Stable Deep-Blue Copolymer Light-Emitting Diodes.

We report a novel approach to achievedeep-blue, high-efficiency, and long-lived solution-processed polymer light-emitting diodes (PLEDs) via a simple molecular level conformation change of an emissive conjugated polymer.We introduce rigid β-phase segments into a 95% fluorene-5% arylamine copolymer emissive layer. The arylamine moieties at low density act as efficient exciton formation sites in PLEDs, whereas the conformational change alters the nature of the dominant luminescence from a broad, charge transfer like emission to a significantly blue-shifted and highly vibronically structured excitonic emission. As a consequence, we observe a significant improvement in the Commission International de L'Eclairage ( x, y) coordinates from (0.149, 0.175) to (0.145, 0.123) while maintaining high efficiency and improved stability. We achieve a peak luminous efficiency, η = 3.60 cd/A, and a luminous power efficiency, ηw = 2.44 lm/W, values that represent state-of-the-art performance for single copolymer deep-blue PLEDs. These values are 5-fold better than for otherwise-equivalent, β-phase poly(9,9-dioctylfluorene) PLEDs (0.70 cd/A and 0.38 lm/W). This report represents the first demonstration of the use of molecular conformation as a simple but effective method to control the optoelectronic properties of a fluorene copolymer; previous examples have been confined to homopolymers.

Tetraphenylphosphonium Bromide as a Cathode Buffer Layer Material for Highly Efficient Polymer Solar Cells.

Here, we introduced the role of small organic molecule tetraphenylphosphonium bromide (QPhPBr) as an electron-transporting layer (ETL) material for fabricating high-efficiency bulk heterojunction polymer solar cells (PSCs). Their significantly higher power conversion efficiency (PCE) in well-known active layer devices (PTB7-Th:PC71BM, PBDTTT-CT:PC71BM, and P3HT:PC71BM) was observed compared to that of the bare Al cathode. The use of N719 as an ETL was also demonstrated. Observed data reveal that QPhPBr-based devices exhibit high PCEs up to 9.18, 8.42, and 4.81% from PTB7-Th, PBDTTT-CT, and P3HT, respectively. For comparisons, the bare Al devices show PCEs of 5.37, 4.75, and 3.01%, respectively. Moreover, further enhancement of PSC efficiency (9.83, 8.69, and 5.35%) is achieved from mixed binary solution of N719:QPhPBr because of modulated adjustment of the work function of the Al electrode. Our results indicate the excellent function of tetraphenylphosphonium bromide and its binary blend as effective small-molecule organic materials to regulate the metal surface properties and the potential used as excellent cathode buffer layer materials for realizing high-efficiency PSCs.

Properties and mechanisms of iodine doped of P3HT and P3HT/PCBM composites

Polymeric conjugated materials are very promising for developing future soft material based semiconductors, conductors, electronic and optoelectronic devices due to their inherent advantages such as lightweight, flexible shape, low-cost, ease of processability, ease of scalability, etc. Like their inorganic counterparts, the addition of certain minority molecules or dopants can significantly alter the electronic and optoelectronic properties of the host conjugated polymers or composites allowing tunablilty for a variety of electronic/optoelectronic applications. In this report, P3HT and P3HT:PCBM doped with various iodine concentrations or doping levels were systematically examined for potential electronic/optoelectronic properties. This study finds that a 5% mole ratio iodine doping resulting in a smallest P3HT inter-layer gap of about 6.5 nm in the P3HT edge-on main chain packing style as well as smallest exciton bandwidth and most intense or ordered H-style aggregates, which may account for an optimal electronic/optoelectronic performance of the 5% doped P3HT/PCBM device. The results and findings could be useful to understand and to guide the design and development of future generation high efficiency molecular or polymer based optoelectronic devices, including solar cells and photodetectors.

Low Cost and High Efficiency Polymer Donor Photovoltaic Materials for Polymer Solar Cells

Low Cost and High Efficiency Polymer Donor Photovoltaic Materials for Polymer Solar Cells

Cyanovinylene-based copolymers synthesized by tin-free Knoevenagel polycondensation for high efficiency polymer solar cells

Cyanovinylene-based copolymers were synthesized by a green, environmentally friendly, and tin-free Knoevenagel polycondensation and used in OPV devices as a donor material. A PCE of 8.54% was obtained with the device based on PdC8ThDT:ITIC.

Atomic-layer-deposited AZO outperforms ITO in high-efficiency polymer solar cells

An aluminum doped zinc oxide electrode grown by atomic layer deposition for polymer solar cells outperforms ITO in high performance PSCs.

Noncovalent phosphorylation of graphene oxide with improved hole transport in high-efficiency polymer solar cells.

Graphene oxide (GO) has been extensively applied as an alternative hole transport layer (HTL) of bulk heterojunction polymer solar cells (BHJ-PSCs) with the function of selectively transporting holes and blocking electrons, but suffers from low electrical conductivity. Herein, using phosphorus pentoxide (P2O5) dissolved in methanol as a precursor, we successfully modified GO via noncovalent phosphorylation for the first time, which showed improved hole transport in BHJ-PSCs compared to the pristine GO. As a result, BHJ-PSC devices based on noncovalently phosphorylated GO (P-GO) HTL show dramatically higher power conversion efficiencies (7.90%, 6.59%, 3.85% for PTB7:PC71BM, PBDTTT-C:PC71BM, P3HT:PC61BM, respectively) than those of the corresponding control devices based on the pristine GO HTL (6.28%, 5.07%, 2.78%), which are comparable to those of devices based on the most widely used HTL-poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS).

High-efficiency polymer solar cells with low temperature solution-processed SnO2/PFN as a dual-function electron transporting layer

SnO2/PFN integrated the function of enhanced electron extraction and reduced charge recombination, exhibiting an efficiency of 11.05%.

Synthesis and Photovoltaic Properties of a Copolymer based on thieno [2, 3-f] benzofuran and thienopyrroledione

A novel donor-acceptor type conjugated polymer PTBFTPD based on two-dimensional (2D) conjugated alkylthienyl substituted thieno[2,3-f]benzofuran (TBF) and thienopyrroledione (TPD) unit, was synthesized and applied as donor material for bulk heterojunction solar cells. The novol polymer possesses a narrow bandgap of 1.83 eV, a deep HOMO energy level (-5.64 eV) and a closer π−π stacking. After conventional devices were fabricated using PTBFTPD as donor blending with PC70BM as acceptor, a power conversion efficiency (PCE) of 4.33% with a high open circuit voltage (Voc) of 1.09 V was obtained. The result indicates the promising potential of thieno [2, 3-f] benzofuran unit for high efficient polymer solar cells with a high voltage.

Achieving over 9.8% Efficiency in Nonfullerene Polymer Solar Cells by Environmentally Friendly Solvent Processing

Nowadays, most of the solution-processed high-efficiency polymer solar cell (PSC) devices are fabricated by halogenated solvents (such as chlorobenzene, 1,2-dichlorobenzene, chloroform, etc.) which are harmful to people and the environment. Therefore, it is essential to develop high-efficiency PSC devices processed by environmentally friendly solvent processing for their industrialization. In this regard, we report a new alkylthio chain-based conjugated polymer PBDB-TS as donor material for environmentally friendly solvent-processed PSCs. PBDB-TS possesses a low-lying HOMO energy level at -5.42 eV and a good solubility in toluene and o-xylene. By using o-xylene and 1% N-methylpyrrolidone as processing solvent, following by the thermal annealing treatment for PBDB-TS:ITIC blend films, well-developed morphological features, and balanced charge transport properties are observed, leading to a high power conversion efficiency (PCE) of 9.85%, higher than that of the device cast from halogenated solvent (PCE = 9.65%). The results suggest that PBDB-TS is an attractive donor material for nonhalogen solvents-processing PSCs.

Toward High Efficiency Polymer Solar Cells: Rearranging the Backbone Units into a Readily Accessible Random Tetrapolymer

AbstractTwo donor–acceptor (D–A) conjugated polymers composed of the same ratio of 5‐fluorobenzothiadiazole and thiophene subunits are synthesized through different routes, providing a precisely regioregular (2TRR) and a random (2TRA) polymer structures. Detailed structural analyses indicate that the backbone of regioregular 2TRR has only one donor segment of bithiophene, while the backbone of random 2TRA consists of three different donor segments: thiophene, bithiophene, and terthiophene (in a ratio of 0.16:0.68:0.16). Synergetic contributions from these segments allow the “tetrapolymer” 2TRA to achieve more favorable film morphology and a higher hole‐mobility relative to 2TRR. Consequently, the random polymer 2TRA achieves a substantially higher power conversion efficiency (8.8%) than the regioregular polymer 2TRR (5.1%). Notably, the “tetrapolymer” 2TRA is readily synthesized from two monomers, rather than through complex conventional preparation required for similar multipolymers. These findings provide a novel route toward the design and synthesis of multipolymeric materials and demonstrate their potential advantages in high‐performance organic electronic applications.

Side Chain Engineering on Medium Bandgap Copolymers to Suppress Triplet Formation for High-Efficiency Polymer Solar Cells.

Suppression of carrier recombination is critically important in realizing high-efficiency polymer solar cells. Herein, it is demonstrated difluoro-substitution of thiophene conjugated side chain on donor polymer can suppress triplet formation for reducing carrier recombination. A new medium bandgap 2D-conjugated D-A copolymer J91 is designed and synthesized with bi(alkyl-difluorothienyl)-benzodithiophene as donor unit and fluorobenzotriazole as acceptor unit, for taking the advantages of the synergistic fluorination on the backbone and thiophene side chain. J91 demonstrates enhanced absorption, low-lying highest occupied molecular orbital energy level, and higher hole mobility, in comparison with its control polymer J52 without fluorination on the thiophene side chains. The transient absorption spectra indicate that J91 can suppress the triplet formation in its blend film with n-type organic semiconductor acceptor m-ITIC (3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone)-5,5,11,11-tetrakis(3-hexylphenyl)-dithieno[2,3-d:2,3'-d']-s-indaceno[1,2-b:5,6-b']-dithiophene). With these favorable properties, a higher power conversion efficiency of 11.63% with high VOC of 0.984 V and high JSC of 18.03 mA cm-2 is obtained for the polymer solar cells based on J91/m-ITIC with thermal annealing. The improved photovoltaic performance by thermal annealing is explained from the morphology change upon thermal annealing as revealed by photoinduced force microscopy. The results indicate that side chain engineering can provide a new solution to suppress carrier recombination toward high efficiency, thus deserves further attention.

Efficient Blue, Green, and Red Electroluminescence from Carbazole-Functionalized Poly(spirobifluorene)s

Based on a carbazole-functionalized polyspirobifluorene with high fluorescence quantum yield and deep-blue emission, a series of blue-, green-, and red-emitting polymers have been successfully developed by independently incorporating dibenzothiophene-S,S-dioxide (3,7SO), 4,7-diphenylbenzothiadiazole (DPBT), and 4,7-dithienylbenzothiadiazole (DTBT) as the copolymerized units to tune the emission color in the whole visible region. The effect of their loadings on the electrochemical, photophysical, and electroluminescent properties is investigated in detail. It is found that PCzSF-3,7SO15, PCzSF-DPBT15, and PCzSF-DTBT03 show the best blue, green, and red device performance, revealing state-of-the-art luminous efficiencies of 5.6, 21.6, and 4.4 cd A–1 along with CIE coordinates of (0.16, 0.16), (0.32, 0.60), and (0.61, 0.34), respectively. The results clearly indicate that the carbazole-functionalized polyspirobifluorene is a promising platform to construct high-efficiency multicolor polymers suitable for PLEDs.