Optimization and Efficiency Enhancement of Modified Polymer Solar Cells.

In this study, an organic bulk heterojunction (BHJ) solar cell with a spiro OMeTAD as a hole transport layer (HTL) and a PDINO as an electron transport layer (ETL) was simulated through the one-dimensional solar capacitance simulator (SCAPS-1D) software to examine the performance of this type of organic polymer thin-film solar cell. As an active layer, a blend of polymer donor PBDB-T and non-fullerene acceptor ITIC-OE was used. Numerical simulation was performed by varying the thickness of the HTL and the active layer. Firstly, the HTL layer thickness was optimized to 50 nm; after that, the active-layer thickness was varied up to 80 nm. The results of these simulations demonstrated that the HTL thickness has rather little impact on efficiency while the active-layer thickness improves efficiency significantly. The temperature effect on the performance of the solar cells was considered by simulations performed for temperatures from 300 to 400 K; the efficiency of the solar cell decreased with increasing temperature. Generally, polymer films are usually full of traps and defects; the density of the defect (Nt) value was also introduced to the simulation, and it was confirmed that with the increase in defect density (Nt), the efficiency of the solar cell decreases. After thickness, temperature and defect density optimization, a reflective coating was also applied to the cell. It turned out that by introducing the reflective coating to the back side of the solar cell, the efficiency increased by 2.5%. Additionally, the positive effects of HTL and ETL doping on the efficiency of this type of solar cells were demonstrated.

Enhanced Emission of Tellurite Glass Doped with Pr3+/Ho3+ and Their Applications.

The shielding and spectroscopic properties of Pr+3 and Pr3+/Ho3+-codoped tellurite glass were investigated. The intensity parameters (Ω2 = 3.24-, Ω4 = 1.64-, Ω6 = 1.10 × 10-20 cm2) as well as the radiative lifetimes of 3F4 + 5S2 and 5I6 excited states of Ho3+ ions were equal to 301 µs and 3.0 µs, respectively. The former value appears to be much higher than that obtained from the lifetime measurement, indicating the presence of various energy transfer processes. The NIR spectrum of Pr3+/Ho3+-co-doped tellurite glass is dominated by strong Ho3+: 5I6 emission at around 1200 nm, being the result of the energy transfer from Pr3+ to Ho3+ ions. The shielding effectiveness of the prepared glasses showed good performance against high-energy photons. These findings suggest that the prepared glasses could be used in laser technology such as photodynamic therapy (PDT) treatment procedures and as shielding for radiation protection.

Polymers in High-Efficiency Solar Cells: The Latest Reports.

Third-generation solar cells, including dye-sensitized solar cells, bulk-heterojunction solar cells, and perovskite solar cells, are being intensively researched to obtain high efficiencies in converting solar energy into electricity. However, it is also important to note their stability over time and the devices' thermal or operating temperature range. Today's widely used polymeric materials are also used at various stages of the preparation of the complete device-it is worth mentioning that in dye-sensitized solar cells, suitable polymers can be used as flexible substrates counter-electrodes, gel electrolytes, and even dyes. In the case of bulk-heterojunction solar cells, they are used primarily as donor materials; however, there are reports in the literature of their use as acceptors. In perovskite devices, they are used as additives to improve the morphology of the perovskite, mainly as hole transport materials and also as additives to electron transport layers. Polymers, thanks to their numerous advantages, such as the possibility of practically any modification of their chemical structure and thus their physical and chemical properties, are increasingly used in devices that convert solar radiation into electrical energy, which is presented in this paper.

Thermo-Optical and Structural Studies of Iodine-Doped Polymer: Fullerene Blend Films, Used in Photovoltaic Structures.

Optical and structural properties of a blend thin film of (1:1 wt.) of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) doped with iodine (I2) and then exposed to a stepwise heating were reported and compared with the properties of doped P3HT films. The UV-Vis(T) absorption measurements were performed in situ during annealing runs, at the precisely defined temperatures, in a range of 20-210 °C. It was demonstrated that this new method allows one to observe the changes of absorption spectra, connected with the iodine release and other structural processes upon annealing. In addition, the thermally-induced changes of the exciton bandwidth (W) and the absorption edge parameters, i.e., the energy gap (EG) and the Urbach energy (EU) were discussed in the context of different length of conjugation and the structural disorder in polymers and blends films. During annealing, several stages were distinguished and related to the following processes as: the iodine escape and an increase in P3HT crystallinity, the orderly stacking of polymer chains, the thermally inducted structural defects and the phase separation caused by an aggregation of PCBM in the polymer matrix. Moreover, the detailed X-ray diffraction studies, performed for P3HT and P3HT:PCBM films, before and after doping and then after their thermal treatment, allowed us to consider the structural changes of polymer and blend films. The effect of iodine content and the annealing process on the bulk heterojunction (BHJ) solar cells parameters was checked, by the impedance spectroscopy (IS) measurements and the J-V characteristics registration. All of the investigated P3HT:PCBM blend films showed the photovoltaic effect; the increase in power conversion efficiency (PCE) upon iodine doping was demonstrated.

Effect of Protonation on Optical and Electrochemical Properties of Thiophene-Phenylene-Based Schiff Bases with Alkoxy Side Groups.

Three polyazomethines and their corresponding model compounds were protonated with trifluoroacetic acid, and its effect on their optical (UV-vis absorption and photoluminescence) properties and electrochemical behavior has been studied, in the context of the presence and elongation of alkoxy side groups. Moreover, the effect of environment dielectric constants (i.e., polarity of the solvent) was considered on the doping process. It has been proven that the presence of alkoxy side groups is necessary for protonation to occur, while unsubstituted compounds undergo hydrolysis to constitutive units. Acid doping of imines consisting of alkoxy side chains has resulted in a distinct bathochromic shift (>200 nm) of the low-energy absorption band. Even the length of alkyl chains has not affected the position of shifted bands; it has been observed that azomethines with smaller, methoxy side groups undergo the protonation process much faster than their octyloxy-substituted analogues, due to the absence of steric hindrance. The electrochemical studies of these alkoxy-substituted imines have indicated a better p-type behavior after protonation induced by the capability of the protonated form to easily oxidize in acetonitrile and to generate the native molecules. The environmental polarity has also had impact on the doping process, which took place only in low-polar media.

The Effect of Alkyl Substitution of Novel Imines on Their Supramolecular Organization, towards Photovoltaic Applications.

Three novel conjugated polyazomethines have been obtained by polycondensation of diamines consisting of the diimine system, with either 2,5-bis(octyloxy)terephthalaldehyde or 9-(2-ethylhexyl)carbazole-3,6-dicarboxaldehyde. Partial replacement of bulky solubilizing substituents with the smaller side groups has allowed to investigate the effect of supramolecular organization. All obtained compounds have been subsequently identified using the NMR and FTIR spectroscopies and characterized by the thermogravimetric analysis, differential scanning calorimetry, cyclic voltammetry, UV-Vis spectroscopy, and X-ray diffraction. Investigated polymers have shown a good thermal stability and high glass transition temperatures. X-ray measurements have proven that partial replacement of octyloxy side chains with smaller methoxy groups induced a better planarization of macromolecule. Such modification has tuned the LUMO level of this molecule and caused a bathochromic shift of the lowest energy absorption band. On the contrary, imines consisting of N-ethylhexyl substituted carbazole units have not been so clearly affected by alkyl chain length modification. Photovoltaic activity of imines (acting as a donor) in bulk-heterojunction systems has been observed for almost all studied compounds, blended with the fullerene derivative (PCBM) in various weight ratios.

Spectroscopic and electrochemical properties of thiophene-phenylene based Shiff-bases with alkoxy side groups, towards photovoltaic applications.

The influence of presence and elongation of alkoxy side chains in the π-conjugated Schiff-bases has been considered on the basis of UV-Vis absorption and photoluminescence spectra of model compounds and polymers solutions in chloroform and binary solvents of different polarity. The results of these investigations have been supported by electrochemical data. It has been demonstrated that introduction of electron donating methoxy side groups decreases the energy gap, however the elongation of alkyl chains only slightly affects the electronic structure of model compounds. In the case of polymers, such octyloxy side chains improves the solubility, enabling formation of longer polymer chains, with the enhanced effective π-conjugation length and narrower energy gap, however the intensity of emission band clearly decreased. Positive solvatochromism has been observed in both absorbance and photoluminescence spectra for all investigated compounds. As the concluding task, bulk-heterojunction (BHJ) photovoltaic (PV) structures, consisting of polyazomethines blended with the fullerene derivative, [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) have been prepared and tested in the context of potential application in solar cells. All investigated polymers have shown the photovoltaic effect, but the best power conversion efficiency and other PV parameters have been obtained for polyazomthine with octyloxy side chains.

Thermal Transitions in P3HT:PC60BM Films Based on Electrical Resistance Measurements.

In this paper, we present research on thermal transition temperature determination in poly (3-hexylthiophene-2,5-diyl) (P3HT), [6,6]-phenyl-C61-butyric acid methyl ester (PC60BM), and their blends, which are materials that are conventionally used in organic optoelectronics. Here, for the first time the results of electrical resistance measurements are explored to detect thermal transitions temperatures, such as glass transition Tg and cold crystallization Tcc of the film. To confirm these results, the variable-temperature spectroscopic ellipsometry studies of the same samples were performed. The thermal transitions temperatures obtained with electrical measurements are well suited to phase diagram, constructed on the basis of ellipsometry in our previous work. The data presented here prove that electrical resistance measurements alone are sufficient for qualitative thermal analysis, which lead to the identification of characteristic temperatures in P3HT:PC60BM films. Based on the carried studies, it can be expected that the determination of thermal transition temperatures by means of electrical resistance measurements will also apply to other semi-conducting polymer films.

P3HT:PCBM blend films phase diagram on the base of variable-temperature spectroscopic ellipsometry.

In this work we present an in-depth study of the how the composition of poly(3-hexylthiophene) (P3HT):[6,6]-phenyl-C61-butyric acid methyl ester (PCBM) blend films influences their phase transitions using variable-temperature spectroscopic ellipsometry. We demonstrate that this non-destructive method is a very sensitive optical technique to investigate the phase transitions and to determine the glass transition temperatures and melting crystallization points of the P3HT:PCBM blend films. By analyzing the influence of the temperature T on the raw ellipsometric data, we have identified a high sensitivity of the ellipsometric angle Δ at a wavelength of 280 nm to temperature changes. Characteristic temperatures determined from the slope changes of the Δ(T) plot appeared to be very good guess values for the phase transition temperatures.

Shape-Memory Terpolymer Rods with 17-ß-estradiol for the Treatment of Neurodegenerative Diseases: an In Vitro and In Vivo Study.

PURPOSE: Estradiol (E2)-loaded poly(L-lactide-co-glycolide-trimethylenecarbonate) (P(L-LA:GA:TMC)) rods with shape-memory were developed for the treatment of neurodegenerative diseases. Usefulness of the extrusion method in the obtaining process was also considered. The influence of structural and surface properties during hydrolytic degradation was developed. The possible therapeutic aspect of rods with E2 was determined. METHODS: The extruded rods were incubated in a PBS solution (pH 7.4, 37°C, 240 rpm). The amount of released E2 in vitro conditions was estimated by UV-VIS method. The following methods in the degradation of rods were applied: NMR, DSC, FTIR, GPC, SEM, and optical microscopy. Changes in water uptake and weight loss were also determined. In vivo study was performed on rats. Measurements of E2 level were performed before and after ovariectomy of rats using ELISA method. A sample of tissue adjacent to the site of the rod implantation was analysed under an optical microscope. RESULTS: A stable and steady degradation process ensured zero-order release of E2. The in vivo study indicated a significant increase in the E2 level in serum after ovariectomy. Moreover, structural and surface features indicated that the extrusion method was appropriate for obtaining E2-loaded rods. CONCLUSIONS: Shape-memory P(L-LA:GA:TMC) rods with E2 are an adequate proposal for further research in the field of neurological disorders.

Local delivery system of doxycycline hyclate based on ε-caprolactone copolymers for periodontitis treatment.

The aim of the study was to evaluate kinetics of doxycycline hyclate release from polymeric bioresorbable implants and to examine suitability of this system for local treatment of periodontitis. Selected trimethylene carbonate/ϵ-caprolactone (TMC/CL) and glycolide/caprolactone (GL/CL) copolymers were synthesized and used as carriers in the form of small elastic rings with 5 wt% and 10 wt% doxycycline hyclate content, or in the form of flakes obtained through electro-spinning technique. The release of the drug under in vitro conditions has been tested. The study has shown that equimolar TMC/CL copolymer loaded with 10 wt% of doxycycline hyclate appears to be the most suitable copolymer for assumed system. The drug release proceeds mainly by diffusion of medium into the polymeric matrix and then the drug is washed out. Daily validation of doxycycline doses released by the system should ensure accurate course of the therapy.

Novel poly(L-lactide-co-ε-caprolactone) matrices obtained with the use of Zr[Acac]4 as nontoxic initiator for long-term release of immunosuppressive drugs.

Slowly degradable copolymers of L-lactide and ε-caprolactone can provide long-term delivery and may be interesting as alternative release systems of cyclosporine A (CyA) and rapamycin (sirolimus), in which available dosage forms cause a lot of side effects. The aim of this study was to obtain slowly degradable matrices containing immunosuppressive drug from PLACL initiated by nontoxic Zr[Acac]4. Three kinds of poly(L-lactide-co-ε-caprolactone) (PLACL) matrices with different copolymer chain microstructure were used to compare the release process of cyclosporine A and rapamycine. The influence of copolymer chain microstructure on drug release rate and profile was also analyzed. The determined parameters could be used to tailor drug release by synthesis of demanded polymeric drug carrier. The studied copolymers were characterized at the beginning and during the degradation process of the polymeric matrices by NMR spectroscopy, GPC (gel permeation chromatography), and DSC (differential scanning calorimetry). Different drug release profiles have been observed from each kind of copolymer. The correlation between drug release process and changes of copolymer microstructure during degradation process was noticed. It was determined that different copolymer composition (e.g., lower amount of caprolactone units) does not have to influence the drug release, but even small changes in copolymer randomness affect this process.

Controlled poly(l-lactide-co-trimethylene carbonate) delivery system of cyclosporine A and rapamycine--the effect of copolymer chain microstructure on drug release rate.

The effect of poly(L-lactide-co-TMC) chain microstructure (and its changes during degradation) on immunosuppressive drugs' release process was analyzed. Three kinds of poly(L-lactide-co-TMC) (PLATMC)--two semiblock and one random were used to prepare matrices containing cyclosporine A or rapamycine and drug free matrices. All of them degraded slowly enough to provide long term delivery of immunosuppressive agents. Moreover, copolymer chain microstructure determined the effect of drug loading on the degradation process. It was observed that matrices without drug obtained from semiblock copolymer degraded differently than matrices containing cyclosporine A or rapamycine, whereas all kinds of matrices obtained from random PLATMC degraded in similar way. This is the evidence that the only in case of semiblock copolymer factors concerning the presence of drug and the kind of drug influenced degradation process. Based on the obtained results, correlations between copolymer degradation and drug release process are proposed. According to our outcomes, regular drug release process may be obtained from highly randomized copolymers (R ≈ 1) that remain amorphous during degradation process. Determination of this factor may help in development of biodegradable systems, in which drug release rate and profile can be tailored by synthesis of polymer with appropriate chain microstructure.

Star-shaped azomethines based on tris(2-aminoethyl)amine. Characterization, thermal and optical study.

The synthesis and detailed (physico)-chemical ((1)H/(13)C NMR, FTIR, UV-vis and elemental analysis) characterizations of new star-shaped compounds based on tris(2-aminoethyl)amine, including in their structure an azomethine function (HCN-) and alkoxysemiperfluorinated (-O-(CH(2))(3)-(CF(2))(7)-CF(3)), octadecyloxy aliphatic (-O-(CH(2))(17)-CH(3)) chain or two phenyl rings (-Ph-Ph-) as a terminal group, were reported. The mesomorphic behavior was investigated by means of differential scanning calorimetry (DSC), polarized optical microscopy (POM) and additionally by FTIR(T) and UV-vis(T) spectroscopy. Wide-angle X-ray diffraction (WAXD) technique was used to probe the structural properties of the azomethines. Moreover, the azomethine A1 was electro-spun to prepare fibers with poly(methyl methacrylate) (PMMA) and investigated by DSC and POM. Additionally, a film of the A1 with PMMA was cast from chloroform and the thermal properties of the film were compared with the thermal properties of the fiber and powder. It was showed that terminal groups dramatically influence the thermal and optical properties of the star-shaped azomethines.

Characterization and optical properties of oligoazomethines with triphenylamine moieties exhibiting blue, blue-green and green light.

New photoluminescence oligoazomethines possessing both hole and electron-transporting units in the main chain were synthesized. Triphenylamine (TPA) was used as the electron-donating group, while 4,4'-diaminooctafluorobiphenyl, 4,4'-(hexafluoro-isopropylidene)dianiline, 4-aminophenylsulfone, 4,4'-(4,4'-isopropylidenediphenyl-1,1'diyldioxy)dianiline and 2,5-bis(4-aminophenyl)-1,3,5-oxadiazole were used as the electron-acceptor or as the electron-donating group. The bifunctional oligomers (D-pi-A and D-pi-D) were soluble in some organic solvents such as chloroform, DMA, HMPA, NMP and formed transparent films on glass support. All oligomers exhibit high glass transition temperature in the range of 188-227 degrees C as determined by differential scanning calorimetry (DSC). The photoluminescence (PL) emission maximum peaks of the oligomers in solution are in the range of 459-552 nm (2.70-2.25 eV) corresponding to blue, blue-green or green light. The solvatochromic and protonation behavior of the oligomers in two solvents (DMA, chloroform) were detected. Oligomers protonated with methanesulfonic acid (MSA) are hypsochromically shifted with respect to the PL spectra of the pristine oligomers measured in solution. Relative PL intensity of the oligomers investigated in chloroform solution was found in the range of 0.10-0.50%, while for protonated ones it was detected in the range of 33-50% in relation to 9,10-diphenylanthracene. Blends of the oligoazomethines with poly(methylmethacrylate) (PMMA) (0.1%, w/w) emitted blue light. Thin films were also doped with iodine. Calculated energy gap for the undoped films following the Tauc relation was in the range of 2.46-2.69 eV while for the iodine doped oligomers in the range of 1.76-2.38 eV was found.

Influence of long-chain aliphatic dopants on the spectroscopic properties of polyketimine containing 3,8-diamino-6-phenylphenanthridine and ethylene linkage in the main chain. Noncovalent interaction: proton transfer, hydrogen and halogen bonding.

The spectroscopic properties of the aromatic polyketimine containing 3,8-diamino-6-phenylphenanthridine and ethylene linkage in the main chain (PK1) before and after doping are dominated by an interplay of electron-donating and electron-withdrawing effects mediated by its nitrogen atom and active groups in the dopants, respectively. Hydrogen and halogen bond formation or molecular recognition between PK1 and decanoic acid (DCA), n-decyl alcohol (DA), 1,10-dibromodecane (DBr), and n-decyl sulfonic acid (DSA) was investigated in comparison with undoped PK1. UV-vis and Fourier transform infrared (FTIR) absorption, wide-angle X-ray diffraction (WAXD), and the atomic force microscopy (AFM) technique are used to probe the spectroscopic properties of the phenanthridine "core" of PK1 as well as its complexes. Spectral changes were observed for the PK1 after doping, which supported the ionic, hydrogen, and halogen bond formation between the PK1 and protonation agents (dopants). This specific interaction of the dopant with the host polymer influences the polyketimine properties, and the following changes were observed: (i) changes in the band gap (E(g)) of the protonated polyketimine, (ii) changes in the FTIR spectra of doped PK1, (iii) changes in optical micrographs of the protonated PK1 (detected by the AFM technique), and (iv) changes in crystalline structure of doped PK1. Our study demonstrates how the properties of conjugated PK1 can be tuned by the supramolecular engineering concepts, which could be important for optoelectronic applications of the materials.

Synthesis and characterization of polyketanils with 3,8-diamino-6-phenylphenanthridine moieties exhibiting light emitting properties molecular and supramolecular engineering concept.

Relationship between structures and properties of new conjugated polyketanils (PKs) with special architectures, synthesized from three diketones, i.e. p-dibenzoylbenzene, dibenzyl, trans-1,2-dibenzoylethylene and 3,8-diamino-6-phenylphenanthridine, was investigated. The photoluminescence (PL) of green, yellow and red emitting light polymers and their blend was studied. These included the effects of excitation wavelength, concentration and film thickness on the PL. Photoluminescence properties of the PKs before and after protonation with 10-Camphorsulfonic acid (CSA) were tested. The structure formation of (PKs)(1)(CSA)(2) complexes are discussed on the basis of FTIR spectroscopy.