Perovskite solar cells (PSCs) with p-i-n architecture attracted particular attention from the research community due to their simple and scalable fabrication at low temperatures. However, the operational stability of p-i-n PSCs has to be improved, which requires the development of advanced charge transport interlayers. Fullerene derivatives such as phenyl-C-61-butyric acid methyl ester (PC61BM) are commonly used as electron transport layer (ETL) materials in PSCs, though they strongly compromise the device stability. Indeed, it has been shown that PC61BM films actively absorb volatile products resulting from photodegradation of lead halide perovskites and transport them towards top metal electrode. Thus, there is an urgent need for development of new fullerene-based electron transport materials with improved properties, in particular the ability to heal defects on the perovskite films surface and block the diffusion of volatile perovskite photodegradation products. To address this challenge, a systematic variation of organic addends structure should be performed in order to tailor the properties of fullerene derivatives. Herein, we rationally designed a series of fullerene derivatives with different side chains and explored their performance as ETL materials in perovskite solar cells. It has been shown that among all studied compounds, a methanofullerene with thiophene pendant group enables both high efficiency and improved device operational stability. The obtained results suggest that further engineering of fullerene-based materials could pave a way for the development of advanced ETL materials enabling long lifetimes of p-i-n perovskite solar cells.

A natural grossular garnet was found to have a luminescence spectrum with a narrow vibrational structure and short decay time that is unusual for minerals. We propose that such emission is generated by Mn2+ accompanied by defect F-centers which both enhance the transition probability and give rise to sensitivity to optical bleaching and reconstitution via irradiation. The elevated Mn concentration in comparison with other potential luminescent impurities was confirmed by LIBS analysis. Such interpretation contradicts the traditional opinion that Mn2+ centers in minerals are characterized only by broadband emission with very long decay times typical of d-d transitions.

The complex dielectric permittivity of a sintered ceramic tablet consisting of 70.5 % BiFeO3 and 27.7% Bi2Fe4O9 was analyzed as a function of temperature from -120 °C to 230 °C. The results reveal a complicated dielectric response with temperature activated relaxation features. They also reveal a ferroelectric phase transition that decayed with repeated heating cycles of the tablet. The source of the behaviour is assigned to relaxation processes happening along the grain boundaries of differing compositions in the tablet. The origin of the phase transition is traced to locally induced strains on grain boundaries because of unit cell size mismatch between BiFeO3 and Bi2Fe4O9.

Ceramic $BiFeO_{3}$ samples were prepared by rapid sintering at $880^OC$. Two compositions were examined. A $56/44\ Bi_{2}O_{3}/Fe_{2}O_{3}\ mole\%$ composition and a $56Bi_{2}O_{3}\cdot44Fe_{2}O_{3}+6.5wt\%\,NaCl$ composition. The samples were heat treated at different times up to $8$ minutes and the phase content was examined as a function of the time using XRD measurements and analysis. It was demonstrated that using both compositions, maximum $BiFeO_{3}$ phase content is obtained after $3.5$ minutes. In the former approximately $50\%$ of the material transformed to $BiFeO_{3}$ while in the latter $98.5\%$.

Monocyclopropanated fullerene derivatives with decreased electron affinity as compared to standard [60]PCBM acceptor were synthesized, characterized, and investigated as promising electron acceptor materials for fullerene-based organic solar cells. This decrease in electron affinity was attributed to the presence of through space electronic interactions between the lone electron pairs of oxygen atoms and electron-deficient pi-system of the fullerene cage. Organic bulk heterojunction solar cells based on the designed materials blended with conjugated polymers P3HT and PCDTBT have demonstrated spectacular increase in open-circuit voltage by >100 mV and improved light power conversion efficiency as compared to the reference devices comprising [60]PCBM. The application of new fullerene-based acceptor materials in combination with the promising low band gap conjugated copolymer may deliver competitive device performances.

One in every 20 people develops kidney stones at some point in their life.

We report the first outdoor study of the intrinsic photochemical stability of a series of samples of conjugated polymers encapsulated in an inert atmosphere and exposed to natural sunlight illumination conditions in the Negev Desert.

We have demonstrated accelerated degradation studies of organic photovoltaic materials using concentrated sunlight, where the atmosphere, temperature and illumination intensity were independently controlled. Testing various schemes for controlling the sample temperature under concentrated sunlight showed that heating of P3HT:PCBM was caused by photons at the absorbed wavelength range and dissipation of excess photon energy, and not necessarily by IR photon absorption. Sunlight chopping was found to be an effective method for independent temperature control under illumination by concentrated sunlight.The first accelerated degradation tests using sunlight concentration applied to P3HT:PCBM blends were reported. P3HT:PCBM blends exposed to concentrated sunlight in the presence of traces of oxygen/humidity showed degradation induced by photo-oxidation of the P3HT backbone within the P3HT:PCBM blend, which is significantly thermally accelerated, in agreement with previous observations. However, this could be demonstrated in a time scale of minutes and hours, that is, significantly accelerated. Exposure of well encapsulated P3HT:PCBM films to concentrated sunlight demonstrated stability up to 3,600 sun*hours, corresponding to about 1.6 years of operating time. This result was obtained at 300 suns exposure after merely 12 h, demonstrating the advantage of using concentrated sunlight for accelerated stability tests. These tests can therefore combine extremely high acceleration factors with profound understanding of the effect of various, independently controlled factors on the degradation mechanisms. (C) 2014 Elsevier B.V. All rights reserved.

Accurate characterization and reporting of organic photovoltaic (OPV) device performance remains one of the important challenges in the field. The large spread among the efficiencies of devices with the same structure reported by different groups is significantly caused by different procedures and equipment used during testing. The presented article addresses this issue by offering a new method of device testing using “suitcase sample” approach combined with outdoor testing that limits the diversity of the equipment, and a strict measurement protocol. A round robin outdoor characterization of roll-to-roll coated OPV cells and modules conducted among 46 laboratories worldwide is presented, where the samples and the testing equipment were integrated in a compact suitcase that served both as a sample transportation tool and as a holder and test equipment during testing. In addition, an internet based coordination was used via plasticphotovoltaics.org that allowed fast and efficient communication among participants and provided a controlled reporting format for the results that eased the analysis of the data. The reported deviations among the laboratories were limited to 5% when compared to the Si reference device integrated in the suitcase and were up to 8% when calculated using the local irradiance data. Therefore, this method offers a fast, cheap and efficient tool for sample sharing and testing that allows conducting outdoor measurements of OPV devices in a reproducible manner.

Here we report a comparative study of seven different cyclopropane-type bisadducts (represented by mixtures of multiple isomers) in organic bulk heterojunction solar cells using poly(3-hexylthiophene) (P3HT) as a donor polymer. It was shown that the material solubility affects both the composite morphology and the photovoltaic performance. A good correlation between the solubility of the fullerene derivatives and parameters of solar cells has been revealed.

The conjugated polymer AnE-PVstat demonstrates competitive photovoltaic characteristics compared with modern "push-pull" polymer systems. AnE-PVstat is distinguished by its PPV-type molecular structure, the absence of heterocyclic units, particularly thiophene rings, and the presence of an anthracene unit bearing two adjacent triple bonds. AnE-PVstat in combination with specially designed [60]fullerene derivatives F3 and F11 shows power conversion efficiencies of >4% in solar cells.

Conjugated PPV-PPE copolymer has been investigated in organic solar cells in combination with twelve different fullerene derivatives. It was shown that the length of solubilizing alkyl chains in the fullerene derivative structures correlates well with the performance of photovoltaic cells.

Two conjugated PPE-PPV copolymers were studied as electron donor materials in bulk heterojunction organic solar cells in combination with a library of electron acceptor fullerene derivatives. It was shown that molecular structure and solubility of the fullerene counterpart significantly affect the photovoltaic performance of both polymers. Use of [60]PCBM as an electron acceptor material yielded quite moderate power conversion efficiencies. The best results were achieved when fullerene derivatives with suitable molecular structures and solubilities were applied. The obtained results suggest that every newly designed conjugated polymer should be evaluated in solar cells using a library of fullerene derivatives instead of just conventional PCBMs. We believe that only this combinatorial approach might bring the best performing donor/acceptor combinations for future generations of efficient organic solar cells.

Novel fullerene derivatives bearing thiophene and furan residues were synthesized and studied as electron acceptor materials in bulk heterojunction organic solar cells, together with poly(3-hexylthiophene) (P3HT) as the donor polymer. Some compounds showed large nanomorphological inhomogenities in blends with P3HT; in particular, clusters with dimensions in the range of 100-1000 nm were formed. However, some blends that showed such large clusters yielded at the same time high power conversion efficiencies in photovoltaic devices, approaching 3.7 %. This is in sharp contrast with previously studied systems, in which a substantial phase separation always resulted in a poor photovoltaic performance. We assume that the attachment of thienyl or furyl groups to the fullerene cage results in a certain ordering of the designed fullerene derivatives I-IX with P3HT in photoactive blends. Both the fullerene derivative and P3HT might assemble via pi-pi stacking of the thiophene units to form the nanostructures observed in the films by optical and atomic force microscopy. The presence of ordered donor and acceptor counterparts in these nanostructures results in superior photovoltaic device operation.

The preparation of 27 different derivatives of C-60 and C-70 fullerenes possessing various aryl (heteroaryl) and/or alkyl groups that are appended to the fullerene cage via a cyclopropane moiety and their use in bulk heterojunction polymer solar cells is reported. It is shown that even slight variations in the molecular structure of a compound can cause a significant change in its physical properties, In particular its solubility in organic solvents. Furthermore, the solubility of a fullerene derivative strongly affects the morphology of its composite with poly(3-hexylthlophene), which is commonly used as active material In bulk heterojunction organic solar cells. As a consequence, the solar cell parameters strongly depend on the structure and the properties of the fullerene-based material. The power conversion efficiencies for solar cells comprising these fullerene derivatives range from negligibly low (0.02%) to considerably high (4.1%) values. The analysis of extensive sets of experimental data reveals a general dependence of all solar cell parameters on the solubility of the fullerene derivative used as acceptor component in the photoactive layer of an organic solar cell. It is concluded that the boo material combinations are those where donor and acceptor components are of similar and sufficiently high solubility in the solvent used for the deposition of the active layer.

Melanoma is responsible for most of the fatalities from skin cancer diseases. Yet, there is no reliable method for a noninvasive early detection of skin cancers. We developed a Fiber-optic Evanescent wave Spectroscopy (FEWS) method based on a Fourier Transform Mid-IR (FTIR) spectrometer and on U shaped silver halide (AgClBr) fibers that are highly transparent in the mid-IR. We measured suspicious lesions on patients, before their excision. The central part of the bent fiber touched the lesion and the mid-IR absorption of this area was measured in situ and in real time. As a background, the same measurement was performed on healthy nearby skin. All discomfort to the patient was avoided. The lesions were then examined by conventional means. Histopathology revealed 5 melanoma tumors out of 90 patients and clear and repeating spectral differences between background and lesion are seen in all patients. We continue to accumulate spectral data of melanoma and of other pathologies, for better statistics and for characterization of other types of skin cancer. It is hoped that this non-invasive method for an early detection and diagnosis of skin cancer will replace biopsy and revolutionize this field.