Organic photovoltaic (OPV) technology is an attractive solarelectric conversion paradigm due to the promise of low cost roll-to-roll production and amenability to fl exible substrates. Substantial progress has been made over the last 5 years, by virtue of optimization of materials processing parameters [1][2][3] and emergence of new conjugated polymers with tailored energy levels. [4][5][6] Power conversion effi ciency (PCE) exceeding 7% has recently been achieved. [ 4 ] The state-of-the-art devices are so called bulk-heterojunction (BHJ) type in which the PV activelayer is coated from a blend of donor and acceptor species. The nanoscale nature of phase separation between the donors and acceptors in a BHJ active-layer alleviates the mismatch between exciton diffusion length ( ∼ 10 nm) and optical absorption length ( > 100 nm). However, there still exists a mismatch between optical absorption length and charge transport scale. BHJ activelayers tend to suffer from cul-de-sacs in the charge transport pathways, and hole mobilities in conjugated polymers remain low. Both of these factors lead to recombination losses, higher series resistances and lower fi ll-factors. [ 7 ] Thus, it is imperative to develop fabrication methodologies that can enable effi cient optical absorption in fi lms thinner than optical absorption length. The most desirable methodology would be one which can also substantially improve absorption at the band edge of conjugated polymers, which usually lies in the red/near-infrared region, and where signifi cant amount of solar fl ux is also located. It is more so important because the charge carriers photoexcited at the band edge were found to have a higher dissociation effi ciency than the ones excited at higher energies. [ 8 ] Textured substrate based light-trapping schemes are a commonplace in traditional inorganic photovoltaic (PV) cells. However, they have not been successfully applied to polymer based PVs due to an obvious problem of solution-processing nanoscale thick and conformal PV layers on topographical surfaces. In this communication, we show that realization of such conformal layers is indeed possible, if the underlying topography has suitable dimensions. We fabricated poly(3-hexylthiophene):[6,6]-phenyl-C61-butyric acid methyl ester (P3HT:PCBM) based BHJ PV cells on grating-type textured substrates possessing several sub-micrometer and micrometer scale topographical dimensions. We discovered that if the height of the underlying topographical features is reduced to sub-micrometer regime (e.g. 300 nm) and the pitch is increased to more than a micrometer (e.g. 2 μ m), the textured surface becomes amenable to coating a conformal PV active-layer. The resultant PV cells showed 100% increase in average light absorption near the band edge due to trapping of higher wavelength photons, and 20% improvement in PCE as compared with the fl at PV cell.Till date, a few light management techniques in ray optics regime have been investigated for enhancement of optical absorption in OPVs, namely, collec...

A novel architecture with high‐aspect‐ratio nanoscale metallic periodic patterns is fabricated as transparent electrodes. The structure shows high visible light transmission and has superior electrical conductivity compared to standard indium tin oxide (ITO) coated glass. A proof‐of‐principle organic photovoltaic device is successfully fabricated with the electrode.

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In this paper, we report on the effect of Sm doping on the phase evolution and properties of phase-pure Bi1−xSmxFeO3 (BSFO) ceramics synthesized via a conventional solid-state-reaction method. We find that upon calcination, Sm doping of bismuth ferrite promotes the formation of perovskitic phase and leads to the elimination of the secondary phases. On the other hand, undoped compositions do not yield completely phase-pure samples and contain secondary phases such as Bi25FeO40. Differential thermal analysis corroborates the sequence of phase evolution as examined from the x-ray diffraction patterns. A thermodynamic analysis, based on the bond energy, has been carried out to explain the effect of doping on the stabilization of perovskite structured phase upon Sm doping and is well supported by the thermal analysis results. Vibrating sample magnetometry measurements show that BSFO samples possess higher room temperature remnant magnetization than the undoped samples. Temperature dependent magnetic measurements suggest an antiferromagnetic behavior in the BSFO samples with a Néel temperature of ∼370°C, absent in the undoped samples. Mössbauer spectroscopy on Sm-doped specimens reveals the presence of phase-pure BSFO with absence of any Fe+2 ions. Interestingly, doped samples exhibit an order of magnitude increase in the leakage current density.

A photoluminescence (PL)-based oxygen and glucose sensor utilizing inorganic or organic light emitting diode as the light source, and polythiophene: fullerene type bulk-heterojunction devices as photodetectors, for both intensity and decay-time based monitoring of the sensing element's PL. The sensing element is based on the oxygen-sensitive dye Pt-octaethylporphyrin embedded in a polystyrene matrix.

To understand the effect of processing conditions such as spin coating speed and drying rate on the density of defects; poly͑3-hexylthiophene͒:fullerene-derivative solar cells A, B, and C were fabricated with solvent drying times of ϳ40 min, 7 min, and 1 min, respectively. We show that slowest grown device A has one order of magnitude less subband gap traps than device C. The open circuit voltage and its light intensity dependence was strongly affected by interfacial recombination of carriers at subgap defect states. The losses due to trap-assisted recombination can even dominate over bimolecular recombination, depending on the density of defect states

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A common material in creating memristors is titanium dioxide (TiO 2 ), grown by atomic layer deposition, sputtering, or sol-gel process. In this letter, we study the memristive behavior in thin TiO 2 films fabricated by brief electrochemical anodization of titanium. The effects of different anodization times and annealing are explored. We discover that inherent oxygenvacancies at the bottom Ti/TiO 2 interface naturally lead to memristive switching in nonannealed films. Annealing induces extra oxygen vacancies near the top metal/oxide interface, which leads to symmetric and ohmic current-voltage characteristics with a collapse of memristive switching. No clear dependence on anodization time was observed for times between 1 s and 1 min.