Generation and recombination of electrons and holes in organic solar cells occurs via charge transfer states located at the donor/acceptor interface. The energy of these charge transfer states is a crucial factor for the attainable open-circuit voltage and its correct determination is thus of utmost importance for a detailed understanding of such devices. This work reports on drastic changes of electroluminescence spectra of bulk heterojunction organic solar cells upon variation of the absorber layer thickness. It is shown that optical thin-film effects have a large impact on optical out-coupling of luminescence radiation for devices made from different photoactive materials, in configurations with and without indium tin oxide. A scattering matrix approach is presented which accurately reproduces the observed effects and thus delivers the radiative recombination spectra corrected for the wavelength-dependent out-coupling. This approach is proven to enable the correct determination of charge transfer state energies.

However, in comparison to established inorganic-based photovoltaic technologies organic solar cells possess still a much lower efficiency. [2,[9][10][11][12] The efficiency η of solar cells is determined bywhere J SC is the short-circuit current density, V OC is the open-circuit voltage, FF is the fill factor, and P in is the incident power density. The relatively poor transport properties (low mobilities) of the disordered organic materials [13,14] applied in OSC lead to a strong accumulation of charge carriers under current flow and thus to an increase in nongeminate recombination. [10] Consequently, the FF is reduced and for cases of extremely low charge carrier mobilities also J SC , which results in a low overall power conversion efficiency. [10,11,15] Further, due to the relatively low permittivity of the organic materials a significant fraction of the absorbed photon energy is required as driving force for the exciton dissociation of the coulombic bound electron-hole pair (offset between the lowest unoccupied molecular orbitals of donor and acceptor) which lowers the achievable power conversion efficiency significantly. [9] In addition to the latter, a key loss mechanism originates from additional nonradiative recombination pathways. Besides the nongeminate recombination via trap states as a first order recombination process, the recombination at the electrodes, i.e., surface recombination, is an additional loss channel. Surface recombination in OSC was investigated intensively in different perspectives which indicates the importance of a thorough understanding of the underlying mechanisms. [16][17][18][19][20] Kirchartz et al. derived the ideality factor differentially by the light intensity dependence of the open-circuit voltage and demonstrated that the presence of surface recombination leads to the occurrence of an ideality factor n id < 1. [18] But also the charge carrier mobility µ dependent efficiency of OSC has been investigated in terms of surface recombination. It seems to be counterintuitive to assume that the device efficiency is maximum at a finite optimum mobility. Yet, this case is in detail discussed by Deibel et al. and Kirchartz et al., who showed that an optimum mobility exists in the presence of not ideally selective contacts and that faster kinetics by mobilities higher than the optimum will result in a reduction of the overall efficiency. [21,22] TressThe selectivity of electrodes of solar cells is a critical factor that can limit the overall efficiency. If the selectivity of an electrode is not sufficient both electrons and holes recombine at its surface. In materials with poor transport properties such as in organic solar cells, these surface recombination currents are accompanied by large gradients of the quasi-Fermi energies as the driving force. Experimental results from current-voltage characteristics, advanced photo-and electroluminescence as well as charge extraction of three different photoactive materials are shown and compared to drift-diffusion simulations. It can be conc...

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M. phaseolina, a global devastating necrotrophic fungal pathogen causes charcoal rot disease in more than 500 host plants. With the aim of understanding the plant-necrotrophic pathogen interaction associated with charcoal rot disease of jute, biochemical approach was attempted to study cellular nitric oxide production under diseased condition. This is the first report on M. phaseolina infection in Corchorus capsularis (jute) plants which resulted in elevated nitric oxide, reactive nitrogen species and S nitrosothiols production in infected tissues. Time dependent nitric oxide production was also assessed with 4-Amino-5-Methylamino-2′,7′-Difluorofluorescein Diacetate using single leaf experiment both in presence of M. phaseolina and xylanases obtained from fungal secretome. Cellular redox status and redox active enzymes were also assessed during plant fungal interaction. Interestingly, M. phaseolina was found to produce nitric oxide which was detected in vitro inside the mycelium and in the surrounding medium. Addition of mammalian nitric oxide synthase inhibitor could block the nitric oxide production in M. phaseolina. Bioinformatics analysis revealed nitric oxide synthase like sequence with conserved amino acid sequences in M. phaseolina genome sequence. In conclusion, the production of nitric oxide and reactive nitrogen species may have important physiological significance in necrotrophic host pathogen interaction.

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(1 of 9)combined with inherent mechanical flexi bility. [1] Accordingly, extensive research efforts are invested in the development of protocols suitable for flexible device fabrication, rolltoroll processing, and printing, [2] and the design and synthesis of high performance materials, specifi cally high mobility semiconductors, [3] gate insulators, [4] and printable conductors. [5] Importantly, because charge injection, extraction, and accumulation occur at the interfaces of different materials, new solution processing methodologies that control the structure and composition of interfaces in OFETs are also essential for high performances. [6] One seminal inter facial electronic process that limits OFET performances is inefficient charge car rier injection from the source electrode to the organic semiconducting channel. Efficient injection into the organic semiconductor requires Ohmic con tacts, i.e., barrierless energy level align ment at the organic/metal interface. [6a,7] The Schottky barriers, and associated contact resistance, can be reduced by aligning either the highest occupied molecular orbital (HOMO) of a ptype organic semicon ductor or the lowest unoccupied molecular orbital (LUMO) of an ntype organic semiconductor, with the work function of the metal electrode. Therefore, tuning the work function of the metal electrode is a practical approach for optimizing charge injection/extraction and hence device performance. [8] A wellestablished strategy to tune the effective work function (EWF) at the organic/metal interface is by introducing ultrathin organic or inorganic interlayers between the metal contact and the organic semiconductor. [9] In case of organic interlayer, polar molecules are placed at the semiconductor/metal interface and modify the EWF by imposing a dipole at the interface. The energy level alignment can be controllably tuned through the chemical composition of the molecule and the direction and magnitude of the dipole. [7,10] The most common techniques of depositing organic interlayers onto substrates are thermal deposition [11] and spin coating from orthogonal solvents. [12] Another wellknown technique is to deposit selfassembled monolayers (SAM) by immersing the substrate with metal electrodes in the SAM solution prior to the semiconductor Contact resistance significantly limits the performance of organic field-effect transistors (OFETs). Positioning interlayers at the metal/organic interface can tune the effective work-function and reduce contact resistance. Myriad techniques offer interlayer processing onto the metal pads in bottom-contactOFETs. However, most methods are not suitable for deposition on organic films and incompatible with top-contact OFET architectures. Here, a simple and versatile methodology is demonstrated for interlayer processing in both p-and n-type devices that is also suitable for top-contact OFETs. In this approach, judiciously selected interlayer molecules are co-deposited as additives in the semiconducting polymer active layer. During top contact dep...

Charge transport in conjugated polymers depends critically on the chemical structure of the polymer chain, morphology, aggregation, and the complex microstructure in the solid state. Recently, molecular planarity and intramolecular electron transport were associated with J-type aggregation, while coplanar stacking and intermolecular hole transport were correlated with H-type aggregation. This fundamental observation suggests that the degree of H-or Jaggregation could be a handle to tune carrier mobility toward desirable device performances. Here, we use a diketopyrrolopyrrole copolymer as a model semiconducting polymer and tune the type and degree of aggregation through film thickness. Optical absorption measurements, grazing incidence wide angle X-ray scattering, and polarized optical microscopy reveal that thin films compose mainly fibrelike J-aggregated structures, and as the films become thicker, the degree of crystallinity and H-aggregation increase. Thickness-dependent charge mobility values, extracted from corresponding organic field effect transistors, confirm that J-aggregated polymer chains are generally preferable for electron mobility, while polymer crystalline H-aggregates support better hole transport. To obtain perfectly balanced ambipolar OFETs, we optimize the microstructure through film thickness and reduce contact resistance by inserting an interlayer of mixed additives at the organic/ contact interfaces. A complementary-like voltage inverter combining two identical ambipolar DPP-T-TT OFETs with a common gate as the input voltage and symmetrical performance confirms that DPP copolymers are a promising candidate for applications in ambipolar devices and integrated circuits.