A. Schulz

Highly efficient polymer solar cells cast from non-halogenated xylene/anisaldehyde solution

Several high performance polymer:fullerene bulk-heterojunction photo-active layers, deposited from the non-halogenated solvents o-xylene or anisole in combination with the eco-compatible additive p-anisaldehyde, are investigated. The respective solar cells yield excellent power conversion efficiencies up to 9.5%, outperforming reference devices deposited from the commonly used halogenated chlorobenzene/1,8-diiodooctane solvent/additive combination. The impact of the processing solvent on the bulk-heterojunction properties is exemplified on solar cells comprising benzodithiophene-thienothiophene co-polymers and functionalized fullerenes (PTB7:PC71BM). The additive p-anisaldehyde improves film formation, enhances polymer order, reduces fullerene agglomeration and shows high volatility, thereby positively affecting layer deposition, improving charge carrier extraction and reducing drying time, the latter being crucial for future large area roll-to-roll device fabrication.

Electronic structures and optical properties of partially and fully fluorinated graphene.

In this Letter, we study the electronic structures and optical properties of partially and fully fluorinated graphene by a combination of ab initio G0W0 calculations and large-scale multiorbital tight-binding simulations. We find that, for partially fluorinated graphene, the appearance of paired fluorine atoms is more favorable than unpaired atoms. We also show that different types of structural disorder, such as carbon vacancies, fluorine vacancies, fluorine vacancy clusters and fluorine armchair and zigzag clusters, will introduce different types of midgap states and extra excitations within the optical gap. Furthermore, we argue that the local formation of sp3 bonds upon fluorination can be distinguished from other disorder inducing mechanisms which do not destroy the sp2 hybrid orbitals by measuring the polarization rotation of passing polarized light.

A universal description of temporal and lateral distributions of ground particles in extensive air showers

Extensive air showers are traditionally described with phenomenological models - often called Lateral Distribution Functions (LDFs) - of the density of particles at the ground and derived quantities. The concept of air shower universality aims at a deeper understanding of the shower development in the atmosphere by taking into account physical properties of different types of secondary particles. Our extended model is based on the well known universal behaviour of the electromagnetic as well as of the muonic component and of its accompanying electromagnetic halo. A fourth component of electromagnetic particles from pion decays close to the observation level is considered in addition. Eventually the model allows for a description of particle distributions at observation level as a function of a few macroscopic quantities: the total energy E, the depth of the shower maximum Xmax, the muon content Nm and the geometry of the shower. The pure electromagnetic component is determined by E and Xmax while differences between hadronic interaction models and primary particles are absorbed in the muon scale, affecting the three remaining components. We will detail the basic concepts of the extended universal description of air showers and describe the application using the detector response of the water-Cherenkov detector array of the Pierre Auger Observatory as an example. Both, the signal response of particles and their time of arrival in the detectors are accounted for in the reconstruction. The universal parametrizations of the components allow us to estimate Xmax and Nm event-by-event solely based on the measured footprint of the air shower at observation level. The shower maximum is reconstructed with a resolution of 30 50 g=cm 2 depending on energy and zenith angle of the shower. The applicability of the method, limitations and model dependence is discussed.

Enhanced thermal stability of organic solar cells comprising ternary D-D-A bulk-heterojunctions

Ternary absorber blends have recently been identified as promising concepts to spectrally broaden the absorption of organic bulk-heterojunction solar cells and hence to improve their power conversion efficiencies. In this work, we demonstrate that D-D-A ternary blends comprising two donor polymers and the acceptor PC61BM can also significantly enhance the thermal stability of the solar cell. Upon harsh thermal stress at 120u2009°C for 2u2009h, the ternary solar cells show only a minor relative deterioration of 10%. Whereas the polymer/fullerene blend PTB7-Th:PC61BM is rather unstable under these conditions, its degradation was efficiently suppressed by incorporating the near infrared-absorbing polymer PDTP–DFBT. Spectroscopic ellipsometry investigations and an effective medium analysis of the ternary absorber blend revealed that the domain conformation in presence of PDTP–DFBT remains stable whereas the domain conformation changes in its absence. The ternary PTB7-Th:PDTP–DFBT:PC61BM solar cells yield thermally stable power conversion efficiencies of up to 6%.Organic solar cells: Polymer mixtures enhance the thermal stabilityOrganic solar cells increase their lifetime by adding another polymer component, paving the way towards commercialization.A team led by Alexander Colsmann at Karlsruhe Institute of Technology, Germany conducted systematic spectroscopic investigations and device characterizations to demonstrate that the degradation of PTB7-Th: PC61BM solar cell can be efficiently suppressed by incorporating the near infrared-absorbing polymer PDTP-DFBT. Upon harsh thermal stress at 120u2009°C for 2u2009h, the ternary solar cells show only a minor relative deterioration of 10% with a high power conversion efficiency of 6%. This work reveals the importance of a third component to lock the phase conformation of the polymer and fullerene domains. This is a key step for the thermally stable power output thus the commercialization of the organic solar cells.