Temperature Variation-Induced Performance Decline of Perovskite Solar Cells.

This paper reports on the impact of outdoor temperature variations on the performance of organo metal halide perovskite solar cells (PSCs). It shows that the open-circuit voltage ( VOC) of a PSC decreases linearly with increasing temperature. Interestingly, in contrast to these expected trends, the current density ( JSC) of PSCs is found to decline strongly below 20% of the initial value upon cycling the temperatures from 10 to 60 °C and back. This decline in the current density is driven by an increasing series resistance and is caused by the fast temperature variations as it is not apparent for solar cells exposed to constant temperatures of the same range. The effect is fully reversible when the devices are kept illuminated at an open circuit for several hours. Given these observations, an explanation that ascribes the temperature variation-induced performance decline to ion accumulation at the contacts of the solar cell because of temperature variation-induced changes of the built-in field of the PSC is proposed. The effect might be a major obstacle for perovskite photovoltaics because the devices exposed to real outdoor temperature profiles over 4 h showed a performance decline of >15% when operated at a maximum power point.

Colloidally stable selenium@copper selenide core@shell nanoparticles as selenium source for manufacturing of copper-indium-selenide solar cells.

Selenium nanoparticles with diameters of 100-400nm are prepared via hydrazine-driven reduction of selenious acid. The as-prepared amorphous, red selenium (a-Se) particles were neither a stable phase nor were they colloidally stable. Due to phase transition to crystalline (trigonal), grey selenium (t-Se) at or even below room temperature, the particles merged rapidly and recrystallized as micronsized crystal needles. As a consequence, such Se particles were not suited for layer deposition and as a precursor to manufacture thin-film CIS (copper indium selenide/CuInSe2) solar cells. To overcome this restriction, Se@CuSe core@shell particles are presented here. For these Se@CuSe core@shell nanoparticles, the phase transition a-Se→t-Se is shifted to temperatures higher than 100°C. Moreover, a spherical shape of the particles is retained even after phase transition. Composition and structure of the Se@CuSe core@shell nanostructure are evidenced by electron microscopy (SEM/STEM), DLS, XRD, FT-IR and line-scan EDXS. As a conceptual study, the newly formed Se@CuSe core@shell nanostructures with CuSe acting as a protecting layer to increase the phase-transition temperature and to improve the colloidal stability were used as a selenium precursor for manufacturing of thin-film CIS solar cells and already lead to conversion efficiencies up to 3%.

De novo Folding of Two-Helix Potassium Channel Blockers with Free-Energy Models and Molecular Dynamics.

We report the predictive de novo folding of three two-helix proteins using the free-energy protein forcefield PFF01. Starting from random initial conformations 40-90% of the members of the simulated ensembles converge to near-native conformations. The energetically lowest conformations approach the conserved part of the native conformations to within 1.64, 1.86, and 1.84 Å for 1WQC, 1WQD, and 1WQE, respectively. An analysis of the low-lying conformations predicts the correct topology of the disulfide bridges, which are formed in additional simulations with a constraining potential. The free energy landscapes of these proteins are very simple, suggesting them as candidates for all-atom molecular dynamics simulations. In five independent simulations we find the formation of the correct secondary structure and several folding events into the tertiary structure.