arXiv subjects

Roland Schmechel

Publications and source records attributed to Roland Schmechel.

4 recordsLinked to original sources

arXiv2019

Influence of the Cathodes Microstructure on the Stability of Inverted Planar Perovskite Solar Cells

One of the main challenges for perovskite solar cells (PSC) is their stability, due to environment-induced perovskite decomposition. The resulting decomposition compounds are mobile and may, therefore, react with charge carrier extraction layers or the contact metallization, in addition to enhancing the recombination rate in the absorber layer. In this contribution, the influence of different contact metallization layers, such as aluminum (Al), silver (Ag), gold (Au) and nickel (Ni) on the storage stability of inverted planar methylammonium lead iodide (MAPI)-based perovskite solar cells without encapsulation has been investigated. For this study current-voltage (J-V) and impedance measurements in combination with scanning electron microscope (SEM) and Energy-dispersive X-ray spectroscopy (EDX) analysis were used to examine and correlate structural device information with the development of PSC electrical properties. While a strong perovskite decomposition and further iodide diffusion to the contacts were detected for devices using Al, Ag or Au as cathode electrodes, the microstructure of Ni cathodes inhibits such decomposition process. This experiment has allowed for the realization of MAPI based solar cells with Ni contacts, which exhibit no efficiency decrease below as-fabricated values for up to one month of storage and select AM1.5 testing in ambient atmosphere.

physics.app-ph↗

arXiv2013

Laser-Doping of Crystalline Silicon Substrates using Doped Silicon Nanoparticles

Crystalline Si substrates are doped by laser annealing of solution processed Si. For this experiment, dispersions of highly B-doped Si nanoparticles (NPs) are deposited onto intrinsic Si and laser processed using an 807.5nm cw-laser. During laser processing the particles as well as a surface-near substrate layer are melted to subsequently crystallize in the same orientation as the substrate. The doping profile is investigated by secondary ion mass spectroscopy revealing a constant B concentration of 2x10^18 cm^-3 throughout the entire analyzed depth of 5μm. Four-point probe measurements demonstrate that the effective conductivity of the doped sample is increased by almost two orders of magnitude. The absolute doping depth is estimated to be in between 8μm and 100μm. Further, a pn-diode is created by laser doping an n-type c-Si substrate using the Si NPs.

cond-mat.mtrl-sci↗

arXiv2012

Reduced Coulomb interaction in organic solar cells by the introduction of inorganic high-k nanostructured materials

In this article a concept is introduced, which allows for reduced Coulomb interaction in organic solar cells and as such for enhanced power conversion efficiencies. The concept is based on the introduction of electrically insulating, nanostructured high-k materials into the organic matrix, which do not contribute to the charge transport, however, effectively enhance the permittivity of the organic active layer and thereby reduce the Coulomb interaction. Using an analytical model it is demonstrated that even at a distance of 20 nm to the organic / inorganic interface of the nanostructure, the Coulomb interaction can be reduced by more than 15 %. The concept is implemented using P3HT:PCBM solar cells with integrated high-k nanoparticles (strontium titanate). It could be demonstrated that in comparison to a reference cell without integrated nanoparticles, the power conversion efficiencies could be improved by ~20 %.

cond-mat.mtrl-sci↗

arXiv2012

Laser-sintered thin films of doped SiGe nanoparticles

We present a study of the morphology and the thermoelectric properties of short-pulse laser-sintered (LS) nanoparticle (NP) thin films, consisting of SiGe alloy NPs or composites of Si and Ge NPs. Laser-sintering of spin-coated NP films in vacuum results in a macroporous percolating network with a typical thickness of 300 nm. The Seebeck coefficient is independent of the sintering process and typical for degenerate doping. The electrical conductivity of LS films rises with increasing temperature, best described by a power-law and influenced by two-dimensional percolation effects.

cond-mat.mtrl-sci↗