arXiv subjects

Sebastian Weitz

Publications and source records attributed to Sebastian Weitz.

4 recordsLinked to original sources

arXiv2025

CsCl seed layer homogenizes co-evaporated perovskite growth for high-efficiency fully textured perovskite-silicon tandem solar cells

Monolithic perovskite-silicon tandem solar cells experienced a significant increase in efficiency, making them viable for industrial applications. Among the various scalable and industry-compatible metal halide perovskite deposition techniques, co-evaporation stands out as particularly well-suited for perovskite-silicon tandem solar cells due to its ability to conformally cover textured silicon bottom cells. Solution-processed [2-(3,6-Dimethoxy-9H-carbazol-9-yl)ethyl]phosphonic acid (MeO-2PACz) is commonly used as a hole-transporting material for co-evaporated metal halide perovskites. However, we show that it covers the textured surface of silicon bottom cells unevenly, impacting the film growth and leading to the formation of residual PbI2 at the buried interface. The present study reveals via X-ray photoemission electron microscopy (XPEEM) and infrared scattering-type scanning near-field optical microscope (IR s-SNOM) that a CsCl seed layer fosters organic precursor incorporation across the MeO-2PACz/perovskite interface, even in the areas with a thin MeO-2PACz layer, thereby preventing the formation of interfacial PbI2 and leading to larger apparent grains. The improvement of the metal halide perovskite film quality on the MeO-2PACz/perovskite interface and the bulk perovskite film led to 30.3% (29.7% certified) efficient perovskite-silicon tandem solar cell. The present work highlights the importance of a seed layer for a robust growth of co-evaporated metal halide perovskite and represents an important milestone for the transfer of perovskite-silicon tandem solar cells from laboratory to industry.

cond-mat.mtrl-sci↗

arXiv2016

Addressing nonlinearities in Monte Carlo

Monte Carlo is famous for accepting model extensions and model refinements up to infinite dimension. However, this powerful incremental design is based on a premise which has severely limited its application so far: a state-variable can only be recursively defined as a function of underlying state-variables if this function is linear. Here we show that this premise can be alleviated by projecting nonlinearities onto a polynomial basis and increasing the configuration space dimension. Considering phytoplankton growth in light-limited environments, radiative transfer in planetary atmospheres, electromagnetic scattering by particles, and concentrated solar power plant production, we prove the real-world usability of this advance in four test cases which were previously regarded as impracticable using Monte Carlo approaches. We also illustrate an outstanding feature of our method when applied to acute problems with interacting particles: handling rare events is now straightforward. Overall, our extension preserves the features that made the method popular: addressing nonlinearities does not compromise on model refinement or system complexity, and convergence rates remain independent of dimension. Published: Dauchet J, Bezian J-J, Blanco S, Caliot C, Charon J, Coustet C, El Hafi M, Eymet V, Farges O, Forest V, Fournier R, Galtier M, Gautrais J, Khuong A, Pelissier L, Piaud B, Roger M, Terr\'ee G, Weitz S (2018) Addressing nonlinearities in Monte Carlo. Sci. Rep. 8: 13302, DOI:10.1038/s41598-018-31574-4

physics.comp-ph↗

arXiv2015

Self-propelled rods exhibit a novel phase-separated state characterized by the presence of active stresses and the ejection of polar clusters

We study collections of self-propelled rods (SPR) moving in two dimensions for packing fractions less than or equal to 0.3. We find that in the thermodynamical limit the SPR undergo a phase transition between a disordered gas and a novel phase-separated system state. Interestingly, (global) orientational order patterns -- contrary to what has been suggested -- vanish in this limit. In the found novel state, the SPR self-organize into a highly dynamical, high-density, compact region - which we call aggregate - which is surrounded by a disordered gas. Active stresses build inside aggregates as result of the combined effect of local orientational order and active forces. This leads to the most distinctive feature of these aggregates: constant ejection of polar clusters of SPR. This novel phase-separated state represents a novel state of matter characterized by large fluctuations in volume and shape, related to mass ejection, and exhibits positional as well as orientational local order. SPR systems display new physics unseen in other active matter systems due to the coupling between density, active stresses, and orientational order (such coupling cannot be reduced simply to a coupling between speed and density).

physics.bio-ph↗

arXiv2013

Attractive asymmetric inclusions in elastic membranes under tension: cluster phases and membrane invaginations

Up-down asymmetric inclusions impose a local, spontaneous curvature to an elastic membrane. When several of them are inserted in a same membrane, they feel effective forces mediated by the membrane, both of elastic and entropic nature. Following an approach initiated by Dommersnes and Fournier in the vanishing tension case [Eur. Phys. J. B 12, 9 (1999)], and also using a pseudo-analytical micellization theory, we derive the statistical mechanics of asymmetric inclusion assemblies when they are also subject to an additional short-range, attractive interaction. Our main conclusion is that generically, when the membrane is under tension, these inclusions live in small clusters at equilibrium, leading to local membrane invaginations. We also propose a novel curvature-induced demixing mechanism: when inclusions imposing local curvatures of opposite sign coexist, they tend to demix in distinct clusters under realistic conditions. This work has potential implications in the context of the thermodynamics of proteins embedded in biological lipid bilayers.

cond-mat.soft↗