arXiv subjects

Michelle Ernst

Publications and source records attributed to Michelle Ernst.

2 recordsLinked to original sources

arXiv2024

Understanding and exploiting interfacial interactions between phosphonic acid functional groups and co-evaporated perovskites

Interfacial engineering has fueled recent development of p-i-n perovskite solar cells (PSCs), with self-assembled monolayer-based hole-transport layers (SAM-HTLs) enabling almost lossless contacts for solution-processed PSCs, resulting in the highest achieved power conversion efficiency (PCE) to date. Substrate interfaces are particularly crucial for the growth and quality of co-evaporated PSCs. However, adoption of SAM-HTLs for co-evaporated perovskite absorbers is complicated by the underexplored interaction of such perovskites with phosphonic acid functional groups. In this work, we highlight how exposed phosphonic acid functional groups impact the initial phase and final bulk crystal structures of co-evaporated perovskites and their resultant PCE. The explored surface interaction is mediated by hydrogen bonding with interfacial iodine, leading to increased formamidinium iodide adsorption, persistent changes in perovskite structure, and stabilization of bulk {\alpha}-FAPbI3, hypothesized as being due to kinetic trapping. Our results highlight the potential of exploiting substrates to increase control of co-evaporated perovskite growth.

cond-mat.mtrl-sci↗

arXiv2020

Frozen-Density Embedding Theory based simulations with experimental electron densities

The basic idea of Frozen-Density Embedding Theory (FDET) is the constrained minimisation of the Hohenberg-Kohn density functional $E^{HK}[ρ]$ performed using the auxiliary functional $E_{v_{AB}}^{FDET}[Ψ_A,ρ_B]$, where $Ψ_A$ is the embedded $N_A$-electron wave-function and $ρ_B(\vec{\mathrm{r}})$ a non-negative function in real space integrating to a given number of electrons $N_B$. This choice of independent variables in the total energy functional $E_{v_{AB}}^{FDET}[Ψ_A,ρ_B]$ makes it possible to treat the corresponding two components of the total density using different methods in multi-level simulations. We demonstrate, for the first time, the applications of FDET using $ρ_B(\vec{\mathrm{r}})$ reconstructed from X-ray diffraction data on a molecular crystal. For eight hydrogen-bonded clusters involving a chromophore (represented with $Ψ_A$) and the glycylglycine molecule (represented as $ρ_B(\vec{\mathrm{r}})$), FDET is used to derive excitation energies. It is shown that experimental densities are suitable to be used as $ρ_B(\vec{\mathrm{r}})$ in FDET based simulations.

physics.chem-ph↗