@article{nokey,

title = {Ground-state structures, electronic structure, transport properties and optical properties of Ca-based anti-Ruddlesden-Popper phase oxide perovskites},

author = {D Han and M-H Du and M Huang and S Wang and G Tang and T Bein and H Ebert},

url = {https://link.aps.org/doi/10.1103/PhysRevMaterials.6.114601},

doi = {10.1103/PhysRevMaterials.6.114601},

year  = {2022},

date = {2022-11-07},

journal = {Physical Review Materials},

volume = {6},

number = {11},

pages = {114601},

abstract = {Anti-Ruddlesden-Popper (ARP) phase oxide perovskites Ca4OA2 (A=P, As, Sb, Bi) have recently attracted great interest in the field of ferroelectrics and thermoelectrics, whereas their optoelectronic application is limited by their indirect band gaps. In this work, we introduce A-site anion ordering in Ca4OA2 (A=P, As, Sb, Bi), and find that it induces an indirect-to-direct band gap transition. Using first-principles calculations, we study the ground-state structures, electronic structure, transport properties and optical properties of anion-ordered ARP phase oxide perovskites Ca4OAA′. Based on analyses of the lattice dynamics, the ground-state structures of Ca4OAsSb and Ca4OAsBi are identified in P4/nmm symmetry and those of Ca4OPSb and Ca4OPBi are in the I222 symmetry. In contrast to the Ruddlesden-Popper (RP) phase oxide and halide counterparts, Ca4OAA′ (AA′=PSb, PBi, AsSb, AsBi) show larger band dispersion along the out-of-plane direction, smaller band gaps and highly enhanced out-of-plane mobilities, which results from the short interlayer distances and the enhanced covalency of the pnictides. Although the out-of-plane mobilities of these n=1 ARP phase perovskites highly increase, the comparatively strong polar optical phonon scattering limits the further enhancement of their mobilities. Furthermore, compared to RP phase halide Cs2PbI2Cl2, Ca4OAA′ show strong optical absorption around the band edges, and their optical absorption coefficients can reach 10^5 cm−1 within the visible light region due to small band gaps. This study reveals that these ARP phase oxide perovskites exhibit the potential for optoelectronic applications.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Mapping structure heterogeneities and visualizing moisture degradation of perovskite films with nano-focus WAXS},

author = {N Li and S Pratap and V K\"{o}rstgens and S Vema and L Song and S Liang and A Davydok and C Krywka and P M\"{u}ller-Buschbaum},

url = {https://doi.org/10.1038/s41467-022-34426-y},

doi = {10.1038/s41467-022-34426-y},

issn = {2041-1723},

year  = {2022},

date = {2022-11-05},

journal = {Nature Communications},

volume = {13},

number = {1},

pages = {6701},

abstract = {Extensive attention has focused on the structure optimization of perovskites, whereas rare research has mapped the structure heterogeneity within mixed hybrid perovskite films. Overlooked aspects include material and structure variations as a function of depth. These depth-dependent local structure heterogeneities dictate their long-term stabilities and efficiencies. Here, we use a nano-focused wide-angle X-ray scattering method for the mapping of film heterogeneities over several micrometers across lateral and vertical directions. The relative variations of characteristic perovskite peak positions show that the top film region bears the tensile strain. Through a texture orientation map of the perovskite (100) peak, we find that the perovskite grains deposited by sequential spray-coating grow along the vertical direction. Moreover, we investigate the moisture-induced degradation products in the perovskite film, and the underlying mechanism for its structure-dependent degradation. The moisture degradation along the lateral direction primarily initiates at the perovskite-air interface and grain boundaries. The tensile strain on the top surface has a profound influence on the moisture degradation.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Picosecond Charge-Transfer-State Dynamics in Wide Band Gap Polymer\textendashNon-Fullerene Small-Molecule Blend Films Investigated via Transient Infrared Spectroscopy},

author = {M Nuber and L V Spanier and S Roth and G N Vayssilov and R Kienberger and P M\"{u}ller-Buschbaum and H Iglev},

url = {https://doi.org/10.1021/acs.jpclett.2c02864},

doi = {10.1021/acs.jpclett.2c02864},

year  = {2022},

date = {2022-11-03},

journal = {The Journal of Physical Chemistry Letters},

pages = {10418-10423},

abstract = {Organic solar cells based on wide band gap polymers and nonfullerene small-molecule acceptors have demonstrated remarkably good device performances. Nevertheless, a thorough understanding of the charge-transfer process in these materials has not been achieved yet. In this study, we use Fano resonance signals caused by the interaction of broad electronic charge carrier absorption and the molecular vibrations of the electron acceptor molecule to monitor the charge-transfer state dynamics. In our time-resolved infrared spectroscopy experiments, we find that in the small-molecule acceptor, they have additional dynamics on the order of a few picoseconds. A change in the solvent used in thin film deposition, leading to different morphologies, influences this time further. We interpret our findings as the dynamics of the charge-transfer state at the interface of the electron donor and the electron- acceptor. The additional mid-infrared transient signal is generated in this state, as both electron and hole polarons can interact with small-molecule acceptor vibrational modes.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}