More than 10,000-fold enhanced magnetic resonance signals with >20-min signal lifetimes on universal biomolecular markers.

Chalcogenides such as CdTe, Cu­(In,Ga)­(S,Se)2 (CIGSSe), and Cu2ZnSn­(S,Se)4 (CZTSSe) have enabled remarkable advances in thin-film photovoltaic performance, but concerns remain regarding (i) the toxicity (CdTe) and (ii) scarcity (CIGSSe/CdTe) of the constituent elements and (iii) the unavoidable antisite disordering that limits further efficiency improvement (CZTSSe). In this work, we show that a different materials class, the BaCu2SnSe x S4–x (BCTSSe) system, offers a prospective path to circumvent difficulties (i–iii) and to target new environmentally friendly and earth-abundant absorbers. Antisite disordering and associated band tailing are discouraged in BCTSSe due to the distinct coordination environment of the large Ba2+ cation. Indeed, an abrupt absorption edge and sharp associated photoluminescence emission demonstrate a reduced impact of band tailing in BCTSSe relative to CZTSSe. Our combined experimental and computational studies of BCTSSe reveal that the compositions 0 ≤ x ≤ 4 exhibit a tunable nearly direct or direct bandgap in the 1.6–2 eV range, spanning relevant values for single- or multiple-junction photovoltaic applications. For the first time, a prototype BaCu2SnS4-based thin-film solar cell has been successfully demonstrated, yielding a power conversion efficiency of 1.6% (0.42 cm2 total area). The systematic experimental and theoretical investigations, combined with proof-of-principle device results, suggest promise for BaCu2SnSe x S4–x as a thin-film solar cell absorber.

For a class of 2D hybrid organic-inorganic perovskite semiconductors based on π-conjugated organic cations, we predict quantitatively how varying the organic and inorganic component allows control over the nature, energy and localization of carrier states in a quantum-well-like fashion. Our first-principles predictions, based on large-scale hybrid density-functional theory with spin-orbit coupling, show that the interface between the organic and inorganic parts within a single hybrid can be modulated systematically, enabling us to select between different type-I and type-II energy level alignments. Energy levels, recombination properties and transport behavior of electrons and holes thus become tunable by choosing specific organic functionalizations and juxtaposing them with suitable inorganic components.Hybrid organic-inorganic perovskites (HOIPs), [1, 2] particularly three-dimensional (3D) HOIPs, are currently experiencing a strong revival in interest as economically processable, optically active semiconductor materials with excellent transport characteristics. Their success is showcased most prominently by record performance gains in proof-of-concept photovoltaic [3][4][5][6][7][8][9][10][11][12] and light-emitting devices. [13][14][15][16][17][18][19][20] The electronic function of 3D HOIPs can be tuned to a limited extent by manipulating the inorganic component (from which the frontier orbitals are derived), but the organic cations are confined by the 3D structure and are thus necessarily small (e.g., methylammonium [3][4][5][6][7][8][13][14][15][16][17][18] and formamidinium [9-11, 19, 21, 22]), with electronic levels that do not contribute directly to the electronic functionality. [23][24][25][26][27][28] However, the accessible chemical space of HOIPs extends well beyond the 3D systems. [1] In particular, the layered, socalled two-dimensional (2D) perovskites do not place a strict length constraint on the organic cation. In these materials, a much broader range of functional organic molecules can be incorporated within the inorganic scaffolds, including complex functional molecules such as oligo-acene or -thiophene derivatives. [1,[29][30][31][32][33][34][35][36][37] Fig. 1a shows the atomic structure of a paradigmatic example of such a 2D HOIP with active organic functionality, bis(aminoethyl)-quaterthiophene lead bromide AE4TPbBr 4 .[34] Similar juxtapositions of targeted organic and inorganic components give rise to a vast, yet systematically accessible space of possible semiconductor materials, [1, 2,[38][39][40] including those in which the molecular carrier levels contribute directly to the low-lying excitations and carrier levels. [1, 30-32, 34, 38, 39, 41] This large space of conceivable organic-inorganic combinations thus offers the unique opportunity to tailor (ideally with computational guidance) materials with particularly desirable semiconductor properties, by intentionally controlling the spatial location and character of the electronic carriers and optical excitations throughout the m...

Using multiwavelets, we have obtained total energies and corresponding atomization energies for the GGA-PBE and hybrid-PBE0 density functionals for a test set of 211 molecules with an unprecedented and guaranteed µHartree accuracy. These quasi-exact references allow us to quantify the accuracy of standard all-electron basis sets that are believed to be highly accurate for molecules, such as Gaussian-type orbitals (GTOs), all-electron numeric atom-centered orbitals (NAOs) and full-potential augmented plane wave (APW) methods. We show that NAOs are able to achieve the so-called chemical accuracy (1 kcal/mol) for the typical basis set sizes used in applications, for both total and atomization energies. For GTOs, a triple-zeta quality basis has mean errors of ∼10 kcal/mol in total energies, while chemical accuracy is almost reached for a quintuple-zeta basis. Due to systematic error cancellations, atomization energy errors are reduced by almost an order of magnitude, placing chemical accuracy within reach also for medium to large GTO bases, albeit with significant outliers. In order to check the accuracy of the computed densities, we have also investigated the dipole moments, where in general, only the largest NAO and GTO bases are able to yield errors below 0.01 Debye. The observed errors are similar across the different functionals considered here.

We quantify the accuracy of different non-self-consistent and self-consistent spin-orbit coupling (SOC) treatments in Kohn-Sham and hybrid density-functional theory by providing a band structure benchmark set for the valence and low-lying conduction energy bands of 103 inorganic compounds, covering chemical elements up to Po. Reference energy band structures for the PBE density functional are obtained using the full-potential (linearized) augmented plane wave code Wien2k, employing its self-consistent treatment of SOC including Dirac-like p 1/2 orbitals in the basis set. We use this benchmark set to benchmark a computationally simpler, non-self-consistent all-electron treatment of SOC based on scalar-relativistic orbitals and numeric atom-centered orbital basis functions. For elements up to Z≈50, both treatments agree virtually exactly. For the heaviest elements considered (Tl, Pb, Bi, Po), the band structure changes due to SOC are captured with a relative deviation of 11% or less. For different density functionals (PBE vs. the hybrid HSE06), we show that the effect of spin-orbit coupling is usually similar but can be dissimilar if the qualitative features of the predicted underlying scalar-relativistic band structures do not agree. All band structures considered in this work are available online via the NOMAD Repository to aid in future benchmark studies and methods development.