Three-dimensional (3D) hybrid organic−inorganic lead halide perovskites (HOIPs) feature remarkable optoelectronic properties for solar energy conversion but suffer from longstanding issues of environmental stability and lead toxicity. Associated two-dimensional (2D) analogues are garnering increasing interest due to superior chemical stability, structural diversity, and broader property tunability. Toward lead-free 2D HOIPs, double perovskites (DPs) with mixed-valent dual metals are attractive. Translation of mixed-metal DPs to iodides, with their prospectively lower bandgaps, represents an important target for semiconducting halide perovskites, but has so far proven inaccessible using traditional spacer cations due to either intrinsic instability or formation of competing non-perovskite phases. Here, we demonstrate the first example of a 2D Ag−Bi iodide DP with a direct bandgap of 2.00(2) eV, templated by a layer of bifunctionalized oligothiophene cations, i.e., (bis-aminoethyl)bithiophene, through a collective influence of aromatic interactions, hydrogen bonding, bidentate tethering, and structural rigidity. Hybrid density functional theory calculations for the new material reveal a direct bandgap, consistent with the experimental value, and relatively flat band edges derived principally from Ag-d/I-p (valence band) and Bi-p/I-p (conduction band) states. This work opens up new avenues for exploring specifically designed organic cations to stabilize otherwise inaccessible 2D HOIPs with potential applications for optoelectronics.

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...

RIR-MAPLE enables thin-film deposition of organic–inorganic materials with tunable synergistic photophysics.