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.

high photoluminescence quantum yield (PLQY), wide wavelength tunability, and high color purity, [4][5][6] they have been attractive for light-emitting diode (LED) applications. Since the first demonstration of perovskite LEDs in 2014, [7] the device external quantum efficiency (EQE) has risen rapidly from 0.1% [7] to ≈20%, [2,4,8] and the efficiency enhancements are mainly attributed to passivation and compositional engineering, [2,8] improved charge balance by optimization of device structure, [9] and efficient light extraction. [4] More recently, these materials are considered as optical gain medium for lasers. In 2014, the first amplified spontaneous emission (ASE) was observed from CH 3 NH 3 PbI 3 thin films with a threshold of 12 µJ cm −2 and a gain of 250 cm −1 , which is ascribed to the large absorption coefficient, low bulk defect density, and slow Auger recombination rate. [10] These ASE threshold and gain values are comparable to the state of art gain media such as colloidal quantum dots [11] and organic thin films. [12] Since then, optically pumped lasers have been demonstrated based on various microcavity structures such as Fabry-Pérot cavities, [13,14] distributed feedback (DFB) gratings, [3,15] and whispering gallery cavities. [16] The flexibility of fabricating hybrid perovskite lasers using solution-processed methods enables large-scale production and is attractive for the realization of on-chip integration of photonic circuits. [17] Quasi-2D perovskites, which are also known as Ruddlesden-Popper (RP) perovskites, are mixed phases of 2D and 3D nanocrystals. In the mixture, 2D domains exhibit quantumwell-like electronic properties with strong exciton binding energy due to the reduced dimensionality. [18] Typically, the 2D perovskite (A') 2 A n−1 B n X 3n+1 domains consist of multilayers of BX 6 octahedra separated by intercalating ammonium cations A', which is too large to fit into the crystal structure and hinder the growth of 3D ABX 3 crystals (A = methylammonium (MA + ), formamidinium (FA + ), or Cs + , B = Pb 2+ , and X = I − , Br − , Cl − ). As a result, the number of layers determine the bandgap of 2D quantum-well-like domains. [19] Different from 3D perovskites, thin films of qausi-2D perovskites typically contain a mixture of domains with different layers. Within such inhomogenous Quasi-2D Ruddlesden-Popper halide perovskites with a large exciton binding energy, self-assembled quantum wells, and high quantum yield draw attention for optoelectronic device applications. Thin films of these quasi-2D perovskites consist of a mixture of domains having different dimensionality, allowing energy funneling from lower-dimensional nanosheets (high-bandgap domains) to 3D nanocrystals (low-bandgap domains). High-quality quasi-2D perovskite (PEA) 2 (FA) 3 Pb 4 Br 13 films are fabricated by solution engineering. Grazing-incidence wide-angle X-ray scattering measurements are conducted to study the crystal orientation, and transient absorption spectroscopy measurements are conducted to study the charge-carr...

Organic solar cells (OSCs) have a bright prospect across applications where light weight, flexibility, low costs, and semi-transparent properties are essential. [1-4] Over the years, tremendous efforts have been devoted to the material design, device engineering, theoretical exploration, and large area manufacture of OSCs. [5-9] With Y6 [10] and its derivatives as acceptors, power conversion efficiencies (PCEs) of over 16% have now

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