Expanding the near-infrared (NIR) response of perovskite materials to approach the ideal bandgap range (1.1-1.4 eV) for single-junction solar cells is an attractive step to unleash the full potential of...

Hot carrier (HC) cooling is a critical photophysical process that significantly influences the optoelectronic performance of hybrid perovskite-based devices. The hot carrier extraction at the device interface is very challenging because of its ultrashort lifetime. Here, ultrafast transient reflectance spectroscopy measurements and time-domain ab initio calculations show how the dielectric constant of the organic spacers can control and slow the HC cooling dynamics in single-crystal 2D Ruddlesden−Popper hybrid perovskites. We find that (EA) 2 PbI 4 (EA = HOC 2 H 4 NH 3 + ) that correspond to a high dielectric constant organic spacer has a longer HC cooling time compared to that of (AP) 2 PbI 4 (AP = HOC 3 H 6 NH 3 + ) and (PEA) 2 PbI 4 (PEA = C 6 H 5 C 2 H 4 NH 3 +). The slow HC relaxation process in the former case can be ascribed to a stronger screening of the Coulomb interactions, a small nonradiative internal conversion within the conduction bands, as well as a weak electron−phonon coupling. Our findings provide a strategy to prolong the hot carrier cooling time in low-dimensional hybrid perovskite materials by using organic spacers with reduced dielectric confinement.

Here, we demonstrate an approach to synthesizing and structurally characterizing three atomically precise anion-templated silver thiolate nanoclusters, two of which form one-and two-dimensional structural frameworks composed of bipyridine-linked nanocluster nodes (referred to as nanocluster-based frameworks, NCFs). We describe the critical role of the chloride (Cl − ) template in controlling the nanocluster's nuclearity with atomic precision and the effect of a single Ag atom difference in the nanocluster's size in controlling the NCF dimensionality, modulating the optical properties, and improving the thermal stability. With atomically precise assembly and size control, nanoclusters could be widely adopted as building blocks for the construction of tunable cluster-based framework materials.

Two-dimensional (2D) Ruddlesden–Popper (RP) perovskites are emerging materials for light-emitting applications. Unfortunately, their desirable narrowband emission coexists with broadband emissions, which limits the color quality and performance of the light source. However, the origin of such broadband emission in ⟨100⟩-oriented perovskites is still under debate. Here, we experimentally and theoretically demonstrate that unlike ⟨110⟩-oriented RP perovskites, the broadband emission of the 2D ⟨100⟩-oriented RP (PEA)2PbI4 (PEA = C6H5C2H4NH3 +) perovskites originates from defect-related luminescence centers. We find that the broadband emission of this prototype 2D structure can be largely suppressed by using excess PEAI treatment. Density functional theory (DFT) calculations indicate that iodine (I) vacancies both in the bulk and on the surface are responsible for the broadband emission. We attribute the decreased broadband emission after PEAI treatment to the passivation of both undercoordinated Pb2+ ions on the surface and I vacancies in the bulk through I– ion migration.

Lead halide compounds, including lead halide perovskite nanocrystals (NCs), have attracted the interest of researchers in optoelectronics and photonics because of their high photoluminescence quantum yields (PLQYs) coupled with relatively short PL lifetimes (on the order of a few nanoseconds). However, lead-free metal halides of high PLQY, including double perovskites and their doped NCs, typically possess long PL lifetimes (up to microseconds) that limit their application space. Here, we introduce CsMnBr3 NCs, which are lead-free and red-emitting, that combine a high PLQY with an exceptionally short radiative lifetime (on the order of picoseconds). We find that the octahedral coordination of Mn2+ in CsMnBr3 induces a red emission centered at ∼643 nm with a PLQY of ∼54% and a fast radiative decay rate. Femtosecond transient absorption and transient PL spectroscopies reveal the existence of a low-lying excited state of Mn2+ that relaxes to the ground state within around 605 ps by emitting light at around 643 nm. At greater excitation energies, higher excited states of Mn2+ relax in the sub-nanosecond time scale to this low-lying excited state. A similarly positioned PL peak with a short picosecond scale PL lifetime and a PLQY of ∼6.7% was also detected in bulk CsMnBr3 single crystals reported in this studya relatively high quantum yield for a bulk material. Our experimental results and density functional theory modelling show that the crystal structure and the strong coupling among Mn2+ ions govern those luminescence properties of CsMnBr3 NCs and single crystals. These findings pave the way for new lead-free materials that combine high PLQY and ultrafast luminescence.