We report the composition-dependent optical properties of Bi-doped Cs 2 Ag 1−x Na x InCl 6 nanocrystals (NCs) having a double perovskite crystal structure. Their photoluminescence (PL) was characterized by a large Stokes shift, and the PL quantum yield increased with the amount of Na up to ∼22% for the Cs 2 Ag 0.4 Na 0.6 InCl 6 stoichiometry. The presence of Bi 3+ dopants was crucial to achieve high PL quantum yields (PLQYs) as nondoped NC systems were not emissive. Density functional theory calculations revealed that the substitution of Ag + with Na + leads to localization of AgCl 6 energy levels above the valence band maximum, whereas doping with Bi 3+ creates BiCl 6 states below the conduction band minimum. As such, the PL emission stems from trapped emission between states localized in the BiCl 6 and AgCl 6 octahedra, respectively. Our findings indicated that both the partial replacement of Ag + with Na + ions and doping with Bi 3+ cations are essential in order to optimize the PL emission of these systems.

A novel liquid-phase exfoliation of layered crystals enables the production of defect-free and high quality 2D-crystal dispersions on a large scale.

Solution-processed few-layer MoS 2 fl akes are exploited as an active buffer layer in hybrid lead-halide perovskite solar cells (PSCs). Glass/FTO/compact-TiO 2 /mesoporous-TiO 2 /CH 3 NH 3 PbI 3 /MoS 2 /Spiro-OMeTAD/Au solar cells are realized with the MoS 2 fl akes having a twofold function, acting both as a protective layer, by preventing the formation of shunt contacts between the perovskite and the Au electrode, and as a hole transport layer from the perovskite to the Spiro-OMeTAD. As prepared PSC demonstrates a power conversion effi ciency ( η ) of 13.3%, along with a higher lifetime stability over 550 h with respect to reference PSC without MoS 2 (Δ η / η = −7% vs. Δ η / η = −34%). Large-area PSCs (1.05 cm 2 active area) are also fabricated to demonstrate the scalability of this approach, achieving η of 11.5%. Our results pave the way toward the implementation of MoS 2 as a material able to boost the shelf life of large-area perovskite solar cells in view of their commercialization.

We report the synthesis of colloidal CsPbX3–Pb4S3Br2 (X = Cl, Br, I) nanocrystal heterostructures, providing an example of a sharp and atomically resolved epitaxial interface between a metal halide perovskite and a non-perovskite lattice. The CsPbBr3–Pb4S3Br2 nanocrystals are prepared by a two-step direct synthesis using preformed subnanometer CsPbBr3 clusters. Density functional theory calculations indicate the creation of a quasi-type II alignment at the heterointerface as well as the formation of localized trap states, promoting ultrafast separation of photogenerated excitons and carrier trapping, as confirmed by spectroscopic experiments. Postsynthesis reaction with either Cl– or I– ions delivers the corresponding CsPbCl3–Pb4S3Br2 and CsPbI3–Pb4S3Br2 heterostructures, thus enabling anion exchange only in the perovskite domain. An increased structural rigidity is conferred to the perovskite lattice when it is interfaced with the chalcohalide lattice. This is attested by the improved stability of the metastable γ phase (or “black” phase) of CsPbI3 in the CsPbI3–Pb4S3Br2 heterostructure.

Colloidal lead sulfide nanosheets have attracted broad interest for a wide variety of device applications, including field-effect transistors, solar cells, and spintronic devices. Whereas confinement effects in PbS quantum dots are well studied, they are still unclear in 2-dimensional ultrathin PbS nanosheets, especially in the 1 nm thickness range. In this work, we report a synthesis of monodisperse, rectangular-shaped PbS nanosheets with a thickness of 1.2 nm, using Pb­(thiocyanate)2 as a single source precursor. These nanosheets have an orthorhombic crystal structure, a direct bandgap, and weak optical absorption properties. This is evident from the lack of both excitonic absorption features and photoluminescence, and was corroborated by density functional theory calculations. Although these properties make the PbS nanosheets unsuitable for emission based applications, the nanosheets are highly photoconductive in films, with a responsivity up to 0.1 A W–1 and a detectivity of 1.3 × 109 Jones. We detected higher photoconductivity of these films under bending stress compared to that of films of PbS quantum dots.