The trap states at grain boundaries (GBs) within polycrystalline perovskite films deteriorate their optoelectronic properties, making GB engineering particularly important for stable high-performance optoelectronic devices. It is demonstrated that trap states within bulk films can be effectively passivated by semiconducting molecules with Lewis acid or base functional groups. The perovskite crystallization kinetics are studied using in situ synchrotron-based grazing-incidence X-ray scattering to explore the film formation mechanism. A model of the passivation mechanism is proposed to understand how the molecules simultaneously passivate the Pb-I antisite defects and vacancies created by under-coordinated Pb atoms. In addition, it also explains how the energy offset between the semiconducting molecules and the perovskite influences trap states and intergrain carrier transport. The superior optoelectronic properties are attained by optimizing the molecular passivation treatments. These benefits are translated into significant enhancements of the power conversion efficiencies to 19.3%, as well as improved environmental and thermal stability of solar cells. The passivated devices without encapsulation degrade only by ≈13% after 40 d of exposure in 50% relative humidity at room temperature, and only ≈10% after 24 h at 80 °C in controlled environment.

Quasi-one-dimensional nanotubes and two-dimensional nanoribbons are two fundamental forms of nanostructures, and integrating them into a novel mixed low-dimensional nanomaterial is fascinating and challenging. We have synthesized a stable mixed low-dimensional nanomaterial consisting of MoS(2) inorganic nanoribbons encapsulated in carbon nanotubes (which we call nanoburritos). This route can be extended to the synthesis of nanoburritos composed of other ultranarrow transition-metal chalcogenide nanoribbons and carbon nanotubes. The widths of previously synthesized MoS(2) ribbons are greater than 50 nm, while the encapsulated MoS(2) nanoribbons have uniform widths down to 1-4 nm and layer numbers down to 1-3, depending on the nanotube diameter. The edges of the MoS(2) nanoribbons have been identified as zigzag-shaped using both high-resolution transmission electron microscopy and density functional theory calculations.

light-emitting diodes, [5][6][7] and photodetectors, [8,9] because of their remarkable structural flexibility, tunability, and excellent stability compared with their 3D perovskite counterparts. [10][11][12] 2D perovskites are generally a class of quantum wells (QWs), including Ruddlesden-Popper (RP), [13][14][15] Dion-Jacobson (DJ), [16][17][18] and alternating cations in the interlayer space (ACI) perovskites. [19,20] The RP and DJ families adopt the general formulas A′ 2 A n−1 M n X 3n+1 and BA n−1 M n X 3n+1 , respectively, where A is a univalent organic cation: methylammonium (MA + ) or formamidinium (FA + ), A′ is a large univalent organic spacer cation like phenylethylammonium (PEA + ), [8,21] or butylammonium (BA + ), etc., [3,22] B is a divalent organic cation like 3-(aminomethyl)piperidinium (3AMP 2+ ) [10] or 1,3-propanediamine. [23] Much work on 2D perovskites to date has focused on the RP and DJ families. For example, it was found that the incorporation of large organic spacer cations leads to the formation of a QW structure with strong quantum confinement, which leads to a higher bandgap and large exciton binding energy. [14,[24][25][26][27] The RP and DJ perovskites feature poor charge dissociation and transportation within the bulk polycrystalline film, which significantly limits the power conversion efficiency (PCE) of solar cells. [28][29][30] To address the issue, a hot-casting strategy was developed to achieve preferential outof-plane alignment of RP QWs. [3] A systematic understanding of how RP perovskites are formed as well as the charge transfer between QWs were also demonstrated, which guided development of the dynamic control of the phase transformation during QWs growth for better compositional and orientation control. [31][32][33][34][35][36] Compositional and solvent engineering were also developed to fabricate high-quality DJ films with significantly improved charge transport. [23,37] For the RP and DJ families, much has been achieved toward a deep understanding of the relationships between molecular chemistry, crystal structure, film quality and optoelectronic properties, leading to outstanding PCEs of 15.42% and 13.3% for PR and DJ perovskite solar cells, respectively. [23,38] The hybrid halide ACI perovskites, which are derived from the oxide perovskite family, are a very new entry in the class 2D perovskites stabilized by alternating cations in the interlayer space (ACI) represent a very new entry as highly efficient semiconductors for solar cells approaching 15% power conversion efficiency (PCE). However, further improvements will require understanding of the nature of the films, e.g., the thickness distribution and charge-transfer characteristics of ACI quantum wells (QWs), which are currently unknown. Here, efficient control of the film quality of ACI 2D perovskite (GA)(MA) n Pb n I 3n+1 (〈n〉 = 3) QWs via incorporation of methylammonium chloride as an additive is demonstrated. The morphological and optoelectronic characterizations unambiguously demonstrate that the additive ena...