Interfacial charge transfer processes in 2D and 3D semiconducting hybrid perovskites: azobenzene as photoswitchable ligand

Abstract

In the vast majority of studies on semiconductor particles ligands or capping agents are used that bind to the surface of the particles covering them with an electrically insulating shell. Since the transport of charge carriers and/or energy across interfaces is desirable for a variety of applications, the use of π-conjugated ligands becomes increasingly interesting. Among them are compounds that react to external stimuli. Molecular switches in particular are fascinating because the properties of the interfaces can be potentially adjusted as required. However, there is debate about how the properties of such special ligands are influenced by the presence of a semiconductor and vice versa. Here ammonium-modified azobenzene compounds were selected as prototypes for molecular switches and organic–inorganic hybrid perovskites as semiconductor materials. The class of ammonium–lead–halide phases as prototypes is peculiar because, in addition to the surface functionalization of 3D crystals, organic compounds can actually be incorporated into the crystal as 2D phases. Thus, for example, layered Ruddlesden–Popper phases are obtained. We present photoswitchable azobenzene ligands with different head-group lengths for the synthesis of 2D and 3D hybrid perovskite phases. The energy transfer mechanisms are influenced by the length of the molecular spacer moiety, which determines the distance between the π system and the semiconductor surfaces. We find huge differences in the photoswitching behaviour between the free, surface-coordinated and integrated ligands between the perovskite layers. Photoswitching of azobenzene ligands incorporated in 2D phases is nearly quenched, while the same mechanism for surface-coordinating ligands is greatly improved, compared to the free ligands. The improvement originates from an energy transfer from perovskite to azobenzene, which is strongly distance-dependent. This study provides evidence for the photoswitching of azobenzenes as ligands of hybrid perovskites, which depends on the spacing between the chromophore and the perovskite phase.

Design of Active Defects in Semiconductors: 3D Electron Diffraction Revealed Novel Organometallic Lead Bromide Phases Containing Ferrocene as Redox Switches

“…However, from the intensity distribution of the profile in the 2θ range between 12° and 40° of the PXRD pattern (Figure S11, Supporting Information, n = 6), it can be deduced that [FcC 6 Br] Pb is a Ruddlesden–Popper phase with the composition (FcC 6 ) 2 PbBr 4 . [ 34 ] A structure was modeled and optimized by DFT‐D (see Figure 2, Table 1; Figure S12, Supporting Information).…”

“…[30] The role of the organic ligands is equally important. [31] Conductive, [30,32] polymerizable, [33] and photoactive [34] organic functionalities have already been incorporated into LHPs. It has not yet been possible to incorporate a ligand with which the electro-optical properties, e.g., the bandgap or photoluminescence properties can actively be controlled.…”

“…One might think that photoactive ligands are most suitable for this purpose, but electronically active transition states are quenched by the semiconductor. [34] Zhang et al presented an important paper on 1D lead halide phase containing ferrocene (Fc) with exceptional piezoelectric properties. [35] The paper envisions that the combination of organometallic compounds with the structurally diverse class of hybrid perovskites opens up novel possibilities.…”

On the Shape-Selected, Ligand-Free Preparation of Hybrid Perovskite (CH3NH3PbBr3) Microcrystals and Their Suitability as Model-System for Single-Crystal Studies of Optoelectronic Properties

“…Recently, we have gained substantial experience in the past with a novel singlesource precursor system for hybrid perovskites (Figure 1b) [43,48,49,[53][54][55]. The precursor is obtained by reacting PbX 2 (X = Br, I) with an equimolar amount of CH 3 NH 3 X and ethylene glycol derivatives such as TEG (tri-ethylene glycol; C 6 H 14 O 2 ).…”

Photoswitchable Molecular Glue for Carbon Nanotubes Reversibly Controls Electronic Mobility with Light

“…Both have their own unique advantages and have been applied in various fields. − MWCNTs have attracted particular focus as they can be produced in large quantities and are easier to purify. Therefore, the cost of production of MWCNTs is significantly lower than that of SWCNTs, which has been a prime reason for the former’s adoption in many scientific research studies. − Both these nanotubes possess similar properties in terms of their high thermal and electrical conductivities. − …”