The electronic wavefunctions of an atom or molecule are affected by its interactions with its environment. These interactions dictate electronic and optical processes at interfaces, and is especially ...relevant in the case of thin film optoelectronic devices such as organic solar cells. In these devices, charge transport and interfaces between multiple layers occur along the thickness or vertical direction, and thus such electronic interactions are crucial in determining the device properties. Here, we introduce a new in-situ spectroscopic ellipsometry data analysis method called DART with the ability to directly probe electronic coupling due to intermolecular interactions along the thickness direction using vacuum-deposited organic semiconductor thin films as a model system. The analysis, which does not require any model fitting, reveals direct observations of electronic coupling between frontier orbitals under optical excitations leading to delocalization of the corresponding electronic wavefunctions with thickness or, equivalently, number of molecules away from the interface in C60 and MeO-TPD deposited on an insulating substrate (SiO2). Applying the same methodology for C60 deposited on phthalocyanine thin films, the analyses shows strong, anomalous features - in comparison to C60 deposited on SiO2 - of the electronic wavefunctions corresponding to specific excitation energies in C60 and phthalocyanines. Translation of such interactions in terms of dielectric constants reveals plasmonic type resonance absorptions resulting from oscillations of the excited state wavefunctions between the two materials across the interface. Finally, reproducibility, angstrom-level sensitivity and simplicity of the method are highlighted showcasing its applicability for studying electronic coupling between any vapor-deposited material systems where real-time measurements during deposition are possible.
Previous theoretical calculations show azetidinium has the right radial size to form a 3D perovskite with lead halides 1, and has been shown to impart, as the A-site cation of ABX3 unit, beneficial ...properties to ferroelectric perovskites 2. However, there has been very limited research into its use as the cation in lead halide perovskites to date. In this communication we report the synthesis and characterization of azetidinium-based lead mixed halide perovskite colloidal nanocrystals. The mixed halide system is iodine and chlorine unlike other reported nanocrystals in the literature where the halide systems are either iodine/bromine or bromine/chlorine. UV-visible absorbance data, complemented with photoluminescence spectroscopy, reveals an indirect-bandgap of about 1.96 eV for our nanocrystals. Structural characterization using TEM shows two distinct interatomic distances (2.98 +/- 0.15 Angstroms and 3.43 +/- 0.16 Angstroms) and non-orthogonal lattice angles (approximately 112 degrees) intrinsic to the nanocrystals with a probable triclinic structure revealed by XRD. The presence of chlorine and iodine within the nanocrystals is confirmed by EDS spectroscopy. Finally, light-induced electron paramagnetic resonance (LEPR) spectroscopy with PCBM confirms the photoinduced charge transfer capabilities of the nanocrystals. The formation of such semiconducting lead mixed halide perovskite using azetidinium as the cation suggests a promising subclass of hybrid perovskites holding potential for optoelectronic applications such as in solar cells and photodetectors.
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