Structural characterization of bulk and nanoparticle lead halide perovskite thin films by (S)TEM techniques

Abstract

In the last few years, lead halide (APbX3) perovskites, which are of interest for applications in photovoltaic and photonic devices, have demonstrated excellent optoelectronic performance. The structural characterization of APbX3 thin films using (scanning) transmission electron microscopy ((S)TEM) techniques can provide valuable information that can be used to understand their optoelectronic performance and device properties. However, since APbX3 perovskites are soft materials, their characterization using (S)TEM is challenging. Here, we study two APbX3 perovskite thin films: bulk CH3NH3PbI3, and nanoparticle (NP) CsPbBr3. Both specimen preparation methods and working conditions for analysis by (S)TEM are optimized. On the one hand, we show that CH3NH3PbI3 thin films grown by a one step method are composed of independent grains with random orientations. The growth method results in the formation of tetragonal perovskite films with good adherence to an underlying TiO2 layer and with a photoluminescence (PL) emission band that has a Gaussian shape and is centered at 775 nm. On the other hand, in the NP CsPbBr3 perovskite thin films the colloidal NPs, which are used as the building blocks of the film, are preserved by the deposition process. Small gaps are observed between adjacent NPs in the deposited film. The crystal structure is cubic, which is beneficial due its optimal band gap. The colloidal NPs shows similar absorption and PL in the thin film as in the colloidal solution, indicating good homogeneity and the absence of aggregation of NPs in the film. Care was required to avoid long electron irradiation times during these studies, even at a low voltage of 80 kV, as the material was observed to decompose through Pb segregation.

Octahedral distortion driven by CsPbI3 nanocrystal reaction temperature – the effects on phase stability and beyond

“…Pronounced segregation of Pb on the surface of halide perovskites has been associated with perovskite degradation. 20 However, the peak fitting of the XPS spectra (Fig. S1 †) does not hint to any degradation process, as the formation of Pb 0 (with binding energies at 136.9 eV and 141.3 eV) 21,22 was not detected.…”

Enhanced UV–visible detection of InGaZnO phototransistors via CsPbBr3 quantum dots

“…There are some fundamental differences exist between perovskite thin film and QDs thin film. First, QDs are small nanoparticles, which is much thinner than perovskite thin film [23][24][25]. Second, the QDs contain ligands that probably prevent effective charge transfer from QDs to IGZO channel [26].…”