The effect of the incorporation of Cs+ and Br− in FAPbl3 investigated by Raman spectroscopy.

Hydrogen bonds impact many material properties due to the bond directionality and collective strength. For them to exist, the atoms connected to hydrogen should possess high electronegativity, the distance between the interacting atoms should be less than their van der Waals radii, and there should be a charge transfer between them. In hybrid perovskites, the impact of hydrogen bonds is ascribed to several phenomena. Among them are the effect of passivation at the surface, structural stability of the mixed cation compounds, structural instability of FAPbI3, and ferroelectric behavior. In this paper, we applied a deterministic method to prove the existence of hydrogen bonds using Raman spectroscopy. This approach was successfully applied to water and is based on the emergence of a Raman mode as a result of the intermolecular charge transfer, which is not measured for the isolated molecule. With the help of DFT calculations, we attributed the Raman modes detected at room temperature (RT) for MAI and FAI and compared them with the Raman spectra of MAPbX3 and FAPbX3. This comparison has shown that there are no hydrogen bonds in hybrid lead halide perovskites at RT.

In this contribution, the impact of thermal stress on Cu(In,Ga)Se 2 (CIGSe) thin film photovoltaic devices is investigated. The tolerance of such devices to high temperatures is of particular interest for processing transparent conductive oxides (TCOs) in order to further close the gap to the theoretical efficiency limit and for their potential use as bottom devices in tandem applications in order to overcome the theoretical efficiency limit of single junction solar cells. When CdS-buffered CIGSe high efficiency solar cells are subjected to thermal stress, elemental interdiffusion of Na and Cd between the absorber and the window layers as well as chemical reactions at the CIGSe/CdS interface result in a degraded power conversion efficiency (PCE). Here, we compare the degradation mechanisms of CdS and GaO x buffered CIGSe solar cells under thermal stress. A model explaining the observed degradation behaviors is proposed. Index Terms-Amorphous buffer layer, Cu(In,Ga)Se 2 (CIGSe) solar cells, CdS, thermal stability, GaO x. I. INTRODUCTION C u(In,Ga)Se 2 (CIGSe) thin film solar cells have attracted the attention of science and industry by attaining a maximum Manuscript

Formamidinium lead iodide (FAPbI3) can exhibit polymorphism at ambient conductions. Three different structural configurations and their thermally activated phase transitions are identified by temperature dependent micro-Raman spectroscopy.