Effects of Environment on Charge Recombination in Organo-Metal-Halide Perovskite Observed by Photoluminescence Microscopy and Spectroscopy

Abstract: Organo-metal-halide (OMH) perovskites form a new class of materials withperovskite crystal structure ABX3 where A is an organic molecule, B is lead (Pb)and X is a halide atom (I or Br). OMH perovskite semiconductors have been widely used in photovoltaics due to their very strong absorption of sun light, very suitable electrical properties, and the ease of preparation. Today the power conversion efficiency of record devices based on OMH is as large as 25.5%.There are still many challenges for commercial application of OMH perovskitebased solar cells and other devices. One of the problems we can formulate assensitivity of the properties of OMP semiconductors and devices based on them on factors like electric field, atmosphere, light, temperature and so on. Despite large efforts spent in the scientific community on investigation of the environmental effects on OMH perovskites and stability of devices many issues are still not wellunderstood.In this thesis, I present results of several research projects where photoluminescence (PL) properties of OMH perovskites were studied by optical luminescence microscopy and spectroscopy under different environmental conditions such as humidity, electric field, local pressure and low temperature. We observed that water molecules can play an important role in the transformation of OMH perovskite from its intermediate phase containing solvent molecules to the perovskite crystal structure. We found that both electric field and local pressure and mechanical damage at nano-scale can create temporal PL quenching in OMH perovskites microand nanocrystals. We propose that PL quenching is induced by deep defects states created by electric field, pressure or mechanical manipulation. However, the destructive influence of all these factors on PL disappears several minutes after the influence was stopped due to self-healing properties of OHP. By comparing PL spectra and PL intensity and cryogenic temperatures and at room temperature we found that the concentration of shallow defect states and deep defect states are proportional to each other.