Beschreibung:
Metal-halide perovskites are promising materials for applications like lasers and solar cells. In this work, we show the importance of an accurate determination of the source material parameters (acoustic impedance ratio and density) for thermal co-evaporation of soft materials like perovskites. We use here methylammonium iodide and lead(II)iodide for the exemplary deposition of methylammoniumlead(II)triiodide. We measure the thickness of the deposited layers by scanning electron microscopy cross sections and monitor the frequency change of the quartz crystal microbalances. We use a model with a one-dimensional acoustical composite resonator for the correct determination of the acoustic impedance ratio, resulting in values of 0.025 ± 0.002 for methylammonium iodide and of 0.11 ± 0.01 for lead(II)iodide. We use the resulting material parameters to deposit a layer of crystalline methylammonium lead triiodide with an accurately controlled stoichiometry of MAPbIx with x = 3.2 ± 0.2. We show the impact assuming false acoustic impedance ratios by simulating the actual evaporation rates of the source materials. We show that the ratio of the evaporation rates changes significantly during the deposition process. This results in a strong stoichiometry gradient in the perovskite layer and a mismatch in the average stoichiometry for a typical absorber thickness of 600 nm.