Alexander Dobrovolsky
Lund University
Dr. Alexander Dobrovolsky is a postdoctoral research fellow at Chemical Physics department at Lund University (Sweden) in the group of Prof. Ivan Scheblykin. He received his PhD in Physics from Moscow State University (Russia) in 2010. Then he was a postdoc at Linköping University (Sweden) in the division of Functional Electronic Materials. His current research activities focus on optical microscopy and spectroscopy of single nanowires and nanoparticles.
Solution-processed organometal halide perovskites are hybrid semiconductors that are of high interest for low-cost and efficient solar cells, light-emitting diodes and laser devices. Despite the rapid development of their applications, there is still limited understanding of the fundamental photophysics in these materials. These soft crystalline solids undergo phase transitions, which alter the electronic and optical properties of the material significantly. In the current contribution, we present the study of transition from the tetragonal to orthorhombic crystal phase in individual methylammonium lead triiodide CH3NH3PbI3 nanowires by temperature-depended photoluminescence microspectroscopy and super-resolution imaging which was very recently published [1].
A wide range of phase transition temperatures in CH3NH3PbI3 has been reported in the literature; however, the cause of this variability remains unclear. Here we studied high-quality CH3NH3PbI3 nanowires grown by a surface-initiated solution fabrication method. We directly observed that tetragonal and orthorhombic crystal phases coexist in the same intact nanowire crystal in the form of nano-domains in the phase transition temperature range below 160 degrees Kelvin. The characteristic sizes of crystal phase domains and their temperature variation were estimated by super-resolution analysis of the photoluminescence images. We show that the temperature of crystal phase transition in these nanowires is strongly influenced by the concentration and nature of local defects. We observed a drastic photoluminescence enhancement during cooling from 160 to 140 K and a high spatial inhomogeneity of the photoluminescence (see spotty intensity pattern on a figure), which can be explained by formation of domains with defects being pushed out to the high-bandgap orthorhombic phase. The photoluminescence then stems from the remaining less-defected low-bandgap tetragonal domains where the charge carriers generated in the orthorhombic domains are trapped.
This effect may lead to new ideas for perovskite material manipulations to enhance their optoelectronic properties.
References
[1] A. Dobrovolsky, A. Merdasa, E.L. Unger, A. Yartsev, I.G. Scheblykin, “Defect-induced local variation of crystal phase transition temperature in metal-halide perovskites,” Nature Communications 8, 34 (2017).
