Specific Features of Photoluminescence of CH 3 NH 3 PBI 3 Perovskites Synthesized on Nanostructured TiO 2 Surface
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Specific Features of Photoluminescence of CH3NH3PBI3 Perovskites Synthesized on Nanostructured TiO2 Surface D. A. Afanasyeva, * and N. Kh. Ibrayeva a Institute
of Molecular Nanophotonics, Buketov Karaganda State University, Karaganda, 100028 Republic of Kazakhstan *е-mail: [email protected] Received February 25, 2020; revised February 25, 2020; accepted April 15, 2020
Abstract—The influence of nanostructured titania surface on the photoluminescence of organometallic perovskite CH3NH3PbI3 films is studied. It is found that the CH3NH3PbI3 luminescence intensity and lifetime decrease on the TiO2 surface, which testifies to charge transfer from perovskite to titania. Charge transfer occurs most efficiently for perovskite films synthesized on the surface of mesoporous TiO2 films. The time dependence of magnetic effect on the luminescence of CH3NH3PbI3 on mesoporous TiO2 films is related to the recombination luminescence caused by forward and backward electron transfer between perovskite and titania. Keywords: titania, perovskite, nanostructured films, luminescence kinetics, magnetic effect DOI: 10.1134/S0030400X20080032
INTRODUCTION Investigations in the field of application of organic materials for fabrication of solar-to-electric energy converters led to the development of two new types of solar cells, namely, dye-sensitized solar cells (DSSCs) and polymer solar cells [1, 2]. Work [3] performed in 2009 and aimed at improvement of DSSCs resulted in the creation of perovskite solar cells (PSCs). These cells are based on organo-inorganic compounds with composition MaPbX3, where Ma is methylammonium and X is a halogen (Br, I, or Cl). For the period from 2009 to 2020, the efficiency of PSCs increased from 3.8 to 25% [4]. The specific features of charge transfer in PSCs are studied by laser kinetic spectroscopy methods. These methods make it possible to estimate lifetimes of charge carriers, determine the efficiency of charge transfer from the perovskite film to semiconductor layers with n- and p-type conductivity, and determine the concentration of defects in perovskite films [5, 6]. Despite the results achieved, some questions still need more detailed studies. One of these questions is the effect of the spin state of charge carriers on the lightto-electric energy conversion efficiency in PSCs. Perovskites have a strong spin–orbit coupling caused by the presence of heavy atoms (Pb, I), which considerably affects the spin–lattice relaxation time for spin-correlated electron–hole pairs. In this case, a change in the spin–orbit coupling value leads to a change in the PSC efficiency [7]. Some well-developed and widely used methods for studying the spin state of free charge carriers and charge-transfer com-
plexes are based on the influence of an external magnetic field (MF) on the photocurrent and the intensity of photo- and electroluminescence [8]. These methods allow one to determine the specific features of the effect of an external MF at the stages of formation, transport, or recombinati
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