Bismuth Doping Alters Structural Phase Transitions in Methylammonium Lead Tribromide Single Crystals

Abstract

We study the effects of bismuth doping on the crystal structure and phase transitions of single crystals of the perovskite semiconductor methylammonium lead tribromide, MAPbBr 3 . By measuring the temperature-dependent specific heat capacity (C p ) we find that, as the Bi doping level increases, the temperatures for the bismuth structural phase transitions shift, and the phase boundary assigned to the transition from the cubic to tetragonal phase decreases in temperature. Furthermore, after doping we only observe one phase transition between 135 and 155 K, in contrast to two transitions observed in the undoped single crystal. These results appear strikingly similar to the previously reported effects of mechanical pressure on the perovskite structure. Using X-ray diffraction, we show that, as more Bi is incorporated into the crystal, the lattice constant decreases, as predicted by density functional theory (DFT). Based on the lattice contraction and DFT, we propose that bismuth substitutional doping on the lead site is dominant, resulting in Bi Pb + centers which induce compressive chemical strain that alters the crystalline phase transitions. TOC GRAPHICSKEYWORDS Bismuth doping, MAPbBr 3 perovskite, specific heat capacity, lattice contraction, X-ray diffraction, Halide perovskites have emerged as promising semiconductor materials for applications including solar cells, light-emitting diodes, photodetectors, and lasers. [1][2][3][4] They exhibit unique and tunable optoelectronic properties via facile tailoring of the chemical composition of the structure.In the archetypal perovskite ABX3 crystal structure, A represents a monovalent cation species (A = Cs + , CH3NH3 + (MA + ), or (NH2)2CH3 + (FA + )), B represents a divalent cation (B = Pb +2 , Sn +2 ), and X represents a halide (X = Cl -, Br -, I -). Diverse electronic and structural motifs are thereby accessible by modification of the chemical composition and the dimensionality of the material. 5

Trojans That Flip the Black Phase: Impurity-Driven Stabilization and Spontaneous Strain Suppression in γ-CsPbI3 Perovskite

“…It is difficult to compare different B-site dopants directly due to limited information available for their respective miscibility and integration into the CsPbI 3 crystal. 35 Nevertheless, considering just the relative change in unit cell volume, the largest relative reduction of 2% for 20% Zn 2+ doping is comparable to the volume change induced by 10% Br incorporation, CsPbI 2.7 Br 0.3 . The latter is a highly unstable material which still exhibits a yellow to black phase transition temperature (294 °C) only marginally lower than pure CsPbI 3 (320 °C).…”

“…Note the impurity fractions represent the nominal concentration of the reported growth conditions and not the final composition of the crystal. 35 In units of Å, the Shannon radius of each dopant is provided in parentheses. also infers improved stability.…”

“…The shaded areas in each plot represent the domains where the CsPbI 3 perovskite phase stability is traditionally expected to benefit from the relative change in the unit cell volume. Note the impurity fractions represent the nominal concentration of the reported growth conditions and not the final composition of the crystal 35. In units of Å, the Shannon radius of each dopant is provided in parentheses.…”

Bi3+ doping in 1D ((CH3)3SO)PbI3: a model for defect interactions in halide perovskites

“…Heterovalent doping has remained relatively less studied until recently due to the complexity of the charge compensation mechanisms that must be considered. In particular, bismuth has been investigated as a donor dopant for various inorganic and hybrid 3D perovskites [9][10][11][12][13][14][15][16] .…”

“…Different point defects compensating for Bi 3+ are possible, whose nature is, however, still unclear. 13 In MAPI, most studies attribute the formation of deep traps to Bi 3+ doping, hindering electron transport 14,16 ; it was also proposed that the Bi donors shift the Fermi level instead, causing, in turn, an increased concentration of Iinterstitials. 10 A careful control of the synthetic conditions was therefore proposed to balance the opposing tendencies towards I-vacancy and I-interstitial formation.…”