Substrate effects on photoluminescence and low temperature phase transition of methylammonium lead iodide hybrid perovskite thin films

Abstract

We examine the effects of substrates on the low temperature photoluminescence (PL) spectra and phase transition in methylammonium lead iodide hybrid perovskite (CH3NH3PbI3) thin films. Structural characterization at room temperature with X-ray diffraction (XRD), scanning electron microscopy (SEM), and Raman spectroscopy indicated that while the chemical structure of films deposited on glass and quartz was similar, the glass substrate induced strain in the perovskite films and suppressed the grain growth. The luminescence response and phase transition of the perovskite thin films were studied by PL spectroscopy. The induced strain was found to affect both the room temperature and low temperature PL spectra of the hybrid perovskite films. In addition, it was found that the effects of the glass substrate inhibited a tetragonal to orthorhombic phase transition such that it occurred at lower temperatures.

Large lattice distortions and size-dependent bandgap modulation in epitaxial halide perovskite nanowires

“…As discussed earlier, the size-dependent emission shift was reported several times in MHPs systems. Prior to our report, a size-dependent emission shift was observed both in MAPbI 3 platelets and polycrystalline thin films 35,36,49 . The emission shift in the platelets system was rationalized in terms of a surface-induced confinement effect which generates effective potential wells that are smaller than the actual size of the nanostructure 36 .…”

“…Using bulk lattice parameters as reference, the calculated mismatch in the in-plane direction between the (110) plane of CsPbBr 3 and the 1 100 ð Þ plane of sapphire at room temperature is +0.7%. This heteroepitaxial mismatch can result in lattice strain and implies that the CsPbBr 3 lattice is dilated along the in-plane direction at the interface with sapphire 37,39,49 . Since the CsPbBr 3 nanowires grow on sapphire at~360°C before being rapidly cooled down to room temperature, we should also take into account the difference in their expansion coefficients, which could also contribute to the effective mismatch in this system.…”

Local Disorder at the Phase Transition Interrupts Ambipolar Charge Carrier Transport in Large Crystal Methylammonium Lead Iodide Thin Films

“…The room temperature synthesis of the MAPI thin films results in a high degree of alignment of the c axis of the tetragonal crystal structure with the substrate; 28 therefore, we do not expect local strain variations to originate from substrate effects here, as reported previously. 25 We observe that the rapid transition occurs both while cooling and heating the sample but that there is a substantial hysteresis, leading to a higher transition temperature in the heating process. This behavior can be explained by the coexistence of phases below the transition, reflected in local phase islands, as observed in the spectral PL maps.…”

“…Below T ≈ 163 K, the crystal structure of MAPI changes from the tetragonal to the orthorhombic phase in a first-order phase transition of the PbI 3 lattice. , During the transition, the MA + ions move from an orientational disordered state in the tetragonal phase to an ordered state in the orthorhombic phase . The transition has been investigated using neutron diffraction, X-ray diffraction, and other methods. ,, Current reports agree that, below the phase transition temperature, there is a temperature range of about 30 K in which the properties of the crystal are in a transitional state. ,− Two distinct PL peaks are usually attributed to the two crystal phases where the low energy peak at around 1.58 eV belongs to the tetragonal high-temperature phase and the high energy peak at 1.68 eV is indicative of the orthorhombic low-temperature phase. Some studies attribute the existence of two peaks in the spectrum to submicron-sized domains of different crystal phases in the samples, , whereas others claim that the reason for the double-peak spectrum lies in domains of different degrees of order and disorder of the MA ions .…”

“…24 The use of very high fluence shows that this coexistence is a metastable state. 26 temperature itself is known to depend on factors such as the substrate, strain, 25 and crystal size. 27 Larger crystals generally exhibit a clearer trend in the PL energy, which reflects smaller total variations of composition and crystal orientation 27 and underlines that microscopic measurements contain information that ensemble-type experiments cannot yield.…”