Organic–inorganic interactions of single crystalline organolead halide perovskites studied by Raman spectroscopy

Abstract

Organolead halide perovskites exhibit superior photoelectric properties, which have given rise to the perovskite-based solar cells whose power conversion efficiency has rapidly reached above 20% in the past few years. However, perovskite-based solar cells have also encountered problems such as current-voltage hysteresis and degradation under practical working conditions. Yet investigations into the intrinsic chemical nature of the perovskite material and its role on the performance of the solar cells are relatively rare. In this work, Raman spectroscopy is employed together with CASTEP calculations to investigate the organic-inorganic interactions in CH3NH3PbI3 and CH3NH3PbBr3-xClx perovskite single crystals with comparison to those having ammonic acid as the cations. For Raman measurements of CH3NH3PbI3, a low energy line of 1030 nm is used to avoid excitation of strong photoluminescence of CH3NH3PbI3. Raman spectra covering a wide range of wavenumbers are obtained, and the restricted rotation modes of CH3-NH3(+) embedded in CH3NH3PbBr3 (325 cm(-1)) are overwhelmingly stronger over the other vibrational bands of the cations. However, the band intensity diminishes dramatically in CH3NH3PbBr3-xClx and most of the bands shift towards high frequency, indicating the interaction with the halides. The details of such an interaction are further revealed by inspecting the band shift of the restricted rotation mode as well as the C-N, NH3(+) and CH3 stretching of the CH3NH3(+) as a function of Cl composition and length of the cationic ammonic acids. The results show that the CH3NH3(+) interacts with the PbX3(-) octahedral framework via the NH3(+) end through N(+)-HX hydrogen bonding whose strength can be tuned by the composition of halides but is insensitive to the size of the organic cations. Moreover, an increase of the Cl content strengthens the hydrogen bonding and thus blueshifts the C-N stretching bands. This is due to the fact that Cl is more electronegative than Br and an increase of the Cl content decreases the lattice constant of the perovskite. The findings of the present work are valuable in understanding the role of cations and halides in the performance of MAPbX3-based perovskite solar cells.

Structural and Photophysical Properties of Methylammonium Lead Tribromide (MAPbBr3) Single Crystals

“…4(b) . The rotation mode of the MA + in MAPbBr 3 single crystal can be weakened when the Br atom is gradually replaced with a Cl atom due to the higher electronegativity strengthens of the Cl − 49 . In this study, the rotation mode of the MA + was entirely restricted when Br was completely substituted by Cl.…”

Synergistic Surface Passivation of CH3NH3PbBr3 Perovskite Quantum Dots with Phosphonic Acid and (3‐Aminopropyl)triethoxysilane

“…Sharpa nd strong Raman bandsa t3 25, 970, 1480, 1586, and 2970 cm À1 can be attributed to CH 3 ÀNH 3 + in CH 3 NH 3 PbBr 3 . [21] With PA and APTES used as capping ligands, new bands at 890, 1178,a nd 1250cm À1 can be attributed to the PÀOs tretch, P=Os tretch, and POÀHs tretcho ft he PA ligands,r espectively. [22] Meanwhile, the bands at 1144, 1424, and 2940 cm À1 are attributed to the SiÀOÀSi stretch, SiÀCH 3 stretch, and NH 3 + stretch of the APTES ligands, respectively.…”

One-step mechanochemical incorporation of an insoluble cesium additive for high performance planar heterojunction solar cells

“…A recent study by Jin et al has demonstrated that a strong electrostatic attraction between Cl and MA + is beneficial for chemical stability and recombination kinetics. 42,43 Furthermore, we measured the J-V characteristics in the dark and in forward direction for triple and triple_Cl devices ( Figure S12). The lower leakage current in the exponential region and lower slope in the high forward bias region for triple_Cl further confirms the lower recombination losses and R S .…”