Mechanical properties of hybrid organic-inorganic CH3NH3BX3 (B = Sn, Pb; X = Br, I) perovskites for solar cell absorbers

Abstract

The crystal structures, elastic and anisotropic properties of CH3NH3BX3 (B = Sn, Pb; X = Br, I) compounds as solar cell absorber layers are investigated by the first-principles calculations. The type and strength of chemical bond B-X are found to determine the elastic properties. B-X bonds and the organic cations are therefore crucial to the functionalities of such absorbers. The bulk, shear, Young's modulus ranges from 12 to 30 GPa, 3 to 12 GPa, and 15 to 37 GPa, respectively. Moreover, the interaction among organic and inorganic ions would have negligible effect for elastic properties. The B/G and Poisson's ratio show it would have a good ductile ability for extensive deformation as a flexible/stretchable layer on the polymer substrate. The main reason is attributed to the low shear modulus of such perovskites. The anisotropic indices AU, AB AG, A1, A2, and A3 show ABX3 perovskite have very strong anisotropy derived from the elastic constants, chemical bonds, and symmetry.

Quasiparticle band gap of organic-inorganic hybrid perovskites: Crystal structure, spin-orbit coupling, and self-energy effects

“…The lattice constants (cell volume) of organometal perovskites can be affected/tuned by various means such as temparature, 22 replacing methylammonium with different organic cations, 17,19 or mechanical strains induced by substrates. 10 Previous theoretical studies have shown a positive band gap deformation potential (a V = ∂E g /∂ln V ) of these materials. 61 We would like to point out, however, that one cannot compare directly the calculated volume-dependent band gap with the measured temperature-dependent band gap [54][55][56] by simply taking into account the thermal expansion effects.…”

“…For example, the band gap and optical absorption can be optimized/tuned by several factors such as the chemical compositions of the inorganic framework, [15][16][17] the organic cations, [17][18][19] and lattice strains possibly induced by substrates. 10 However, this rich design space also brings substantial complexity as multiple degrees of freedom may play distinct roles or may couple with each other to ultimately determine the optical properties of these materials. Therefore, an in-depth understanding of the excited states properties of these materials and how they are affected by various factors are critical for a theory-guided rational design or optimization.…”

A New Perspective on the Role of A‐Site Cations in Perovskite Solar Cells

“…Meanwhile, recent studies suggest LO phonons as the main source of polaron states. [19,20] The working temperature of cubic CH3NH3PbI3 ( 330 K) [21] is well above the Debye temperature Θ D ∼175 K [22] which is a representative excitation energy scale of the highest phonon mode. Therefore, it is plausible that at working temperatures of PSC, high energy PbI3 LO phonons are largely populated.…”

Mechanical signatures of degradation of the photovoltaic perovskite CH3NH3PbI3 upon water vapor exposure

“…In this paper, we present an investigation of the mechanical characteristics of MAPbI 3 -to which relatively limited attention has so far been paid [25][26][27] -and, in particular, to their variation under exposure to humid environments. Indeed, given that future devices will be exposed to diverse external mechanical forces (shocks, bending), characterization of the mechanical properties is undoubtedly crucial, especially to move from prototype to real large-scale applications.…”