First-Principles Calculation of the Bulk Photovoltaic Effect in CH₃NH₃PbI₃ and CH₃NH₃PbI_3–xCl_x

Abstract

Hybrid halide perovskites exhibit nearly 20% power conversion efficiency, but the origin of their high efficiency is still unknown. Here, we compute the shift current, a dominant mechanism of the bulk photovoltaic (PV) effect for ferroelectric photovoltaics, in CH₃NH₃PbI₃ and CH₃NH₃PbI(3-x)Cl(x) from first-principles. We find that these materials give approximately three times larger shift current PV response to near-IR and visible light than the prototypical ferroelectric photovoltaic BiFeO₃. The molecular orientations of CH₃NH₃⁺ can strongly affect the corresponding PbI₃ inorganic frame so as to alter the magnitude of the shift current response. Specifically, configurations with dipole moments aligned in parallel distort the inorganic PbI₃ frame more significantly than configurations with near-net-zero dipole, yielding a larger shift current response. Furthermore, we explore the effect of Cl substitution on shift current and find that Cl substitution at the equatorial site induces a larger response than does substitution at the apical site.

From soft harmonic phonons to fast relaxational dynamics inCH3NH3PbBr3

“…Measurements and calculations of the frequency-dependent dielectric response and electronic gap energies provide evidence that molecular vibrations are coupled to the electronic properties [16,35] and this has been further suggested by recent QENS results on the PbI 3 framework based compounds. [36,37] Further indications of the importance of the molecular vibrations come from the temperature dependent lifetime of the photoluminescence that shows an emission at 1.62 eV with a FWHM of 103 meV, sharp- ening at ∼ 150 K where molecular orientational order occurs.…”

“…[40] The strong coupling between the PbBr 3 framework and the MA molecular motions may also affect band structure details as predicted in Ref. 16.…”

“…[15] This, in turn, has been suggested to enhance the the photovoltaic properties. [16] To this end, we apply neutron inelastic scattering to study the dynamics of the MA molecular cation, the PbBr 3 framework, and the coupling between the two sets of dynamics. The experiments were performed on the MARI (ISIS, UK), NEAT (HMI, Germany), IN4, and IN10 (ILL, France) spectrometers.…”

Enhancement of the Bulk Photovoltaic Effect in Topological Insulators

“…The shift vector R can be understood as a generalized gauge invariant k-space derivative of the p operator [32,33], and it is odd under the interchange of c and v bands. We apply this formalism to perform first-principles DFT calculations [34][35][36][37] of the shift current BPVE of the polar layered material BiTeI. This material is a normal insulator under ambient pressure, and DFT predicts that it becomes a topological insulator at pressures higher than 1.7 GPa [38].…”

New class of planar ferroelectric Mott insulators via first-principles design

“…Fortunately, the recent application of shift current theory has provided significant insight into the latter phenomenon, and it is apparent that strong polarization and covalency are necessary ingredients for enhancing the photocurrent 8,9 . While hybrid perovskite materials can satisfy the general requirements of the BPE 8,[10][11][12][13][14] , their instability against water due to weak halide bonding and environmental issues associated with lead are still very serious problems 13 . Therefore, satisfying the BPE criteria in transition metal oxides is a very important open problem in materials physics.…”