Lattice Distortion and Low-Frequency Anharmonic Phonons Suppress Charge Recombination in Lead Halide Perovskites upon Pseudohalide Doping: Time-Domain Ab Initio Analysis

Abstract

Perovskite solar cells have witnessed a surge in interest as a promising technology for low-cost, high-efficiency photovoltaics with certified power conversion efficiencies beyond 25%. However, their commercial development is hindered by poor stability and nonradiative losses that restrict their approach to the theoretical efficiency limit. Using ab initio nonadiabatic molecular dynamics, we demonstrate that nonradiative charge recombination is suppressed when the iodide in formamidinium lead iodide (FAPbI 3 ) is partially replaced with pseudohalide anions (SCN – , BF 4 – , and PF 6 – ). The replacement breaks the symmetry of the system and creates local structural distortion and dynamic disorder, decreasing electron–hole overlap and nonadiabatic electron–vibrational coupling. The charge carrier lifetime is found to increase with increased structural distortion and is the longest for PF 6 – . This work is fundamentally relevant to the design of high-performance perovskite materials for optoelectronic applications.

Prolonged Exciton Lifetime Is Achieved in Porphyrin Nanoring by Template Engineering: A Nonadiabatic Tight Binding Approach

“…To mimic natural photosynthesis, macromolecular porphyrin analogous such as nanoring, − nanotube, , nanoball, , and nanoribbon are utilized as promising photoactive materials because they exhibit strong light absorption at the UV–vis region, , tunable electronic structure, , charge transport properties, and long exciton lifetime. , Even in purple photosynthetic bacteria, ring-shaped light harvesting porphyrin complexes are participated in the photosynthesis process . Porphyrin ring-like structures can delocalize the exciton in ultrafast time scale along the ring network. , Photoinduced charge recombination is detrimental to the efficient solar cell as it reduces the current voltage by decreasing the exciton density. , Therefore, to achieve the desired efficiency, the charge transfer should be fast along with sufficiently slow recombination. , The photoexcited charge recombination is guided by several factors such as energy gap, , nonadiabatic (NA) coupling and quantum coherence, midgap and trap states originating from doping or defects, and the geometry. ,− External factors such as pressure, , pH, humidity, dielectric constant, and temperature , have also a prominent effect on the recombination. Likewise, it is evidenced that strain in a system affects the carrier lifetime .…”