Presentation Details
| First-Principles Analysis of Iodine Migration and Electronic Degradation in MAPbI₃ (yes) Andre Slonopas1, Matthew Limpert2, Nam Le1, James Spicer1. 1Johns Hopkins University, Baltimore, MD, USA.22Army Training and Transformation Command, Aberdeen Proving Grounds, MD, USA |
Abstract
Halide perovskites continue to deliver remarkable photovoltaic efficiencies, yet their long-term instability remains a fundamental barrier. Researchers often invoke iodine migration as a degradation pathway; however, the microscopic electronic and structural origins remain debated. We employ first-principles density functional theory, combined with nudged elastic band calculations, to investigate how iodine vacancies influence both electronic degradation and ionic mobility in MAPbI₃. Our results show that iodine vacancies act as shallow donors rather than deep electronic traps. Projected density of states reveals additional states just above the conduction band minimum, with no mid-gap defect levels. These findings challenge common assumptions about vacancy-induced recombination centers and suggest that subtle carrier imbalance is a key driver of degradation. Charge density analysis reveals highly directional redistribution upon iodine removal: electrons are depleted at the vacancy site and accumulate on neighboring atoms, most prominently along the YZ direction. This anisotropy signals a local symmetry breaking of the lattice and hints at preferred ion migration pathways. Consistent with this picture, vacancy formation substantially lowers the energy barrier for iodide migration. A single dominant activated hop, characterized by a smooth energy profile and the absence of intermediate metastable sites, defines the minimum energy path. The transition state is delocalized, reflecting cooperative lattice relaxation rather than a rigid bottleneck. Spatially projected densities confirm a confined, lattice-guided migration channel, tightly coupled to local structural softening of the Pb–I framework. Together, these results suggest a unified degradation mechanism. Shallow donor states increase n-type character, shift the Fermi level, and perturb carrier lifetimes over time. Vacancy-assisted iodide migration enables long-range compositional drift. The strong coupling between electronic redistribution, lattice relaxation, and ionic motion provides a microscopic explanation for the light-induced degradation and hysteresis observed experimentally in MAPbI₃, highlighting an intrinsic susceptibility of the perovskite lattice to iodine migration under operational conditions.
No part of this publication may be reproduced, distributed, or transmitted in any form or by any means, including photocopying, recording, or other electronic or mechanical methods, without the prior written permission of the author.
No part of this publication may be reproduced, distributed, or transmitted in any form or by any means, including photocopying, recording, or other electronic or mechanical methods, without the prior written permission of the author.
Content Locked. Log into a registered attendee account to access this presentation.