Quantification of Spin Relaxation Rates for Chiral Lead Halide Perovskites

Abstract

Chirality is the property of an object that cannot be superimposed onto its mirror
image. Chiral materials exhibit circular dichroism (CD) which can selectively populate
one spin state over the other upon optical excitation, creating a spin-polarized
carrier population. In chiral hybrid organic-inorganic perovskites, chirality is transferred
from the organic spacer to the inorganic framework, making these materials
strong candidates for spintronic applications where spin polarization can be generated
optically without external magnetic fields. The spin lifetimes of these materials
depends on the measurement technique and the standard helicity-difference method
carries implicit assumptions that limits its physical transparency. Here we investigate
the spin dynamics of (R/S/RAC-MBA)2PbI4 with circularly polarized transient
absorption ( CP-TA ) and obtain the lifetimes by the hellicity-difference method and
we also propose a new kinetic model to obtain the spin rate constant. Thin films
were characterized by steady-state absorption and circular dichroism spectroscopy
and CP-TA with 480 nm pump and 8μJ/cm2 fluence for different pump-probe polarization
configurations was used to study the carrier dynamics.
The spin lifetimes were obtained by the helicity-difference method and for a coupled
two-population kinetic model that separates the carrier decay into its different contributions
including excitonic recombination (kr), Auger-Meitner recombination (kA),
and spin relaxation (ks). Both methods confirm polarization-dependent dynamics
and faster spin relaxation in the racemic sample than in the pure enantiomers, consistent
with the chiral organic molecule prolonging spin polarization through the
chiral induced spin selectivity ( CISS ) effect. The kinetic model yields spin lifetimes
of 43-249 ps, shorter than the 136-751 ps extracted by the helicity-difference
method, confirming that spin lifetime is a model-dependent quantity. These results
establish new insights into the quantification of spin relaxation rates in chiral hybrid
perovskites and highlight the need for standardized approaches in this rapidly
growing field.

Popular Abstract

Take a look at your left hand and then your right hand. Although they look identical,
if you put one on top of the other you will see that they do not match up
perfectly,just like a right-hand glove cannot fit your left hand. They are mirror images
of each other but not interchangeable. This property is called chirality.
Chirality can be found in nature, where for example, DNA is in its majority
right-handed. This seemingly innocent property cannot be overlooked, because having
“the left hand” molecule instead of the right one can have serious consequences,
like the case of the Thalidomide scandal where this medicine was given to pregnant
women to combat morning sickness. While “the left hand” acted as a good medicine,
“the right hand” caused deformities to the fetus and miscarriages, and more than
10,000 children were born with deformities.
This property has been studied in many fields, one of them being spintronics.
This word refers to the field that studies and applies the properties of the spin of an
electron to make devices for carrying and sending information (such as a hard disk
drive, quantum computers or even AI). Now you might be asking yourself: what is
the spin of an electron? Short answer: no one really knows. Longer answer: it is a
property that the electron “just has” and it can be either up or down.
So in order to make devices for spintronic applications you need a material that
has most of its electrons in either its up or down form, that is how the information
is sent and preserved.
In this work we want to study perovskites, a class of materials that have a
particular structure that is very good for interacting with light. We want to study
for how long the spin up or down information is kept when chirality is added to
these materials. Perovskites are not chiral, but scientists discovered that when a
chiral molecule is placed next to one, it behaves like a chiral material.
In this work we have studied chiral perovskites and how long they keep their spin up
or down information, using light, because light interacts differently with the right
or left hand of a material. We have shown that there is a dependency when using
”right” or ”left” light with these chiral perovskites and obtained the amount of time
the spin up or down information is kept, giving new insights for future spintronic
applications

• author: Planelles Samper, Jan
• supervisor: Prasenjit Mandal
• organization: Department of Chemistry
• course: KEMR30 20252
• year: 2026
• type: H2 - Master's Degree (Two Years)
• subject: Chemistry
• keywords: ultrafast spectroscopy, transient absorption (TA), spin dynamics, chiral perovskites, lead halide perovskites, spin lifetimes, chemical physics
• language: English
• id: 9234934
• date added to LUP: 2026-06-11 11:56:55
• date last changed: 2026-06-11 11:56:55