Introduction
In recent years, organic-inorganic perovskites have received a huge
amount of attention due to their promise for photovoltaic
application1-3. Generally, perovskite refers to the
ABX3 three-dimensional structural frameworks with “A” as an organic
cation (usually the cation of amines), “B” as a metal, and “X” as a
halogen.1,2. The chemical diversity of amines used in
perovskites for PV applications is large as they appear in both 3D and
2D perovskite structures.4,5 For instance, in a recent
review study by Saparov and Mitzi, more than 60 distinct perovskite
amine structures have been mentioned for the design of versatile
perovskite materials.6
With the rapid development of new classes of perovskite chemistry with
promising physical properties, the concerns in identifying amine
chemistries that have a minimal environmental/ health footprint become
more challenging.7 In looking at the full life cycle
of perovskites used in PV applications, we now need to consider the
toxicity of the organic molecules, along with metal elements such as Pb,
at all stages of the materials synthesis and
degradation.8-17 For example, previous studies on the
toxicity of amines have concluded that many aromatic amines (e.g.
aniline, diphenylamine) are potential carcinogens, while the aliphatic
amines are less hazardous.18-21 However, in aquatic
environments, there are potential formations of toxic compounds
including nitrosamines and nitramines from the reaction between amines
and nitrite oxidants.19,21 As the perovskite materials
become more and more popular, it is critical to perform a systematic
study on the toxicity of both the existing amines that have been part of
the 3-D and lower-dimensional perovskites and the potential perovskite
amines that have similar structures to the existing ones. In this study,
we present a machine learning aided molecular structure-toxicity
analysis to screen the potential toxicity of amines used for the
synthesis of hybrid organic-inorganic perovskites.
Our training and test database of perovskite amines is based on open
source literature along with a structural similarity search on PubChem
(https://pubchem.ncbi.nlm.nih.gov), a well-acknowledged database for
chemical structure and functionality22. For toxicity
data of perovskite amines, instead of fetching data from different
literature without a common standard, we performed searches on PubChem
Bioactivity Assays database23 which is based on
similar data standards that are more suitable to study at a systematic
level. This study aims to establish a structure-toxicity relationship of
perovskite amines, help identify safer alternatives for use in
perovskite structures.