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.