Monomer morphology selection rules for an accurate design of bulk heterojunction: An updated theoretical account

Abstract

Theoretical simulation of film morphology with bulk heterojunction (BHJ) has become a technological breakthrough point for material and performance development in recent years. Stemming from the precision of calculation and the boom of materials, the unified process for predicting the relevant properties of BHJ through monomers needs to be further updated. This study analyzed the sensibilities of environmental changes (monomers, the acceptors of D/A and A/A in morphology) on structures and properties from fullerene to non-fullerene materials. The results showed that it is inaccurate to predict morphology only by optimizing the monomer through employing a unified process. Due to material specificity, excessive environmental sensitivity could lead to prediction errors. In different environments, the properties of C60 with rigid structure vary greatly. The stability of fused ring electron acceptors (FREAs) is determined by the type and number of bridge bonds (single and ethylenic bonds) in main backbones, where a small number and strong conjugation are favorable. As a result, flexible ITIC is insensitive to the environment, which could be performed using a unified process. This may be the main reason for their excellent properties. This work puts forward higher requirements for the accuracy of a theoretical calculation process, and also provides an updated theoretical account for an accurate design of bulk heterojunction.