Perylenediimide derivatives with branched imide substituents: Aggregation behaviour and impact on photovoltaic properties

Abstract

Although organic photovoltaics has witnessed significant growth in their power conversion efficiency still there is need to develop novel electron transport materials that can improve the electron extraction through energy level tuning. Perylenediimide (PDI) is one of the known n-type semiconductor which forms highly ordered self-assembled aggregates by intermolecular interactions. Considering the facile processability of these, herein we report perylenediimide (PDI) derivatives with branched end groups via Michael addition reaction. This work describes the synthesis of two PDI derivatives, i.e., MA-PDI-EDA and MA-PDI-PPD via two-step process and these were further studied for the effect of branched end groups on aggregation behaviour as well as its correlation with the opto-electronic properties. The self-assembling and charge transport properties of the synthesized molecules are fine tuned by branched imide substituent which allows improved performance of these materials as electron transport layer in organic solar cell devices in comparison to their PDI precursors. MA-PDI-EDA forming J-type aggregate showed improved power conversion efficiency in comparison to MA-PDI-PPD undergoing H-type aggregation. Ultrafast transient absorption spectroscopy was also performed for understanding the charge carrier dynamics in the two MA products. A complete rational for the observation is discussed using the theoretical fitting of device I-V characteristics.