Non‐Equal Ratio Cocrystal Engineering to Improve Charge Transport Characteristics of Organic Semiconductors: A Case Study on Indolo[2,3‐a]carbazole

Abstract Rare studies of cocrystal engineering have focused on improving carrier mobility of organic semiconductors mainly because of the generation of ambipolarity, the alteration of the charge carrier polarity or the reduction of electronic couplings. Herein, we utilize indolo[2,3‐a]carbazole (IC) as the model compound and 2,6‐diphenylanthraquinone (DPAO) and 9‐fluorenone (FO) as the coformers to construct IC2‐DPAO and IC‐FO cocrystals with 2 : 1 or 1 : 1 ratios, respectively, through hydrogen bonds and donor–acceptor interactions. Interestingly, the more appropriate packing structure, possessing not only enhanced electronic couplings but also increased intermolecular distances, is achieved in IC2‐DPAO, which shows an improved carrier mobility of 0.11 cm 2 V −1 s −1 by four orders of magnitude relative to the IC crystal. These results suggest that non‐equal ratio cocrystal engineering opens up the possibility to develop organic semiconductors with enhanced charge transport behaviors.