Structure-Property Relationships of Precisely Chlorinated Thiophene-Substituted Acceptors

Systematic investigation of three nonfullerene acceptors, BTIC-4Cl-T, BTIC-4Cl-TCl-gamma, and BTIC-4Cl-TCl-b, with or without a chlorine substituent at the gamma/b-position of the side chain thiophene ring, reveals that molecular planarity, stacking structure, and photovoltaic performance of the compounds are dependent on the position of the chlorine substituent. Of the materials using thiophenes in conjugated side chains, BTIC-4Cl-T shows a relatively lower open-circuit voltage of 0.81 V, decreased current density, leading to an efficiency of only 10.86%. BTIC-4Cl-TCl-gamma with chlorine at the gamma-position of the conjugated thiophene shows a 3D network structure, a greatly increased current density, and an efficiency of 14.35%. BTIC-4Cl-TCl-b, with a chlorine atom in b-position, is found to have been reformed to a quasi-3D network, in which electron hopping can be efficiently realized in adjacently positioned, linearly arranged molecules due to S center dot center dot center dot S interactions. With this quasi-3D network, BTIC-4Cl-TCl-b promotes the open-circuit voltage up to 0.86 V and has the highest efficiency (15.65%) among the three acceptors. These results prove that chlorination is an effective strategy to improve photovoltaic performance and highlights the decisive relationship between structural regulation and molecular arrangement. It also provides a good starting point for the exploration and design of next generation high-performance materials.

Automated summary

The systematic investigation of three nonfullerene acceptors with chlorine substituents at different positions reveals the importance of structural regulation and molecular arrangement in improving photovoltaic performance. Chlorination can effectively enhance efficiency, with BTIC-4Cl-TCl-b showing the highest efficiency due to its quasi-3D network structure facilitating efficient electron transport.