Polymer Based on Asymmetrically Halogenated Benzotriazole Enables High Performance Organic Solar Cells Prepared in Nonhalogenated Solvent.

Halogenation on the A unit of the D-π-A-type polymer donor has been proven as an effective strategy to improve the performance of organic solar cells (OSCs). Compared with fluorination, chlorination usually increases the open-circuit voltage because of the downward shift of energy levels, but decreases the charge transport ability due to the large steric hindrance of the chlorine atom. We reported herein a method to balance the energy loss and charge transport through asymmetric halogenation on the benzotriazole (BTA) unit of the polymer.