Donor–Donor Block Copolymers for Ternary Organic Solar Cells

Abstract

We describe a fully conjugated diblock copolymer, poly(3-thiohexylthiophene)-block-(3-hexylthiophene) (P3THT-b-P3HT), which is composed of two equally proportioned blocks that have distinct electronic structure and is suitable for testing in a donor–donor–acceptor solar cell. Calculations and optoelectronic characterization demonstrate communication between blocks in silico and in solution. In the solid state, powder X-ray diffraction and atomic force microscopy show that the polymer is semicrystalline and has a distinct morphology (relative to a 1:1 physical blend of its constituent homopolymers), both with and without a fullerene-derivative (PC71BM) acceptor. When tested in a device configuration (P3THT-b-P3HT:PC71BM), the deep HOMO level of the P3THT block increases the open circuit voltage (Voc) to a value that is equal to a P3THT:PC71BM control device. This shows that the Voc of an equally proportioned ternary organic solar cell can reach the upper limit of the corresponding binary devices. The block...