High-Performance Terpolymers with Well-Defined Structures Facilitate PCE Over 19% for Polymer Solar Cells

Abstract

Ternary copolymerization is a cost-effective and time-saving approach to improve device performance and batch stability of polymer donors. However, the structure of the ternary polymer donor obtained by the traditional one-pot polymerization is vague due to the different monomer reaction order, which has a great influence on the absorption, crystallization, molecular stacking, and device performance. Therefore, it is necessary to obtain terpolymers with definite structures, and systematically study the differences in device properties of polymers with different sequence structures. Herein, three terpolymers D1, D2, and D3 are developed. Random copolymer D3 is obtained via the traditional one-pot method while alternating copolymer donor D1 and block copolymer D2 are synthesized by stepwise polymerization. Because the block copolymer D2 possess periodic sequence distribution and retains the excellent properties of the two polymer matrix very well, the D2-based device shows enhanced tightened pi-face-on molecular stacking, distinguished efficient exciton dissociation, and decreased energy loss. As a result, the D2:L8-BO-based polymer solar cells achieve one of a record power conversion efficiency of 19.03%. The work demonstrates changing the sequence structure of the polymers to synthesize well-defined structures polymer donors not only maintains the features of polymer matrix, but also combines the advantages of ternary copolymerization. Breaking the traditional one-pot polymerization method, three terpolymers with different sequence structures are developed, namely alternate copolymer (D1), block copolymer (D2), and random copolymer (D3). The D2-based device shows more efficient exciton dissociation, smaller energy loss, and better molecular stacking orientation than D1 and D3-based, resulting in D2:L8-BO-based device obtaining one of a record PCE of 19.03%. image