Acceptor-induced reorientation enables vertically and laterally optimized charge-transport devices with a single polymer

Abstract

Molecular orientation dictates anisotropic charge transport in conjugated polymers. Here, we show that acceptor-induced reorientation enables a polymer system to align with both lateral and vertical transport geometries. A series of terpolymers (PTTzF-Th, PTTzF-TT, and PTTzF-BT) was synthesized by partially replacing 2F-thiophene units in PTTzF with non-fluorinated thiophene comonomers. All terpolymers display edge-on orientation in neat films, with PTTzF-BT having the highest edge-on fraction; upon blending with Y6, acceptor templating induces a pronounced reorientation toward face-on, most strongly in PTTzF-BT:Y6. As a result, PTTzF-BT achieves the highest thermoelectric (conductivity: 3.7 S cm-1; Seebeck coefficient: 69.3 & micro;V K-1) and photovoltaic (power conversion efficiency: 16.1%) performance among the series. Mechanistic analysis highlights coupled kinetic and thermodynamic effects: in neat films, a longer film-formation window favors edge-on orientation; in blends, improved donor-acceptor miscibility and slower acceptor crystallization enhance templating and promote reorientation to face-on. These insights demonstrate a conceptual framework for programmable molecular orientation in conjugated polymers and illustrate how a single polymer platform can be aligned with distinct charge transport geometries in different organic electronic devices.