Functionalized near-infrared absorbing diketopyrrolopyrrole-based push-pull copolymers for semitransparent organic photovoltaics

Abstract

Near-infrared (NIR) absorbing and/or emitting organic materials are increasingly important for next-generation optoelectronic devices. Narrow-gap push-pull conjugated polymers have gained particular attention in this respect because of their tunable optical properties and promising performance in (semitransparent) organic photovoltaics and NIR photodetectors. In this study, three novel diketopyrrolopyrrole (DPP) based narrow-gap donor polymers containing fluorine-, chlorine-, or nitrile-substituted thiophene units are rationally designed and synthesized with the aim of enhancing the open-circuit voltage in NIR-active (semitransparent) organic solar cells. The P-DPP-3T(F):Y6 blend affords a power conversion efficiency of 5.2%, surpassing the P-DPP-3T:Y6 reference combination (yielding 4.5%). Further optimization with other NIR-absorbing non-fullerene acceptors gives an enhanced solar cell efficiency of 6.6% for the P-DPP-3T(F):Y16F combination, and even 7.8% for P-DPP-3T:Y16F. When utilized with a semitransparent top electrode, the latter affords an efficiency of 5.0% with an average visible transmittance of 33%.