Poly(pentacyclic lactam-alt-diketopyrrolopyrrole) for field-effect transistors and polymer solar cells processed from non-chlorinated solvents

Abstract

A semi-crystalline conjugated polymer based on two electron-deficient units, pentacyclic lactam (PCL) and diketopyrrolopyrrole (DPP), was designed and synthesized for application in field-effect transistors (FETs) and polymer solar cells (PSCs). The polymer has a high molecular weight, near-infrared absorption up to 900 nm and good solubility in toluene. When the polymer thin films were solution-processed from toluene with diphenyl ether as an additive, the FET devices achieved a high hole mobility of 0.81 cm² V⁻¹ s⁻¹. With the same solution-processing solvents, bulk-heterojunction solar cells based on this polymer as an electron donor provided a power conversion efficiency of 4.7% with an optimal energy loss of 0.65 eV due to its deep lowest unoccupied molecular orbital level. Further study on the morphology of the pure polymer or blend thin films by atomic force microscopy, transmission electron microscopy and 2D grazing-incidence wide-angle X-ray scattering reveals that the new polymer has good crystalline property, which is mainly due to the coplanar nature of the conjugated backbone. This work demonstrates that conjugated polymers incorporating several electron-deficient units can be potentially used in high performance FETs and PSCs.