Developing Benzodithiophene-Free donor polymer for 19.36% efficiency Green-Solvent-Processable organic solar cells.

A benzodithiophene-free donor polymer was designed for enabling 19.36% efficiency green-solvent-processable organic solar cells (OSCs), which is the highest value for OSCs processed by halogen-free solvents. [Display omitted] • A high molecular weight benzodithiophene-free donor polymer of PDTP-BDD was developed for organic solar cells. • The layer-by-layer processing of PDTP-BDD based devices in halogen-free solvents was studied. • The champion power conversion efficiency of 19.36% was achieved finally. In this work, a newly benzodithiophene-free D-A polymer donor, named PDTP-BDD, was developed for realizing green-solvent processed high-performance OSCs. By bridging two electron-rich unit of dithieno[3,2-b:2′,3′-d]pyridin-5(4H)-one (DTP) and electron-deficient benzo[1,2-c:4,5c′]dithiophene-4,8-dione (BDD) with thiophene units, PDTP-BDD possesses high absorption in the short wavelength range and a deep HOMO energy level. The rigid building blocks also make PDTP-BDD has strong aggregation and poor solubility in common halogen-free solvents (such as o -xylene) at room temperature, but it is readily dissolved and disaggregated at high temperature (120 °C). After cooling down to a lower temperature (60 °C), PDTP-BDD self-assembled and pre-aggregated slowly in the solution at a long time. By employing a delayed processing strategy in the layer-by-layer processed OSCs (LbL-OSCs), an optimized fibril network of the underling layer was realized, enabling the permeation of acceptor into the donor network. The optimized PDTP-BDD/L8-BO-based LbL-OSCs realized a high PCE of 18.42 %. By adding a small amount of D18 to further optimize the PDTP-BDD fibril network, an impressive PCE of 19.36 % was achieved finally in the resulting ternary LbL-OSCs, which is the highest value for OSCs processed by halogen-free solvents. [ABSTRACT FROM AUTHOR]