Nonhalogenated solvent-processed thick-film ternary nonfullerene organic solar cells with power conversion efficiency >13% enabled by a new wide-bandgap polymer

Although several donor polymers have been synthesized for use in nonfullerene organic solar cells (NFOSCs), the number of efficient π-conjugated donor polymers compatible with nonhalogenated solvent-processed thick active layer NFOSCs is limited. Two wide-bandgap π-conjugated donor polymers functionalized with a siloxane side chain, P1 (chlorine-free) and P2 (chlorinated), are designed and synthesized. The siloxane-functionalized side chains and/or Cl π-conjugated donor polymers increase the absorption coefficients, reduce the energy losses, increase the charge-carrier mobility, and suppress the bimolecular recombination, which are beneficial to achieve high-performance thick-film ternary NFOSCs. Toluene-processed devices based on P2:IT-4F:BTP-4Cl, and P2:IT-4F:BTP-4F exhibit high power conversion efficiencies (PCEs) of 13.25% and 11.02% with fill factors (FFs) of 70.03% and 71.60%, respectively. A P2:IT-4F binary NFOSC exhibits a PCE of 10.38% with an FF of 69.78%, lower than that of the ternary NFOSC. The ternary device PCE of 13.25% is achieved using a 300 nm-thick active layer, indicating that the siloxane-functionalized side-chain π-conjugated polymer easily controls the bulk heterojunction blend film thickness of the NFOSC. The findings may potentially aid the development of nonhalogenated solvent-processed thick-film ternary NFOSCs that can satisfy future production requirements.