Solution-based processing of materials for electrical doping of organic semiconductor interfaces is attractive for boosting the efficiency of organic electronic devices with multilayer structures. To simplify this process, self-doping perylene diimide (PDI)-based ionene polymers are synthesized, in which the semiconductor PDI components are embedded together with electrolyte dopants in the polymer backbone. Functionality contained within the PDI monomers suppresses their aggregation, affording self-doping interlayers with controllable thickness when processed from solution into organic photovoltaic devices (OPVs). Optimal results for interfacial self-doping lead to increased power conversion efficiencies (PCEs) of the fullerene-based OPVs, from 2.62% to 10.64%, and of the nonfullerene-based OPVs, from 3.34% to 10.59%. These PDI-ionene interlayers enable chemical and morphological control of interfacial doping and conductivity, demonstrating that the conductive channels are crucial for charge transport in doped organic semiconductor films. Using these novel interlayers with efficient doping and high conductivity, both fullerene- and nonfullerene-based OPVs are achieved with PCEs exceeding 9% over interlayer thicknesses ranging from ≈3 to 40 nm.

Polymer zwitterions were synthesized by nucleophilic ring-opening of 3,3'-(but-2-ene-1,4-diyl)bis(1,2-oxathiolane 2,2-dioxide) (a bis-sultone) with functional perylene diimide (PDI) or fullerene monomers. Integration of these polymers into solar cell devices as cathode interlayers boosted efficiencies of fullerene-based organic photovoltaics (OPVs) from 2.75 % to 10.74 %, and of non-fullerene-based OPVs from 4.25 % to 10.10 %, demonstrating the versatility of these interlayer materials in OPVs. The fullerene-containing polymer zwitterion (C -PZ) showed a higher interfacial dipole (Δ) value and electron mobility than its PDI counterpart (PDI-PZ), affording solar cells with high efficiency. The power of PDI-PZ and C -PZ to improve electron injection and extraction processes when positioned between metal electrodes and organic semiconductors highlights their promise to overcome energy barriers at the hard-soft materials interface of organic electronics.

A new and highly efficient cathode interlayer material for organic photovoltaics (OPVs) was produced by integrating C60 fullerene monomers into ionene polymers. The power of these novel “C60‐ionenes” for interface modification enables the use of numerous high work‐function metals (e.g., silver, copper, and gold) as the cathode in efficient OPV devices. C60‐ionene boosted power conversion efficiencies (PCEs) of solar cells, fabricated with silver cathodes, from 2.79 % to 10.51 % for devices with a fullerene acceptor in the active layer, and from 3.89 % to 11.04 % for devices with a non‐fullerene acceptor in the active layer, demonstrating the versatility of this interfacial layer. The introduction of fullerene moieties dramatically improved the conductivity of ionene polymers, affording devices with high efficiency by reducing charge accumulation at the cathode/active layer interface. The power of C60‐ionene to improve electron injection and extraction between metal electrodes and organic semiconductors highlights its promise to overcome energy barriers at the hard‐soft materials interface to the benefit of organic electronics.

The efficient operation of polymer-and perovskite-based photovoltaic devices depends on selective charge extraction layers that are placed between the active layer and electrodes. Herein, we demonstrate that integration of a tetra-n-butyl ammonium iodide-doped zwitterionic fulleropyrrolidine derivative, C 60 -SB, as a cathode modification interlayer significantly improves the photovoltaic device performance. Compared to the intrinsic (undoped) zwitterionic material, which is an efficient interlayer itself, the doped interlayers further improve average power conversion efficiencies from 8.37% to 9.68% in polymer-based devices and from 12.53% to 15.31% in perovskite-based devices. Ultraviolet photoelectron spectroscopy revealed that doping increases the interfacial dipole at the C 60 -SB/Ag interface, i.e., reduces the effective work function of the resultant composite cathode. This effect originates from the population of negative polaron states in C 60 -SB by extrinsic charges that prevent directional charge transfer from Ag to the integer charge-transfer states in C 60 -SB, pinning the Fermi level at higher energy. The reduced resistivity of the doped interlayer, as measured by impedance spectroscopy, enables efficient device operation with a broad range of interlayer thicknesses, thus simplifying the solution-based device fabrication process.

A series of perylene diimide (PDI)-containing ionene and zwitterionic polymers were prepared by the Menschuktin reaction and by nucleophilic ring-opening of a novel bis-sultone monomer. PDI derivatives containing tertiary amine moieties at the imide position, and bromides or phenyl groups within the aromatic core, provided sites for polymerization and imparted solubility during the polymerization, respectively. The solution photophysical behavior of the polymers was studied by UV–vis and photoluminescence spectroscopy as a function of PDI incorporation and cationic/zwitterionic functionality, resulting in the observation of tunable solution spectral features induced by core functionality and/or interzwitterion interactions. This new PDI-based polymer platform affords opportunities to modulate conjugation and charge density within the polymers and examine the effects of cationic vs zwitterionic groups on the resultant optoelectronic properties.