In this work, we report high electron transport and hole blocking capability of hybrid photoconductive interlayer materials manufactured from an aqueous solution, which are achieved by doping perylene bisimide dyes into zinc oxide (ZnO) through the formation of ionic bonding between the organic dopants and the inorganic matrix. Benzenesulfonic acid functional groups are introduced to perylene bisimide dye molecules, which enhance the solubility of the dye molecules in water and form ionic bonds with zinc atoms during the fabrication of the hybrid thin films. The ionic bonding assisted molecular dispersion endows the hybrid thin film with full photoconductive properties, which improves electron transport by photoinduced electron transfer from organic dye molecules to the conduction band of ZnO. Especially, the hole blocking ability is also highly increased. Both increased electron transport and hole blocking are benefits to the charge selectivity of the cathode interlayer, which results in a high fill factor in organic solar cells. A power conversion efficiency of up to 15.4% is achieved on the basis of such an aqueous solution processed hybrid interlayer when using PM6:Y6 as the active layer. In addition, the optimized thermal annealing temperature for the fabrication of the hybrid thin film is as low as 150 °C, which is a benefit for the application of such photoconductive materials in flexible devices.

Poly[(9,9-dioctyl-2,7-fluorene)- alt-(9,9-bis(3'-( N, N-dimethylamino)propyl)-2,7-fluorene)] (PFN) is a very important interfacial modifier in organic photovoltaic and organic light-emitting diodes to improve device performance, where their molecular dipole has been regarded to play a key role. In this work, we have reported a spontaneous interfacial dipole orientation effect in acetic acid dissolved PFN, which is strongly related to the interfacial dipole and the corresponding device performance. In direct spin-coating, the interfacial dipole is 1.08 Debye with interfacial contact angle 84.8°, whereas after self-assembly of 10 min, the interfacial dipole is balanced at 4.21 Debye, with the interfacial contact angle decreasing to 76.8°. Without strong interaction with the substrate, the energy of upward amine groups is much lower than that of downward ones in theoretical simulation, which would be the driving force of this spontaneous process. The preferred conformations of PFN molecules on hydroxylated substrates have over 99% amine groups outward, and the theoretical average dipole calculated from the weight of these conformations is 4.48 Debye, which is close to the experimental result and indicates a high ratio of upward amine groups in self-assembled films. This effect obviously changes the device performance, such as an obvious positive threshold voltage shift in transistors and a distinct increase of the short-circuit current/open-circuit voltage in organic solar cells. This effect provides a deeper understanding of the PFN interlayer mechanism and has potential application in optoelectronic devices.

Suitable work function (WF) of the cathode in polymer solar cells (PSCs) is of essential importance for the efficient electron extraction and collection to boost the power conversion efficiency. Herein, we report a facile and efficient method to tune the surface WF of aluminum-doped zinc oxide (AZO) through building of a definite interfacial dipole, which is realized by the construction of a layered structure of positive and negative ionized species. A cross-linked perylene bisimide (poly-PBI) thin film is deposited onto the AZO surface first, and then it is reduced to the radical anion state (poly-PBI) in an electrochemical cell, using tetraoctylammonium (TOA), a bulky cation, as a counter ion. Owing to the huge volume of TOA, it is absorbed on the surface of the cross-linked PBI thin film through Coulomb force, and thus a definite interface dipole is formed between the two ionized layers. Because of the definite interface dipole, the surface WF of the electrode modified with ionized layers is decreased dramatically to 3.9 eV, which is much lower than that of the electrode modified with the neutral PBI layer (4.5 eV). By using this novel cathode interlayer with a definite interface dipole in PSCs, a significantly increased open-circuit voltage ( V) is obtained. The results indicate that it is a facile and unique method by the construction of a definite interface dipole to tune the surface WF of the electrode for the application in organic electronic devices.

With the rapid development of near-infrared absorbing acceptor materials, the photoelectric conversion efficiency of polymer solar cells (PSCs) has been greatly improved in the past several years. However, serious charge...