Covalent organic frameworks are a class of crystalline organic porous materials that can utilize π–π-stacking interactions as a driving force for the crystallization of polygonal sheets to form layered frameworks and ordered pores. However, typical examples are chemically unstable and lack intrasheet π-conjugation, thereby significantly limiting their applications. Here we report a chemically stable, electronically conjugated organic framework with topologically designed wire frameworks and open nanochannels, in which the π conjugation-spans the two-dimensional sheets. Our framework permits inborn periodic ordering of conjugated chains in all three dimensions and exhibits a striking combination of properties: chemical stability, extended π-delocalization, ability to host guest molecules and hole mobility. We show that the π-conjugated organic framework is useful for high on-off ratio photoswitches and photovoltaic cells. Therefore, this strategy may constitute a step towards realizing ordered semiconducting porous materials for innovations based on two-dimensionally extended π systems.

Three‐layered organic solar cell with an interlayer of codeposited pigments of n‐type perylene tetracarboxylic derivative (Me‐PTC) and p‐type metal‐free phthalocyanine (H₂Pc) in between the respective pigment layers, was fabricated. Two times larger photocurrent compared to the double‐layered cell without an interlayer was obtained due to the efficient carrier photogeneration in a codeposited layer. The power conversion efficiency reached 0.7% under the intense white light of 100 mW cm⁻².

Three‐layered organic solar cells, having a sandwiched interlayer of co‐deposited p‐type phthalocyanine (Pc) pigments and n‐type perylene derivative (PTC) pigments, exhibited photocurrent enhancement when compared with two‐layered cells without the interlayer. A large number of Pc/PTC molecular contacts within the interlayer serve as active sites for effective charge carrier photogeneration. The photovoltaic characteristics of the three‐layered configuration suggest the formation of a p‐i‐n like structure, in which the built‐in potential produced by Fermi level differences in the respective pigment layers is mainly distributed across the co‐deposited interlayer. Inorganic semiconductor films are also shown to be applicable to the present p‐i‐n cell structure as an n layer to obtain larger photovoltages.

Tandem type organic solar cell consisting of two combined unit cells was fabricated. Each unit cell was two-layer organic solar cell composed of metal-free phthalocyanine and perylene tetracarboxylic derivative. When ultra-thin Au layer was inserted between unit cells, photovoltage increased about 2 times, while photocurrent density was much dependent on the thickness of the inserted Au layer.

Large photocurrent multiplication reaching 10 000 times has been observed in a perylene pigment film sandwiched between Au electrodes. The phenomenon occurs at the interface between the perylene film and a negatively biased Au electrode and is found to be associated with electron injection from the Au electrode to the perylene film through the depletion layer formed in the pigment film under a high electric field, which is built up by the photoaccumulated space charges of trapped holes near the interface.

Three-layered organic solar cells incorporating a codeposited interlayer of fullerene and metal-free phthalocyanine, whose nanostructure was optimized by controlling the substrate temperature during coevaporation, showed a photoelectric conversion efficiency of 2.5% under illumination with simulated solar light. The three-layered cells were concluded to have a p-i-n-like energetic structure.