NOVELTY - A n-type ladder copolymer formed with alternating perylene and pyridine units (A) having two end groups, where the perylene units having at least one solubilizing group attaching at position(s) 1, 6, 7, and/or 12 is new.    USE - The copolymer is useful in photonic, electronic, photovoltaic, energy detecting, energy harvesting, or solar energy collecting device(s) (claimed).    DETAILED DESCRIPTION - A n-type ladder copolymer formed with alternating perylene and pyridine units of formula (A) having two end groups, where the perylene units having at least one solubilizing group attaching at position(s) 1, 6, 7, and/or 12 is new.    R1-R4 = solubilizing group(s) comprising aryl, alkyl aryl, alkoxy aryl, or aryloxy aryl; and    n = 4-400.    INDEPENDENT CLAIMS are also included for:    (1) organic heterojunction layer, comprising: organic heterojunction blend having at least one solution-processible p-type organic material and at least one solution-processible n-type ladder copolymer where the copolymer formed with alternating perylene and pyridine units and having of formula (D1) and the perylene units having at least one solubilizing group attaching at position(s) 1,6,7, and/or 12;    (2) liquid pre-cursor solution, comprising: at least one solvent and n-type ladder copolymer(s); where the copolymer formed with alternating perylene and pyridine units having chemical structure E, where the solvent(s) comprising toluene, xylene, other aromatic hydrocarbons, anisole, veritrol, other aryl ethers, dimethylformamide, n-methyl pyrrolidinone, dimethylacetamide, chlorobenzene, dichlorobenzene, other halogenated aromatic hydrocarbons, halogenated aliphatic hydrocarbons, or other common organic solvents; and    (3) forming organic heterojunction film, comprising: providing liquid solution having at least one solvent, at least one p-type organic material, and at least one n-type ladder copolymer; casting the solution on a substrate providing at least one solvent-swollen film; and removing the residual solvent from the solvent-swollen film with vacuum and/or heat producing at least one the heterojunction film.    At least one of R1a-R4a = aryl, alkyl aryl, alkoxy aryl, and aryloxy aryl.