NOVELTY - Carboxy group-containing fused ring compounds (I) are new.    USE - (I) are useful in manufacturing organic solar cell.    ADVANTAGE - (I) improve light efficiency, thermal stability and service life of the organic solar cell.    DETAILED DESCRIPTION - Carboxy group-containing fused ring compounds of formula (I) are new.    n = 1-20;    m = 1-3;    Cy = aliphatic fused ring, aromatic fused ring, N, O, P and/or S atoms-containing aliphatic fused heterocyclic ring, N, O, P and/or S atoms-containing aromatic fused heterocyclic ring, fused ring of an aliphatic ring and an aromatic ring, fused ring of N, O, P and/or S atoms-containing aliphatic heterocyclic ring, N, O, P and/or S atoms-containing aromatic heterocyclic ring, fused ring of hydrocarbon ring and N, O, P and/or S atoms-containing heterocyclic ring, or C60-C84 fullerene;    A, R' = alkyl, cycloalkyl, alkoxy, aryl, arylalkyl, aryloxy, alkylthio, arylthio, alkyl sulfoxide group, aryl sulfoxide group, alkenyl, silyl group, boron group, alkylamine group, aralkylamine group, arylamine group, heteroarylamine group, aryl, fluorenyl group, carbazole group, N, O and/or S atoms-containing heterocyclic group (all are optionally substituted), H, deuterium, halo, cyano, nitro, imide group, amide group, OH, ester group or carbonyl group;    X = cycloalkyl group, aryl group, N, O and/or S atoms-containing divalent heterocyclic group (all are optionally substituted), S, O, NR' or CH2; and    R = alkyl, cycloalkyl, aryl, N, O and/or S atoms-containing heterocyclic group (all are optionally substituted with deuterium, halo, alkyl, alkenyl, alkoxy, cycloalkyl, silyl, arylalkenyl, aryl, arylalkyl, thioalkyl, alkyl sulfoxide group, aryl sulfoxide group, boron group, alkylamine group, aralkylamine group, arylamine group, heteroaryl, carbazole group, heteroarylamine group, aryl, fluorenyl group, cyano, nitro, OH, aromatic or aliphatic cyclic ketone group), H or deuterium.    Provided that: when n is 2-20, X are same or different from each other; when m is 2 or 3, the structural units inside the bracket are same or different from each other. INDEPENDENT CLAIMS are also included for:    (1) organic solar cell comprising a first electrode (102), a second electrode (105) placed opposite to the first electrode, and an organic layer placed provided between the first electrode and the second electrode, where the organic layer is composed of (I); and    (2) manufacturing organic solar cell, comprising preparing a substrate (101), forming a first electrode on top of the substrate, forming a photoactive layer (104)-containing organic layer on top of the first electrode, and then forming a second electrode on top of the organic layer.    DESCRIPTION OF DRAWING(S) - The diagram shows a schematic representation of organic solar cell.    Substrate (101)    First electrode (102)    Hole transport layer (103)    Photoactive layer (104)    Second electrode (105)