TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Composition: The organic layer comprises hole transport layer (103) and/or hole injection layer comprising the copolymer, electron injection layer and/or electron-transport layer comprising the copolymer. The photoactive layer (104) of the organic solar cell comprises electron donor and/or electron acceptor. The electron donor and electron acceptor comprise bulk heterojunction. The photoactive layer comprises bi-layer thin film structure including n-type organic compound layer and p-type organic compound layer.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Composition: The electron acceptor is chosen from fullerene, fullerene derivative, carbon nanotube, carbon nanotube derivative, basocuproin semiconductive element, and semiconductive compound.    TECHNOLOGY FOCUS - POLYMERS - Preferred Composition: The copolymer further comprises pyridine derivative of formula (III), cyclopenta-1,3-diene derivative of formula (IV) and 5-(cyclopenta-2,4-dien-1-yl)cyclopenta-1,3-diene derivative of formula (V). The copolymer further comprises 2-(2-(4-(4-(4-(6-(cyclopenta-1,3-dien-1-yl)-4,8-bis(thiophen-2-yl)-1,5-dihydro-s-indacen-2-yl)cyclopenta-1,3-dien-1-yl)-2,3,5,6-tetrahydropentalen-1-yl)cyclopenta-1,3-dien-1-yl)-8-(thiophen-2-yl)-1,5-dihydro-s-indacen-4-yl)thiophene derivative of formula (1-1), 2-(cyclopenta-1,3-dien-1-yl)-6-(4-(4-(4-(4,8-dioxo-1,5-dihydro-s-indacen-2-yl)cyclopenta-1,3-dien-1-yl)-2,3,5,6-tetrahydropentalen-1-yl)cyclopenta-1,3-dien-1-yl)-1,5-dihydro-s-indacene-4,8-dione derivative of formula (1-2), and 2-(6-(4-(4-(4-(6-(4-(cyclopenta-1,3-dien-1-yl)cyclopenta-1,3-dien-1-yl)-4,8-bis(thiophen-2-yl)-1,5-dihydro-s-indacen-2-yl)cyclopenta-1,3-dien-1-yl)-2,3,5,6-tetrahydropentalen-1-yl)cyclopenta-1,3-dien-1-yl)-8-(thiophen-2-yl)-1,5-dihydro-s-indacen-4-yl)thiophene derivative of formula (1-3). The electron donor comprises the copolymer. The content of unit (A) is 0.01-30 mol%, the content of unit (B') is 50-80 mol%, and the content of unit (C) is 0.01-30 mol%, with respect to total content of copolymer. The p-type organic compound comprises the copolymer. The unit (B') of the copolymer is electron donor and unit (C') of the copolymer is electron acceptor.X,Xa=CRR', NR, O, SiRR', PR, S, GeRR', Se or Te;Y1=N;Y',Y"=CR, N, SiR, P or GeR;a=1-3;andR1,R2,R2',R,R',R10,R11,R10',R11',R14,R17,R20,R",R'",R18,R19=H, D, halo, nitrile, nitro, imido, amido, hydroxy, optionally substituted alkyl, optionally substituted cycloalkyl, optionally substituted alkoxy, optionally substituted aryl, optionally substituted alkylthio, optionally substituted arylthio, optionally substituted alkyl sulfoxido, optionally substituted aryl sulfoxido, optionally substituted alkenyl, optionally substituted silyl, optionally substituted alkylamino, optionally substituted aralkyl, optionally substituted amino, optionally substituted arylamino, or optionally heterocyclyl.Preferred Properties: The number average molecular weight of the copolymer is 500-1000000 g/mol. The molecular weight distribution of the copolymer is 1-100.