TECHNOLOGY FOCUS - POLYMERS - Preferred Method: The step of forming the photoactive layer comprises: forming a solution by dissolving electron donor polymers, electron acceptor polymers, and block copolymers in a solvent; and spreading the solution on the hole transport layer. The electron donor polymers form grains through a self-assembly process to form the electron donor layer. The method further comprises performing heat treatment after forming the photoactive layer or the upper electrode. The heat treatment is performed at a temperature of 140-200 degrees C for 5-30 minutes. Preferred Components: The photoactive layer comprises: the electron donor layer consisting of grains of electron donor polymers; the silica thin film layer formed around the electron donor layer; and the electron acceptor layer in contact with the silica thin film layer. The electron donor layer: has a network structure; and includes poly(thiophene) derivatives, poly(fluorene) derivatives, poly(2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene), poly(2-methoxy-5-(3,7-dimethyloctyloxy)-1,4-phenylenevinylene), poly(2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta(2,1-b:3,4-b)dithiophene)-alt-4,7(2,1,3-benzothiadiazole)), poly-dithieno(3,2-b:2',3'-d)germole thieno(3,4-c)pyrrole-4,6-dione, poly(4,8-bis(2-ethylhexyloxy)-benzo(1,2-b:4,5-b)dithiophene-2,6-diyl-alt-(4-octanoyl-5-fluoro-thieno(3,4-b)thiophene-2-carboxylate)-2,6-diyl), poly((4,8-bis((2-ethylhexyl)oxy)benzo(1,2-b:4,5-b')dithiophene-2,6-diyl)(3-fluoro-2-((2-ethylhexyl)carbonyl)thieno(3,4-b)thiophenediyl)), or poly(N-9'-heptadecanyl-2,7-carbazole-alt-5,5-(4,7-di-2-thienyl-2',1',3'-benzothiadiazole)). The electrons generated in the electron donor layer tunnel through the silica thin film layer to be transported to the electron acceptor layer and holes generated in the electron donor layer are blocked by the silica thin film layer to be transported to the hole transport layer along the electron donor layer. The silica precursor is at least one of polymers of formulae (I)-(X) including (CH2=CHC(=O)-O-(CH2)n1-Si(OCH3)3) (I), (CH2=CHC(=O)-O-(CH2)n2-Si(OCH2CH3)3) (II), (CH2=CHC(=O)-O-(CH2)n3-Si(OiC3H7)3) (III), (CH2=C(CH3)-C(=O)-O-(CH2)n4-Si(OCH3)) (IV), (CH2=C(CH3)-C(=O)-O-(CH2)n5-Si(OCH2CH3)) (V), (CH2=C(CH3)-C(=O)-O-(CH2)n6-Si(OCH2CH3)) (VI), (CH2=CH(CH2)n9Si(OCH3)3) (IX), and (CH2=CH(CH2)n10Si(OCH3CH3)3) (X). The block copolymers include the electron donor polymers and silica precursors. The silica thin film layer is formed by cross-linking of the silica precursors using the heat treatment. The electron acceptor layer consists of phenyl-61C-butyric-acid-methyl ester, phenyl-C71-butyric-acid-methyl ester, phenyl-C85-butyric-acid-methyl ester, or their derivatives. In formula (I):n1 = 1-3, provided that when the number of methoxy groups combined with the Si atom is less than 3, the other group combined with the Si element is a methyl group.In formula (II):n2 = 1-3, provided that when the number of ethoxy groups combined with the Si atom is less than 3, the other group combined with the Si element is a methyl group.In formula (III):n3 = 1-3, provided that when the number of isopropoxy groups combined with the Si atom is less than 3, the other group combined with the Si element is a methyl group.In formula (IV):n4 = 1-3, when the number of methoxy groups combined with the Si atom is less than 3, the other group combined with the Si element is a methyl group.In formula (V):n5 = 1-3, provided that when the number of ethoxy groups combined with the Si atom is less than 3, the other group combined with the Si element is a methyl group.In formula (VI):n6 = 1-3, provided that when the number of isopropoxy groups combined with the Si atom is less than 3, the other group combined with the Si element is a methyl group.In formula (VII):n7 = 1-3.In formula (VIII):n8 = 1-3, where an allyl-based silica precursor is of formula (CH2=CHCH2O(CH2)n11Si(OCH3)3) (XI), or (CH2=CHCH2O(CH2)n12-Si(OCH3CH3)3) (XII).In formula (IX):n9 = 1-12, provided that when the number of methoxy groups combined with the Si atom is less than 3, the other group combined with the Si element is a methyl group.In formula (X):n10 = 1-12, provided that when the number of ethoxy groups combined with the Si atom is less than 3, the other group combined with the Si element is a methyl group.In formula (XI):n11 = 1-12, provided that when the number of methoxy groups combined with the Si atom is less than 3, the other group combined with the Si element is a methyl group.In formula (XII):n12 = 1-12, provided that when the number of ethoxy groups combined with the Si atom is less than 3, the other group combined with the Si element is a methyl group, where an isocyanate-based silica precursor is represented by the following chemical formulae (NCO-(CH2)n13-Si(OCH3)3) (XIII), and NCO-(CH2)n14-Si(OCH3CH3)3 (XIV).In formula (XIII):n13 = natural number of 1-12, provided that when the number of methoxy groups combined with the Si atom is less than 3, the other group combined with the Si element is a methyl group.In formula (XIV):n14 = natural number of 1-12, provided that when the number of ethoxy groups combined with the Si atom is less than 3, the other group combined with the Si element is a methyl group.