TECHNOLOGY FOCUS - POLYMERS - Preferred Properties: The surface layer portion is a membrane. Concentration of the photocatalyst in the membrane becomes higher towards the outer exposed surface from the surface which touches the base material of the solar-cell cover. The number average particle diameter of the modified photocatalyst is 400 nm or less.Preferred Photocatalyst: The photocatalyst is a modified photocatalyst, modified by using at least one type of modified compound (b) chosen from group having tri organosilane unit of formula: R3Si-, mono-oxy diorganosilane unit of formula: -(R2SiO)-, dioxy organosilane unit of formula (3) and/or fluorinated methylene unit (-CF2-).R = linear or branched 1-30C alkyl group, 5-20C cycloalkyl group, linear or branched 1-30C fluoroalkyl group, linear or branched 2-30C alkenyl group, phenyl group, 1-20C alkoxy group or hydroxyl group.Preferred Binder: The binder component contains phenyl group containing silicone (S1) of formula: R1pR2qXrSiO(4-p-q-r)/2 and phenyl group containing silicone (S2) of formula: R1sXtSiO(4-s-t)/2. The silicone (S2) is free of alkyl group.R1 = phenyl group;R2 = linear or branched 1-30C alkyl group, 5-20C cycloalkyl group or linear or branched 2-30C alkenyl group;X = H atom, hydroxyl group, 1-20C alkoxy group, 1-20C acyloxy group, aminoxy group, 1-20C oxime group and halogen atom;0 less than p less than 4; 0at mostq less than 4; 0at mostr less than 4; 0 less than (p+q+r) less than 4; p/(p+q) is 0.05-1; 0 less than s less than 4; 0/tau less than 4; and 0 less than (s+t) less than 4.The binder component further contains an alkyl group containing silicone (S3) of formula: R2uXvSiO(4-u-v)/2.R2, X = same as above;0 less than u less than 4; 0at mostv less than 4; and 0 less than (u+v) less than 4.The silicone (S3) has mono-oxy diorganosilane unit of formula: -(R22SiO)-, and dioxysilane unit of formula (8).R2 = 1-30C linear or branched group, 5-20C cycloalkyl group or 2-30C linear or branched alkenyl group.Preferred Composition: The surface layer portion is formed from photocatalyst composition containing a photocatalyst and a binder component.Preferred Compound: The modified compound (b) is a silicon-hydrogen group containing silicone compound (b1), of formula: HxRySiO(4x-y)/2.R = same as above;0 less than 4; 0 less than y less than 4; and (x+y)at most4.The compound (b1) is a mono silicon-hydrogen group-containing compound of formula (10), both terminal silicon-hydrogen group-containing compound of formula: H-(R32SiO)n-SiR32-H, silicone compound of formula (12): (R3HSiO)a(R32SiO)b(R33SiO1/2)c.R3 = linear or branched 1-30C alkyl group, 5-20C cycloalkyl group, linear or branched 2-30C alkenyl group, linear or branched 1-30C fluoro alkyl group, phenyl group or siloxy group of formula: -O-(R42SiO)m-SiR43;R4 = linear or branched 1-30C alkyl group, 5-20C cycloalkyl group, linear or branched 2-30C alkenyl group, linear or branched 1-30C fluoro alkyl group or phenyl group;0at mostnat most1000; a = integer greater than 0; b = 0 or more; (a+b) = integer greater than 1 and at most10000; 0at mostmat most1000; and c = 0-2.When c = 0, silicone of formula (12) is cyclic silicone, and when c = 2, silicone of formula (12) is chain shaped silicone.Preferred Arrangement: The surface layer portion has a phase separation structure about the silicones (S2, S3). The photocatalyst exist in the alkyl group containing silicone (S1) phase.Preferred Method: Portion(s) of organic group coupled with silicon atom existing in the vicinity of the photocatalyst particle is substituted with a hydroxyl group and/or siloxane coupling, by irradiation with a light having energy higher than the band-gap energy of the photocatalyst.