NOVELTY - Polyimide polymer solution comprises: a solvent; and a polyimide polymer having at least one of bicyclic repeating units (I) and a bicyclic repeating unit (II), and at least one of bicyclic repeating unit (III) and a bicyclic repeating unit (IV).    USE - The polyimide polymer solution is useful: for making transparent film; and in displaying device and in solar cell (all claimed), where the transparent film is useful in flexible electronics, liquid crystal displays and micro-electro-mechanical systems.    ADVANTAGE - The polyimide polymer solution provides the transparent film the film that exhibits high transmittance, properties of colorless, good thermo-duration at high temperature, good flexibility, anti-corrosive to the chemicals (e.g. photo-resist, oxalic acid, developer, and stripper), good UV resistance, and anti-yellow under UV-radiation.    DETAILED DESCRIPTION - Polyimide polymer solution comprises: a solvent; and a polyimide polymer having at least one of bicyclic repeating unit of formula (I) and a bicyclic repeating unit of formula (II), and at least one of bicyclic repeating unit of formula (III) and a bicyclic repeating unit of formula (IV).    A, A1 = cyclo-aliphatic compound (including bicyclo(2.2.1)heptan-2,3,5,6-tetrayl, bicyclo(2.2.2)octan-2,3,5,6-tetrayl, or bicyclo(2.2.2)oct-2-en-5,6,7,8-tetrayl), or aromatic compound (including4,4'-oxybis(benz-1,2-diyl), or 4,4'-(perfluoropropane-2,2-diyl)bis(benz-1,2-diyl)), where a molar ratio of the cyclo-aliphatic compound to the aromatic compound is 1-4; and    D, D1 = 4,4'-oxybis(benz-1yl), 3,4'-oxybis(benz-1yl), 4,4'-(4,4'-(propane-2,2-diyl)bis(4,1-phenylene))bis(oxy)bis(4,1-phenylene), 4,4'-(perfluoropropane-2,2-diyl)bis(4,1-phenylene)bis(oxy)bis(biphenyl-4',4-diyl), 4',4''-(4,4'-sulfonylbis(4,1-phenylene)bis(oxy))bis(biphenyl-4',4-diyl), biphenyl-2,4,2',4'-tetrayl, or 2,2'-bis(trifluoromethyl)biphenyl-4,4'-diyl.    INDEPENDENT CLAIMS are also included for:    (1) the polyimide polymer;    (2) a transparent film made of the polyimide polymer;    (3) a displaying device, comprising a first substrate and a second substrate disposed oppositely, where one of the first and second substrates is made of a polyimide polymer; and    (4) a solar cell, comprising a first film, a first electrode on the first film, an element layer, and a second electrode, where the element layer is present between the first electrode and the second electrode, and the first film is made of the polyimide polymer