NOVELTY - A polymerization liquid comprises a solvent containing 100-80 %mass water and 0-20 %mass organic solvent, monomer(s) chosen from thiophene having a substituent at 3-position and 4-position, and a boron complex (I) of carboxylic acid or hydroxycarboxylic acid and/or its salt, as supporting electrolyte, excluding the presence of only boro-subsalicylate and boro-subsalicylate salt.    USE - Polymerization liquid is used for forming electroconductive polymer films of electrode components used as anode in organic thin-film solar cell and dye-sensitized solar cells (all claimed). Can also be used for solid electrolytic capacitors, display elements, polymer batteries, antistatic films, and sensors.    ADVANTAGE - The polymerization liquid is economical and environmentally-friendly, and provides conductive polymer films having excellent electrochemical activity and catalytic-reduction ability.    DETAILED DESCRIPTION - A polymerization liquid comprises a solvent containing 100-80 %mass water and 0-20 %mass organic solvent, monomer(s) chosen from thiophene having a substituent at 3-position and 4-position, and a boron complex of formula (I) of carboxylic acid or hydroxycarboxylic acid and/or its salt, as supporting electrolyte, excluding the presence of only boro-subsalicylate and boro-subsalicylate salt.    X,Y'=-C(=O)-(-CR1R2-)m-C(=O)-, -C(=O)-CR3=CR4-C(=O)-, -(CR5R6-)n-C(=O)-, or group of formula (i) or (ii);    m=0-4;    R1-R6=H, or methyl or phenyl (both optionally substituted by carboxy and/or hydroxy), carboxy, or hydroxy;    n=1 or 2;and    R7-R10=H, carboxy or hydroxy.    (i) When m is 1, R1, R2, carbon coupled with these groups, and carbon atom optionally substituted by carboxy, hydroxy and/or phenyl may form 5- or 6-membered saturated ring; (ii) When m is 2, R1, carbon coupled with the group, and carbon atom optionally substituted by carboxy, hydroxy and/or phenyl may form 5- or 6-membered saturated ring; (iii) When n is 1, R5, R6, carbon coupled with these groups, and carbon atom optionally substituted by carboxy, hydroxy and/or phenyl may form 5- or 6-membered saturated ring; and (ii) When n is 2, R5, carbon coupled with the group, and carbon atom optionally substituted by carboxy, hydroxy and/or phenyl may form 5- or 6-membered saturated ring. INDEPENDENT CLAIMS are included for the following:    (1) electroconductive polymer film obtained by introducing a substrate having an electroconductive portion on the surface, into the polymerization liquid;    (2) electrode component provided with a substrate having an electroconductive portion on the surface, and an electroconductive polymer film laminated on the electroconductive portion;    (3) organic thin-film solar cell consisting of a photoelectric-conversion layer, an anode provided with an electroconductive portion on the surface, a hole taking-out layer laminated on the electroconductive portion, and a hole transport component laminated on the hole taking-out layer, and a cathode laminated on the photoelectric-conversion layer. The electrode component is used as a component comprising the anode and hole taking-out layer; and    (4) dye-sensitized solar cell consisting of a cathode having a semiconductor layer containing a photosensitizer and a dye, an electrolyte layer containing oxidation species and reduction species, laminated on the semiconductor layer, and an anode having a conductive polymer layer which acts as a catalyst for converting oxidation species into reduction species, laminated on the electrolyte layer. The electrode component is used as the anode.