NOVELTY - A new polymer consists of a structural unit (I) derived from thieno(2,3-f)(1)benzothiophene-4,8-diol.    USE - New polymer is used as charge transport material in solid layers of photoelectric conversion elements of solar cells (all claimed) e.g. dye-sensitized solar cell and solid type solar cell. Can also be used for optical switching device and sensors.    ADVANTAGE - The new polymer has excellent charge transport ability, light absorption property, and thermal stability. The polymer provides photoelectric conversion elements having excellent photoelectric conversion efficiency and durability.    DETAILED DESCRIPTION - A new polymer consists of a structural unit of formula (I) derived from thieno(2,3-f)(1)benzothiophene-4,8-diol.    R1,R2=H or optionally substituted 1-20C hydrocarbyl;    R3=group of formula (i or ii);    R4=H, cyano, or 2-20C alkoxycarbonyl, 1-20C alkoxy, or 1-30C hydrocarbyl (all optionally substituted);and    R5=H or optionally substituted 1-30C hydrocarbyl.    INDEPENDENT CLAIMS are included for the following:    (1) photoelectric conversion element having a solid layer (4) containing a polymer, provided between a pair of electrodes;    (2) manufacture of polymer;    (3) halogenated thienylacrylic acid derivative of formula (III);    (4) manufacture of compound (III), which involves reacting an ester compound of formula: R4-CH2-C(=O)-OR5 and a halogenated thiophene-carbaldehyde compound of formula (V);    (5) halogenated thieno-thienylacrylic acid derivative of formula (IV); and    (6) manufacture of compound (IV), which involves reacting the ester compound and a halogenated thieno-thiophene-carbaldehyde compound of formula (VI).    R6,R7=H or optionally substituted 1-20C hydrocarbyl;and    X1,X2=halo.    DESCRIPTION OF DRAWING(S) - The drawing shows a sectional view of the photoelectric conversion element.    Glass substrate (1)    Transparent conductive layer (2)    Donor buffer layer (3)    Solid layer (4)    Electronic buffer layer (5)