NOVELTY - 3,4,5-Trimethoxybenzoic acid is decarboxylated and nitrified. The obtained 1,2,3-trimethoxy-5-nitrobenzene is reduced, obtained 3,4,5-trimethoxyaniline is diazotized and reacted with potassium ethyl xanthate, to obtain ethyl ((3,4,5-trimethoxyphenyl)sulfanyl)methanethioate. Aromatic amine (II) is diazotized and resultant product is reacted with sodium iodide to obtain aromatic iodo compound (III). 3,4,5-Trimethoxybenzenethiol is reacted with aromatic chloro compound (IV) or aromatic iodo compound (III) in presence of alkaline catalyst, to obtain trimethoxybenzenethiol derivative (I).    USE - Manufacture of trimethoxybenzenethiol derivative used for electron transfer layer of solar cell.    ADVANTAGE - The solar cell comprising trimethoxybenzenethiol derivative has high open-circuit voltage and excellent device characteristics.    DETAILED DESCRIPTION - 3,4,5-Trimethoxybenzoic acid is decarboxylated and nitrified to obtain 1,2,3-trimethoxy-5-nitrobenzene. The obtained 1,2,3-trimethoxy-5-nitrobenzene is reduced, obtained 3,4,5-trimethoxyaniline is diazotized and reacted with potassium ethyl xanthate, to obtain ethyl ((3,4,5-trimethoxyphenyl)sulfanyl)methanethioate. Aromatic amine of formula (II) is diazotized, and resultant product is reacted with sodium iodide to obtain aromatic iodo compound of formula (III). Ethyl((3,4,5-trimethoxyphenyl)sulfanyl)methanethioate is reduced to obtain 3,4,5-trimethoxybenzenethiol. The 3,4,5-trimethoxybenzenethiol is reacted with aromatic chloro compound of formula (IV) or aromatic iodo compound (III) in presence of alkaline catalyst, to obtain trimethoxybenzenethiol derivative of formula (I). The polymerization degree of the trimethoxybenzenethiol derivative as polymer is 1-300.    A=4-nitro-substituted phenyl of formula (i), 4-alkoxy-substituted phenyl of formula (ii), or group of formula (iii) or (iv);    R1-R8,R10-R18=H, halo, hydroxy, amino, cyano, 1-6C alkoxy, nitro, acid radical, 1-6C alkoxycarbonyl or acyloxy;    R9=1-3C alkyl or 1-3C substituted alkyl;and    X,Y'=N, O or S.