TECHNOLOGY FOCUS - POLYMERS - Preparation (disclosed): Preparation of the electron-donating polymer comprises:(1) adding 0.25 mmol 2,6-bis(trimethyl tin)-1 ,8-bis ((2-ethylhexyl)oxy)benzo(1 ,2-b:4,5-b')dithiophene and 0.25 mmol 4,6-dibromothieno(3,4-b)thiophen-2-yl(phenyl)methanone may be added to 5 mL dimethylformamide (DMF)/toluene (DMF/toluene) at a volume ratio of 1:4, adding catalyst of 0.01 mmol tetrakis(triphenylphosphine)palladium (Pd(PPh3)4), and agitating at 120 degrees C for 6 hours;(2) adding 0.4 mmol 2,6-bis(trimethyl tin)-1,8-bis ((2-ethylhexyl)oxy)benzo(1 ,2-b:4,5-b')dithiophene, 0.1 mmol 4,6-dibromothieno(3,4-b)thiophen-2-yl(phenyl)methanone, and 0.3 mmol 5-ethoxy-5-oxopentyl-4,6-dibromothieno(3,4-b)thiophene-2-carboxylate to 8 mL DMF/toluene at a volume ratio of 1:4, and adding a catalyst of 0.017 mmol Pd(PPh3)4, and agitating at 120 degrees C for 6 hours;(3) adding 0.5 mmol 2,6-bis(trimethyl tin)-1,8-bis ((2-ethylhexyl)oxy)benzo(1 ,2-b:4,5-b')dithiophene, 0.25 mmol 4,6-dibromothieno(3,4-b)thiophen-2-yl(phenyl)methanone, and 0.25 mmol 5-ethoxy-5-oxopentyl-4,6-dibromothieno(3,4-b)thiophene-2-carboxylate to 10 mL DMF/toluene at a volume ratio of 1:4, and adding a catalyst of 0.02 mmol Pd(PPh3)4, and agitating at 120 degrees C for 6 hours; or(4) adding 0.4 mmol 2,6-bis(trimethyl tin)-1,8-bis ((2-ethylhexyl)oxy)benzo(1 ,2-b:4,5-b')dithiophene, 0.3 mmol 4,6-dibromothieno(3,4-b)thiophen-2-yl(phenyl)methanone, and 0.1 mmol 5-ethoxy-5-oxopentyl-4,6-dibromothieno(3,4-b)thiophene-2-carboxylate to 8 mL DMF/toluene at a volume ratio of 1:4, and adding a catalyst of 0.017 mmol Pd(PPh3)4, and agitating at 120 degrees C for 6 hours.Preferred Component: The repeating unit A includes repeating units of formulae (V), (VI), and/or (VII). The electron-donating polymer further comprises a repeating unit B including a repeating unit (I) and a repeating unit of formula (VIII). The repeating unit of formula (VIII) is preferably (VIIIa) or (VIIIb). The repeating unit B includes a repeating unit of formula (IX). The mole ratio of the repeating unit A and the repeating unit B is 1:10-10:1. The repeating unit (I) is an electron donating group, and the repeating unit (II)-(IV) includes an electron accepting functional group. The electron-donating polymer is a single phase polymer.X3=electron-accepting group including two ester residual groups and one of optionally substituted divalent aliphatic organic group linking the ester residual groups, preferably groups of formulae (X) or (XI);X4=H, halo, optionally substituted 1-20C aliphatic organic group, OH, optionally substituted 1-20C alkoxy group, optionally substituted 1-20C ester group, thiol group, or SR107; andR107=optionally substituted 1-20C aliphatic organic group, optionally substituted 2-30C aromatic organic group, or optionally substituted 2-30C heterocycloalkyl group.X5-X7=optionally substituted divalent 1-20C aliphatic organic group; andR12, R13=H, or optionally substituted 1-20C aliphatic organic group. EXAMPLE - An electron-donating polymer was prepared by adding 0.25 mmol 2,6-bis(trimethyl tin)-1 ,8-bis ((2-ethylhexyl)oxy)benzo(1 ,2-b:4,5-b')dithiophene and 0.25 mmol 4,6-dibromothieno(3,4-b)thiophen-2-yl(phenyl)methanone may be added to 5 mL dimethylformamide (DMF)/toluene (DMF/toluene) at a volume ratio of 1:4, adding catalyst of 0.01 mmol tetrakis(triphenylphosphine)palladium (Pd(PPh3)4), and agitating at 120 degrees C for 6 hours.