TECHNOLOGY FOCUS - POLYMERS - Preferred Components: (II) has a structure of formula (a1)-(a4). The organic solvent is xylene or toluene.Ar1 = aryl;R6, R7 = R1;p = 1-10000;q = 1-20000;r = 0-10000;x, y = 0.1-0.9; andz = 0-0.9.Provided that the sum of x, y and z is 1 or the sum of x and y is 1. SPECIFIC COMPOUNDS - The use of poly((9,9-dioctylfluorene-2,7-diyl)-co-(bithiophen-2,5'-diyl)-co-(N,N-bis(4-(1,1-dimethylethyl)phenyl)-benzidine-N,N-diphenylene-1,4-diyl)) of formula (IIa), poly((9,9-dioctylfluorene-2,7-diyl)-co-(thiophene-2,5-diyl)-co-(N,N-bis(4-(1,1-dimethylethyl)phenyl)-benzidine-N,N-diphenylene-1,4-diyl)), poly((bithiophene-2,5'-diyl)-co-(N,N-bis(4-(1,1-dimethylethyl)phenyl)-benzidine-N,N'-diphenylene-1,4-diyl)) and poly((9,9-dioctylfluorene-2,7-diyl)-alt-(benzothiadiazole-4,7-diyl)) is disclosed as (II).    EXAMPLE - An anode of indium tin oxide was formed on a glass substrate. The glass substrate with the anode was cleaned using ion-exchange water, 2-propanol and acetone in series, and the surface was processed with ozone gas by emitting UV rays. A hole transport layer was formed on the anode by spin coating a mixture of poly(p-styrenesulfonic acid) salt of poly (3,4-ethylenedioxyphen) and poly(p-styrenesulfonic acid) having a structure of formula (A) (PEDOT:PSS). The PEDOT:PSS film was formed to a thickness of 50 nm by baking at 200degrees C for 10 minutes in air after spin coating, and then baking at 80degrees C for 30 minutes under reduced pressure. A p-type polymer layer containing poly((9,9-dioctylfluorene-2,7-diyl)-co-(bitiophen-2,5'-diyl)-co-(N,N-bis(4-(1,1-dimethylethyl)phenyl)-benzidine-N,N-diphenylene-1,4-diyl)) (IIa) was formed by spin coating the solution of p-type polymer on the hole transport layer. The p-type polymer solution was adjusted by using xylene as a solvent. An electron transport layer was formed on the p-type polymer layer by accumulating 3,4,9,10-perylenetetracarboxy-bis-benzimidazole under vacuum. A cathode was formed on the electron transport layer by accumulating silver under vacuum to form the organic photovoltaic cell.