Comparison of various solution processed electron transport layers for high efficiency polymer solar cells

In this work we made a comparative study between the electrical performances of three different electron transport layers (ETLs), used to build inverted polymer solar cells (PSCs). Two different metal oxides are prepared with a solution process: the first one is zinc oxide, prepared by a solgel procedure dissolving zinc acetate and ethanolamine in the 2-methoxyethanol, the second one is titanium oxide, prepared by spin coating a solution of commercial Titanium(IV)isoproxide in 2-methoxyethanol. The last ETL is an alcohol soluble conjugated polymer: poly[(9,9-bis(3´-(N,Ndimethylamino)propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)](PFN). Inverted PSCs with the configuration glass/ITO/ETL/ photoactive layer/MoO3/Ag were realized in order to investigate the performance of different ETL thin films. The photoactive layer was a blend of poly[(4,8-bis-(2ethylhexyloxy)-benzo[1,2-b;4,5-b´] dithiophene)-2,6-diyl-alt(4-(2-ethylhexanoyl)-thieno[3,4-b]thiopene)-2,6-diyl] and [6,6]-phenyl C71 butyric acid methyl ester. The best power conversion efficiency (6.4%) under simulated AM1.5G illumination of 100 mW/cm2, was achieved for the PSCs fabricated using a ZnO and PFN films.