Long-lived bulk heterojunction solar cells fabricated with photo-oxidation resistant polymer

We report the fabrication of long-lived polymer solar cells using a new donor–acceptor type alternating copolymer, poly(5,5,10,10-tetrakis(2-ethylhexyl)-5,10-dihydroindeno[2,1-α]indene-2,7-diyl)-co-4,7-di-2-thienyl-2,1,3-benzothiadiazole (PININE–DTBT) in bulk heterojunction composites with the fullerene derivative [6,6]-phenyl C70-butyricacidmethyl ester (PC70BM). The PININE–DTBT:PC70BM solar cells exhibit an extended device lifetime (as compared with other polymer systems) with a reasonable power conversion efficiency of ∼2.7% under air mass 1.5 global (AM 1.5 G) irradiation of 100 mW/cm2. The long-lived feature of the devices originates from the photo-oxidation resistant backbone unit and the deep HOMO (highest occupied molecular orbital) level of PININE–DTBT.