A highly efficient PTB7-Th polymer donor bulk hetero-junction solar cell with increased open circuit voltage using fullerene acceptor CN-PC70BM

Abstract Modified [6,6]-phenyl-C 70 -butyric acid methyl ester ( CN-PC 70 BM ) is employed as an electron acceptor along with poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b; 4,5-b']dithiophene-2,6-diyl-alt-(4-(2-ethylhexyl)-3-fluorothieno[3,4- b ]thiophene-)-2-carboxylate-2-6-diyl)] (PTB7-Th) polymer as donor for solution-processed organic solar cells. Inverted device architecture is adopted to fabricate the photovoltaic devices. Using chloronaphthalene as an additive, a high power conversion efficiency (PCE) of 8.2% is achieved with an excellent open circuit voltage ( V oc ) of 0.9 V, short-circuit current density ( J sc ) of 13.5 mA cm −2 and fill factor of 0.68 as compared to PCE of 5.4% from the reference solar cell using PC 70 BM.