Efficient charge extraction in thick bulk heterojunction solar cells through infiltrated diffusion doping

A new strategy for improving the charge extraction in thick bulk heterojunction (BHJ) polymer solar cells (PSCs) is reported. By the deposition of a solution-processed vanadium oxide (s-VO_x) onto BHJ active layers, conductive charge-transport channels are formed inside the active layer via a charge-transfer doping reaction between the lone-pair electrons of the sulfur atoms in the polymer and the Lewis-acidic vanadium atoms of the s-VO _x. Because the charge-transport channels significantly reduce charge recombination in the BHJ films, high internal quantum efficiencies (IQEs) of over 80% are achieved in the thick inverted PSCs (≈420 nm). This finding represents a new strategy for improving the efficiency and feasibility of printable photovoltaic devices. Efficient inverted polymer solar cells with thick active layers and a high internal quantum efficiency are demonstrated using solution-processed conductive charge-transport channels. The conductive transport channels are formed by using the infiltration-doping ability of soluble vanadium oxide into bulk heterojunction (BHJ) films and can effectively extract photogenerated charge carriers in thick BHJ films by reducing trap-assisted recombination.