Organic tandem Schottky junction cells with high open circuit voltage

• Tandem dye-based cells with two serially connected Schottky junctions were fabricated and tested.
• The photovoltage in both subcells was boosted by introducing MoOx as anode material.
• Composite LiF/Ag/MoOx intermediate layer was used to connect bottom subcell with SubPc photoabsorber and top subcell with InClPc photoabsorber.
• The thickness of inorganic/organic components was optimized so that the open circuit voltage in the tandem cell with minimum functional layers in stack was 1.92 V.

In our previous work [Synth.Met.200(2015)99], we demonstrated dye-based tandem photovoltaic cells with vertically stacked Schottky junctions that generate open circuit voltage Uoc = 1.0 V. In present work, using the same concept we reached Uoc = 1.92 V. Such a progress is basically associated with optimization of the anode material in both subcells. Two axially substituted phthalocyanine complexes were used as absorbers: boron chloride subphthalocyanine SubPc in the bottom subcell and indium chloride phthalocyanine InClPc in the top subcell. Inorganic semiconducting oxide MoOx was introduced twice. First, MoOx layer was deposited over the ITO anode in the bottom subcell. This largely increases Uoc as compared to the archetypal Schottky-type cell ITO/SubPc/Al. For the bottom subcell with bilayer LiF/Ag cathode Uoc = 1.23 V. Second, MoOx was used in the composite intermediate layer (LiF/Ag/MoOx) that assembles subcells in stack, thus acting as anode buffer in the top subcell.