All-oxide MoO_x/SnO_x charge recombination interconnects for inverted organic tandem solar cells

Multijunction solar cells are designed to improve the overlap with the solar spectrum and to minimize losses due to thermalization. Aside from the optimum choice of photoactive materials for the respective sub-cells, a proper interconnect is essential. This study demonstrates a novel all-oxide interconnect based on the interface of the high-work-function (WF) metal oxide MoO_x and low-WF tin oxide (SnO_x). In contrast to typical p-/n-type tunnel junctions, both the oxides are n-type semiconductors with a WF of 5.2 and 4.2 eV, respectively. It is demonstrated that the electronic line-up at the interface of MoO_x and SnO_x comprises a large intrinsic interface dipole (≈0.8 eV), which is key to afford ideal alignment of the conduction band of MoO_x and SnO_x, without the requirement of an additional metal or organic dipole layer. The presented MoO_x/SnO_x interconnect allows for the ideal (loss-free) addition of the open circuit voltages of the two sub-cells.