Solution-Processed Tin Oxide-PEDOT:PSS Interconnecting Layers for Efficient Inverted and Conventional Tandem Polymer Solar Cells

Tin oxide nanoparticles are employed as an electron transporting layer in solution-processed polymer solar cells. Tin oxide based devices yield excellent performance and can interchangeably be used in conventional and inverted device configurations. In combination with poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) as a hole transporting layer, tin oxide forms an effective interconnecting layer (ICL) for tandem solar cells. Conventional and inverted tandem cells with this ICL provide efficiencies up to 10.4% in good agreement with optical-electrical modeling simulations. The critical advantage of tin oxide in an ICL in a conventional tandem structure over the commonly used zinc oxide is that the latter requires the use of a pH-neutral formulation of PEDOT:PSS to fabricate the ICL, limiting the open-circuit voltage (V-OC) because of its low work function. The SnO2/PEDOT:PSS ICL, on the other hand, provides a nearly loss-free V-OC.