A New Interconnecting Layer of Metal Oxide/Dipole Layer/Metal Oxide for Efficient Tandem Organic Solar Cells.

A new metal-oxide-based interconnecting layer (ICL) structure of all-solution processed metal oxide/dipole layer/metal oxide for efficient tandem organic solar cell (OSC) is demonstrated. The dipole layer modifies the work function (WF) of molybdenum oxide (MoO x ) to eliminate preexisted counter diode between MoO x and TiO2. Three different amino functionalized water/alcohol soluble conjugated polymers (WSCPs) are studied to show that the WF tuning of MoO x is controllable. Importantly, the results show that S-shape current density versus voltage ( J- V) characteristics form when operation temperature decreases. This implies that thermionic emission within the dipole layer plays critical role for helping recombination of electrons and holes. Meanwhile, the insignificant homotandem open-circuit voltage ( Voc) loss dependence on dipole layer thickness shows that the quantum tunneling effect is weak for efficient electron and hole recombination. Based on this ICL, poly(3-hexylthiophene) (P3HT)-based homotandem OSC with 1.20 V Voc and 3.29% power conversion efficiency (PCE) is achieved. Furthermore, high efficiency poly(4,8-bis(5-(2-ethylhexyl)-thiophene-2-yl)-benzo[1,2-b54,5-b9]dithiophene-alt alkylcarbonylthieno[3,4-b]thiophene) (PBDTTT-C-T)-based homotandem OSC with 1.54 V Voc and 8.11% PCE is achieved, with almost 15.53% enhancement compared to its single cell. This metal oxide/dipole layer/metal oxide ICL provides a new strategy to develop other qualified ICL with different hole transporting layer and electron transporting layer in tandem OSCs. [ABSTRACT FROM AUTHOR]