High Efficiency Tandem Polymer Solar Cells with MoO3/Ni/ZnO:PEOz Hybrid Interconnection Layers
Here we report high efficiency tandem polymer solar cells with hybrid electron-collecting buffer layers (ECBLs) for interconnection between front and rear cells. The hybrid ECBLs, poly(2-ethyl-2-oxazoline) (PEOz)-embedded ZnO (ZnO:PEOz), were prepared via low-temperature sol-gel processes on the nickel (Ni) interlayers that are desposited on the molybdenum oxide (MoO3) buffer layers. The Ni interlayers were employed to act as an electrical conductor as well as a protection layer for the MoO3 layers against the attack of solvent during spin-coating of the ZnO:PEOz layers. New conjugated polymer was synthesized and mixed with soluble fullerenes to make polymer:fullerene bulk heterojunction (BHJ) layers for front cells, while polymer:nonfullerene BHJ layers were employed for rear cells. The thickness of the Ni interlayers was varied up to 10 nm in order to investigate the trade-off between optical transmittance and electrical conductivity in the tandem cells. Results showed that the ZnO:PEOz ECBLs delivered a nanocrated surface in the tandem polymer solar cells and the device performaces were greatly affected by the Ni thickness. The optimized tandem polymer solar cells exhibited the power conversion efficiency of 14.22% at the Ni thickness of 6 nm.