Atomic Layer Deposition of Highly Transparent Platinum Counter Electrodes for Metal/Polymer Flexible DyeSensitized Solar Cells

Atomic layer deposition (ALD) is used to deposit Pt nanoparticles at low temperature (25-150 degrees C) to fabricate highly transparent counter electrodes (CEs) for flexible dye-sensitized solar cells (DSCs). The Pt nanoparticles (NPs) are deposited for different number of ALD cycles on indium tin oxide (ITO)/polyethylene naphthalate (PEN) substrates. Rutherford backscattering spectroscopy (RBS) and transmission electron microscopy (TEM) are used to assess the Pt NP loading, density, and size. There is a trade-off between transparency and catalytic activity of the CE, and the best cell performances of back-side-illuminated DSCs (approximate to 3.7% efficiency) are achieved for Pt ALD at temperatures in the range of 100-150 degrees C, even though deposition at 25 degrees C is also viable. The best cell produced with ALD platinized CE (100 cycles at 100 degrees C) outperforms the reference cells fabricated with electrodeposited and sputtered Pt CEs, with relative improvements in efficiency of 19% and 29%, respectively. In addition, these parameters are used to fabricate a large area CE for a sub-module (active area of 17.6 cm(2)), resulting in an efficiency of 3.1%, which demonstrates the scalability of the process.