| AVS 60th International Symposium and Exhibition | |
| Thin Film | Monday Sessions |
| Session TF+EN-MoM |
| Session: | ALD for Energy |
| Presenter: | M. Creatore, Eindhoven University of Technology, Netherlands |
| Authors: | M. Creatore, Eindhoven University of Technology, Netherlands D. Garcia-Alonso, Eindhoven University of Technology, Netherlands A.J.M. Mackus, Eindhoven University of Technology, Netherlands V. Zardetto, University of Rome "Tor Vergata", Italy T.M. Brown, University of Rome "Tor Vergata", Italy W.M.M. Kessels, Eindhoven University of Technology, Netherlands |
| Correspondent: | Click to Email |
Atomic Layer Deposition (ALD) has been applied to different photovoltaic technologies, including Dye-Sensitized Solar Cells (DSCs), due to its exceptional control of film thickness and composition, high conformality on high aspect ratio structures and uniformity. Thermal ALD for DSCs has been employed to deposit metal oxides for passivation layers on mesoporous TiO2 photoelectrodes and recombination blocking layers (TiO2 and HfO2)on TCOs. In this work, we investigate other potential benefits of ALD not yet applied to DSCs. Low temperature processing by plasma-assisted ALD (PA-ALD) has been successfully applied in flexible DSCs to deliver the synthesis of nano-particles (NPs) for the Pt counter-electrode, and the deposition of compact layers. We demonstrate the potential of low temperature PA-ALD processes to deposit metallic Pt NPs on PEN/ITO substrates with the control in particle size. The counter-electrode (CE) layer (for back-side illumination) requires high transparency and small, evenly distributed particles to enhance its catalytic activity. Two newly developed PA-ALD processes were applied for the deposition of Pt CE layers at 150 oC. The Pt CE electrocatalytic activity towards the iodine-based electrolyte was analysed by electrochemical impedance spectroscopy (EIS). Pt CE layers deposited by both processes exhibit similar transmittance for less than 100 ALD cycles while the charge transfer resistance (RCT) values show a significant difference for a number of ALD cycles lower than 50. Pt layers deposited using between 50 and 150 cycles yielded the best compromise between RCT and transparency, and fulfil the requirements for back-side illuminated DSCs, allowing for an efficiency of 3.5%. When compared to sputtered or electro-deposited Pt layers, the PA-ALD Pt NPs lead to higher solar cell efficiency due to the enhancement in JSC and VOC because of the increased number of photons reaching the active material due to the higher Pt ALD layer transmittance. We also used PA-ALD to successfully deposit TiO2 compact layers and ultra-thin dielectric Al2O3. The aim of these layers is to decrease the recombination processes at the interface between the PEN/ITO substrate and the mediator (liquid electrolyte or organic material), especially at low light intensity, and thus to increase the performance of flexible DSCs for indoor applications. Both compact layers reduce the recombination path at the TCO/electrolyte interface without any effect on the electron collection (EIS analysis). The compact layers improve the generated power as compared to a compact layer-free DSC (Al2O3: +26% and TiO2: +40 %) under low level illumination (300 lux, CFL lamp).