| AVS 61st International Symposium & Exhibition | |
| Thin Film | Tuesday Sessions |
| Session TF+EN+PS-TuA |
| Session: | ALD for Energy |
| Presenter: | Mariadriana Creatore, Eindhoven University of Technology, Netherlands |
| Authors: | V. Zardetto, Eindhoven University of Technology, Netherlands F. di Giacomo, University of Rome "Tor Vergata", Italy T.M. Brown, University of Rome "Tor Vergata", Italy A. di Carlo, University of Rome "Tor Vergata", Italy A. D'Epifanio, University of Rome "Tor Vergata", Italy S. Licoccia, University of Rome "Tor Vergata", Italy W.M.M. Kessels, Eindhoven University of Technology, Netherlands M. Creatore, Eindhoven University of Technology, Netherlands |
| Correspondent: | Click to Email |
Atomic Layer Deposition (ALD) is widely acknowledged in the field of c-Si and thin film PV technologies, for the fabrication of ultra-thin, uniform and conformal layers.[1] Thermal ALD has been applied also in the case of more challenging interfaces, e.g. dye-sensitized solar cells (DSCs) and the novel hybrid organo-lead-halide perovskite solar cells. Particularly, TiO2 blocking layers have been developed on glass/TCO substrates with the aim of decreasing the charge recombination processes at the interface between the ITO and the mediator. Recently, we have explored the benefit of plasma-assisted ALD (PA-ALD) in terms of low temperature processing applied to flexible DSCs for the development of highly transparent Pt counterelectrodes on ITO/PEN. [2] In this work, we further explore PA-ALD for the deposition of ultra-thin, highly compact TiO2 blocking layers on ITO-polymer substrates for DSCs and perovskite solar cells. The layers were prepared in a remote plasma reactor (FlexALTM) at 150 °C using an heteroleptic alkylamido precursor Ti(CpMe)(NMe2)3 alternated with an O2 plasma. For DSCs with an iodide-based electrolyte, the introduction of the blocking layer is essential at low light intensity, in order to increase the indoor performance of the cell. It is found that the presence of ultra-thin (6 nm) TiO2 layers slightly affects the performance of the cell under sun simulator, whereas it definitely improves the generated power (+40%) under low level illumination (300 lux). The blocking behaviour of the PA-ALD deposited TiO2 towards the tri-iodide reduction has been investigated by electrochemical impedance spectroscopy and Tafel plot analysis. We pinpointed that an increase in the TiO2 layer thickness above 6 nm leads to a decrease of the recombination processes at the TCO/electrolyte interface, as well as to a dramatic reduction of the electron collection at the TCO, accompanied by a decrease in cell performance. For mesostructured perovskite (CH3NH3PbI2Cl- based) solar cells, the application of a TiO2 blocking layer is essential for the performance of the device, due the higher current exchange at the interface TCO-hole transport material, i.e. Spiro-OMeTAD, typically used in this architecture. The application of a 11 nm- thick TiO2 layer resulted in an efficiency of 7.4%. In conclusion, ALD is a valid approach for controlling electrochemical charge-transfer processes in mesoscopic solar cells.
[1] J.A. van Delft, D. Garcia-Alonso , W. M. M. Kessels, Semicond. Sci. Technol., 27, 74002 (2012)
[2] D. Garcia-Alonso, V. Zardetto, A.J.M. Mackus, F. De Rossi, M.A. Verheijen, T.M. Brown, W.M.M. Kessels, M. Creatore, Adv. En. Mater. 4, 1300831 (2014)