Low temperature Atomic Layer Deposition of TiO2 Compact Layers for Flexible Perovskite Cells on Plastics

Mariadriana Creatore^a^,^d, Valerio Zardetto^a^,^d, Wilhelmus Kessels^a^,^d, Francesco Di Giacomo^b, Giulia Lucarelli^b, Thomas Brown^b, Aldo Di Carlo^b, Silvia Licoccia^c, Alessandra D'Epifanio^c

^aEindhoven University of Technology, Department of Applied Physics, 5600MB, Eindhoven, Netherlands

^bElectronic Engineering, University of Rome “Tor Vergata”, via del Politecnico 1, 00133 Rome, Italy

^cUniversity of Rome Tor Vergata, Department of Chemical Science and Technologies, Italy, Via della Ricerca Scientifica, 1, Roma, Italy

^dSolliance, High Tech Campus 21, Eindhoven, 5656AE, Netherlands

Materials for Sustainable Development Conference (MATSUS)
Proceedings of nanoGe September Meeting 2015 (NFM15)

Santiago de Compostela, Spain, 2015 September 6th - 15th

Oral, Valerio Zardetto, presentation 238
Publication date: 8th June 2015

Perovskite solar cells have attracted attention in the photovoltaic (PV) community due to the high performance and the easy solution manufacturing steps. In mesoscopic perovskite devices a compact TiO2 blocking layer is required to avoid recombination processes at the interface between the tranparent conductive oxide (TCO) and perovskite or the hole transport layer (HTL). Atomic Layer Deposition (ALD) is nowadays widely acknowledged for the fabrication of ultra-thin, uniform and conformal layers also at low temperature. In this contribution we investigate the role of plasma-assisted ALD compact TiO2 deposited on ITO-PET substrates for a hybrid halide (CH3NH3PbI3-xClx) perovskite solar cells, in planar and mesostructured architectures comparing also the performance with a conventional solution processed TiO2. We observe that the absence of the TiO2 on the TCO is extremely detrimental when the device is fabricated on a conductive polymer (ITO-PET). Very low open circuit voltage (VOC = 50mV) and efficiency (η = 0.01%) have been measured. The analysis of JV dark current revealed the lack of rectifying behavior at this interface with a consequent high value of the exchange current (7 mA∙cm-2) as well as high current under reverse bias (V<0). The introduction of the ultrathin ALD layers brought to an increment in all the photovoltaic parameters (JSC, VOC and FF), with the saturation of the efficiency for layers thicker than 5.5 nm. Above this value (up to 44nm), we observed a reduction of both the exchange current and the dark reverse current up to three orders of magnitude, pointing out that an efficient blocking behaviour can be achieved already with ultrathin film over 5.5 nm. The high quality of ALD layer led to a maximum performance of 9.2% with 11 nm (200 cycles), overcoming the 4% in efficiency achieved with a conventional sol gel TiO2 compact layer (20 nm thick). Interestingly, when the same layer works also as electron transport material (without the mesoporous TiO2) in the planar configuration, the efficiency of the device decrease to 1.3% due to the ineffective electron injection at the interface between the perovskite and the ALD TiO2 compact layer

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