Low-temperature deposition of TiO2 compact layers for metal-organic perovskite solar cells on plastic

Thomas M. Brown^a, Aldo Di Carlo^a, Fabio Matteocci^a, Stefano Razza^a, Francesco Di Giacomo^a, Maria Luisa Grilli^b, Andrea Capasso^b, Nicola Lisi^b, Wilhelmus M.M. Kessels^c, Valerio Zardetto^c, Mariadriana Creatore^c, Silvia Licoccia^d, Alessandra D'Epifanio^d

^aCHOSE - Centre for Hybrid and Organic Solar Energy, University of Rome ‘‘Tor Vergata’’, Via del Politecnico, 1, Roma, Italy

^bDepartment of Materials and New Technologies, ENEA, Casaccia Research Centre, Via Anguillarese 301, 00123, Rome

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

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

Proceedings of International Conference Solution processed Semiconductor Solar Cells (SSSC14)

Organizers: Henry Snaith and Samuel Stranks

Poster, Andrea Capasso, 084
Publication date: 1st July 2014

Organic-inorganic perovskites demonstrated to be a potentially disruptive material for photovoltaics. Power conversion efficiencies (PCE) in the order of 18% and 10% have been recently reached on glass and plastic substrates, respectively[1, 2]. Plastic solar cells are attractive in many technological areas, but their fabrication poses more strict constrains in terms of processing temperatures. In perovskite-based cell, an electron-transporting layer on top of the cathode appears necessary to correctly collect the charges at the electrode without inducing recombination. A TiO₂ compact layer is usually deposited on glass electrodes by spray pyrolysis to this end. However, such process implies temperatures exceeding 400°C which are unsuitable for plastic substrates. Here we present a comparison of low-temperature TiO₂ compact layers on PET/ITO/TiO₂/CH₃NH₃PbI₃-xClx/Spiro-O-MeTAD/Au structures (with and without mesoporous TiO₂). The TiO₂ compact layers were deposited by two techniques under 150°C: sputtering and plasma enhanced atomic layer deposition (PE-ALD).The planar architecture exhibited a very high V_OC (970 mV for 40 nm of sputtered TiO₂ and 880 mV for 11 nm of PE-ALD TiO₂) but with current densities below 1.5 mA cm^-2. When a UV-sintered TiO₂ mesoporous scaffold was used to guide the perovskite growth and increase the charge injection, an increase of the PCE of one order of magnitude was obtained (from 0.3 to 5.8% for sputtering and from 0.8 to 7.4 for PE-ALD). As a further proof of the importance of the compact TiO₂, mesostructured devices without compact layer were realized; as expected, the high recombination rate between the perovskite and the ITO limited the V_OC below 50 mV. In summary, three new low-temperature TiO₂ processing techniques (i.e., sputtering, PE-ALD, and UV-sintering) were successfully adopted to fabricate efficient flexible metal-organic perovskite solar cells with efficiency up to 7.4%.

References

[1] NREL, http://www.nrel.gov/ncpv/images/efficiency_chart.jpg 2014.

[2] D. Liu, T. L. Kelly, Nature Photonics 2013, 8, 133.

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