S-1 SUPPORTING INFORMATION Nano-Structured TiO 2 grown by Low-Temperature Reactive Sputtering for Planar Perovskite Solar Cells Alessandra Alberti* # , Emanuele Smecca # , Salvatore Sanzaro # , Corrado Bongiorno # , Filippo Giannazzo # , Giovanni Mannino # , Antonino La Magna # # CNR-IMM zona industriale strada VIII n°5, 95121 Catania, Italy Maning Liu, § Paola Vivo § § Faculty of Engineering and Natural Sciences, Tampere University, P.O. Box 541, FI-33101 Tampere, Finland Andrea Listorti ^,% ^CNR NANOTEC, Institute of Nanotechnology, Via Monteroni, 73100 Lecce, Italy %Dipartimento di Fisica, Universit del Salento, Strada Provinciale Lecce-Monteroni, Campus Ecotekne, Lecce 73100, Italy Emanuele Calabrò $ , Fabio Matteocci $ , Aldo Di Carlo** $,& $ CHOSE (Centre for Hybrid and Organic Solar Energy), Department of Electronic Engineering, University of Rome—Tor Vergata, via del Politecnico 1, I-00133, Rome, Italy & LASE – Laboratory of Advanced Solar Energy, National University of Science and Technology “MISiS”, Leninsky prospect 4, 119049, Moscow, Russia. Supporting Information Mott-Schottky analysis of electrochemical data In theory, the equilibrium of the Fermi level established in a semiconductor (n-type or p-type) with the chemical potential of an electrolyte induces the flow of majority carriers to the semiconductor-electrolyte interface (SEI), causing band bending in the near-surface region. 1 Here, we employed a classic Mott-Schottky equation to correlate the separation of charge (as a measurable capacitance) with the electrolyte chemical potential: 1 (S1)   ―2 = ( ―2  0  2 )( ―   ―   ) where ε is the relative dielectric constant of the semiconductor (ε TiO2 = 55 2 ), ε 0 is the permittivity of free space, N is the carrier concentration (negative for electrons, positive for holes), A is the area of the SEI, Ф is the electrode potential, Ф fb is the flat-band potential at which there is no band bending, k is the Boltzmann constant, T is the temperature, and e is the unit charge. By plotting as a   ―2 function of the applied potential, the flat-band potential can be extracted by the intercept of the curve with the potential axis, while the carrier concentration N can be extracted from the slope of the curve. Furthermore, we used the successful model of van der Krol et al. 2 for the Mott-Schottky analysis of the impedance of thin-film TiO 2 in a similar electrolyte. Based on this model, a constant phase element (Z’) is in parallel with a so-called resistor-in-series-with-capacitor element (Z’’).