title: Control and Study of the Stoichiometry in Evaporated Perovskite Solar Cells.
abstract: Herein, we present the precise stoichiometric control of methlyammonium lead iodide perovskite thin-films using high vacuum dual-source vapor-phase deposition. We found that UV/Vis absorption and emission spectra were inadequate for assessing precisely the perovskite composition. Alternatively, inductively coupled plasma mass spectrometry (ICP-MS) is used to give precise, reproducible, quantitative measurements of the I/Pb ratio without systematic errors that often result from varying device thicknesses and morphologies. This controlled deposition method enables better understanding of the evaporation and deposition processes; methylammonium iodide evaporation appears omnidirectional, controlled using the chamber pressure and incorporated in the film through interaction with the unidirectionally evaporated PbI2. Furthermore, these thin-films were incorporated into solar cell device architectures with the best photovoltaic performance and reproducibility obtained for devices made with stoichiometric perovskite active layers. Additionally, and particularly pertinent to the field of perovskite photovoltaics, we found that the I-V hysteresis was unaffected by varying the film stoichiometry.
authors.affiliation: Laboratoire de Photonique et Interfaces, Institut des Sciences et Ingénierie Chimiques, École polytechnique fédérale de Lausanne (EPFL), 1015, Lausanne, Switzerland. joel.teuscher@epfl.ch.
authors.forename: Joël
authors.initials: J
authors.lastname: Teuscher
authors.affiliation: Institut des Sciences de la Terre, Université de Lausanne, 1015, Lausanne, Switzerland.
authors.forename: Alexey
authors.initials: A
authors.lastname: Ulianov
authors.affiliation: Institut des Sciences de la Terre, Université de Lausanne, 1015, Lausanne, Switzerland.
authors.forename: Othmar
authors.initials: O
authors.lastname: Müntener
authors.affiliation: Laboratoire de Photonique et Interfaces, Institut des Sciences et Ingénierie Chimiques, École polytechnique fédérale de Lausanne (EPFL), 1015, Lausanne, Switzerland. michael.graetzel@epfl.ch.
authors.forename: Michael
authors.initials: M
authors.lastname: Grätzel
authors.affiliation: Laboratoire de Photonique et Interfaces, Institut des Sciences et Ingénierie Chimiques, École polytechnique fédérale de Lausanne (EPFL), 1015, Lausanne, Switzerland.
authors.forename: Nicolas
authors.initials: N
authors.lastname: Tétreault
mesh_terms: D017610:Calcium Compounds / Q000737:chemistry*; D011211:Electric Power Supplies; D010087:Oxides / Q000737:chemistry*; D013472:Sunlight; D014025:Titanium / Q000737:chemistry*; D014835:Volatilization
chemical_list: D017610:Calcium Compounds; D010087:Oxides; C059910:perovskite; D014025:Titanium
keywords: mass spectrometry; perovskite; solar cell; stoichiometry; thermal evaporation