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Castro-Méndez AF, Perini CAR, Hidalgo J, Ranke D, Vagott JN, An Y, Lai B, Luo Y, Li R, Correa-Baena JP. Formation of a Secondary Phase in Thermally Evaporated MAPbI 3 and Its Effects on Solar Cell Performance. ACS Appl Mater Interfaces 2022; 14:34269-34280. [PMID: 35561234 DOI: 10.1021/acsami.2c02036] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
Thermal evaporation is a promising deposition technique to scale up perovskite solar cells (PSCs) to large areas, but the lack of understanding of the mechanisms that lead to high-quality evaporated methylammonium lead triiodide (MAPbI3) films gives rise to devices with efficiencies lower than those obtained by spin coating. This work investigates the crystalline properties of MAPbI3 deposited by the thermal coevaporation of PbI2 and MAI, where the MAI evaporation rate is controlled by setting different temperatures for the MAI source and the PbI2 deposition rate is controlled with a quartz crystal microbalance (QCM). Using grazing incident wide-angle X-ray scattering (GIWAXS) and X-ray diffraction (XRD), we identify the formation of a secondary orthorhombic phase (with a Pnma space group) that appears at MAI source temperatures below 155 °C. With synchrotron-based X-ray fluorescence (XRF) microscopy, we show that the changes in crystalline phases are not necessarily due to changes in stoichiometry. The films show a stochiometric composition when the MAI source is heated between 140 to 155 °C, and the samples become slightly MAI rich at 165 °C. Increasing the MAI temperature beyond 165 °C introduces an excess of MAI in the film, which promotes the formation of films with low crystallinity that contain low-dimensional perovskites. When they are incorporated in solar cells, the films deposited at 165 °C result in the champion power conversion efficiency, although the presence of a small amount of low-dimensional perovskite may lead to a lower open-circuit voltage. We hypothesize that the formation of secondary phases in evaporated films limits the performance of PSCs and that their formation can be suppressed by controlling the MAI source temperature, bringing the film toward a phase-pure tetragonal structure. Control of the phases during perovskite evaporation is therefore crucial to obtain high-performance solar cells.
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Affiliation(s)
- Andrés-Felipe Castro-Méndez
- School of Materials Science and Engineering, Georgia Institute of Technology, North Avenue NW, Atlanta, Georgia 30332, United States
| | - Carlo A R Perini
- School of Materials Science and Engineering, Georgia Institute of Technology, North Avenue NW, Atlanta, Georgia 30332, United States
| | - Juanita Hidalgo
- School of Materials Science and Engineering, Georgia Institute of Technology, North Avenue NW, Atlanta, Georgia 30332, United States
| | - Daniel Ranke
- School of Materials Science and Engineering, Georgia Institute of Technology, North Avenue NW, Atlanta, Georgia 30332, United States
| | - Jacob N Vagott
- School of Materials Science and Engineering, Georgia Institute of Technology, North Avenue NW, Atlanta, Georgia 30332, United States
| | - Yu An
- School of Materials Science and Engineering, Georgia Institute of Technology, North Avenue NW, Atlanta, Georgia 30332, United States
| | - Barry Lai
- Advanced Photon Source, Argonne National Laboratory, 9700 Cass Avenue, Lemont, Illinois 60439, United States
| | - Yanqi Luo
- Advanced Photon Source, Argonne National Laboratory, 9700 Cass Avenue, Lemont, Illinois 60439, United States
| | - Ruipeng Li
- National Synchrotron Light Source II, Brookhaven National Laboratory, Upton, New York 11973, United States
| | - Juan-Pablo Correa-Baena
- School of Materials Science and Engineering, Georgia Institute of Technology, North Avenue NW, Atlanta, Georgia 30332, United States
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