Title: Formation of a Secondary Phase in Thermally Evaporated MAPbI₃ and Its Effects on Solar Cell Performance

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 crystallinitymore » 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. Further, 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.« less

Authors:

Castro-Méndez, Andrés-Felipe ^[1]; Perini, Carlo R. ^[1]; Hidalgo, Juanita ^[1]; Ranke, Daniel ^[1]; Vagott, Jacob N. ^[1]; An, Yu  ^[1];

• Search DOE PAGES for author "An, Yu"
• Search DOE PAGES for ORCID "0000-0002-1382-5293"

Lai, Barry ^[2]; Luo, Yanqi ^[2]; Li, Ruipeng ^[3]; Correa-Baena, Juan-Pablo  ^[1]

• Search DOE PAGES for author "Correa-Baena, Juan-Pablo"
• Search DOE PAGES for ORCID "0000-0002-3860-1149"

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+ Show Author Affiliations

1. Georgia Institute of Technology, Atlanta, GA (United States)
2. Argonne National Lab. (ANL), Lemont, IL (United States)
3. Brookhaven National Lab. (BNL), Upton, NY (United States)

Publication Date:

Fri May 13 00:00:00 EDT 2022

Research Org.:

Brookhaven National Lab. (BNL), Upton, NY (United States); Argonne National Lab. (ANL), Argonne, IL (United States). Advanced Photon Source (APS)

Sponsoring Org.:

USDOE Office of Science (SC), Basic Energy Sciences (BES); National Science Foundation (NSF); Georgia Institute of Technology; US Department of State; Colombian Ministry of Sciences and Technology

OSTI Identifier:

1889630

Alternate Identifier(s):

OSTI ID: 1969116

Report Number(s):

BNL-223432-2022-JAAM
Journal ID: ISSN 1944-8244

Grant/Contract Number:  

SC0012704; ECCS-1542174; P200A180075; AC02-06CH11357

Resource Type:

Accepted Manuscript

Journal Name:

ACS Applied Materials and Interfaces

Additional Journal Information:

Journal Volume: 14; Journal Issue: 30; Journal ID: ISSN 1944-8244

Publisher:

American Chemical Society (ACS)

Country of Publication:

United States

Language:

English

Subject:

36 MATERIALS SCIENCE; perovskite solar cells; thermal evaporation; thin films; crystalline phases; x-ray diffraction; x-ray fluorescence; methylammonium lead triiodide; 37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY