In situ investigation of the formation and metastability of formamidinium lead tri-iodide perovskite solar cells
- 23 May 2016
- journal article
- research article
- Published by Royal Society of Chemistry (RSC) in Energy & Environmental Science
- Vol. 9 (7), 2372-2382
- https://doi.org/10.1039/c6ee01079b
Abstract
Organic–inorganic perovskites have emerged as an important class of next generation solar cells due to their remarkably low cost, band gap, and sub-900 nm absorption onset. Here, we show a series of in situ observations inside electron microscopes and X-ray diffractometers under device-relevant synthesis conditions focused on revealing the crystallization process of the formamidinium lead-triiodide perovskite at the optimum temperature of 175 °C. Direct in situ observations of the structure and chemistry over relevant spatial, temporal, and temperature scales enabled identification of key perovskite formation and degradation mechanisms related to grain evolution and interface chemistry. The lead composition was observed to fluctuate at grain boundaries, indicating a mobile lead-containing species, a process found to be partially reversible at a key temperature of 175 °C. Using low energy electron microscopy and valence electron energy loss spectroscopy, lead is found to be bonded in the grain interior with iodine in a tetrahedral configuration. At the grain boundaries, the binding energy associated with lead is consequently shifted by nearly 2 eV and a doublet peak is resolved due presumably to a greater degree of hybridization and the potential for several different bonding configurations. At the grain boundaries there is adsorption of hydrogen and OH− ions as a result of residual water vapor trapped as a non-crystalline material during formation. Insights into the relevant formation and decomposition reactions of formamidinium lead iodide at low to high temperatures, observed metastabilities, and relationship with the photovoltaic performance were obtained and used to optimize device processing resulting in conversion efficiencies of up to 17.09% within the stability period of the devices.Keywords
Funding Information
- U.S. Department of Energy (DE-AC36-08-GO28308)
This publication has 48 references indexed in Scilit:
- Quantifying the low-energy limit and spectral resolution in valence electron energy loss spectroscopyUltramicroscopy, 2013
- In-situ liquid and gas transmission electron microscopy of nano-scale materialsMicroscopy and Microanalysis, 2012
- Quantitative local profile analysis of nanomaterials by electron diffractionScripta Materialia, 2010
- Gentle STEM: ADF imaging and EELS at low primary energiesUltramicroscopy, 2010
- Prospects for analyzing the electronic properties in nanoscale systems by VEELSUltramicroscopy, 2008
- Atomic-Resolution in Situ Transmission Electron Microscopy of a Promoter of a Heterogeneous CatalystScience, 2001
- EELS analysis of SiC crystals under hydrogen and helium dual-ion beam irradiationNuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 1998
- Cryo-electron energy loss spectroscopy: observations on vitrified hydrated specimens and radiation damageUltramicroscopy, 1995
- X-ray and electron-energy-loss spectroscopies of PbI2, PbF2 and CdI2Journal of Electron Spectroscopy and Related Phenomena, 1989
- Ultraviolet properties and band structure of SnS2, SnSe2, CdI2, PbI2, BiI3and BiOI crystalsJournal of Physics C: Solid State Physics, 1978