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Monovalent Cation Doping of CH3NH3PbI3 for Efficient Perovskite Solar Cells
Published on: March 19, 2017
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Multi-cation perovskites prevent carrier reflection from grain surfaces.
Makhsud I Saidaminov1,2, Kristopher Williams3, Mingyang Wei1
1Department of Electrical and Computer Engineering, University of Toronto, Toronto, Ontario, Canada.
Nature Materials
|February 12, 2020
Summary
In perovskite solar cells, composition impacts carrier diffusion in films but not single crystals. Methylammonium incorporation ensures uniform grain composition, enhancing electron diffusion for better optoelectronics.
Area of Science:
- Materials Science
- Solid-State Physics
- Photovoltaics
Background:
- State-of-the-art perovskite solar cells utilize complex compositions (AxByC1-x-yPbXzY3-z) for optimized performance.
- The precise role of each compositional component and the underlying mechanisms governing carrier transport remain incompletely understood.
- This knowledge gap hinders the exploration of the vast chemical space for advanced perovskite materials.
Purpose of the Study:
- To elucidate the role of compositional variations on carrier diffusivity in perovskite materials.
- To investigate the impact of different cations, specifically methylammonium (MA) and caesium-formamidinium (CsFA), on carrier transport properties.
- To develop a mechanistic understanding of crystallization processes influencing perovskite film performance.
Main Methods:
- Transient photoluminescence microscopy was employed to study carrier diffusivity in perovskite single crystals and polycrystalline thin films.
- Elemental composition studies, including vertical carrier transport and surface potential measurements, were conducted on various perovskite compositions.
- A computational model was developed to explain the observed crystallization phenomena and their effect on carrier diffusion.
Main Results:
- Carrier diffusivity in perovskite single crystals was found to be independent of composition.
- Methylammonium (MA)-based perovskite films exhibited high carrier diffusivity (0.047 cm2 s-1).
- MA-free mixed caesium-formamidinium (CsFA) films showed significantly lower carrier diffusivity (an order of magnitude less) due to graded grain composition and curtailed electron diffusion.
- Incorporation of MA into CsFA films (CsMAFA) resulted in uniform grain composition and improved diffusivity (0.034 cm2 s-1).
Conclusions:
- Composition critically influences carrier diffusion in polycrystalline perovskite films, but not in single crystals.
- Uniform grain composition, achieved through the incorporation of methylammonium, is crucial for enhancing electron diffusion and overall optoelectronic performance.
- Understanding and controlling crystallization processes offer a pathway to optimize perovskite solar cell efficiency.
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