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C: Physical Processes in Nanomaterials and Nanostructures
Size Dependence of Charge Carrier Dynamic in Organometal Halide Perovskite Nanocrystals: Deciphering the Radiative vs Non-Radiative Components Sara Bonabi Naghadeh, Binbin Luo, Ying-Chih Pu, Zachary Schwartz, William R. Hollingsworth, Sarah A. Lindley, Amanda S. Brewer, Alexander L. Ayzner, and Jin Z. Zhang J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.9b00711 • Publication Date (Web): 04 Feb 2019 Downloaded from http://pubs.acs.org on February 5, 2019
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The Journal of Physical Chemistry
Size Dependence of Charge Carrier Dynamic in Organometal Halide Perovskite Nanocrystals: Deciphering the Radiative vs NonRadiative Components Sara Bonabi Naghadeh1, Binbin Luo2, Ying-Chih Pu3, Zachary Schwartz1, William R. Hollingsworth1, Sarah A. Lindley1, Amanda S. Brewer1, Alexander L. Ayzner1, Jin Z. Zhang1*
1. Department of Chemistry and Biochemistry, University of California, Santa Cruz, CA 95064, United States of America 2. Department of Chemistry, Shantou University, Shantou, Guangdong 515063, China
3. Department of Materials Science, National University of Tainan, Tainan 70005, Taiwan
Corresponding Author’s Email:
[email protected] 1
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Abstract In this work, we have synthesized and characterized three differently sized (3.1, 5.7, and 9.3 nm) methyl ammonium lead bromide (CH3NH3PbBr3) perovskite nanocrystals (PNCs) passivated using (3-Aminopropyl) triethoxysilane (APTES) and oleic acid (OA) as capping ligands. These PNCs show size-dependent absorption and photoluminescence (PL), with the middle-sized PNCs exhibiting the highest PL quantum yield (~91%). The effect of size on their exciton/charge carrier dynamic is studied using transient absorption spectroscopy (TA) and time resolved photoluminescence (TRPL). The middle-sized PNCs show slower early time recombination compared to that of the larger and smaller PNCs, suggesting optimized passivation of surface trap states. The observed PL lifetime and QY are analyzed to determine the size dependence of the radiative and non-radiative decay components. The radiative lifetime is found to decrease with decreasing PNC size, which seems to be primarily determined by the PNC core, while the non-radiative lifetime is longest for the middle-sized PNCs, which is strongly influenced by the presence of bandgap states that depend on surface passivation. A kinetic model is proposed to explain the observed dynamics results. This study demonstrates the competing effect between size and surface properties in determining the dynamics and optical properties of PNCs.
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The Journal of Physical Chemistry
Introduction Organometal halide perovskites (OMHP) have been widely studied in recent years due to their promising applications in the field of photonics, especially photovoltaics (PV). Their novel optical and electrical properties include high absorption coefficients, tunable and narrow emission, long exciton lifetimes, and fast charge carrier diffusion (8-33 cm2 V-1 s-1).1-3 When combined with easy and low cost processing, they demonstrate strong potential for applications beyond PV, such as light emitting diodes (LEDs), photodetectors, sensors, lasers, and photoelectrochemical cells.4-8 Since the first reported power conversion efficiency (PCE) of ~3.8% for a perovskite-based PV cells in 2009,9 significant progress has been made in understanding the fundamental properties of the materials and improving solar cell structures for higher efficiency. Recently, a PCE exceeding 25% has been reported for a tandem siliconOMHP solar cell.10 Despite significant potential, there are challenges limiting large-scale application of OMHPs. Instability toward environmental factors such as UV light, humidity, oxygen, solvent and temperature are some of the most challenging issues. Several studies have correlated these instabilities to OMHP surface properties such as the presence of defects.11,12 These defects, which can be formed as a result of chemical and structural changes in the material,13 are also a detrimental factor impacting device performance as they provide recombination channels for photogenerated charge carriers.11,14,15 Therefore, various strategies for surface modification and defect passivation, including addition of molecular capping ligands, organic polymers, and metal oxide shells, have been used in order to improve the chemical and physical stability that is critical for maintaining device performance over time.16-18 Because perovskite nanocrystals (PNCs) or perovskite quantum dots (PQDs) have a large
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surface-to-volume (S/V) ratio, they are considered to be great models for developing stabilization and passivation strategies.19 In addition, PNCs possess tunable energy levels and optical properties due to the quantum confinement effects, especially when their size is smaller than the Bohr exciton radius.20 This can be used to control the functionalities of the materials for different applications. For instance, PNCs with diameters of
