Joshua J. Choi

At the nanoscale, quantum mechanical effects and various other mechanisms cause the properties of semiconductors to strongly depend on the size, shape and surface of the material. For example, when the size of a semiconductor crystal becomes smaller than the size of electronic wave function (typically few to tens of nanometers in semiconductors), manipulating the spatial extension of the carrier wave function becomes possible simply by changing the size of the crystal. This 'wave function engineering' gives rise to intriguing cases where, depending on the size of the crystal, semiconductors with the identical composition can have drastically different band gaps, carrier-carrier Coulomb interaction strengths and excited state dynamics. In addition to the size-tunability, properties of semiconductor nanomaterials can be manipulated by forming hetero-nanostructures with other semiconductors, metals and organic molecules as well as tuning their collective interactions within their assemblies. This extremely wide tunability in properties of semiconductor nanomaterials presents many intriguing scientific questions and unique opportunities for transformative advances in technological applications. 

Currently, our research group (https://engineering.virginia.edu/choi-lab) is focused on studying metal-organic perovskites and colloidal quantum dots - both material systems exhibit intriguing properties tunable by design while looking set to revolutionize the field of solution processed optoelectronic devices. We are developing novel and advanced synthetic methods to achieve robust heterostructure formation, surface structure and impurity doping. We seek to understand and control the structure-property relationships in these materials. To this end, we employ a wide variety of techniques, including synchrotron based X-ray diffraction methods, to study their structure and self-assembly behavior from atomic to macroscopic length scales. We also employ optical spectroscopy and electrical transport measurement techniques to examine properties of the materials as functions of their structure. Newly obtained insights are applied to fabrication and testing of prototype devices to demonstrate improved performance. Particularly, our efforts will be focused on solution processing based device fabrication methods to simultaneously achieve a low-cost and high performance required for wide spread commercial deployment.

Peer-reviewed Journal Publications

(H-index: 26, cumulative citation count: 4091 as of 8/23/2020)

41. D. Zhang, X. Hu, T. Chen, D. L. Abernathy, R. Kajimoto, M. Nakamura, M. Kofu, B. J. Foley, M. Yoon, J. J. Choi, S.-H. Lee* “Temporally-decoherent and spatially-coherent vibrations in metal halide perovskite”, arXiv preprint arXiv:2008.07021 (2020)

40. A. Giri^†, A. Z. Chen^†, A. Mattoni, K. Aryana, D. Zhang, X. Hu, S.-H. Lee, J. J. Choi, P. E. Hopkins* “Ultralow thermal conductivity of two-dimensional metal halide perovskites” Nano Letters, 20, 3331–3337 (2020) (^†co-first authors)

39. K. A Dagnall, B. J. Foley, S. A Cuthriell, M. R. Alpert, X. Deng, A. Z Chen, Z. Sun, M. C Gupta, K. Xiao, S.-H. Lee, Y.-Z. Ma, J. J Choi* “Relationship Between the Nature of Monovalent Cations and Charge Recombination in Metal Halide Perovskites” ACS Applied Energy Materials, 3, 1298-1304 (2020) (*corresponding author)

38. A. Z. Chen* and J. J. Choi* “Crystallographic orientation and layer impurities in two-dimensional metal halide perovskite thin films” Journal of Vacuum Science & Technology A, 38, 010801 (2020) (*corresponding authors)

37. X. Hu, D. Zhang, T. Chen, A. Z Chen, E. N. Holmgren, Q. Zhang, D. M. Pajerowski, M. Yoon, G. Xu, J. J. Choi, Seung-Hun Lee* “Crystal structures and rotational dynamics of a two-dimensional metal halide perovskite (OA)₂PbI₄” The Journal of Chemical Physics,

152, 014703 (2020)

36. A. Z. Chen, M. Shiu, X. Deng, M. Mahmoud, D. Zhang, B. J. Foley, S.-H. Lee, G. Giri, J. J. Choi* “Understanding the Formation of Vertical Orientation in Two-dimensional Metal Halide Perovskite Thin Films” Chemistry of Materials, 31, 1336-1343 (2019) (*corresponding author)

35. S. Guthrie, L. Huelsenbeck, A. Salahi, W. Varhue, N. Smith, X. Yu, L. U. Yoon, J. J. Choi, N. Swami, G. Giri* “Crystallization of high aspect ratio HKUST-1 thin films in nanoconfined channels for selective small molecule uptake” Nanoscale Advances, 1, 2946-2952 (2019) (Impact factor: Not available)

34. B. J. Foley*, S. A. Cuthriell, S. Yazdi, A. Z. Chen, S. M. Guthrie, X. Deng, G. Giri, S.-H. Lee, K. Xiao, B. Doughty, Y.-Z. Ma*, J. J. Choi* “Impact of Crystallographic Orientation Disorders on Electronic Heterogeneities in Metal Halide Perovskite Thin Films” Nano Letters, 18, 6271-6278 (2018) (*corresponding authors)

33. M. R. Alpert, J. S. Niezgoda, A. Z. Chen, B. J. Foley, S. Cuthriell, L. U. Yoon and J. J. Choi* “Colloidal Nanocrystals as a Platform for Rapid Screening of Charge Trap Passivating Molecules for Metal Halide Perovskite Thin Films” Chemistry of Materials, 30, 4515-4526 (2018) (*corresponding author)

32. A. Z. Chen, M. Shiu, J. H. Ma, M. R. Alpert, D. Zhang, B. J. Foley, D.-M. Smilgies, S.-H. Lee and J. J. Choi* “Origin of vertical orientation in two-dimensional metal halide perovskites and its effect on photovoltaic performance” Nature Communications, 9, 1336 (2018) (*corresponding author)

31. G. C. Wilkes, X. Deng, J. J. Choi, M. C. Gupta “Laser Annealing of TiO₂ Electron-Transporting Layer in Perovskite Solar Cells” ACS Applied Materials & Interfaces, 10, 41312–4131 (2018)

30. Z. Sun, X. Deng, J. J. Choi, M. C. Gupta “Silicon Surface Passivation by Laser Processing a Sol–Gel TiO_x Thin Film” ACS Applied Energy Materials, 1, 5474–5481 (2018)

29. X. Deng, G. C. Wilkes, A. Z. Chen, N. Prasad, M. C. Gupta, J. J. Choi* “Room Temperature Processing of TiOx Electron Transporting Layer for Perovskite Solar Cells” The Journal of Physical Chemistry Letters, 8, 3206–3210 (2017). (*corresponding author)

28. T. Chen, W.-L. Chen, B. J. Foley, J. Lee, J. P. C. Ruff, J. Y. P. Ko, C. M. Brown, L. W. Harriger, D. Zhang, C. Park, M. Yoon, Y.-M. Chang, J. J. Choi^*, and S.-H. Lee^* “Origin of Long Lifetime of Band-Edge Charge Carriers in Organic-Inorganic Lead Iodide Perovskites” Proceedings of the National Academy of Sciences, 114, 7519-7524 (2017) (*corresponding author) 

27. J. S. Niezgoda, B. J. Foley, A. Z. Chen and J. J. Choi* “Improved Charge Collection in Highly Efficient CsPbBrI₂ Solar Cells with Light-Induced Dealloying” ACS Energy Letters, 2, 1043 – 1049 (2017) (*corresponding author) 

26. A. Z. Chen, B. J. Foley, J. H. Ma, M. R. Alpert, J. S. Niezgoda, and J. J. Choi* “Crystallographic Orientation Propagation in Metal Halide Perovskite Thin Films” Journal of Materials Chemistry A, 5, 7796 – 7800 (2017) (*corresponding author) 

25. B. J. Foley, J. Girard, B. A. Sorenson, A. Z. Chen, J. S. Niezgoda, M. R. Alpert, A. F. Harper, D.-M. Smilgies, P. Clancy, W. A. Saidi, and J. J. Choi* “Controlling Nucleation, Growth, and Orientation of Metal Halide Perovskite Thin Films with Rationally Selected Additives” Journal of Materials Chemistry A, 5, 113 - 123 (2017) (inside front cover) (*corresponding author)

24. T. Chen, B. J. Foley, C. Park, C. M. Brown, L. W. Harriger, J. Lee, J. Ruff, M. Yoon, J. J. Choi*, and S.-H. Lee* “Entropy Driven Structural Transition and Kinetic Trapping in Formamidinium Lead Iodide Perovskite” Science Advances, 2, e1601650 (2016) (*corresponding authors)

23. W. A. Saidi* and J. J. Choi “Nature of the Cubic to Tetragonal Phase Transition in Methylammonium Lead Iodide Perovskite” The Journal of Chemical Physics, 145, 144702 (2016) (*corresponding authors)

22. J. J. Choi* and S. J. L. Billinge* "Perovskites at the nanoscale: from fundamendtals to applications", Nanoscale, 8, 6206 – 6208 (2016) (^*corresponding authors)

21. A. Slonopas, B. J. Foley, J. J. Choi,* M. C. Gupta* “Charge Transport in Bulk CH₃NH₃PbI₃ Perovskite”, Journal of Applied Physics 119, 074101 (2016) (^*corresponding authors)

20. T. Chen,^§ B. J. Foley,^§ B. Ipek, M. Tyagi, J. R. D. Copley, C. M. Brown, J. J. Choi,* S.-H. Lee* "Rotational Dynamics of Organic Cations in CH₃NH₃PbI₃ Perovskite", Physical Chemistry Chemical Physics, 17, 31278 - 31286 (2015) (^§equal contributions, ^*corresponding authors)

19. B. J. Foley,  D. L. Marlowe,  K. Sun,  W. A. Saidi,  L. Scudiero,^* M. C. Gupta,^* J. J. Choi,^* “Temperature Dependent Energy Levels of Methylammonium Lead Iodide Perovskite” Applied Physics Letters, 106, 243904 (2015)  (^*corresponding authors)

Prior to University of Virginia

18. J. J. Choi,^§ X. Yang,^§ Z. M. Norman, S. J. L. Billinge, J. S. Owen, "Structure of Methylammonium Lead Iodide Within Mesoporous Titanium Dioxide: Active Material in High-Performance Perovskite Solar Cells" Nano Letters, 14, 127-133 (2014) (^§equal contribution)

17. B. R. Hyun, J. J. Choi, K. L. Seyler, T. Hanrath, F. W. Wise, "Heterojunction PbS Nanocrystal Solar Cells with Oxide Charge-Transport Layers" ACS Nano, 7, 10938-10947 (2013)

16. N. C. Anderson, M. P. Hendricks, J. J. Choi, J. S. Owen, "Ligand Exchange and the Stoichiometry of Metal Chalcogenide Nanocrystals: Spectroscopic Observation of Facile Metal-Carboxylate Displacement and Binding" Journal of the American Chemical Society, 135, 18536-18548 (2013)

15. M. T. Trinh, M. Y. Sfeir, J. J. Choi, J. S. Owen, X. Zhu, "A Hot Electron-Hole Pair Breaks the Symmetry of a Semiconductor Quantum Dot" Nano Letters, 13, 6091-6097 (2013)

14. J. J. Choi, K. Bian, W. J. Baumgardner, D. M. Smilgies, T. Hanrath, “Interface-induced Nucleation, Orientational Alignment and Symmetry Transformations in Nanocube Superlattices” Nano Letters, 12, 4791-4798 (2012)

13. L. Sun^§, J. J. Choi^§, D. Stachnik, A. C. Bartnik, B. R. Hyun, G. G. Malliaras, T. Hanrath, F. W. Wise, "Bright infrared quantum-dot light-emitting diodes through inter-dot spacing control" Nature Nanotechnology, 7, 396-373. (2012) (^§equal contribution)

12. C. R. Bealing, W. J. Baumgardner, J. J. Choi, T. Hanrath, R. G. Hennig, "Predicting Nanocrystal Shape through Consideration of Surface-Ligand Interactions" ACS Nano, 6, 2118-2127 (2012)

11. Y. F. Lim, J. J. Choi, T. Hanrath, "Facile Synthesis of Colloidal CuO Nanocrystals for Light-Harvesting Applications" Journal of Nanomaterials, Article ID 393160 (2012)

10. W. J. Baumgardner, J. J. Choi, K. Bian, L. F. Kourkoutis, D. M. Smilgies, M. O. Thompson, T. Hanrath, "Pulsed Laser Annealing of Thin Films of Self-Assembled Nanocrystals" ACS Nano, 5, 7010-7019 (2011)

9.  J. J. Choi^§, W. N. Wenger^§, R. S. Hoffman^§, Y. F. Lim, J. Luria, J. Jasieniak, J. A. Marohn, T. Hanrath, “Solution Processed Nanocrystal Quantum Dot Tandem Solar Cells” Advanced Materials, 23, 3144-3148 (2011) (^§equal contribution)

8.  K. Bian^§, J. J. Choi^§, A. Prakash, P. Clancy, D. M. Smilgies, T. Hanrath, “Shape-anisotropy Driven Symmetry Transformations in Nanocrystal Superlattice Polymorphs” ACS Nano, 5, 2815–2823 (2011) (^§equal contribution)

7.  J. J. Choi, C. R. Bealing, K. Bian, K. J. Hughes, W. Zhang, D. M. Smilgies, R. G. Hennig, J. R. Engstrom, T. Hanrath, “Controlling Nanocrystal Superlattice Symmetry and Shape-anisotropic Interactions Through Variable Ligand Surface Coverage” Journal of the American Chemical Society, 133, 3131-3138 (2011)

6.  W. J. Baumgardner, J. J. Choi, Y. F. Lim, T. Hanrath, “SnSe Nanocrystals: Synthesis, Structure, Optical Properties, and Surface Chemistry” Journal of American Chemical Society, 132, 9519-9521 (2010)

5.  J. J. Choi, J. Luria, B. R. Hyun, A. C. Bartnik, L. Sun, Y. F. Lim, J. A. Marohn, F. W. Wise, T. Hanrath, “Photogenerated Exciton Dissociation in Highly Coupled Lead Salt Nanocrystal Arrays” Nano Letters, 10, 1805-1811 (2010)

4.  B. R. Hyun, A. C. Bartnik, J. K. Lee, H. Imoto, L. F. Sun, J. J. Choi, Y. Chujo, T. Hanrath, C. K. Ober, F. W. Wise, “Role of Solvent Dielectric Properties on Charge Transfer from PbS Nanocrystals Molecules” Nano Letters, 10, 318-323 (2010)

3.  J. J. Choi, Y. F. Lim, M. B. Santiago-Berrios, M. Oh, B. R. Hyun, L. Sun, A .C. Bartnik, A. Goedhart, G. G. Malliaras, H. D. Abruña, F. W. Wise and T. Hanrath, “PbSe Nanocrystal Excitonic Solar Cells” Nano Letters, 9, 3749-3755 (2009)

2. T. Hanrath, J. J. Choi, and D. M. Smilgies, “Structure/Processing Relationships of Highly Ordered Lead Salt Nanocrystal Superlattices” ACS Nano, 3, 2975-2988 (2009)

1. T. Hanrath, D. Veldman, J. J. Choi, C. G. Christova, M. M. Wienk, and R. A. J. Janssen, “PbSe Nanocrystal Network Formation during Pyridine Ligand Displacement” ACS Applied Materials and Interfaces, 1, 244–250 (2009)