Scaffold-directed crystallization of solution-processable semiconductors

We are using scaffolds to direct the solution-phase crystallization of small-molecule organic semiconductors and metal halide perovskites into vertical crystal arrays optimized for maximum light absorption and charge transport. These scaffolds can dictate the size, location, and orientation of crystals by controlling nucleation at the early stages of crystal growth. Our method is compatible with solution dip coating to continuously deposit vertical crystal arrays onto device platforms.

Y. Zhang, A. Chen, M.W. Kim, A. Alaei, S.S. Lee. "Nanoconfining solution-processed organic semiconductors for emerging optoelectronics." Chemical Society Reviews, 50, 9375 (2021).

A. Alaei, K. Zong, K. Asawa, T.M. Chou, A. Briseno, C.-H. Choi, S.S. Lee. "Orienting and shaping organic semiconductor single crystals through selective nanoconfinement." Soft Matter, 17, 3603 (2021). Part of the 2021 Emerging Investigator Series.

K. Zong, K. M. Asawa, A. Circelli, N. Sparta, C.-H. Choi, S.S. Lee. "Graphoepitaxy-directed assembly of organic semiconductor single crystals into trellis structures." ACS Materials Letters, 2, 721 (2020).

Twisting Organic Semiconductor Crystals

In collaboration with the Kahr group, we are exploring crystal twisting in organic semiconductors. Crystal twisting occurs spontaneously in many molecular compounds when they are cooled from the melt as spherulites. As fibrils grow radially outwards from the spherulite center, they twist in concert with one another about the growth direction. We are exploring the role of twisting on the optoelectronic properties of organic semiconductor crystals for solar cells, transistors and photodetectors.

Y. Yang, K. Zong, S.J. Whittaker, Z. An, M. Tan, H. Zhou, A. Shtukenberg, B. Kahr, S.S. Lee. “Twisted tetrathiafulvalene crystals.” Molecular System Design and Engineering, 7, 569-675 (2022). Part of the themed collection “Molecular assembly of organic electronics” and selected as a MSDE Recent HOT Article.

Y. Yang, Y. Zhang, C.T. Hu, M. Sun, S. Jeong, S.S. Lee, A.G. Shtukenberg, B. Kahr. “Transport in twisted crystalline charge transfer complexes.” Chemistry of Materials, 34, 1778-1788 (2022).

Nanoconfining Metal Halide Perovskites

Metal halide perovskites are emerging as frontrunners for solution-processable semiconductors to harvest sunlight, but suffer from sensitivity to air and moisture. We are exploring the use of nanoconfinement in fibers and scaffolds to stabilize halide perovskites against detrimental polymorph transitions and degradation. This research is based in part on the governing thermodynamic principle that increasing the surface area-to-volume ratio can shift the Gibbs free energy of crystals and polymorph transition temperatures.

Y. Yang, J. Robbins, L. Ezeonu, Y. Ma, N. Sparta, X. Kong, S. Strauf, S. Podkolzin, S.S. Lee. "Probing lattice vibrations of stabilized CsPbI3 polymorphs via low-frequency Raman spectroscopy." Journal of Materials Chemistry C, 8, 8896 (2020).

X. Kong, K. Shayan, S. Hua, S. Strauf, S.S. Lee. “Complete suppression of detrimental perovskite polymorph transitions in all-inorganic perovskites via nanoconfinement.” ACS Applied Energy Materials, 2, 2948 (2019).

A. Alaei, A. Circelli, Y. Yuan, Y. Yang, S.S. Lee. "Polymorphism in Metal Halide Perovskites." Materials Advances, 2, 47-63 (2021). Selected as a HOT article.

X. Kong, K. Shayan, S. Lee, C. Ribeiro, S. Strauf, S.S. Lee. “Remarkable long-term stability of nanoconfined metal-halide perovskite crystals against degradation and polymorph transitions.” Nanoscale, 10, 8320 (2018).