Choi Laboratory for Optoelectronic Nanomaterials Department of Chemical Engineering
Research 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 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 novel nanomaterials as well as their self-assembled ensembles. 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 and magnetic spectroscopy techniques and electrical transport measurement techniques to examine properties of the nanomaterials 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.