UCLA

The ability to deposit and modulate conducting and semiconducting bulk materials and films on various substrates, including silicon and plastics, is of central importance for contemporary and future solid-state electronics, thermoelectrics and photovoltaics. Current approaches, such as chemical vapor deposition (CVD) or high vacuum physical vapor deposition (PVD) processes, are usually too costly and require too high processing temperature, and are not typically compatible with the growing demand of low-cost and large-area electronics, such as the emerging wearable devices. As a result, solution processes, with the potential advantages of low cost, low temperature and compatibility with plastic substrate, have emerged as an attractive approach for next-generation flexible electronic devices and thermoelectrics, wearable computers and large-area displays/photovoltaics. The key component of the solution process is the formulation of an easy-to-handle ink. Therefore, in my dissertation, I mainly investigated two types of method to prepare semiconducting or conducting ink solution, including utilizing two-dimensional (2D) nanoplates dispersion and a formulated co-solvent. In the first part, 2D nanoplates (Bi2Se3, Bi2Te3, SnS2, SnSe2, etc.) were synthesized with a ultra-small thickness (~ 6-15 nm) to form a stable ink solution which could be processed into highly uniform thin films with superior electrical performance. Taking a step further, I have also developed a new solution epitaxial approach for the growth of van der Waals heterostructures, which can be further used to create a quasi-superlattice structure with superior thermoelectric properties. The following chapters discuss the preparation of a co-solvent which could directly dissolve a variety of semiconductor solid to form ink solution at room temperature with a greatly simplified procedure. The ink solution could be used to fabricate highly uniform electronic thin films with excellent performance via conventional solution deposition approaches. And such ink solution could produce a flexible high-performance thermoelectric Cu2Se thin film. The development of those new fabrication strategies for the solution processable ink is an exciting advancement and offers great opportunities in the facile fabrication of semiconducting and conducting thin films/bulk for large-area high-performance flexible electronics, thermoelectrics and photovoltaics with high throughput, greatly reduced cost and improved safety.