Designing High-Performance CdSe Nanocrystal Thin-Film Transistors Based on Solution Process of Simultaneous Ligand Exchange, Trap Passivation, and Doping

We report a simple, solution-based, and postsynthetic process for simultaneous ligand exchange, surface passivation, and doping of CdSe nanocrystals (NCs) for the design of high-performance field-effect transistors (FETs). Strong electronic coupling, effective surface trap passivation, and n-type doping of the NCs could be achieved by simply immersing the as-synthesized CdSe NC thin films into InX₃ (X = Cl, Br, I) solution. The optical, chemical, and structural properties of these CdSe NC thin films were analyzed, revealing successful ligand exchange and In doping. It is demonstrated that the doping level could be precisely controlled from lightly doped films to degenerately doped films by adjusting the type and concentration of halogen used in the ligand exchange solution. Ultraviolet photoelectron spectroscopy, first-principles calculation, and temperature-dependent electrical characterization of the InX₃-treated CdSe NC FETs were performed to fundamentally understand their electronic structure and charge transport behavior. Combinational studies show that halides, as well as In, significantly affect the charge transport behavior in terms of halide-induced trap states as well as both tunneling and hopping transport mechanisms. It is demonstrated that Cl induces strong electronic coupling, effective trap passivation, and moderate In doping, resulting in optimized FETs with a mobility of over 10 cm² V^-1 s^-1, I_ON/I_OFF of over 10⁷, and low activation energy of around 1 meV or even band-like transport behavior. This work provides a novel technological strategy and fundamental information on nanoscience for the design of cost-efficient, high-performance NC-based electronic, and optoelectronic devices.