The Role of Dopant Ions on Charge Injection and Transport in Electrochemically Doped Quantum Dot Films

The Role of Dopant Ions on Charge Injection and Transport in Electrochemically Doped Quantum Dot Films

Gudjónsdóttir, S. (TU Delft ChemE/Opto-electronic Materials; TU Delft ChemE/Chemical Engineering)
van der Stam, W. (TU Delft ChemE/Chemical Engineering; TU Delft ChemE/Opto-electronic Materials)
Kirkwood, Nicholas
Evers, W.H. (TU Delft BN/Technici en Analisten; TU Delft ChemE/Chemical Engineering; Kavli institute of nanoscience Delft)
Houtepen, A.J. (TU Delft ChemE/Chemical Engineering; TU Delft ChemE/Opto-electronic Materials)

ChemE/Chemical Engineering

2018

Control over the charge density is very important for implementation of colloidal semiconductor nanocrystals into various optoelectronic applications. A promising approach to dope nanocrystal assemblies is charge injection by electrochemistry, in which the charge compensating electrolyte ions can be regarded as external dopant ions. To gain insight into the doping mechanism and the role of the external dopant ions, we investigate charge injection in ZnO nanocrystal assemblies for a large series of charge compensating electrolyte ions with spectroelectrochemical and electrochemical transistor measurements. We show that charge injection is limited by the diffusion of cations in the nanocrystal films as their diffusion coefficient are found to be ∼7 orders of magnitude lower than those of electrons. We further show that the rate of charge injection depends strongly on the cation size and cation concentration. Strikingly, the onset of electron injection varies up to 0.4 V, depending on the size of the electrolyte cation. For the small ions Li⁺ and Na⁺ the onset is at significantly less negative potentials. For larger ions (K⁺, quaternary ammonium ions) the onset is always at the same, more negative potential, suggesting that intercalation may take place for Li⁺ and Na⁺. Finally, we show that the nature of the charge compensating cation does not affect the source-drain electronic conductivity and mobility, indicating that shallow donor levels from intercalating ions fully hybridize with the quantum confined energy levels and that the reorganization energy due to intercalating ions does not strongly affect electron transport in these nanocrystal assemblies.

http://resolver.tudelft.nl/uuid:92711678-eb6b-45ec-bfc0-74a345f6d659

https://doi.org/10.1021/jacs.8b01347

0002-7863

Journal of the American Chemical Society, 140 (21), 6582-6590

Institutional Repository

journal article

© 2018 S. Gudjónsdóttir, W. van der Stam, Nicholas Kirkwood, W.H. Evers, A.J. Houtepen