Field-effect measurements of mobility and carrier concentration of Cu2S colloidal quantum dot thin films after ligand exchange

• Colloidal Cu2S quantum dots were synthesized and characterized.
• Ligand exchange was performed to alter the Cu2S nanocrystal properties.
• Ligand exchange was studied using photoluminescence and infrared spectroscopy.
• Field effect mobility and carrier concentration were directly measured.
• Carrier concentration was compared to estimates from surface plasmon resonances.

Colloidal quantum dots (CQDs) of copper sulfide (Cu2S), an earth-abundant semiconductor, have a number of intriguing applications that require knowledge of their electrical properties. Depending on stoichiometry, mobility, and surface treatment, applications include photoabsorbers for solar cells, tunable plasmonics, and counter-electrodes for polysulfate electrolytes. However, there have not been any direct measurements of electrical properties in Cu2S CQD thin films. Here, we exchange as synthesized dodecanethiol ligands with short ethanedithiol or ethylenediamine ligands to form thin films of coupled Cu2S CQDs. The mobility and carrier concentration were found to vary by ligand treatment from 10− 5 cm2/Vs and 1019 holes/cm3 for ethanedithiol ligands to 10− 3 cm2/Vs and 1020 holes/cm3 for ethylenediamine. These results are consistent with the carrier concentrations inferred from sub-bandgap surface-plasmon-resonances measured by infrared spectroscopy. These results will be useful when designing Cu2S materials for future applications.