Heavy metal-free semiconductor nanocrystals such as copper indium sulfide quantum dots (QDs) have attracted substantial attention in recent years due to environmental issues and diverse applications. We report the synthesis and characterization of copper-zinc-indium-sulfide (CZIS) QDs and CZIS treated with excess Zn 2+ at different temperatures, denoted here as CZIS/ZnS 100 and CZIS/ZnS 200. Zn 2+ can diffuse into the lattice by an exchange-cation reaction, replacing Cu + and In 3+. We employed transient absorption (TA) spectroscopy to study the role of Zn 2+ in the lattice. The data were treated by global analysis, which yielded the decay associated spectra (DAS). Through DAS and second-order derivative absorption spectra, we could isolate the excitonic contribution from the metal ligand conduction band charge transfer (MLCBCT) absorption in the TA spectrum, finding the hole localization lifetime by its spectral and dynamical features. The hole localization lifetime increases from 0.3 to 1.7 ps by increasing the Zn 2+ concentration. We also measured the electron trapping constants to be 30 ps and larger than 1 ns. Finally, we concluded that the improvement in the photoluminescence quantum yield originates from accelerated radiative transition relative to the nonradiative component. A detailed mechanism was proposed, and our results suggest that the introduction of Zn 2+ in the lattice of CIS QDs could be beneficial for charge extraction.