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In this study, quantum dot light-emitting diodes based on non-toxic silicon quantum dots functionalized with hexyl and dodecyl organic ligands showed a negative capacitance effect. Current density-voltage (<inline-formula><tex-math notation="LaTeX">$J-V$</tex-math></inline-formula>) measurements revealed the charge transport mechanisms in the QLEDs. The capacitance-voltage (<inline-formula><tex-math notation="LaTeX">$C-V$</tex-math></inline-formula>) characteristics were measured with an LCR meter over a wide range of frequencies (<inline-formula><tex-math notation="LaTeX">$200 \,\mathrm{Hz}$</tex-math></inline-formula> to <inline-formula><tex-math notation="LaTeX">$1 \,\mathrm{MHz}$</tex-math></inline-formula>) and at temperatures from <inline-formula><tex-math notation="LaTeX">$-40 \,{{\mathrm{^{\circ }}{\mathrm{C}}}}\,\mathrm{to}\, 60 \,{{\mathrm{^{\circ }}{\mathrm{C}}}}$</tex-math></inline-formula>. The classical heterojunction theory can describe the operation of quantum LEDs, but an effect not predicted by Shockley&#x2019;s theory was observed. Negative capacitance values were recorded in both fabricated LEDs, which were not observed in SiQD-LEDs before. Hence, we investigate the negative capacitance origin and its influence on the device performance. We attribute the negative capacitance to trap-mediated recombination, where charges at defect sub-bandgap states contribute to the recombination but cannot be replenished fast enough. As a result, a current flows to re-establish the equilibrium, which lags behind the applied voltage, and the NC appears. By comparing the two functionalizations, we also observed a different temperature dependence of the positive capacitance peak and a stronger negative capacitance effect for dodecyl functionalized SiQDs. This effect is attributed to their improved charge carrier confinement abilities.