Owing to their superior photostability, green-emitting graded alloy core/shell giant quantum dots (g-QDs) can be applied in optoelectronics. However, it is essential to understand how the shell thickness affects interfacial charge separation. This work explores the impact of shell thickness on photoinduced electron transfer (PET) and photoinduced hole transfer (PHT) with an electron acceptor benzoquinone and a hole acceptor phenothiazine, respectively. Four graded alloy core/shell green-emitting g-QDs with different shell thicknesses were synthesized. The PET and PHT rate constants were obtained from photoluminescence and PL lifetime decay measurements. Our study concludes that g-QDs with a diameter of ∼7.14 show a substantial improvement in charge transfer compared with g-QDs ≥8.5 nm in diameter. Similarly, the PET and PHT rates are 3.7 and 4.1 times higher for 7.14 nm g-QDs than for the 10.72 nm sample. The calculated electron and hole transfer rate constants (ket/ht) of g-QDs with 7.14 nm in diameter are 10.80 × 107 and 14 × 107 s-1, which are 8.5 and 8 times higher compared to g-QDs with 10.72 nm in diameter. These results highlight the impact of shell thickness on the excited-state interactions of green-emitting g-QDs and conclude that g-QDs with a relatively thin shell can be a better choice as photoactive materials for photocatalyst, photodetector, and solar cells.