The optical responses and memory effects of photoelectric synaptic devices based on CdSe quantum dots (QDs) and poly(3-hexylthiophene) (P3HT) are studied in this work. Compared with devices only incorporating CdSe QDs, the devices based on CdSe QDs and P3HT exhibit higher photocurrents because the heterojunction formed by CdSe QDs and P3HT enhances the separation of photogenerated excitons, and the loss of excitons in the QDs reduces. In addition, due to the effect of the surface defect trapping charge of CdSe QDs, the photocurrent of the device can still be maintained for more than 100 seconds under the condition of zero gate voltage. Finally, the device can perform each synaptic activity with a low power consumption of 12.9 pJ by adjusting the concentration of QDs.