Phototransistors that can detect visible light have been fabricated using solution processed zinc oxide channel / zirconium oxide gate insulator thin film transistors (TFTs) and room temperature synthesized perovskite quantum dots (PeQDs) as active layer. Typical ZnO thin film transistors did not show a photocurrent under visible light illumination. However, ZnO TFTs decorated with PeQDs exhibited enhanced photocurrent upon exposure to visible light. The device had a responsivity of 567 A/W (617 A/W), a high detectivity of 6.59 × 10¹³ Jones (1.85 × 10¹⁴ J) and a high sensitivity of 10⁷ (10⁸) under green (blue) light at a low drain voltage of 0.1 V. The high photo-responsivity and detectivity under green light resulted from the combination of short ligands in the QDs films and the high mobility of the spray coated ZnO films. Those results are relevant for the development of low cost and low energy consumption phototransistors working in the visible range.