Effect of film thickness of ZnO as the electron transport layer on the performance of organic photodetectors

Organic photodetectors with bulk heterojunctions were constructed with a structure of ITO/ZnO/P3HT:PC 61 BM/MoO 3 /Al. The effect of the thickness of the ZnO layer on the properties of the device were investigated by fabricating photodetectors with different ZnO layer thicknesses: 20, 40, 50, 60, and 80 nm. The 40 nm-thick ZnO electron transport layer provided the device with a low dark current density (1.7 × 10 −9 A/cm 2 ), high specific detectivity (2.7 × 10 13 Jones), wide linear dynamic range (78.9 dB), and fast response speed ( τ r / τ f  = 0.61/0.75 μs). The results show that an optimal thickness of the ZnO electron transport layer can effectively block hole injection into the active layer, which is a promising strategy to improve the performance of organic photodetectors.