Achieving High-detectivity Near Infrared Organic Photodetectors through Optimizing Film Thickness and Polymer Molecular Weight

The wide-bandgap polymer (PTzBI-Cl) contains an electron-deficient [1,2,3]triazolo[4,5-f]isoindole-5,7(2H,6H)-dione (TzBI) unit, which can be used as an electron-donating polymer to combine with a non-fullerene acceptor, namely Y6DT, to fabricate organic photodetectors (OPDs) that bear inverted device structure. The devices based on high molecular weight PTzBI-Cl-H exhibited lower dark current density and thus superior photodetectivity. The dark current density can be significantly suppressed by optimizing the film thickness of active layer, while the external quantum efficiency can be maintained at a relatively high level. The combination of these advantages leads to an obvious increase in the detectivity. When the active layer thickness increased up to 330 nm, the device exhibited a very low dark current density of 2.3x10(-10) A.cm(-2) at -0.1 V, and the rectification ratio is 10(6) in the range of +/- 2 V. Under -0.1 V bias, the detectivity of the device is higher than 10(13) cm.Hz(-1/2).W-1 in the range of 500-880 nm, with a maximum of 6.1x10(13) cm.Hz(-1/2).W-1 and a responsivity of 0.52 A.W-1 at a working wavelength of 830 nm, both of which are among the highest values of thus far reported OPDs based on the inverted structure at the working wavelength of 830 nm without extra gains. [GRAPHICS] .