Conjugated Polyelectrolyte Interfacial Modifier for High Performance Near-infrared Quantum-dot Photodetectors
Photodetecting properties of near-infrared quantum-dot photodetectors (NIR-QPDs) have been significantly improved by introducing novel cationic conjugated polyelectrolytes (CCPs) as the interfacial modifier. The formation of quaternary ammonium salt at the end of pendant groups of CCPs generate permanent dipole moment on the ZnO surface and effectively modify the work function of ZnO, improving the charge transport at the interfaces between the ZnO and QD layers. The cationic charge density and the geometrical structures of CCP1–3 were crucial effects on determining the photo-responsivity (R) and detectivity (D*) of NIR-QPDs. The higher cationic charge density of CCP2 improved the electron accepting properties of ZnO, resulting in 1.6–5.1-fold increased R values under 940 nm IR irradiation (0.1 mW·cm-2, -1 V) compared to ZnO-, ZnO/CCP1-, and ZnO/CCP3-based devices. Notably, horizontally-aligned backbone of CCP2 toward the substrate make uniform film surface and insulating layer on the ZnO, which improved the charge transport and maintained a relatively low and constant dark current against negative bias. As a result, the D* of CCP2-treated NIR-QPDs was increased by up to 1,880% compared to pristine ZnO-based devices, and by 200–250% compared to CCP1- and CCP3-based devices.