Inkjet Printing Multicolor Pixelated Quantum Dots on Graphene for Broadband Photodetection

Pixelated broadband photoconductors consisting of chemical vapor deposition (CVD) grown graphene on Si/SiO2 and colloidal ZnO and PbS quantum dots (QDs) and FeS2 nanocrystals (NCs) are fabricated by inkjet printing of the QDs and NCs onto predefined graphene channels between Au electrodes. For a comparison, tandem devices with multilayers of QDs were also fabricated on graphene. The optoelectronic performance of these devices was characterized at different wavelengths in the ultraviolet-visible-near-infrared spectra. Specifically, the photoresponsivities are 97.5 A/W (24.4 A/WV), 7.41 A/W (1.85 A/W-V), and 6.81 A/W (1.70 A/WV) on the ZnO (340 nm), FeS2 (550 nm), and PbS (900 nm) channels, respectively, which correspond to the external quantum efficiencies (EQE) of 35580%, 1670%, and 940% for the three channels. In addition, the dynamic response of the ZnO-QD/graphene, PbS-QD/graphene, and FeS2-QD/graphene devices are 2 s/29 s, 300 ms/3.2 s, and 204 ms/240 ms for the rise and fall times, respectively, where the ZnO-QD, PbS-QD, and FeS2-QD device channels are measured at wavelengths of 340, 900, and 550 nm, respectively, all at a 1.0 V bias. In contrast, the photoresponsivities are 0.67 and 20.8 A/W for 900 and 340 nm, respectively, for the tandem device and with EQE values of 90% and 7590%, in addition to response times of 12.1 and 40.3 s at 900 nm and no appreciable response time to 340 nm. This result shows that the pixelated photoconductor benefits from direct charge transfer to the graphene channel whereas the tandem devices suffer from inefficient charge transfer between different QD layers that reduces the responsivity and response speed. This low-cost printed pixelated QD/graphene device shows the viability of printed broadband photoconductors compared to more expensive routes of device fabrication, in addition to offering compatibility to current standard complementary metal oxide semiconductor devices.