Ultrasensitive near-infrared phototransistors based on Lead sulfide (PbS) quantum dots (QDs)-graphene hybrid channel are fabricated by facile solution processing. The device combines the advantages of the large light absorbance of QDs high mobility of graphene. Under light illumination, the photogenerated carriers will transfer from QDs to graphene. As result, the phototransistor exhibits fast response speed with rise time of 1.4 ms and fall time of 1.3 ms at 36 mW/cm2 illumination of 808 nm wavelength, meaning the device can follow a fast switched optical signal. The responsivity (R), effective quantum efficiency (EQE) of the device are 6 A/W and 961% under 166mW/cm2 illumination, respectively. It expected that the PbS QDs–graphene hybrid devices are promising for fast response, low-cost and easy fabrication photoelectronics
The optical responsivity of bulk-heterojunction field effect phototransistors (BH-FEpTs) based on poly [2-methoxy-5-(2´- ethylhexyloxy-p-phenylenevinylene)] (MEH-PPV) and PbS quantum dot hybrids is very low. A main reason for the low responsivity is the low carrier mobility of the blends. To overcome the shortcoming, graphene with high carrier mobility (~200,000 cm2V-1s-1) can be used for improving the responsivity of BH-FEpTs. However, the influence of monolayer graphene on the photo response of BH-FEpTs still has been not studied. In this papers, BH-FEpTs and GBH-FEpTs (single layer graphene beneath the BH layer in BH-FEpTs) were fabricated. Experimentally, the GBH-FEpTs showed ultrahigh mobility for both holes and electrons (μH and μE) of 183 and 169 cm2V−1s−1, while 11.3 and 6.2 cm2V−1s−1 in BH-FEpT. Due to the greatly promoted carrier mobility and highly ordered channels for GBH-FEpTs, higher α, μ and β are obtained for GBH-FEpTs. The responsivity of GBH-FEpTs is improved to 101 A/W, which is two orders magnitude larger than BH-FEpTs (10-1 A/W).
We fabricate and investigate the photoelectrical characterization of PbSe QDs FEpTs Field Effect photo Transistors in lateral (LQFEpT) and vertical architectures (VQFEpT) respectively. Both LQFEpT and VQFEpT apply PbSe quantum dots as active layer, with different channel length of 0.1mm and 678nm respectively. The VQFEpT apply Au/Ag nanowires (NWs) as source transparent electrode connecting with Au source electrode. The ambipolar operation of both FEpTs show low power consumption, delivering high drain current at VSD = VG = ± 4 V. The VQFEpT exhibit higher photocurrent up to 4mA, three orders magnitude higher than that in LQFEpTs (16μA), owing to the superior carrier transportion in the shorter channel. As a result, higher photo responsivity (8×104A/W), specific detectivity (2×1012Jones) and gain (1.3× 105) are achieved in VQFEpT. The all-solution processing vertical architecture provide a convenient way for IR photo detectors with high performances.