Jianlong Wang

Broadband Phototransistor Based on CH3NH3PbI3 Perovskite and PbSe Quantum Dot Heterojunction

Organic lead halide perovskites have received a huge amount of interest since emergence, because of tremendous potential applications in optoelectronic devices. Here field effect phototransistors (FEpTs) based on CH3NH3PbI3 perovskite/PbSe colloidal quantum dot heterostructure are demonstrated. The high light absorption and optoelectric conversion efficiency, due to the combination of perovskite and quantum dots, maintain the responsivities in a high level, especially at 460 nm up to 1.2 A/W. The phototransistor exhibits bipolar behaviors, and the carrier mobilities are determined to be 0.147 cm2V-1s-1 for holes and 0.16 cm2V-1s-1 for electrons. The device has a wide spectral response spectrum ranging from 300 to 1500 nm. A short photoresponse time is less than 3 ms due to the assistance of heterojunction on the transfer of photoexcitons. The excellent performances presented in the device especially emphasize the CH3NH3PbI3 perovskite-PbSe quantum dot as a promising material for future photoelectronic applications.

Bulk- and layer-heterojunction phototransistors based on poly [2-methoxy-5-(2-ethylhexyloxy-p-phenylenevinylene)] and PbS quantum dot hybrids

The responsivity (R) of a thin film photodetector is proportional to the product of its photo-induced carrier density (n) and mobility (μ). However, when choosing between layer heterojunction (LH) and bulk heterojunction (BH) field-effect phototransistors (FEpTs), it is still unclear which of the two device structures is more conducive to photodetection. A comparison study is performed on the two structures based on polymer and PbS quantum dot hybrids. Both devices exhibit ambipolar behavior, with μE ≈ μH = 3.7 cm2 V−1 s−1 for BH-FEpTs and μH = 36 cm2 V−1 s−1 and μE = 52 cm2 V−1 s−1 for LH-FEpTs. Because of the improvements in μ and the channel order degree (α), the responsivity of LH-FEpTs is as high as 101 A/W, which is as much as two orders of magnitude higher than that of BH-FEpTs (10−1A/W) under the same conditions. Although the large area of the BH improves both the exciton separation degree (β) and n in the BH-FEpT, the lack of an effective transport mechanism becomes the main constraint on high de...

Platinum-scatterer-based random lasers from dye-doped polymer-dispersed liquid crystals in capillary tubes

The resonance characteristics of platinum-scatter-based random lasers from dye-doped polymer-dispersed liquid crystals (DDPDLCs) in capillary tubes were researched for the first time, to the best of our knowledge. After adding platinum nanoparticles (Pt NPs) into the liquid crystal mixtures, the emission spectra of DDPDLCs revealed a lower lasing threshold in comparison with those of DDPDLCs without Pt NPs due to light scattering of liquid crystal droplets and the local field enhancement around Pt NPs. Furthermore, the full width at half-maximum (FWHM) and the lasing threshold were determined by the doping density of the Pt NPs. The threshold was decreased by about half from 17.5  μJ/pulse to 8.7  μJ/pulse on the condition that around 1.0 wt. % was the optimum concentration of Pt NPs doped into the DDPDLCs. The FWHM of the peaks sharply decreased to 0.1 nm. Our work provides an extremely simple method to enhance random lasers from DDPDLCs doped with Pt NPs, and it has potential applications in random fiber lasers or laser displays.

Improved hybrid polymer/PbS quantum dot infrared phototransistors incorporating single-layer graphene

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).

Amplified spontaneous emission in distributed feedback active microcavities fabricated by the sol–gel dip-coating method

Abstract Amplified spontaneous emission (ASE) is demonstrated in a distributed feedback (DFB) active microcavity, formed by rhodamine B molecules in a Bragg grating (BG). The BG was fabricated by alternately depositing titanium dioxide and silicon dioxide sol–gel thin films. The reflectance spectrum of BG simulated by the transfer matrix method was consistent with experimental results, demonstrating that the BG had good periodic structures. With rhodamine B molecules embedded, the ASE was observed from the DFB active microcavity in optical pumped conditions. The full-width-half-maximum and threshold of ASE were 7.5 nm and 0.2 mJ/pulse. The slope efficiency of 3% was measured. The DFB active microcavity is promising for low-cost ASE.

An effective method to enhance working temperature range of lasers from dye-doped cholesteric liquid crystals

Stable and homogeneous dye-doped cholesteric liquid crystals (DDCLCs) were prepared. The lasers generated from DDCLCs can be tuned by temperature, and the working temperature range of DDCLCs was from 20 °C to 60 °C. After adding bi-functional monomer RM257 and photoinitiator Irgacure 2959, the working temperature range of lasers from DDCLCs was enhanced from 20-60 °C to 20-70 °C.

The ambipolar operation of lateral and vertical PbSe quantum dots field effect phototransistors

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.