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Colloidal quantum dots (CQDs) are promising materials for infrared (IR) light detection due to their tunable bandgap and their solution processing; however, to date, the time response of CQD IR photodiodes is inferior to that provided by Si and InGaAs. It is reasoned that the high permittivity of II-VI CQDs leads to slow charge extraction due to screening and capacitance, whereas III-Vs-if their surface chemistry can be mastered-offer a low permittivity and thus increase potential for high-speed operation. In initial studies, it is found that the covalent character in indium arsenide (InAs) leads to imbalanced charge transport, the result of unpassivated surfaces, and uncontrolled heavy doping. Surface management using amphoteric ligand coordination is reported, and it is found that the approach addresses simultaneously the In and As surface dangling bonds. The new InAs CQD solids combine high mobility (0.04 cm

Solution-processed optoelectronic materials offer a route to low-cost photodetectors, large-area solar cells, and integrated optical sources. While significant progress has been reported in organic and polymer spin-cast optoelectronics, colloidal quantum dots offer a distinct further advantage — the convenient tuning of absorption onset via the quantum size effect. Electronic transport has recently been enhanced in sizeeffect-tuned colloidal quantum dot films using ligand exchange, resulting in ultrasensitive photodetectors in both visible and infrared wavelengths; however, solid-film ligand exchange generally results in rough film morphologies, incompatible with high-uniformity image sensors. The frequent cracking of films is attributed to the significant loss of volume during the exchange process. Here, we report a new route to visiblewavelength spin-cast PbS-nanocrystal photoconductive photodetectors with sub-1% roughness, compared to the 10% roughness obtained using previously reported approaches. The new procedure yields devices that exhibit 10 A W 1 responsivities and reveal an added significant advantage: when illumination conditions change, the photodetectors respond with a single time constant of 20 ms. This compares very favorably with the multisecond and multi-time-constant response of previously reported PbS-nanocrystal photoconductive photodetectors. To be relevant to imaging applications, a top-surface photodetector must exhibit three key traits: high sensitivity to the illumination of interest, spatial uniformity across an imaging array, and video-frame-rate speed of response. Sensitivity derives from the photoconductive gain—the number of electrical carriers collected per incident photon given at a specific light level—and the noise-equivalent power (NEP)—the lowest light level that can be distinguished from noise. Spatial uniformity better than 1% across a pixel array is sought to minimize the introduction of spatial noise, which produces an image photoresponse nonuniformity of the same order. Speed of response allowing video-capture frame rates demands sub-100 ms time constants. Large photoconductive gains, as high as thousands of electrons collected per incident photon, and large dark resistivities have recently been shown to enable record high

We report a method for producing colloidal crystals heavily loaded with PbS quantum dots (QDs). The approach employed uses capillary forces to load the QDs in the interstitial voids of the colloid crystals and yields highly ordered structures with a high loading of QDs. The infiltration process is qualitatively monitored using confocal fluorescence microscopy and scanning electron microscopy. The optical properties of the resulting composite structure are examined using optical spectroscopy. The shift in the stopband resulting from the infiltration of the colloid crystal shows that the PbS QDs occupy nearly 100 % of the volume of the interstitial space.

We report efficient electroluminescence in the near-infrared from PbS–MEH-PPV (poly(2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene)) large-area, solution-cast nanocomposite devices. We employ multivariate optimization of the structural and materials components that govern the radiative, energy-transfer, and bipolar-injection efficiencies into the devices. As a result, we report an external electroluminescence quantum efficiency of 0.27 %, which corresponds to an internal electroluminescence quantum efficiency of 1.9 %. The very best devices exhibit internal-radiative-efficiency-limited performance and not transport- or capture-limited performance, indicating that further gains in efficiency may be achieved if the internal radiative efficiency of the nanocrystal–polymer composite can be further increased without compromising transfer and device bipolar-injection efficiency.

Lead sulfide colloidal quantum dot (CQD) solar cells with a solar power conversion efficiency of 5.6% are reported. The result is achieved through careful optimization of the titanium dioxide electrode that serves as the electron acceptor. Metal-ion-doped sol-gel-derived titanium dioxide electrodes produce a tunable-bandedge, well-passivated materials platform for CQD solar cell optimization.