Flexible and broadband colloidal quantum dots photodiode array for pixel-level X-ray to near-infrared image fusion.

Combining information from multispectral images into a fused image is informative and beneficial for human or machine perception. Currently, multiple photodetectors with different response bands are used, which require complicated algorithms and systems to solve the pixel and position mismatch problem. An ideal solution would be pixel-level multispectral image fusion, which involves multispectral image using the same photodetector and circumventing the mismatch problem. Here we presented the potential of pixel-level multispectral image fusion utilizing colloidal quantum dots photodiode array, with a broadband response range from X-ray to near infrared and excellent tolerance for bending and X-ray irradiation. The colloidal quantum dots photodiode array showed a specific detectivity exceeding 1012 Jones in visible and near infrared range and a favorable volume sensitivity of approximately 2 × 105 µC Gy-1 cm-3 for X-ray irradiation. To showcase the advantages of pixel-level multispectral image fusion, we imaged a capsule enfolding an iron wire and soft plastic, successfully revealing internal information through an X-ray to near infrared fused image.

Matching Charge Extraction Contact for Infrared PbS Colloidal Quantum Dot Solar Cells.

Infrared solar cells (IRSCs) can supplement silicon or perovskite SCs to broaden the utilization of the solar spectrum. As an ideal infrared photovoltaic material, PbS colloidal quantum dots (CQDs) with tunable bandgaps can make good use of solar energy, especially the infrared region. However, as the QD size increases, the energy level shrinking and surface facet evolution makes us reconsider the matching charge extraction contacts and the QD passivation strategy. Herein, different to the traditional sol-gel ZnO layer, energy-level aligned ZnO thin film from a magnetron sputtering method is adopted for electron extraction. In addition, a modified hybrid ligand recipe is developed for the facet passivation of large size QDs. As a result, the champion IRSC delivers an open circuit voltage of 0.49 V and a power conversion efficiency (PCE) of 10.47% under AM1.5 full-spectrum illumination, and the certified PCE is over 10%. Especially the 1100 nm filtered efficiency achieves 1.23%. The obtained devices also show high storage stability. The present matched electron extraction and QD passivation strategies are expected to highly booster the IR conversion yield and promote the fast development of new conception QD optoelectronics.

Triplet energy migration pathways from PbS quantum dots to surface-anchored polyacenes controlled by charge transfer.

Sensitization of molecular triplets using PbS quantum dots (QDs), followed by efficient triplet fusion, has been developed as a novel route to near-infrared-to-visible photon upconversion. Fundamentally, however, the mechanisms of triplet energy transfer (TET) from PbS QDs to surface-anchored polyacence acceptors remain highly debated. Here we study and side-by-side compare the kinetic pathways of TET from photoexcited PbS QDs to surface-anchored tetracene and pentacene derivatives using broad-band transient absorption spectroscopy spanning multiple decades of timescales. We find that the TET pathways are dictated by charge-transfer energetics at the QD/molecule interface. Charge transfer from QDs to tetracene was strongly endothermic, and hence spectroscopy showed one-step transformation from QD excited states to tetracene triplets in 302 ns. In contrast, hole transfer from QDs to pentacene was thermodynamically favoured and was confirmed by the formation of pentacene cation radicals in 13 ps, which subsequently evolved into pentacene triplets through a 101 ns electron transfer process. These results not only are consistent with a recently-established framework of charge-transfer-mediated TET, but also provide a route to manipulate triplet sensitization using lead-salt QDs for efficient upconversion of near-infrared photons.

Efficiently Passivated PbSe Quantum Dot Solids for Infrared Photovoltaics.

Infrared (IR) solar cells are promising devices for significantly improving the power conversion efficiency of common solar cells by harvesting the low-energy IR photons. PbSe quantum dots (QDs) are superior IR photon absorbing materials due to their strong quantum confinement and thus strong interdot electronic coupling. However, the high chemical activity of PbSe QDs leads to etching and poor passivation in ligand exchange, resulting in a high trap-state density and a high open circuit voltage (VOC) deficit. Here we develop a hybrid ligand co-passivation strategy to simultaneously passivate the Pb and Se sites; that is, halide anions passivate the Pb sites and Cd cations passivate the Se sites. The cation and anion hybrid passivation substantially improves the quality of PbSe QD solids, giving rise to an excellent trap-state control and prolonged carrier lifetime. A high VOC and a high short circuit current density (JSC) are achieved simultaneously in the IR QD solar cells based on this hybrid ligand treatment. Finally, a IR-PCE of 1.31% under the 1100-nm-filtered solar illumination is achieved in the PbSe QD solar cells, which is the highest IR-PCE for PbSe QD IR solar cells at present. Additionally, the PbSe QD devices show a high external quantum efficiency of 80% at ∼1295 nm.