Selective p- and n‑Doping of Colloidal PbSe Nanowires To Construct Electronic and Optoelectronic Devices

We report the controlled and selective doping of colloidal PbSe nanowire arrays to define pn junctions for electronic and optoelectronic applications. The nanowires are remotely doped through their surface, p-type by exposure to oxygen and n-type by introducing a stoichiometric imbalance in favor of excess lead. By employing a patternable poly(methyl)methacrylate blocking layer, we define pn junctions in the nanowires along their length. We demonstrate integrated complementary metal-oxide semiconductor inverters in axially doped nanowires that have gains of 15 and a near full signal swing. We also show that these pn junction PbSe nanowire arrays form fast switching photodiodes with photocurrents that can be optimized in a gated-diode structure. Doping of the colloidal nanowires is compatible with device fabrication on flexible plastic substrates, promising a low-cost, solution-based route to high-performance nanowire devices

Advanced Architecture for Colloidal PbS Quantum Dot Solar Cells Exploiting a CdSe Quantum Dot Buffer Layer

Advanced architectures are required to further improve the performance of colloidal PbS heterojunction quantum dot solar cells. Here, we introduce a CdI₂-treated CdSe quantum dot buffer layer at the junction between ZnO nanoparticles and PbS quantum dots in the solar cells. We exploit the surface- and size-tunable electronic properties of the CdSe quantum dots to optimize its carrier concentration and energy band alignment in the heterojunction. We combine optical, electrical, and analytical measurements to show that the CdSe quantum dot buffer layer suppresses interface recombination and contributes additional photogenerated carriers, increasing the open-circuit voltage and short-circuit current of PbS quantum dot solar cells, leading to a 25% increase in solar power conversion efficiency

<i>In Situ</i> Repair of High-Performance, Flexible Nanocrystal Electronics for Large-Area Fabrication and Operation in Air

Colloidal semiconductor nanocrystal (NC) thin films have been integrated in light-emitting diodes, solar cells, field-effect transistors (FETs), and flexible, electronic circuits. However, NC devices are typically fabricated and operated in an inert environment since the reactive surface and high surface-to-volume ratio of NC materials render them sensitive to oxygen, water, and many solvents. This sensitivity has limited device scaling and large-scale device integration achievable by conventional fabrication technologies, which generally require ambient air and wet-chemical processing. Here, we present a simple, effective route to reverse the detrimental effects of chemical and environmental exposure, by incorporating, <i>in situ</i>, a chemical agent, namely, indium metal, which is thermally triggered to diffuse and repair the damage. Taking advantage of the recovery process, CdSe NC FETs are processed in air, patterned using the solvents of lithography, and packaged by atomic layer deposition to form large-area and flexible high-performance NC devices that operate stably in air