Alexandros Stavrinadis

Institute of Photonic Sciences

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Gerasimos Konstantatos

Institute of Photonic Sciences

Santanu Pradhan

Indian Institute of Technology Roorkee

Sotirios Christodoulou

University of Cyprus

Shuchi Gupta

Institute of Photonic Sciences

Yu Bi

ZTE (China)

Andrew A. R. Watt

University of Oxford

Jason M. Smith

University of Oxford

César Magén

Instituto de Nanociencia y Materiales de Aragón

M. Bernechea

Instituto de Nanociencia y Materiales de Aragón

Silke L. Diedenhofen

Delft University of Technology

Cooperative Institutions

Institute of Photonic Sciences

University of Oxford

Institute of Science and Technology

Barcelona Institute for Science and Technology

Shanghai Institute for Science of Science

Centre National de la Recherche Scientifique

University of Cambridge

University of St Andrews

Imperial College London

Universidad de Zaragoza

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The role of surface passivation for efficient and photostable PbS quantum dot solar cells

Nature Energy (2016)

Yiming Cao Alexandros Stavrinadis Tania Lasanta David So Gerasimos Konstantatos

Passivation

Quantum Efficiency

10.1038/nenergy.2016.35

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Citations (321)

Nanooptomechanical sensing of carbon nanotube-based resonators

Conference on Lasers and Electro-Optics (2016)

Alexandros Tavernarakis Alexandros Stavrinadis Ioannis Tsioutsios A. K. Nowak P. Verlot

In this paper we present our first experimental results towards the exploration of nano-optomechanical detection in the limit of a weak optical coupling. We have been able to measure and actively control SiC nanowires and carbon nanotube-based resonators.

10.1364/cleo_qels.2016.ftu3b.5

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High-Efficiency Light-Emitting Diodes Based on Formamidinium Lead Bromide Nanocrystals and Solution Processed Transport Layers

Chemistry of Materials (2018)

Francesco Di Stasio I. Ramiro Yu Bi Sotirios Christodoulou Alexandros Stavrinadis

Perovskite nanocrystal light-emitting diodes (LEDs) employing architecture comprising a ZnO nanoparticles electron-transport layer and a conjugated polymer hole-transport layer have been fabricated. The obtained LEDs demonstrate a maximum external-quantum-efficiency of 6.04%, luminance of 12998 Cd/m2 and stable electroluminescence at 519 nm. Importantly, such high efficiency and brightness have been achieved by employing solution processed transport layers, formamidinium lead bromide nanocrystals (CH(NH2)2PbBr3 NCs) synthesized at room-temperature and in air without the use of a Schlenk line, and a procedure based on atomic layer deposition to insolubilize the NC film. The obtained NCs show a photoluminescence quantum yield of 90% that is retained upon film fabrica-tion. The results show that perovskite NC LEDs can achieve high-performance without the use of transport layers deposited through evapo-ration in ultra-high-vacuum.

Formamidinium

Quantum yield

10.1021/acs.chemmater.8b03079

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Citations (32)

Dopant incorporation in PbS quantum dots for solarcells

F. Boscherini Konstantatos Gerasimos Alexandros Stavrinadis

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The Influence of Doping on the Optoelectronic Properties of PbS Colloidal Quantum Dot Solids

Scientific Reports (2016)

Paris Papagiorgis Alexandros Stavrinadis Andreas Othonos Gerasimos Konstantatos Grigorios Itskos

We report on an extensive spectroscopic investigation of the impact of substitutional doping on the optoelectronic properties of PbS colloidal quantum dot (CQD) solids. N-doping is provided by Bi incorporation during CQD synthesis as well as post-synthetically via cation exchange reactions. The spectroscopic data indicate a systematic quenching of the excitonic absorption and luminescence and the appearance of two dopant-induced contributions at lower energies to the CQD free exciton. Temperature-dependent photoluminescence indicates the presence of temperature-activated detrapping and trapping processes of photoexcitations for the films doped during and after synthesis, respectively. The data are consistent with a preferential incorporation of the dopants at the QDs surface in the case of the cation-exchange treated films versus a more uniform doping profile in the case of in-situ Bi incorporation during synthesis. Time-resolved experiments indicate the presence of fast dopant- and excitation-dependent recombination channels attributed to Auger recombination of negatively charged excitons, formed due to excess of dopant electrons. The data indicate that apart from dopant compensation and filling of dopant induced trap states, a fraction of the Bi ionized electrons feeds the QD core states resulting in n-doping of the semiconductor, confirming reported work on devices based on such doped CQD material.

Auger effect

10.1038/srep18735

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Citations (39)

White and Brightly Colored 3D Printing Based on Resonant Photothermal Sensitizers

Nano Letters (2018)

Alexander W. Powell Alexandros Stavrinadis Ignacio de Miguel Gerasimos Konstantatos Romain Quidant

The use of photothermal sensitizers to facilitate the sintering of polymer powders is rapidly becoming a pivotal additive manufacturing technology, impacting multiple sectors of industry. However, conventional carbon-based sensitizers can only produce black or gray objects. To create white or colorful prints with this method, visibly transparent equivalents are needed. Here, we address this problem by designing resonant photothermal sensitizers made of plasmonic nanoparticles that strongly absorb in the near-infrared, while only minimally interacting with visible light. Gold nanorods were coated with silica before being mixed with polyamide powders to create stable colorful nanocomposite powders. At resonance, these composites showed greatly improved light-to-heat conversion compared with equivalent composites using the industry standard carbon black as a sensitizer and could be sintered using low-power light sources. Furthermore, they appear much whiter and can produce brightly colored 3D objects when mixed with dyes. Our results open a new route to utilize plasmonic nanoparticles to produce colorful and functional 3D-printed objects.

Nanorod

Photothermal effect

Colored

Visible spectrum

10.1021/acs.nanolett.8b01164

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Citations (31)

Colloidal Quantum Dot Tandem Solar Cells Using Chemical Vapor Deposited Graphene as an Atomically Thin Intermediate Recombination Layer

ACS Energy Letters (2018)

Yu Bi Santanu Pradhan Mehmet Zafer Akgül Shuchi Gupta Alexandros Stavrinadis

Two-terminal tandem cell architectures are believed to be an effective way to further improve the power conversion efficiency in solution processed photovoltaics. To design an efficient tandem solar cell, two key issues need to be considered. First, subcells with well-matched currents and complementary absorption characteristics are a prerequisite for high efficiency. Second, identifying the appropriate intermediate layer (IML) to connect the subcells is necessary to minimize the optical and electronic losses. PbS colloidal quantum dots (CQDs) are a notable choice for the subcells due to their low cost, solution processability, and remarkable wide range band gap tunability. Single-layer graphene (Gr) has been proposed to be a promising IML due to its high transparency and conductivity. Here, as a proof of concept, we demonstrate a solution-processed, two-terminal PbS CQDs tandem solar cell employing chemical vapor deposited Gr as the IML. In doing so, we report a PbS CQD cell comprising subcells with bandgaps of 1.4 and 0.95 eV that delivers power conversion efficiency in excess of 7%, substantially higher than that of previously reported CQD tandem cells.

Tandem

10.1021/acsenergylett.8b00675

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Citations (41)

Superstructures of PbS nanocrystals in a conjugated polymer and the aligning role of oxidation

Nanotechnology (2009)

Alexandros Stavrinadis Sen Xu Jamie H. Warner J. L. Hutchison Jason M. Smith

We present a method to directly align PbS nanocrystals in micron-sized superstructures within a conjugated polymer. First, lead sulfide nanocrystals are directly synthesized in a MEH-PPV suspension via a single pot, surfactant-free method. Post-synthesis precipitation of the composite solution involving mild oxidation of the nanocrystals results in the formation of nanocrystal–polymer and nanocrystal-oxide superstructures. Detailed TEM is used to study the crystallographic nature of these structures and the roles of polymer and lead sulfate. An epitaxial relationship between lead sulfide and lead sulfate at the nanoscale is shown, giving insight into the oxidation rates of the PbS nanocrystals' facets.

Lead sulfide

10.1088/0957-4484/20/44/445608

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SnS/PbS nanocrystal heterojunction photovoltaics

Nanotechnology (2010)

Alexandros Stavrinadis Jason M. Smith Christopher A. Cattley A. Cook Patrick S. Grant

We report advances in the growth, characterization and photovoltaic properties of SnS nanocrystals, with controlled < 10 nm size, and their inclusion into a lead chalcogenide solar cell. The SnS/PbS nanocrystalline film heterojunction is shown to display a type II band alignment, in which the direction of flow of the photocurrent depends on the order of the layers and not the relative work functions of the contacts. On placing the SnS layer next to the indium tin oxide (ITO) cathode we observe a dramatic increase in V(oc) to as much as 0.45 V. Our results suggest that SnS nanocrystal films can be used in multi-junction solar cells, that a SnS/PbS heterojunction on its own shows photovoltaic behaviour, and that a SnS layer in an ITO/SnS/PbS/Al device is acting to suppress the flow of an electron injection current.

Photocurrent

Nanocrystalline material

Indium tin oxide

10.1088/0957-4484/21/18/185202

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Citations (63)

Aliovalent Doping in Colloidal Quantum Dots and Its Manifestation on Their Optical Properties: Surface Attachment versus Structural Incorporation

Chemistry of Materials (2016)

Alexandros Stavrinadis Jacopo Stefano Pelli Cresi F. D’Acapito César Magén F. Boscherini

Doping colloidal quantum dots (CQDs) with aliovalent cations is a promising, yet underexplored, approach to control the optoelectronic properties in CQDs. In CQD doping, kinetics determine whether a dopant element will incorporate into the host crystal structure, while thermodynamics dictate the mechanism of dopant incorporation. Here, we show that those mechanisms can be readily monitored by simple optical measurements and XRD studies in CQD ensembles. Based on this, we outline the critical role of dopant solubility limit in CQD doping, bridging the gap between nanocrystalline and bulk semiconductors. Finally, we present a combined simulation and X-ray absorption fine structure (XAFS) data study to shed new insights on the origin of charge compensation upon doping in CQD materials that has, thus far, limited high doping efficacy, even under efficient dopant incorporation schemes.

Nanocrystalline material

10.1021/acs.chemmater.6b01445

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Citations (15)