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28 results on '"Akgul, Mehmet Zafer"'

1. Solution Processed Infrared- and Thermo- Photovoltaics based on 0.7 eV Bandgap PbS Colloidal Quantum Dots

Author

Bi, Yu, Bertran, Arnau, Gupta, Shuchi, Ramiro, Iñigo, Pradhan, Santanu, Christodoulou, Sotirios, Majji, Shanmukh-Naidu, Akgul, Mehmet Zafer, and Konstantatos, Gerasimos

Subjects
Condensed Matter - Materials Science, Physics - Applied Physics
Abstract

Harnessing low energy photons is of paramount importance for multi-junction high efficiency solar cells as well as for thermo-photovoltaic applications. However, semiconductor absorbers with bandgap lower than 0.8 eV have been limited to III-V (InGaAs) or IV (Ge) semiconductors that are characterized by high manufacturing costs and complicated lattice matching requirements in their growth and integration with the higher bandgap cells. Here, we have developed solution processed low bandgap photovoltaic devices based on PbS colloidal quantum dots (CQDs) with a bandgap of 0.7 eV suited for both thermo-photovoltaic as well as low energy solar photon harvesting. By matching the spectral response of those cells to that of the infrared solar spectrum, we report a record high short circuit current (JSC) of 37 mA/cm2 under full solar spectrum and 5.5 mA/cm2 when placed at the back of a silicon wafer resulting in power conversion efficiencies (PCE) of 6.4 % and 0.7 % respectively. Moreover, the device reached an above bandgap PCE of ~6 % as a thermo-photovoltaic cell recorded under a 1000 {\deg}C blackbody radiator.

Published
2019

2. Colloidal Quantum Dot Tandem Solar Cells Using CVD Graphene as An Atomically Thin Intermediate Recombination Layer

Author

Bi, Yu, Pradhan, Santanu, Akgul, Mehmet Zafer, Gupta, Shuchi, Stavrinadis, Alexandros, Wang, Jianjun, and Konstantatos, Gerasimos

Subjects
Physics - Applied Physics
Abstract

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. Firstly, subcells with well-matched currents and complementary absorption characteristics are a prerequisite for high efficiency. Secondly 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 processibility 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 previously reported CQD tandem cells.

Published
2019

3. Cation Disorder and Local Structural Distortions in AgxBi1–xS2 Nanoparticles

Author

Kesavan, Jagadesh Kopula, d’Acapito, Francesco, Scardi, Paolo, Stavrinadis, Alexandros, Akgul, Mehmet Zafer, Burgués-Ceballos, Ignasi, Konstantatos, Gerasimos, Boscherini, Federico, Kesavan, Jagadesh Kopula, d’Acapito, Francesco, Scardi, Paolo, Stavrinadis, Alexandros, Akgul, Mehmet Zafer, Burgués-Ceballos, Ignasi, Konstantatos, Gerasimos, and Boscherini, Federico

Abstract

By combining X-ray absorption fine structure and X-ray diffraction measurements with density functional and molecular dynamics simulations, we study the structure of a set of AgxBi1−xS2 nanoparticles, a materials system of considerable current interest for photovoltaics. An apparent contradiction between the evidence provided by X-ray absorption and diffraction measurements is solved by means of the simulations. We find that disorder in the cation sublattice induces strong local distortions, leading to the appearance of short Ag–S bonds, the overall lattice symmetry remaining close to hexagonal, Peer Reviewed, Postprint (published version)

Published
2020

5. Colloidal Quantum Dot Tandem Solar Cells Using CVD Graphene as An Atomically Thin Intermediate Recombination Layer

Author

Bi, Yu, Pradhan, Santanu, Akgul, Mehmet Zafer, Gupta, Shuchi, Stavrinadis, Alexandros, Wang, Jianjun, Konstantatos, Gerasimos, and Universitat Politècnica de Catalunya. Institut de Ciències Fotòniques

Subjects
grafè, Física [Àrees temàtiques de la UPC], FOS: Physical sciences, Applied Physics (physics.app-ph), Physics - Applied Physics, Graphene
Abstract

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.

Published
2018

6. Infrared Solution‐Processed Quantum Dot Solar Cells Reaching External Quantum Efficiency of 80% at 1.35 µm and Jsc in Excess of 34 mA cm−2

Author

Bi, Yu, Pradhan, Santanu, Gupta, Shuchi, Akgul, Mehmet Zafer, Stavrinadis, Alexandros, and Universitat Politècnica de Catalunya. Institut de Ciències Fotòniques

Subjects
Física [Àrees temàtiques de la UPC], Quantum dots, Òptica quàntica
Abstract

Developing low‐cost photovoltaic absorbers that can harvest the short‐wave infrared (SWIR) part of the solar spectrum, which remains unharnessed by current Si‐based and perovskite photovoltaic technologies, is a prerequisite for making high‐efficiency, low‐cost tandem solar cells. Here, infrared PbS colloidal quantum dot (CQD) solar cells employing a hybrid inorganic–organic ligand exchange process that results in an external quantum efficiency of 80% at 1.35 µm are reported, leading to a short‐circuit current density of 34 mA cm−2 and a power conversion efficiency (PCE) up to 7.9%, which is a current record for SWIR CQD solar cells. When this cell is placed at the back of an MAPbI3 perovskite film, it delivers an extra 3.3% PCE by harnessing light beyond 750 nm.

Published
2018

8. Colloidal Quantum Dot Tandem Solar Cells Using CVD Graphene as An Atomically Thin Intermediate Recombination Layer

Author

Universitat Politècnica de Catalunya. Institut de Ciències Fotòniques, Bi, Yu, Pradhan, Santanu, Akgul, Mehmet Zafer, Gupta, Shuchi, Stavrinadis, Alexandros, Wang, Jianjun, Konstantatos, Gerasimos, Universitat Politècnica de Catalunya. Institut de Ciències Fotòniques, Bi, Yu, Pradhan, Santanu, Akgul, Mehmet Zafer, Gupta, Shuchi, Stavrinadis, Alexandros, Wang, Jianjun, and Konstantatos, Gerasimos

Abstract

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., Peer Reviewed, Postprint (author's final draft)

Published
2018

9. Infrared Solution‐Processed Quantum Dot Solar Cells Reaching External Quantum Efficiency of 80% at 1.35 µm and Jsc in Excess of 34 mA cm−2

Author

Universitat Politècnica de Catalunya. Institut de Ciències Fotòniques, Bi, Yu, Pradhan, Santanu, Gupta, Shuchi, Akgul, Mehmet Zafer, Stavrinadis, Alexandros, Universitat Politècnica de Catalunya. Institut de Ciències Fotòniques, Bi, Yu, Pradhan, Santanu, Gupta, Shuchi, Akgul, Mehmet Zafer, and Stavrinadis, Alexandros

Abstract

Developing low‐cost photovoltaic absorbers that can harvest the short‐wave infrared (SWIR) part of the solar spectrum, which remains unharnessed by current Si‐based and perovskite photovoltaic technologies, is a prerequisite for making high‐efficiency, low‐cost tandem solar cells. Here, infrared PbS colloidal quantum dot (CQD) solar cells employing a hybrid inorganic–organic ligand exchange process that results in an external quantum efficiency of 80% at 1.35 µm are reported, leading to a short‐circuit current density of 34 mA cm−2 and a power conversion efficiency (PCE) up to 7.9%, which is a current record for SWIR CQD solar cells. When this cell is placed at the back of an MAPbI3 perovskite film, it delivers an extra 3.3% PCE by harnessing light beyond 750 nm., Peer Reviewed, Postprint (author's final draft)

Published
2018

15. Macrocrystals Of Colloidal Quantum Dots In Anthracene: Exciton Transfer And Polarized Emission

Author

Soran-Erdem, Zeliha, Erdem, Talha, Hernandez-Martinez, Pedro Ludwig, Akgul, Mehmet Zafer, Gaponik, Nikolai, and Demir, Hilmi Volkan

Abstract

In this work, centimeter-scale macrocrystals of nonpolar colloidal quantum dots (QDs) incorporated into anthracene were grown for the first time. The exciton transfer from the anthracene host to acceptor QDs was systematically investigated, and anisotropic emission from the isotropic QDs in the anthracene macrocrystals was discovered. Results showed a decreasing photoluminescence lifetime of the donor anthracene, indicating a strengthening energy transfer with increasing QD concentration in the macrocrystals. With the anisotropy study, QDs inside the anthracene host acquired a polarization ratio of similar to 1.5 at 0 degrees collection angle, and this increases to similar to 2.5 at the collection angle of 60 degrees. A proof-of-concept application of these excitonic macrocrystals as tunable color converters on light-emitting diodes was also demonstrated.

Published
2015

18. Mn2+-Doped CdSe/CdS Core/Multishell Colloidal Quantum Wells Enabling Tunable Carrier–Dopant Exchange Interactions

Author

Delikanli, Savas, primary, Akgul, Mehmet Zafer, additional, Murphy, Joseph R., additional, Barman, Biplob, additional, Tsai, Yutsung, additional, Scrace, Thomas, additional, Zhang, Peiyao, additional, Bozok, Berkay, additional, Hernández-Martínez, Pedro Ludwig, additional, Christodoulides, Joseph, additional, Cartwright, Alexander N., additional, Petrou, Athos, additional, and Demir, Hilmi Volkan, additional

Published
2015
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25. Low-temperature colloidal synthesis of CuBiS2 nanocrystals for optoelectronic devices.

Author

Wang, Jian-Jun, Akgul, Mehmet Zafer, Bi, Yu, Christodoulou, Sotirios, and Konstantatos, Gerasimos

Abstract

A new facile colloidal synthesis of CuBiS2 (CBS) nanocrystals with monodispersed size and good quality has been developed. The CBS nanocrystal films were deposited by solid-state ligand exchange and their field effect transistor and photoconductive characteristics were characterized. The prototype solar cell has presented a decent performance. The suitable bandgap and highly appealing photoresponsivity demonstrate the as-synthesized CBS nanocrystals as an alternative to existing Cd- and Pb-containing nanocrystals for optoelectronic and photovoltaic devices. [ABSTRACT FROM AUTHOR]

Published
2017
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28. Cation Disorder and Local Structural Distortions in Ag x Bi 1-x S 2 Nanoparticles.

Author

Kopula Kesavan J, d'Acapito F, Scardi P, Stavrinadis A, Akgul MZ, Burgués-Ceballos I, Konstantatos G, and Boscherini F

Abstract

By combining X-ray absorption fine structure and X-ray diffraction measurements with density functional and molecular dynamics simulations, we study the structure of a set of Ag x Bi 1-x S 2 nanoparticles, a materials system of considerable current interest for photovoltaics. An apparent contradiction between the evidence provided by X-ray absorption and diffraction measurements is solved by means of the simulations. We find that disorder in the cation sublattice induces strong local distortions, leading to the appearance of short Ag-S bonds, the overall lattice symmetry remaining close to hexagonal.

Published
2020
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