Robert Hoye | Massachusetts Institute of Technology (MIT) (original) (raw)

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Papers by Robert Hoye

Research paper thumbnail of Fabrication of ZnO/Cu2O heterojunctions in atmospheric conditions: Improved interface quality and solar cell performance

Solar Energy Materials and Solar Cells, 2015

a b s t r a c t Zn 1 À x Mg x O/Cu 2 O heterojunctions were successfully fabricated in open-air a... more a b s t r a c t Zn 1 À x Mg x O/Cu 2 O heterojunctions were successfully fabricated in open-air at low temperatures via atmospheric atomic layer deposition of Zn 1 À x Mg x O on thermally oxidized cuprous oxide. Solar cells employing these heterojunctions demonstrated a power conversion efficiency exceeding 2.2% and an open-circuit voltage of 0.65 V. Surface oxidation of Cu 2 O to CuO prior to and during Zn 1 À x Mg x O deposition was identified as the limiting factor to obtaining a high quality heterojunction interface. Optimization of deposition conditions to minimize Cu 2 O surface oxidation led to improved device performance, tripling the open-circuit voltage and doubling the short-circuit current density. These values are the highest reported for a ZnO/Cu 2 O interface formed in air, and highlight atmospheric ALD as a promising technique for inexpensive and scalable fabrication of ZnO/Cu 2 O heterojunctions. (Y. Ievskaya). Please cite this article as: Y. Ievskaya, et al., Fabrication of ZnO/Cu 2 O heterojunctions in atmospheric conditions: Improved interface quality and solar cell performance, Solar Energy Materials and Solar Cells (2014), http://dx.

Research paper thumbnail of Engineering Schottky Contacts in Open-Air Fabricated Heterojunction Solar Cells to Enable High Performance and Ohmic Charge Transport

ACS Applied Materials & Interfaces, 2014

The efficiencies of open-air processed Cu 2 O/Zn 1−x Mg x O heterojunction solar cells are double... more The efficiencies of open-air processed Cu 2 O/Zn 1−x Mg x O heterojunction solar cells are doubled by reducing the effect of the Schottky barrier between Zn 1−x Mg x O and the indium tin oxide (ITO) top contact. By depositing Zn 1−x Mg x O with a long band-tail, charge flows through the Zn 1−x Mg x O/ITO Schottky barrier without rectification by hopping between the sub-bandgap states. High current densities are obtained by controlling the Zn 1−x Mg x O thickness to ensure that the Schottky barrier is spatially removed from the p−n junction, allowing the full built-in potential to form, in addition to taking advantage of the increased electrical conductivity of the Zn 1−x Mg x O films with increasing thickness. This work therefore shows that the Zn 1−x Mg x O window layer sub-bandgap state density and thickness are critical parameters that can be engineered to minimize the effect of Schottky barriers on device performance. More generally, these findings show how to improve the performance of other photovoltaic system reliant on transparent top contacts, e.g., CZTS and CIGS.

Research paper thumbnail of Improved Exciton Dissociation at Semiconducting Polymer:ZnO Donor:Acceptor Interfaces via Nitrogen Doping of ZnO

Advanced Functional Materials, 2014

Research paper thumbnail of Enhanced Performance in Fluorene-Free Organometal Halide Perovskite Light-Emitting Diodes using Tunable, Low Electron Affinity Oxide Electron Injectors

Advanced Materials, 2015

www.advmat.de www.MaterialsViews.com Figure 3. Effect of the electron injecting material on the c... more www.advmat.de www.MaterialsViews.com Figure 3. Effect of the electron injecting material on the color purity of CH 3 NH 3 PbBr 3 PeLEDs. a) Normalized electroluminescence spectra of ITO/PEDOT:PSS/CH 3 NH 3 PbBr 3 /F8/Ca/Ag driven at 5, 7, and 11 V. b) Normalized time-resolved electroluminescence spectra of ITO/ PEDOT:PSS/F8/Ca/Ag driven at 9 V after 0, 3, 4, and 7 s. c) Normalized PeLED electroluminescence spectrum with Zn 0.56 Mg 0.44 O electron injector driven at 9 and 11 V. d) Normalized electroluminescence spectrum of PeLED with Zn 0.56 Mg 0.44 O electron injector driven at 9 V compared with the normalized photoluminescence spectrum from the bare perovskite and normalized electroluminescence spectrum from an F8BT polymer LED. 5 wileyonlinelibrary.com Published online: Figure 4. Demonstration of the potential of fl uorene-free PeLED technology using SAALD Zn 1− x Mg x O by applying SAALD Zn 1− x Mg x O to effi cient PLEDs. Luminous effi ciency versus applied bias of the highest performing a) F8BT PLED and b) aryl-F8:0.5 wt%TFB PLED. Change in operating voltage with Mg content in Zn 1− x Mg x O of c) F8BT and d) aryl-F8:0.5 wt%TFB PLEDs. The average (dark markers) and lowest (light markers) operating voltages measured are shown. These voltages decrease until x > 0.44 in SAALD Zn 1− x Mg x O, when an insulating phase appears. [ 25 ]

Research paper thumbnail of Fabrication of ZnO/Cu2O heterojunctions in atmospheric conditions: Improved interface quality and solar cell performance

Solar Energy Materials and Solar Cells, 2015

a b s t r a c t Zn 1 À x Mg x O/Cu 2 O heterojunctions were successfully fabricated in open-air a... more a b s t r a c t Zn 1 À x Mg x O/Cu 2 O heterojunctions were successfully fabricated in open-air at low temperatures via atmospheric atomic layer deposition of Zn 1 À x Mg x O on thermally oxidized cuprous oxide. Solar cells employing these heterojunctions demonstrated a power conversion efficiency exceeding 2.2% and an open-circuit voltage of 0.65 V. Surface oxidation of Cu 2 O to CuO prior to and during Zn 1 À x Mg x O deposition was identified as the limiting factor to obtaining a high quality heterojunction interface. Optimization of deposition conditions to minimize Cu 2 O surface oxidation led to improved device performance, tripling the open-circuit voltage and doubling the short-circuit current density. These values are the highest reported for a ZnO/Cu 2 O interface formed in air, and highlight atmospheric ALD as a promising technique for inexpensive and scalable fabrication of ZnO/Cu 2 O heterojunctions. (Y. Ievskaya). Please cite this article as: Y. Ievskaya, et al., Fabrication of ZnO/Cu 2 O heterojunctions in atmospheric conditions: Improved interface quality and solar cell performance, Solar Energy Materials and Solar Cells (2014), http://dx.

Research paper thumbnail of Engineering Schottky Contacts in Open-Air Fabricated Heterojunction Solar Cells to Enable High Performance and Ohmic Charge Transport

ACS Applied Materials & Interfaces, 2014

The efficiencies of open-air processed Cu 2 O/Zn 1−x Mg x O heterojunction solar cells are double... more The efficiencies of open-air processed Cu 2 O/Zn 1−x Mg x O heterojunction solar cells are doubled by reducing the effect of the Schottky barrier between Zn 1−x Mg x O and the indium tin oxide (ITO) top contact. By depositing Zn 1−x Mg x O with a long band-tail, charge flows through the Zn 1−x Mg x O/ITO Schottky barrier without rectification by hopping between the sub-bandgap states. High current densities are obtained by controlling the Zn 1−x Mg x O thickness to ensure that the Schottky barrier is spatially removed from the p−n junction, allowing the full built-in potential to form, in addition to taking advantage of the increased electrical conductivity of the Zn 1−x Mg x O films with increasing thickness. This work therefore shows that the Zn 1−x Mg x O window layer sub-bandgap state density and thickness are critical parameters that can be engineered to minimize the effect of Schottky barriers on device performance. More generally, these findings show how to improve the performance of other photovoltaic system reliant on transparent top contacts, e.g., CZTS and CIGS.

Research paper thumbnail of Improved Exciton Dissociation at Semiconducting Polymer:ZnO Donor:Acceptor Interfaces via Nitrogen Doping of ZnO

Advanced Functional Materials, 2014

Research paper thumbnail of Enhanced Performance in Fluorene-Free Organometal Halide Perovskite Light-Emitting Diodes using Tunable, Low Electron Affinity Oxide Electron Injectors

Advanced Materials, 2015

www.advmat.de www.MaterialsViews.com Figure 3. Effect of the electron injecting material on the c... more www.advmat.de www.MaterialsViews.com Figure 3. Effect of the electron injecting material on the color purity of CH 3 NH 3 PbBr 3 PeLEDs. a) Normalized electroluminescence spectra of ITO/PEDOT:PSS/CH 3 NH 3 PbBr 3 /F8/Ca/Ag driven at 5, 7, and 11 V. b) Normalized time-resolved electroluminescence spectra of ITO/ PEDOT:PSS/F8/Ca/Ag driven at 9 V after 0, 3, 4, and 7 s. c) Normalized PeLED electroluminescence spectrum with Zn 0.56 Mg 0.44 O electron injector driven at 9 and 11 V. d) Normalized electroluminescence spectrum of PeLED with Zn 0.56 Mg 0.44 O electron injector driven at 9 V compared with the normalized photoluminescence spectrum from the bare perovskite and normalized electroluminescence spectrum from an F8BT polymer LED. 5 wileyonlinelibrary.com Published online: Figure 4. Demonstration of the potential of fl uorene-free PeLED technology using SAALD Zn 1− x Mg x O by applying SAALD Zn 1− x Mg x O to effi cient PLEDs. Luminous effi ciency versus applied bias of the highest performing a) F8BT PLED and b) aryl-F8:0.5 wt%TFB PLED. Change in operating voltage with Mg content in Zn 1− x Mg x O of c) F8BT and d) aryl-F8:0.5 wt%TFB PLEDs. The average (dark markers) and lowest (light markers) operating voltages measured are shown. These voltages decrease until x > 0.44 in SAALD Zn 1− x Mg x O, when an insulating phase appears. [ 25 ]

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