BEGIN:VCALENDAR VERSION:2.0 PRODID:-//jEvents 2.0 for Joomla//EN CALSCALE:GREGORIAN METHOD:PUBLISH BEGIN:VEVENT UID:222bb3a7ce934af7a8fae5b9708e6e61 CATEGORIES:Seminar CREATED:20180507T160824 SUMMARY:Todd Deutsch Ph.D. DESCRIPTION:
Monday June 18, 2018
10:00AM , CCB Room 1203
"Recent Advances in Hydrogen Fuel Generation via III-V Multijunction Semiconductor Photo- Electrochemical Water Splitting"
In order to economically generate renewable hydrogen fuel from solar energy using semiconductor-bas ed devices, the U.S. Department of Energy Fuel Cells Technology Office has established technical targets of over 20% solar-to-hydrogen (STH) efficienc y with several thousand hours of stability under operating conditions [1]. We have modeled attainable efficiencies of tandem absorbers that, for the f irst time, considered the absorption of sunlight by water [2]. We used this modeling to identify top and bottom semiconductor bandgap combinations tha t should be targeted to achieve maximal STH efficiency. We had to employ se veral key solid-state technological advances to achieve STH efficiencies ex ceeding 16% [3]. The first improvement was to increase the device photocurr ent via extending the infrared absorption using a non-lattice-matched 1.2 e V InGaAs junction, created by the inverted metamorphic multijunction techni que developed by NREL’s III-V photovoltaics group. The second modification was to add a thin n-GaInP2 layer to p-GaInP2 to generate a "buried junction ", which increased the open-circuit voltage (and derived photocurrent onset ) of the device by several hundred mV and enabled 14% STH efficiency. Finally, we increased the top junction photon conversion efficiency by addi ng an AlInP "window layer", which is commonly used in solid-state PV device s to reduce surface recombination. Through the use of a collimating tube, w e measured our devices outdoors under direct solar illumination and verifie d over 16% STH conversion efficiency. I will also briefly introduce pitfall s of common experimental procedures that can influence the accuracy of measured STH efficiencies, which can be exaggerated for mulitjunction abso rbers.
The largest loss in our current system is reflection at the se miconductor/electrolyte interface, so I will address the photon management strategies we use to achieve greater parity between measured efficiency and the theoretical limit. Capturing a significant portion of the ~25% of phot ons lost to reflection at this interface should allow the realization of de vices that exceed 20% STH efficiency.
X-ALT-DESC;FMTTYPE=text/html:Monday June 18, 2018
10:00AM, CCB Room 1203
"Recent Advances in Hydrogen Fuel Generation via III-V Multij unction Semiconductor Photo-Electrochemical Water Splitting"
In order to economically generate renewable hydrogen fuel from solar en ergy using semiconductor-based devices, the U.S. Department of Energy Fuel Cells Technology Office has established technical targets of over 20% solar -to-hydrogen (STH) efficiency with several thousand hours of stability unde r operating conditions [1]. We have modeled attainable efficiencies of tand em absorbers that, for the first time, considered the absorption of sunligh t by water [2]. We used this modeling to identify top and bottom semiconduc tor bandgap combinations that should be targeted to achieve maximal STH eff iciency. We had to employ several key solid-state technological advances to achieve STH efficiencies exceeding 16% [3]. The first improvement was to i ncrease the device photocurrent via extending the infrared absorption using a non-lattice-matched 1.2 eV InGaAs junction, created by the inverted meta morphic multijunction technique developed by NREL’s III-V photovoltaics gro up. The second modification was to add a thin n-GaInP2 layer to p-GaInP2 to generate a "buried junction", which increased the open-circuit voltage (an d derived photocurrent onset) of the device by several hundred mV and enabled 14% STH efficiency. Finally, we increased the top junction photon c onversion efficiency by adding an AlInP "window layer", which is commonly u sed in solid-state PV devices to reduce surface recombination. Through the use of a collimating tube, we measured our devices outdoors under direct so lar illumination and verified over 16% STH conversion efficiency. I will al so briefly introduce pitfalls of common experimental procedures that can in fluence the accuracy of measured STH efficiencies, which can be exagge rated for mulitjunction absorbers.
The largest loss in our current sy stem is reflection at the semiconductor/electrolyte interface, so I will ad dress the photon management strategies we use to achieve greater parity bet ween measured efficiency and the theoretical limit. Capturing a significant portion of the ~25% of photons lost to reflection at this interface should allow the realization of devices that exceed 20% STH efficiency.
DTSTAMP:20240328T170129 DTSTART:20180618T140000 DTEND:20180618T150000 SEQUENCE:0 TRANSP:OPAQUE END:VEVENT END:VCALENDAR