Turning water into a protonic diode and solar cell via doping and dye sensitization
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Schulte, Leanna↗
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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
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Thin-Film Organic-Based Solar Cells for Space Power
Recent advances in dye-sensitized and organic polymer solar cells have lead NASA to investigate the potential of these devices for space power generation. Dye-sensitaized solar cells were exposed to simulated low-earth orbit conditions and their performance evaluated. All cells were characterized under simulated air mass zero (AM0) illumination. Complete cells were exposed to pressures less than 1 x 10 (exp -7)torr for over a month, with no sign of sealant failure or electrolyte leakage. Cells from Solaronix SA were rapid thermal cycled under simulated low-earth orbit conditions. The cells were cycled 100 times from -80 C to 80 C, which is equivalent to 6 days in orbit. The best cell had a 4.6% loss in efficiency as a result of the thermal cycling. In a separate project, novel -Bridge-Donor-Bridge-Acceptor- (-BDBA-) type conjugated block copolymer systems have been synthesized and characterized by photoluminescence (PL). In comparison to pristine donor or acceptor, the PL emissions of final -B-D-B-A- block copolymer films were quenched over 99%. Effective and efficient photo induced electron transfer and charge separation occurs due to the interfaces of micro phase separated donor and acceptor blocks. The system is very promising for a variety high efficiency light harvesting applications. Under an SBIR contract, fullerene-doped polymer-based photovoltaic devices were fabricated and characterized. The best devices showed overall power efficiencies of approximately 0.14% under white light. Devices fabricated from 2% solids content solutions in chlorobenzene gave the best results. Presently, device lifetimes are too short to be practical for space applications.
Bailey, Sheila G.↗
Low-spin cobalt(ii) redox shuttle by isocyanide coordination
Coordination of the strong-field ligand 2,6-dimethylphenyl isocyanide (DMP-CN) to the Co(PY5Me 2 ) framework, where PY5Me 2 represents the pentadentate ligand 2,6-bis(1,1-bis(2-pyridyl)ethyl)pyridine, has resulted in a new low-spin Co(II) complex with a relatively low reorganization energy and fast electron-transfer kinetics compared to the prototypical cobalt tris-bipyridine redox shuttle, [Co(bpy) 3 ] 3+/2+ , where bpy represents 2,2'-bipyridine. Despite nearly 160 mV reduced regeneration driving force, the [Co(PY5Me 2 )(DMP-CN)]3+/2+ redox shuttle displayed an increased regeneration efficiency relative to [Co(bpy)3] 3+/2+ , however recombination losses hinder the performance as evidenced by a reduced recombination resistance. Finally, future directions point to low-spin Co(II) redox shuttles with more negative redox potentials to be paired with a dye or dye mixture that absorbs into the near infrared region.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Electronic and Vibrational Coherence in Heterogeneous Electron Transfer (Final Report)
Interfacial electron transfer reactions constitute key physical phenomena central to a variety of energy related transport and conversion processes such as catalysis, photocatalysis, photovoltaics, energy storage, molecular electronics, etc. Heterogeneous material systems like organic/inorganic interfaces are of particular interest because they provide great potential to tailor properties according to application specific requirements. While electron transfer dynamics has been studied intensively in heterogeneous systems many questions remain unanswered. The significance of electronic-vibrational coupling and coherence is one aspect that has yet to be fully explored. The objective of this project is to develop and implement new ultrafast spectroscopic techniques based on pump four-wave mixing spectroscopy (pump-FWM) for studying the dynamics of vibrational coupling and coherence in heterogeneous electron transfer (HET) at molecule/semiconductor interfaces. The implementation of the spectroscopic setup allows to explore different four-wave mixing techniques and thus to identify a suitable approach to study the significance of vibrational as well as electronic coherence in HET.
14 SOLAR ENERGY↗
Device Performance of Emerging Photovoltaic Materials (Version 1)
Abstract Emerging photovoltaics (PVs) focus on a variety of applications complementing large scale electricity generation. Organic, dye‐sensitized, and some perovskite solar cells are considered in building integration, greenhouses, wearable, and indoor applications, thereby motivating research on flexible, transparent, semitransparent, and multi‐junction PVs. Nevertheless, it can be very time consuming to find or develop an up‐to‐date overview of the state‐of‐the‐art performance for these systems and applications. Two important resources for recording research cells efficiencies are the National Renewable Energy Laboratory chart and the efficiency tables compiled biannually by Martin Green and colleagues. Both publications provide an effective coverage over the established technologies, bridging research and industry. An alternative approach is proposed here summarizing the best reports in the diverse research subjects for emerging PVs. Best performance parameters are provided as a function of the photovoltaic bandgap energy for each technology and application, and are put into perspective using, e.g., the Shockley–Queisser limit. In all cases, the reported data correspond to published and/or properly described certified results, with enough details provided for prospective data reproduction. Additionally, the stability test energy yield is included as an analysis parameter among state‐of‐the‐art emerging PVs.
36 MATERIALS SCIENCE↗
A molecular tandem cell for efficient solar water splitting
Artificial photosynthesis provides a way to store solar energy in chemical bonds. Achieving water splitting without an applied external potential bias provides the key to artificial photosynthetic devices. We describe here a tandem photoelectrochemical cell design that combines a dye-sensitized photoelectrosynthesis cell (DSPEC) and an organic solar cell (OSC) in a photoanode for water oxidation. When combined with a Pt electrode for H 2 evolution, the electrode becomes part of a combined electrochemical cell for water splitting, 2H 2 O → O 2 + 2H 2 , by increasing the voltage of the photoanode sufficiently to drive bias-free reduction of H + to H 2 . The combined electrode gave a 1.5% solar conversion efficiency for water splitting with no external applied bias, providing a mimic for the tandem cell configuration of PSII in natural photosynthesis. The electrode provided sustained water splitting in the molecular photoelectrode with sustained photocurrent densities of 1.24 mA/cm 2 for 1 h under 1-sun illumination with no applied bias.
14 SOLAR ENERGY↗
Understanding and controlling the fundamental photochemistry of protonic solar energy conversion (Final Scientific/Technical Report)
The selectivity and activity of most fuel-forming reactions are tunable by the concentration of electrons, holes, protons, and/or hydroxides. That is one reason why traditional solar energy conversion processes are used to drive these reactions, where light directly increases the concentration of electrons and holes. We, instead, took a different approach, using light to increase the concentration of protons and/or hydroxides. For this, we leveraged photophysical and solid-state physics theories, techniques, and design strategies previously developed for the study of traditional solar energy conversion processes. We designed and fabricated several materials platforms based on molecular photoacid and photobase dyes coupled with ion-exchange polymer membranes and assessed their fundamental photoelectrochemistry. We demonstrated control over built-in electric potentials, photovoltages, proton-transfer kinetics, and efficiency limits to our approach. Understanding the basic science of these dye-sensitized protonic membranes and their photochemical mechanisms is of use to the DOE-relevant processes of solar photochemical fuel formation, solar photodialytic desalination, and solar cells. Moreover, functional materials that we developed from this project may be of use to several broad-reaching fields and may provide the foundation for a completely new, inexpensive, and robust solar energy conversion technology.
14 SOLAR ENERGY↗
Effects of Anionic Polymer Modification of Dye‐Sensitized Niobate Photocatalysts on Solar‐Driven Z‐Scheme Overall Water Splitting
Pt‐intercalated calcium niobate nanosheets (Pt/HCa 2 Nb 3 O 10 ) sensitized by a Ru(II) complex dye are good photocatalysts for producing H 2 from aqueous solutions containing I − as a reversible electron donor. These materials are applicable to Z‐scheme overall water splitting in combination with a WO 3 ‐based O 2 ‐evolving photocatalyst under simulated sunlight. In this work, the effects of anionic polymer modification of the dye‐sensitized nanosheets are examined by adsorbing sodium poly(styrenesulfonate) (PSS), sodium polyacrylate, sodium polymethacrylate (PMA), or sodium poly(4‐styrenesulfonic‐ co ‐maleic acid) onto the dye‐sensitized nanosheet surface. For half‐cell H 2 ‐evolution reaction in the presence of NaI, all of the polymers have a positive impact on the activity under visible light at lower light intensity, whereas only PMA is effective under high light‐intensity condition. For Z‐scheme overall water splitting with PtO x /H‐Cs‐WO 3 , PSS and PMA give almost the same solar‐to‐hydrogen energy conversion efficiencies (0.12% ± 0.01%) under optimized conditions. However, PMA operates better than PSS at relatively low and high NaI concentrations, which are in general disadvantageous for the H 2 ‐ and O 2 ‐evolving components of the Z‐scheme, respectively.
Energy & Fuels↗
Oligomeric Ruthenium Polypyridyl Dye for Improved Stability of Aqueous Photoelectrochemical Cells
Water-splitting dye-sensitized photoelectrochemical cells rely on molecular sensitizers to harvest light energy and drive the catalytic reactions necessary to generate hydrogen and oxygen from water. The desorption of sensitizer molecules from the semiconductor–aqueous electrolyte interface is a significant barrier to the practical implementation of these cells. To address this problem, we synthesized an oligomeric ruthenium dye ([RuP] n ) that has dramatically improved stability as a photosensitizer for TiO 2 electrodes over the pH range of interest (4–7.8) for DSPECs. Additionally, the efficiency of photoelectrochemical charge separation is known to depend on the rate of cross-surface hole diffusion between dye molecules. The oligomeric dye ([RuP] n ) shows an order of magnitude faster cross-surface hole diffusion than the commonly used monomeric [Ru(bpy) 2 (4,4-PO 3 H 2 ) 2 bpy] 2+ (RuP) sensitizer. Finally, the enhanced stability of the polymeric dye also enables the use of intensity-modulated photovoltage spectroscopy to measure the recombination rate of photogenerated electrons and holes as a function of electrolyte pH.
14 SOLAR ENERGY↗
Status report on emerging photovoltaics
This report provides a snapshot of emerging photovoltaic (PV) technologies. It consists of concise contributions from experts in a wide range of fields including silicon, thin film, III-V, perovskite, organic, and dye-sensitized PVs. Strategies for exceeding the detailed balance limit and for light managing are presented, followed by a section detailing key applications and commercialization pathways. A section on sustainability then discusses the need for minimization of the environmental footprint in PV manufacturing and recycling. The report concludes with a perspective based on broad survey questions presented to the contributing authors regarding the needs and future evolution of PV.
14 SOLAR ENERGY↗