Surface plasmon polariton mediated energy transfer from external antennas into organic photovoltaic cells

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2006.Includes bibliographical references (leaves 47-52).Despite significant improvements in the performance of organic photovoltaic devices in recent years, the tradeoff between light absorption and charge separation efficiency remains pervasive; increasing light absorption by increasing the device thickness leads to a decrease in exciton diffusion efficiency and vice versa. In this thesis, I demonstrate organic solar cells with an external light absorbing antenna. Light is absorbed by the external antenna and subsequently transferred into the photovoltaic cell via surface plasmon polariton modes in an interfacial thin silver contact. By decoupling the optical and electrical functions of the cell, this new architecture has the potential to circumvent the tradeoff between light absorption and charge separation efficiency. Non-radiative energy transfer is discussed and modeling finds that efficient energy transfer is mediated by surface plasmon polaritons. Devices with two very different antenna systems are demonstrated experimentally. Antennas with high photoluminescence efficiency are found to exhibit energy transfer efficiencies of approximately 50% while strongly absorbing antennas exhibit increases in photocurrent as high as 700% when compared to devices with non-functioning antennas even with very low photoluminescence efficiencies near 4%. These results suggest that this new device architecture could lead to significantly higher power conversion efficiencies by allowing the independent optimization of the optical and electrical components of organic photovoltaic cells.by Timothy David Heidel.M.Eng

Photosynthesis-inspired device architectures for organic photovoltaics

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2010.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from student submitted PDF version of thesis.Includes bibliographical references (p. 153-166).Organic semiconductor photovoltaics offer a promising route to low-cost, scalable, emissions-free electricity generation. However, achieving higher power conversion efficiencies is critical before these devices can play a larger role in our future energy generation landscape. Organic photovoltaic devices are currently limited by two primary challenges: (1) a trade-off between light absorption and exciton diffusion and (2) low open-circuit voltage due to charge recombination at the donor-acceptor interface. In this work, we demonstrate two new device architectures inspired by photosynthesis that aim to overcome these two challenges. First, we overcome the trade-off between light absorption and exciton diffusion by introducing an external light absorbing antenna layer. We model energy transfer from the antenna to the charge generating layers via surface plasmon polariton modes in the interfacial thin silver contact and via radiation into waveguide modes. We experimentally demonstrate devices with both single layer antennas and strongly absorbing resonant cavity antennas. We measure energy transfer efficiency from the antenna layer to the PV active layers as high as 51±10%. We discuss structural design criteria and describe ideal antenna material characteristics. Second, we reduce charge transfer state recombination in organic photovoltaics by inserting a thin interfacial layer at the donor-acceptor interface. The thin interfacial layer creates a cascade energy structure that destabilizes the Coulombically bound charge transfer state formed immediately following exciton dissociation. We nd the optimal interfacial layer thickness to be approximately 1.5 nm. In CuPc/C₆₀ devices, under simulated solar illumination the short-circuit current increased 34%, the open-circuit voltage increased 33%, and the power conversion eciency increased 49%. Thin interfacial layers can also be used to study the physics of exciton separation.by Timothy David Heidel.Ph.D

Tradeoffs between revenue enhancements and emissions reductions with energy storage-coupled photovoltaics

Thesis (S.M. in Technology and Policy)--Massachusetts Institute of Technology, Engineering Systems Division, Technology and Policy Program, 2009.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Includes bibliographical references (p. 111-114).Energy storage has the potential to dramatically change the operation of photovoltaics by allowing for a delay between generation and use. This flexibility has the potential to impact both the revenue from generating electricity using photovoltaics and the associated emissions reductions. This thesis attempts to quantify the impacts of adding energy storage to photovoltaics. The thesis formulates an optimization problem to solve for the optimal use of photovoltaics with energy storage from 2000 to 2005 in New England. The optimization is first solved using perfect information about historical solar generation, energy prices, and marginal emissions rates. Then, the model is solved using forecasted energy prices and emissions rates. The analysis finds that adding energy storage to photovoltaics can increase annual revenues by over 30%. With energy storage capacity and power equal to solar capacity, annual revenues were found to increase between 19.3% and 31.1% with an energy storage efficiency of 100%. Unfortuneately, the potential revenue increases were found to fall to between 9.1% and 21.3% with 80% efficient storage and between 3% and 14.5% with 60% efficient storage. However, when owners utilize energy storage to maximize revenue, the changes in avoided emissions with energy storage are found to be negligible. Alternatively, it is possible to achieve significant increases in the emissions offset by photovoltaics with energy storage. However, when energy storage is utilized to maximize emissions reductions, revenue decreases.(cont.) This tradeoff between the economic and environmental benefits that can be achieved when energy storage is added to photovoltaics means it is unlikely to be possible, without policy, to simultaneously achieve large increases in both revenue and avoided emissions. Policy mechanisms could be used to enable energy storage to enhance both the revenue from photovoltaics and avoided emissions.by Timothy David Heidel.S.M.in Technology and Polic

Gridlock in 2030?

A few years ago, former Secretary of Energy Bill Richardson characterized the U.S. electric grid, the system of physical and human systems linking generators to loads, as “third-world.” 1 More recently, others have claimed that smart grid technologies promise to “spur the kind of transformation the Internet has already brought to the way we live, work, play and learn.” [superscript 2

Avian Influenza Pre-Pandemic Procurement: Recommendations for the US Federal Government

Many experts fear that an influenza pandemic will occur in the near future. There is currently much debate about how the US should best prepare. Previous US responses give only minimal guidance as the last major influenza pandemic occurred nearly a century ago—before flu viruses had ever been isolated

Lack of interferon response in animals to naked siRNAs

RNA interference (RNAi) is rapidly becoming the method of choice for the elucidation of gene function and the identification of drug targets. As with other oligonucleotide-based strategies, RNAi is envisioned to ultimately be useful as a human therapeutic. Unlike previous nucleic acid therapeutics, small interfering RNAs have the potential to elicit immune responses via interactions with Toll-like receptor 3 and trigger interferon responses like long, double-stranded RNA and its analogs, such as poly(I:C). Recently, the safety of siRNAs has been questioned because they have been shown to trigger an interferon response in cultured cells. We show here that it is possible to administer naked, synthetic siRNAs to mice and downregulate an endogenous or exogenous target without inducing an interferon response

Impact of Spacecraft Shielding on Direct Ionization Soft Error Rates for Sub-130 nm Technologies

We use ray tracing software to model various levels of spacecraft shielding complexity and energy deposition pulse height analysis to study how it affects the direct ionization soft error rate of microelectronic components in space. The analysis incorporates the galactic cosmic ray background, trapped proton, and solar heavy ion environments as well as the October 1989 and July 2000 solar particle events

Recent Single Event Effects Compendium of Candidate Electronics for NASA Space Systems

We present the results of single event effects (SEE) testing and analysis investigating the effects of radiation on electronics. This paper is a summary of test results