September 30, 2010 — Beaverton, Ore. — Voxtel has demonstrated solar cell devices with the first measured signals from signal amplification due to multiple exciton generation (MEG) in quantum dot structures. This is the first practical verification of the MEG approach for improving the efficiency of solar cells, a ‘third-generation’ solar energy technique. The approach offers the potential for highly efficient, inexpensive photovoltaics that could be printed directly onto surfaces. This groundbreaking finding was
published in the prestigious journal Science by a partnership between researchers at Voxtel Inc. and the University of Wyoming. Voxtel is headquartered in Beaverton, Oregon, and Voxtel’s photovoltaic research team is based in Eugene, Oregon.

Voxtel’s approach promises to overcome the Shockley–Queisser limit, the well-known performance ceiling of about 34% efficiency for conventional ‘first-generation’ silicon cells. To overcome this limit, Voxtel developed an approach using quantum dots — semiconductor materials about one-billionth of a meter in diameter. The response of these custom-made materials can be tuned to match the sun’s light — including the infrared portion of the spectrum that silicon cells can not harness.

The engineered use of such quantum dots offers a maximum of about 66% efficiency, but in Voxtel’s MEG approach, the fundamental efficiency limit is raised to approximately 75%. For most photovoltaic technologies, a photon of solar energy can produce only one excited electron in the solar cell, but the MEG design allows multiple excited electrons to be produced and collected when a single photon is absorbed. This effectively multiplies the electrical current that can be produced from the absorption of energy from the sun. Although previous experiments showed that MEG was possible, today’s Science report demonstrated the process in an actual photovoltaic device, using Voxtel’s quantum dots to double the collection of electrons from high-energy photons.

Says George Williams, Voxtel’s president and founder, “Harnessing solar energy using MEG has profound implications for the next generation of solar cells. Today, a typical domestic rooftop installation can power at most a dozen light bulbs, but the potential efficiency of quantum dot solar cells would make solar power a much more practical alternative to fossil fuels.”

The quantum dot approach also has significant benefits in terms of cost. Says Mr. Williams, “Quantum dot solar cells can be fabricated directly from chemicals, and the quantum dot inks can be directly deposited on flexible substrates using roll-to-roll printing techniques, including ink jet printing. This is a major departure from conventional silicon solar cell manufacturing, which relies on costly infrastructure and intensive processing, and also generates a considerable amount of waste.” Both efficiency and cost are crucial in the pursuit of practical photovoltaic systems; for example, a solar cell that is only 15% efficient would have to be supplied at no cost in order to be financially practical when installed.

Regarding the Science report of the first demonstration of MEG in a working device, Mr. Williams says, “in the laboratory, we and others have see evidence of two, three, and more excitons using laboratory equipment, and this data has shown that, in order to extract the extra signal generated in the quantum dots, we needed to extract the carriers from the quantum dot in less than one picosecond — one millionth of one millionth of a second — or else they would recombine with each other. Voxtel used chemical coatings on the quantum dots to induce an electric dipole, which allowed us to capture the amplified signal before the carriers were annihilated.”

This result is a major step in a years-long effort to advance the technology to where it can be manufactured in commercial devices. “This is an extraordinary achievement, but there is also a lot of work remaining to realize the full benefits of quantum dot solar cells. The maximum efficiency of quantum dot cells has been about 7% so far, and despite the potential benefits of MEG, it will be several years before quantum dot solar cells exceed the efficiency of silicon, and several more years more before we realize the cost benefits of printed solar cells.”

Initial press coverage of this development has been brisk:

Upping the Limit on Solar Cell Efficiency — MIT Technology Review
…Two major hurdles remain before the trick can be used to make ultraefficient solar cells. Parkinson used lead-sulfide quantum dots with a crystalline titanium-dioxide electrode. Researchers need to try other combinations of quantum dots and electrode materials to find ones that can convert more photons into multiple electrons. Parkinson says his new methods for making quantum dot solar cells will help them directly test these other combinations. Researchers also need to increase the total amount of light that the quantum dot solar cells can absorb…

Solar cells get two electrons for the price of one, efficiency bonus — Ars Technica
…The technology demonstrated in this paper is particularly interesting for several reasons. First, it is a true “nanomaterial” application where the size of the semiconductor particles enable truly unique properties by confining the excitons to quantum length scales. During my daily abstract scan, it is all too common to find “nano-” papers that simply involve small particles rather than truly novel properties enabled by the scale of the materials.
The work also concentrated on extracting electrons from the nanoparticles rather than just trying to break efficiency records for electron generation…Finally, the experimental setup for this study is largely consistent with dye sensitized solar cells, which are easy to manufacture compared to silicon technologies…

New technology that captures “exciton” particles could replace today’s solar cells — IO9.com
…This offers a chance for solar cells to trap excitons in a similar way. As long as the cells are coupled with the appropriate electrodes, they too can capture these quasiparticles before they degrade, which means they would save most of the heat and hang onto it as useful energy. It would greatly improve the efficiency of solar cells, all without even having to do anything to the basic photon capture technology.

Work light twice as hard to make cheap solar cells — New Scientist
…Now Bruce Parkinson and Justin Sambur at the University of Wyoming in Laramie, and Thomas Novet of Voxtel in Beaverton, Oregon, have taken the first steps along another route to super-efficient solar cells. Their approach involves harnessing particularly energetic photons – those with more than twice the energy needed to free an electron – and using them to free two electrons rather than one, potentially doubling the current generated…

June 30, 2010 — Beaverton, Ore. — Voxtel announces the immediate availability of its newest product, the YVX-657 time-to-digital converter. This processor has been designed for time-of-flight measurements for applications including time-correlated spectroscopy, flash LADAR, medical imaging, and quantum cryptography.

The FPGA-based processor records the differential time of arrival between a reference time and pulse arriving on any of the 8 CMOS input channels or 64 LVDS channels, with <35 ps of timing jitter. For each channel, up to 65,535 32-bit time stamps can be recorded, at a maximum input event rate of up to 125 million events per second for each channel. The time stamps are stored in on-board memory before download to PC through gigabit Ethernet at a data rate of 100 MB/s.

The product was designed for easy integration with silicon photomultiplier (SiPM) and single-photon-sensitive Geiger-mode avalanche photodiode detectors. The product is available for immediate delivery to OEM system integrators.

Responsibilities
The successful applicant will be responsible for the design, planning, and execution of photodiode manufacturing processes run at foundry partners. This includes photomask layout, process specification, and foundry interface. Other responsibilities include working with foundry partners to develop packaging and hybridization processes, management of photoreceiver circuit development by in-house electrical engineers, and oversight of Voxtel’s in-house device testing personnel. The successful applicant will be responsible for coordinating the design interface between photodiodes and receiver circuitry, and will be expected to assist test engineers in designing experiments and interpreting device characterization data. Lastly, the successful applicant will be expected to participate in business development and program management activities, including authorship of technical proposals and reports, customer interface, and planning and deploying company resources to meet customer goals.

March 15, 2010 — Beaverton, Ore. — Voxtel has announced the release of an avalanche photodiode (APD) receiver with 1-gigahertz bandwidth and a large 200-μm-diameter optical area. The company believes it to be the highest-bandwidth large-area NIR APD receiver, which makes it optimal for a broad range of laser rangefinders and laser designators, and for applications in free-space optical communications, optical instrumentation, and LADAR/LIDAR.

The model RIP1-NJAC APD photoreceiver is the latest entry in Voxtel’s Siletz™ line of single-carrier multiplication avalanche photodiode (SCM-APD) products. The receiver integrates the low-excess-noise SCM-APD with a low-noise transimpedance amplifier (TIA). Voxtel’s Siletz™ SCM-APDs are the lowest-excess-noise NIR–SWIR APDs available (with an equivalent ionization coefficient k_eff < 0.02), and allow for the receiver to operate at high avalanche gain, boosting the optical signal over the amplifier noise level without the degrading effects of avalanche-induced excess noise. The ultra-low excess noise and high gain make the RIP1-NJAC the most sensitive photoreceiver available on the market, offering a maximum responsivity over 50 A/W at 1550 nm, with operating gain up to 50.

A single-stage thermoelectric (TE) cooler is included to eliminate temperature-induced gain variation and allow optimal performance over the range of application environments. The receiver is available with an optional fiber pigtail.

The product is immediately available for sale.

About Voxtel

Voxtel, Inc. of Beaverton, Ore. is a provider of optoelectronic devices using novel semiconductor architectures and engineered nanostructured materials, and a leading developer of sophisticated detectors and electro-optical imaging systems for a wide range of government, industrial, and scientific markets. Voxtel’s product technologies include near-infrared laser radar (LADAR) receivers, radiation-hardened imagers for space applications, highly sensitive avalanche photodiodes for fiber and free-space telecommunications, and nanotechnology-engineered materials. For more information, visit Voxtel’s homepage.

February 15, 2010 — Beaverton, Ore. — Voxtel has announced the release of its latest product line, the Deschutes BSI™ series of back-side-illuminated APDs.

The Deschutes BSI™ APDs are available on ceramic submounts, with a co-mounted temperature sensor. Compared to front-side-illuminated APDs, they offer superior responsivity and lower capacitance. Deschutes BSI™ APDs offer typical responsivity greater than 1.0 A/W at 1550 nm and 0.73 A/W at 1064 nm, and operating gain from 3 to 20. These InGaAs/InAlAs APDs have been custom-designed for low excess noise, with a design exploiting the non-local behavior of impact ionization. The resulting APDs, which are characterized by an equivalent ionization coefficient of k_eff < 0.2, have 40% less excess noise than conventional telecom InGaAs/InP APDs, which makes them ideal for optical communications, laser radar (LADAR) and LIDAR, and laser rangefinding/designating applications. Configured for low capacitance, the parts are well suited for high-bandwidth applications. The Deschutes BSI™ model series VFC-1000 is available in 30-, 75-, and 200-μm-diameter versions; it is available on submounts, in hermetic packages with optional thermoelectric cooling, and packaged into photoreceivers. All packaged versions are available with optional fiber pigtails.

The product is immediately available for sale.

About Voxtel

Voxtel, Inc. of Beaverton, Ore. is a provider of optoelectronic devices using novel semiconductor architectures and engineered nanostructured materials, and a leading developer of sophisticated detectors and electro-optical imaging systems for a wide range of government, industrial, and scientific markets. Voxtel’s product technologies include near-infrared laser radar (LADAR) receivers, radiation-hardened imagers for space applications, highly sensitive avalanche photodiodes for fiber and free-space telecommunications, and nanotechnology-engineered materials. For more information, visit Voxtel’s homepage.

“Voxtel, based in Beaverton, Oregon, has begun trialing a continuous production process, which can manufacture kilogram quantities a week of most quantum dots for less than $10 per gram, according to chief executive George Williams.”

Just as important as Voxtel’s cost leadership is our product quality: Voxtel’s process is not only much more cost-effective than past synthesis methods, but also makes a higher-quality product with less size dispersity. Combined with our ability to provide most of our products using environmentally friendly materials, Voxtel has a clear advantage in quality, price, and ease of use.

May 11, 2009 – Beaverton, Oregon – Voxtel has announced the release of its ‘Siletz’ series of APD receivers, responding to the demand for eye-safe and highly sensitive optical communications, LIDAR, and LADAR in the near infrared (NIR) spectrum. Voxtel’s Siletz APD receiver optical subassembly provides sensitivity 2 to 4 dBm improved over any other APD receiver currently available on the market covering the 950–1700 nm spectral range, and operates at frequencies up to 2.7 GHz.

Voxtel’s Siletz receiver series is based on its patented single carrier multiplication InGaAs APD (SCM-APD). The SCM-APD provides higher gain (M > 50) and lower excess noise (F(M) ~ 2) than conventional APDs. The higher gain and lower avalanche noise of the SCM-APD provides amplification of the NIR optical signal over the amplifier noise floor, providing better than –44 dBm noise equivalent power (NEP) and superior bit error rate (BER) performance over the entire frequency range. The SCM-APDs provide 2x better temperature stability compared to conventional APDs, reducing demands on bias stabilization and temperature compensation.

The REP-1XJ0A model Siletz receiver is packaged in a hermetic TO-8 package with a thermoelectric cooler (TEC). The TEC provides the ability to stabilize the APD temperature, easing the system integration effort. The APD receiver is available with the option for single- and multi-mode fiber tails.

Voxtel’s SCM-APD receiver is a high-performance product not yet available from any other manufacturer.

About Voxtel

Voxtel, Inc. of Beaverton, Ore. is a provider of devices using novel semiconductor architectures and engineered nanostructured materials, and a leading developer of sophisticated detectors and electro-optical imaging systems for a wide range of government, industrial, and scientific markets. Their product technologies include near-infrared laser radar (LADAR) receivers, radiation-hardened imagers for space applications, highly sensitive avalanche photodiodes for fiber and free-space telecommunications, and nanotechnology-engineered materials. For more information, visit Voxtel’s homepage.