Eli Yablonovitch

• University of California, Berkeley

Photovoltaics—a mature technology—is set to play a vital role in achieving a carbon-free energy system. This article examines the pivotal role of optics in advancing photovoltaics. We identify key scientific research areas where the optics community can make significant contributions. We are guided by the central question: How can optics facilitate...

Photovoltaics—a mature technology—is set to play a vital role in achieving a carbon-free energy system. This article examines the pivotal role of optics in advancing photovoltaics. We identify key scientific research areas where the optics community can make significant contributions. We are guided by the central question: How can optics facilitate...

Photovoltaics, a mature technology, is set to play a vital role in achieving a carbon-free energy system. This article examines the pivotal role of optics in advancing photovoltaics. We identify key scientific research areas where the optics community can make significant contributions. We are guided by the central question: How can optics facilita...

It has gradually been recognized that incoming sunlight can be trapped within a high refractive index semiconductor, n~3.5, owing to the narrow 16degree escape cone. The solar light inside a semiconductor is 4n^2 times brighter than incident sunlight. This is called light trapping and has increased the theoretical and practical efficiency of solar...

Coupled-bistable-oscillator machines have recently generated significant interest due to their observed ability to rapidly produce high-quality solutions to nondeterministic-polynomial-time-complete optimization problems. While the dynamics of such systems are often derived in the literature, it has hitherto been unclear why exactly the system dyna...

Inverse design is a powerful tool in wave physics for compact, high-performance devices. To date, applications in photonics have mostly been limited to linear systems and it has rarely been investigated or demonstrated in the nonlinear regime. In addition, the “black box” nature of inverse design techniques has hindered the understanding of optimiz...

Inverse design is a powerful tool in wave-physics and in particular in photonics for compact, high-performance devices. To date, applications have mostly been limited to linear systems and it has rarely been investigated or demonstrated in the nonlinear regime. In addition, the "black box" nature of inverse design techniques has hindered the unders...

We demonstrate the first inverse-designed device for enhancing photon-pair generation rate in silicon photonics with compact footprint. The proposed inverse-design approach can be generalized to other nonlinear photon generation processes.

There has been a recent surge of interest in physics-based solvers for combinatorial optimization problems. We present a dynamical solver for the Ising problem that is comprised of a network of coupled parametric oscillators and show that it implements Lagrange multiplier constrained optimization. We show that the pump depletion effect, which is in...

We evaluate near-field thermophotovoltaic (TPV) energy-conversion systems focusing in particular on their open-circuit voltage (VOC). Unlike previous analyses based largely on numerical simulations with fluctuational electrodynamics, here, we develop an analytic model that captures the physics of near-field TPV systems and can predict their perform...

The III–V InP/InGaAsP/InGaAs material family is important for photonic devices due to its optical emission and absorption in the 1.55 and 1.3 μm telecommunication bands for optical interconnects. However, InGaAsP/InGaAs generally suffer from relatively high surface recombination velocity—compared to Si [Das et al., in 2020 47th IEEE Photovoltaic Sp...

We evaluate near-field thermophotovoltaic (TPV) energy conversion systems focusing in particular on their their open-circuit voltage (Voc). Unlike previous analyses based largely on numerical simulations with fluctuational electrodynamics, here, we develop an analytic model that captures the physics of near-field TPV systems and can predict their p...

The rate of spontaneous emission from an optical emitter can be greatly enhanced using a metallic optical antenna at the penalty of efficiency. In this paper we propose a metal-dielectric antenna that eliminates the tradeoff between spontaneous emission enhancement and radiative efficiency by using nanoscopic dielectric structures at the antenna ti...

The new record efficiency in Thermophotovoltaics relies upon a highly reflective rear mirror. The excellent rear mirror boosts voltage by enhancing the luminescence extraction, and separately also reflects low energy photons, which would otherwise be useless in thermophotovoltaics. The reflected low energy photons reheat the thermal emitter, and re...

Significance All through human civilization, optimization has played a major role, from aerodynamics to airline scheduling, delivery routing, and telecommunications decoding. Optimization is receiving increasing attention, since it is central to today’s artificial intelligence. All of these optimization problems are among the hardest for human or m...

In tunnel field-effect transistors (tFETs), the preferred mechanism for switching occurs by alignment (ON) or misalignment (off) of two energy levels or band edges. Unfortunately, energy levels are never perfectly sharp. When a quantum dot interacts with a wire, its energy is broadened. Its actual spectral shape controls the current/voltage respons...

Optimization is a major part of human effort. While being mathematical, optimization is also built into physics. For example, physics has the principle of Least Action; the principle of Minimum Entropy Generation; and the Variational Principle. Physics also has physical annealing which, of course, preceded computational Simulated Annealing. Physics...

Silicon photonics is a rapidly maturing platform for optical communication and sensing. As systems leveraging silicon photonics have grown in size and complexity, so too has the demand for high performance silicon photonics components. In order to meet these demands, we propose a hierarchical approach to design and optimization of silicon photonics...

Significance Thermophotovoltaic conversion utilizes thermal radiation to generate electricity in a photovoltaic cell. On a solar cell, the addition of a highly reflective rear mirror maximizes the extraction of luminescence, which in turn boosts the voltage. This has enabled the creation of record-breaking solar cells. The rear mirror also reflects...

Efficient high-speed nanoscale optical sources are required for low-power next-generation data communication. Here we propose an integrated antenna-LED on a single-mode optical waveguide. By leveraging inverse design optimization, we achieved a waveguide coupling efficiency of 94% and an antenna efficiency of 64%, while maintaining a high average e...

Defects in conventional semiconductors substantially lower the photoluminescence (PL) quantum yield (QY), a key metric of optoelectronic performance that directly dictates the maximum device efficiency. Two-dimensional (2D) transition metal dichalcogenides (TMDCs), such as monolayer MoS2, often exhibit low PL QY for as-processed samples, which has...

Electrostatic doping boosts emission Although monolayers of transition-metal dichalcogenides such as molybdenum disulfide (MoS 2 ) and tungsten disulfide (WS 2 ) should exhibit strong photoluminescence, in practice, defects in these materials can lead to very low quantum yields (less than 1%). Lien et al. show that as-formed MoS 2 and WS 2 monolaye...

Optical antennas can enhance the modulation bandwidth and output power of nanoscale LEDs. Here we analyze a wavelength division multiplexer that uses high Q optical antennas in parallel to further increase the total optical power.

Classical analog processors are now solving hard Computer Science problems that were thought to require a Quantum Computer. There are now classical machines that solve Ising type optimizations, opening the door toward other NP-hard problems as well.

Inverse electromagnetic design has emerged as a way of efficiently designing active and passive electromagnetic devices. This maturing strategy involves optimizing the shape or topology of a device in order to improve a figure of merit–a process which typically requires that we compute the gradient of a figure of merit which describes device perfor...

Optical antennas can enhance the spontaneous emission rate from nanoemitters by orders of magnitude, enabling the possibility of an ultrafast, efficient, nanoscale LED. Semiconductors would be the preferred material for such a device to allow for direct high-speed modulation. However, efficient nanoscale devices are challenging to implement because...

Electroluminescence—the conversion of electrons to photons in a light-emitting diode (LED)—can be used as a mechanism for refrigeration, provided that the LED has an exceptionally high quantum efficiency. We investigate the practical limits of present optoelectronic technology for cooling applications by optimizing a GaAs/GaInP double heterostructu...

Lead halide materials have seen a recent surge of interest from the photovoltaics community following the observation of surprisingly high photovoltaic performance, with opto-electronic properties similar to GaAs. This begs the question; what is the limit for the efficiency of these materials? It has been known that at 1-sun the efficiency limit of...

The rate of spontaneous emission can be enhanced using either a metallic antenna or a dielectric cavity. Here we adapt elements of both types for a novel metallo-dielectric structure that exhibits ultra-low mode volume, Veff = 4.53 × 10−6 휆3.

We find that under 1-sun the luminescence efficiency of MAPbI3 is limited to ~95% at open-circuit due to Auger recombination. Yet, an oddly high fill-factor compensates this, leading to a nearly ideal power conversion efficiency.

Efficient luminescence extraction enables us to use the photovoltaic band gap as the spectral filter for thermophotovoltaics. Using this concept, we demonstrate a 28.2% conversion efficiency, higher than the previously reported value for the range of the emitter temperature (700oC–1250oC) used.

We propose a broadband and efficient structure for single-mode spontaneous emission coupling of an electrically-injected slot antenna based nanoLED. Using FDTD simulations and inverse design, we achieved 93% waveguide coupling and 50.77% spontaneous emission coupling.

We demonstrate bright electroluminescence in WSe2 monolayers using pulsed injection, without the use of split gates, chemical doping, or heterostructures. Electroluminescence quantum efficiency approaches that of photoluminescence, indicating efficient exciton formation with injected carriers.

We consider a near-field electroluminescent refrigeration device. The device uses a GaAs light emitting diode as the cold side, and a Si photovoltaic cell as the hot side. The two sides are brought in close proximity to each other across a vacuum gap. The cooling is achieved by applying a positive bias on the GaAs light emitting diode. We show that...

Understanding edge effects and quantifying their impact on the carrier properties of two-dimensional (2D) semiconductors is an essential step toward utilizing this material for high performance electronic and optoelectronic devices. WS2 monolayers patterned into disks of varying diameters are used to experimentally explore the influence of edges on...

There are many passive electromagnetic components whose behavior can be controlled by modifying the shape of the device's material boundaries. In this paper, we take advantage of continuous smoothing of material boundaries on a rectangular grid in order to accurately calculate the gradient of a figure of merit with respect to perturbations to the b...

Efficient coupling between integrated optical waveguides and optical fibers is essential to the success of integrated photonics. While many solutions exist, perfectly vertical grating couplers which scatter light out of a waveguide in the direction normal to the waveguide's top surface are an ideal candidate due to their potential to reduce packagi...

We introduce a first principles, end-to-end analysis of opto-electronic communication links which incorporates a thorough model of the receiver circuitry, in addition to the more familiar laser transmitter optimization. In particular, we optimize receiver sensitivity and power by studying their dependence on front-end design as well as follow-on di...

The photovoltaic cell and the LED are really the reciprocal of one another. The slogan: “A great solar cell has to be a great LED” has led to all the new solar cell efficiency records. Very efficient light emitting diodes (LED’s), surprisingly, do actually become cold as they operate, since LED light carries away entropy. This refrigeration require...

A novel double stage high-concentration hybrid solar photovoltaic thermal (PV/T) collector using nonimaging optics and world record thin film single-junction gallium arsenide (GaAs) solar cells has been developed. We present a detailed design and simulation of the system, experimental setup, prototype, system performance, and economic analysis. The...

Thermophotovotaics convert thermal radiation from local heat sources to electricity. A new breakthrough in creating highly efficient thin-film solar cells can potentially enable thermophotovoltaic systems with unprecedented high efficiency. The current 28.8% single-junction solar efficiency record, by Alta Devices, was achieved by recognizing that...

A novel hybrid solar concentrated photovoltaic thermal (PV/T) collector is designed, simulated, and tested. The PV/T system uses a parabolic trough to focus sunlight towards a nonimaging compound parabolic concentrator (CPC) that is formed of single junction Gallium Arsenide (GaAs) solar cells to simultaneously generate electricity and high tempera...

We present a new optical interconnect platform consisting of a multilayer integrated optical circuit board which provides unprecedented communications capacity with minimal signal loss at circuit board scales. The enhancement in spatial communication density could reduce the size of large distributed systems by up to two orders of magnitude (and he...

Many in the microelectronics field view tunneling field-effect transistors (TFETs) as society's best hope for achieving a >10× power reduction for electronic devices; however, despite a decade of considerable worldwide research, experimental TFET results have significantly underperformed simulations and conventional MOSFETs. To explain the discrepa...

Recent progress in the design and realization of optical antennas enclosing fluorescent materials has demonstrated large spontaneous-emission enhancements and, simultaneously, high radiation efficiencies. We discuss here that an important objective of such work is to increase spontaneous-emission rates to such a degree that light-emitting diodes (L...

Over the past few years, the application of the physical principle, i.e., "luminescence extraction," has produced record voltages and efficiencies in photovoltaic cells. Luminescence extraction is the use of optical design, such as a back mirror or textured surfaces, to help internal photons escape out of the front surface of a solar cell. The prin...

For decades, progress in the field of optical (including solar) energy conversion was dominated by advances in the conventional concentrating optics and materials design. In recent years, however, conceptual and technological breakthroughs in the fields of nanophotonics and plasmonics combined with a better understanding of the thermodynamics of th...

One of the major challenges facing the rapidly growing field of two-dimensional (2D) transition metal dichalcogenides (TMDCs) is the development of growth techniques to enable large area synthesis of high-quality materials. Chemical vapor deposition (CVD) is one of the leading techniques for the synthesis of TMDCs, however, the quality of the mater...

One of the major challenges facing the rapidly growing field of two-dimensional (2D) transition metal dichalcogenides (TMDCs) is the development of growth techniques to enable large-area synthesis of high-quality materials. Chemical vapor deposition (CVD) is one of the leading techniques for the synthesis of TMDCs; however, the quality of the mater...

The greatest source of loss in conventional single-junction photovoltaic cells is their inefficient utilization of the energy contained in the full spectrum of sunlight. To overcome this deficiency, we propose a multijunction system that laterally splits the solar spectrum onto a planar array of single-junction cells with different band gaps. As a...

In any solar cell that begins to approach the theoretical limits of performance, an intense internal luminescence photon gas must be present (see the figure) ( 1 ). On page [1430][1] of this is sue, Pazos-Outon et al. ( 2 ) provide evidence for such an internal photon gas in lead halide photovoltaic cells. These materials thus have properties simil...

We present a new photonic interconnect platform consisting of silicon photonic optical interposers and a multilayer optical circuit board which provides unprecedented communications capacity at circuit board scales.

We show that photon recycling utilizing the spectral selectivity of the photovoltaic band edge enables 48% thermophotovoltaic heat-to-electricity conversion efficiency at 1200oC with In0.47Ga0.53As cells, and present experimental methods to demonstrate this concept.

Hybrid organic-inorganic halide perovskite based semiconductor materials are attractive for use in a wide range of optoelectronic devices because they combine the advantages of suitable optoelectronic attributes and simultaneously low-cost solution processability. Here we present a two-step low pressure vapor-assisted solution process to grow high...

Two-dimensional (2D) transition metal dichalcogenides have emerged as a promising material system for optoelectronic applications, but their primary figure of merit, the room-temperature photoluminescence quantum yield (QY), is extremely low. The prototypical 2D material molybdenum disulfide (MoS2) is reported to have a maximum QY of 0.6%, which in...

Slides from the discussion of the OSA Technical group 'Optics for Energy' at CLEO 2014

We experimentally demonstrate 204x spontaneous emission rate enhancement from an electrically-injected nanoLED coupled to a cavity-backed optical slot antenna. This places the spontaneous emission rate on par with the stimulated emission rate.

Phototransistors built this way offer a low-capacitance, high-speed integrated solution for receivers, with decoupled absorption and amplification regions. Having the first stage of gain directly integrated with the absorption region of the transistor means that the sensitivity of the device can be greatly increased, thanks to it's low capacitance...

Tunneling field-effect transistors (TFETs) have been investigated as a low-voltage replacement for the conventional field-effect transistor with a turn-on response steeper than 60 mV/dec. However, to date no device has achieved a steep turn-on at low voltage with an on-off ratio of 10 6 or greater. Among the main issues is the finite density of sta...

The spontaneous emission rate of light emitters has been shown to have strong dependence on their local electromagnetic environment 1 . Optical antennas exploit this effect and can be used to greatly increase the spontaneous emission rate of a coupled light emitter. There have been several demonstrations of this effect with promising results using...

Increasing the sensitivity of optical receivers is of paramount importance to reduce the energy cost of optical communications [1]. For this, the signal to noise ratio (SNR) of the front-end detector and amplifier must be improved. A very efficient way of achieving this is to introduce gain right at the detection level. Avalanche photo detectors (A...

We experimentally demonstrate 200x spontaneous emission rate enhancement from an electrically-injected nanoLED coupled to a cavity-backed optical slot antenna. Such a nanoLED device could be used as a fast, efficient, and nanoscale light source for on-chip optical interconnects.

Interconnects accounts for a significant portion of energy consumption in integrated circuits. Optical interconnects, now widely used to link electronic systems such as servers and top of rack switches in data centers, can potentially reduce the energy consumption of electrical interconnects. However, current state-of-the-art optical links consumes...

Nanoelectromechanical (NEM) switches have emerged as a promising competing technology to the conventional metal-oxide semiconductor (MOS) transistors. NEM switches exhibit abrupt switching behavior with large on-off current ratios, near-zero off-state leakage currents and sub-threshold slopes below the 60 mV/decade theoretical limit of conventional...

An analytical model is developed to assess the switching energy of a nanomechanical switch. Alternative switch designs are proposed to leverage spring-restoring force to counterbalance surface adhesion force, reducing the depth of the potential energy well created by contact adhesion and thereby overcoming the surface adhesion energy limit.