We utilize CdSe/CdS seeded nanorods as a tunable lumophore for luminescent concentration. Transfer-printed, ultrathin crystalline Si solar cells are embedded directly into the luminescent concentrator, allowing the study of luminescent concentrators with an area over 5000 times the area of the solar cell. By increasing the size of the CdS rod with respect to the luminescent CdSe seed, the reabsorption of propagating photons is dramatically reduced. At long luminescence propagation distances, this reduced reabsorption can overcome the diminished quantum yield inherent to the larger semiconductor structures, which is studied with lifetime spectroscopy. A Monte Carlo ray tracing model is developed to explain the performance of the luminescent concentrator and is then used as a design tool to determine the effect of luminescence trapping on the concentration of light using both CdSe/CdS nanorods and a model organic dye. We design an efficient luminescence trapping structure that should allow the luminescent concentrator based on CdSe/CdS nanorods to operate in the high-concentration regime.

Luminescent solar concentrators doped with CdSe/CdS quantum dots provide a potentially low-cost and high-performance alternative to costly highband-gap III−V semiconductor materials to serve as a top junction in multijunction photovoltaic devices for efficient utilization of blue photons. In this study, a photonic mirror was coupled with such a luminescent waveguide to form an optical cavity where emitted luminescence was trapped omnidirectionally. By mitigating escape cone and scattering losses, 82% of luminesced photons travel the length of the waveguide, creating a concentration ratio of 30.3 for blue photons in a waveguide with a geometric gain of 61. Further, we study the photon transport inside the luminescent waveguide, showing unimpeded photon collection across the entire length of the waveguide. L uminescent solar concentrators 1−4 (LSCs) have been studied extensively for the last three decades as low-cost alternatives to single-and multijunction photovoltaic (PV) devices. As silicon prices have fallen, it has become increasingly clear that future solar panels will need to have both low cost and high efficiency. One promising strategy for achieving a higher efficiency is to use different parts of the solar spectrum in photovoltaic materials with varying band gaps to minimize losses associated with carrier thermalization and incomplete photon absorption. For these multijunction (MJ) PV devices, there is a strong need for developing low-cost, high-band-gap solar cells for efficient utilization of the high-energy part of the solar spectrum. A luminescent solar concentrator could provide exactly this function, serving as the top junction in a multijunction architecture by converting blue photons into guided luminescence. Due to the concentration effect, only small amounts of high-performing but expensive III−V photovoltaic materials are needed to collect the light from an inexpensive luminescent waveguide. Such a device requires high concentration factors to reduce the cost of the III−V photovoltaic material. High concentration also allows the Stokes shift of the lumophore to be recovered in the operating voltage of the photovoltaic cell.The concentration factor and collection efficiency achieved by LSCs to date have been limited due to parasitic losses such as nonunity quantum yields of the lumophores, imperfect light trapping within the waveguide, and reabsorption and scattering of propagating photons. 5 Previous studies have sought to solve each of these parasitic losses individually, resulting in modest performance improvements. 6−15 Here we achieve a luminescent concentration ratio greater than 30 with an optical efficiency of 82% for blue photons by simultaneously addressing the materials and optical challenges of the LSC system. These concentration ratios are achieved through the combination of designer quantum dot lumophores and photonic mirrors, and microscale silicon photovoltaic cells are used to detect the concentration of light in the waveguide. To the best of our knowledge, this is the highest ...

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 better understanding of the thermodynamics of the photon energy conversion processes re-shaped the landscape of energy conversion schemes and devices. Nanostructured devices and materials that make use of size quantization effects to manipulate photon density of states offer a way to overcome the conventional light absorption limits. Novel optical spectrum splitting and photon recycling schemes reduce the entropy production in the optical energy conversion platforms and boost their efficiencies. Optical design concepts are rapidly expanding into the infrared energy band, offering new approaches to harvest waste heat, reduce the thermal emission losses, and achieve non-contact radiative cooling of solar cells as well as of optical and electronic circuitry. Light-matter interaction enabled by nanophotonics and plasmonics underlie the performance of the third-and fourth-generation energy conversion devices, including up-and downconversion of photon energy, near-field radiative energy transfer, and hot electron generation and harvesting. Finally, the increased market penetration of alternative solar energy conversion technologies amplifies the role of cost-driven and environmental considerations.This roadmap on optical energy conversion provides a snapshot of the state-of-the art in optical energy conversion, remaining challenges, and most promising approaches to address these challenges. Leading experts authored 19 focused short sections of the roadmap, where they share their vision on a specific aspect of this burgeoning research field. The roadmap opens up with a tutorial section, which introduces major concepts and terminology. It is our hope that the roadmap will serve as an important resource for the scientific community, new generations of researchers, funding agencies, industry experts and investors.

Escape cone loss is one of the primary limiting factors for efficient photon collection in large-area luminescent solar concentrators (LSCs). The Stokes shift of the luminophore, however, opens up an opportunity to recycle the escaped luminescence at the LSC front surface by utilizing a photonic band-stop filter that reflects photons in the luminophore’s emission range while transmitting those in its absorption range. In this study, we examine the functional attributes of such photonic filter designs, ones realized here in the form of a distributed Bragg reflector (DBR) fabricated by spin-coating alternating layers of SiO2 and SnO2 nanoparticle suspensions onto a supportive glass substrate. The central wavelength and the width of the photonic stopband were programmatically tuned by changing the layer thickness and the refractive index contrast between the two dielectric materials. We explore the design sensitivities for a DBR with an optimized stopband frequency that can effectively act as a top angle-restricting optical element for a microcell-based LSC device, affording further capacities to boost the current output of a coupled photovoltaic cell. Detailed studies of the optical interactions between the photonic filter and the LSC using both experimental and computational approaches establish the requirements for optimum photon collection efficiencies.

Traditional concentrating photovoltaic (CPV) systems utilize multijunction cells to minimize thermalization losses, but cannot efficiently capture diffuse sunlight, which contributes to a high levelized cost of energy (LCOE) and limits their use to geographical regions with high direct sunlight insolation. Luminescent solar concentrators (LSCs) harness light generated by luminophores embedded in a light-trapping waveguide to concentrate light onto smaller cells. LSCs can absorb both direct and diffuse sunlight, and thus can operate as flat plate receivers at a fixed tilt and with a conventional module form factor. However, current LSCs experience significant power loss through parasitic luminophore absorption and incomplete light trapping by the optical waveguide. Here we introduce a tandem LSC device architecture that overcomes both of these limitations, consisting of a PLMA polymer layer with embedded CdSe/CdS quantum dot (QD) luminophores and InGaP micro-cells, which serve as a high bandgap absorber on top of a conventional Si photovoltaic. We experimentally synthesize CdSe/CdS QDs with exceptionally high quantum-yield (99%) and ultra-narrowband emission optimally matched to fabricated III-V InGaP microcells. Using a Monte Carlo ray-tracing model, we show the radiative limit power conversion efficiency for a module with these components to be 30.8% diffuse sunlight conditions. These results indicate that a tandem LSC-on-Si architecture could significantly improve upon the efficiency of a conventional Si photovoltaic module with simple and straightforward alterations of the module lamination steps of a Si photovoltaic manufacturing process, with promise for widespread module deployment across diverse geographical regions and energy markets.