Low-power upconversion via sensitized triplet–triplet annihilation (TTA-UC) is a useful and versatile process that allows for the conversion of optical radiation into photons of higher energy. While this effect had been known to occur in solution for some 50 years, it was only very recently realized for the first time in polymers. The possibility to realize the TTA-UC process in solid materials is important for a variety of applications that range from the optimization of photovoltaic devices to bioimaging. This article provides a brief introduction to the field, summarizes the underlying photophysical aspects, reviews the design concepts for TTA-UC in polymers, and summarizes the recent advances in the development of such materials.

Low-power photon upconversion through triplet–triplet annihilation in polymers

Spectral beam splitting is a promising method to achieve high efficiency solar energy conversion. Its potential applications include multi-junction PV receivers, hybrid collectors and even biomass production. Although spectral splitting receivers can achieve high theoretical conversion efficiencies, they have not yet evolved to the commercial level. In this paper, we provide a review on the recently published research in this field and discuss the drawbacks associated with practical applications. Suggestions are made which we believe will lead to improvements in optical efficiency (including geometrical limitations) and the fabrication costs of spectrally splitting solar receivers.

Spectral beam splitting for efficient conversion of solar energy - A review

Combined solar photovoltaic-thermal systems (PVT) facilitate conversion of solar radiations into electricity and heat simultaneously. A significant amount of work has been carried out on these systems since 1970. Different PVT systems have been invented in the last thirty years. Several theoretical, mathematical, numerical and experimental models are introduced by many investigators across the world. The present article gives a broad classification and review of published research work on these systems. The article mostly covers the experimental work carried out on the different types of PVT systems in the last decade. The latest technology of liquid spectrum filters for PVT systems are also explored in depth.

Photovoltaic -Thermal systems (PVT): Technology review and future trends

Solar thermoelectric generators (STEGs) are solid state heat engines that generate electricity from concentrated sunlight. In this paper, we develop a novel detailed balance model for STEGs and apply this model to both state-of-the-art and idealized materials. This model uses thermoelectric compatibility theory to provide analytic solutions to device efficiency in idealized materials with temperature-dependent properties. The results of this modeling allow us to predict maximum theoretical STEG efficiencies and suggest general design rules for STEGs. With today's materials, a STEG with an incident flux of 100 kW m−2 and a hot side temperature of 1000 °C could achieve 15.9% generator efficiency, making STEGs competitive with concentrated solar power plants. Future developments will depend on materials that can provide higher operating temperatures or higher material efficiency. For example, a STEG with zT = 2 at 1500 °C would have an efficiency of 30.6%.

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Concentrated solar thermoelectric generators

Lanthanide nanomaterials with photon management characteristics for photovoltaic application

We review several examples of how spectrally-selective photonic structures may be used to improve solar cell systems. Firstly, we introduce different spectrally-selective structures that are based on interference effects. Examples shown include Rugate filter, edge filter and 3D photonic crystals such as artificial opals. In the second part, we discuss several examples of photovoltaic (PV) concepts that utilize spectral selectivity such as fluorescence collectors, upconversion systems, spectrum splitting concepts and the intermediate reflector concept. The potential of spectrally selective filters in the context of solar cells is discussed.

Bernhard Groß

Papers

Spectrally-Selective Photonic Structures for PV Applications