The need for optics technology in the energy and environment fields is growing rapidly at this time. The energy subfields in the optics domain are dominated by solar and solid-state lighting, while optical techniques are used extensively for monitoring the environment. This Focus Issue touches upon these topics by highlighting contributions from authors who presented promising concepts at OSA’s Renewable Energy and the Environment Optics and Photonics Congress held in Eindhoven, the Netherlands in November 2012. This Congress was comprised of four topical meetings: Optical Instrumentation for Energy and Environmental Applications (E2), Optical Nanostructures and Advanced Materials for Photovoltaics (PV), Optics for Solar Energy (SOLAR), and Solid State and Organic Lighting (SOLED). This is a recent Congress started by the OSA, but in its first few years, each meeting is growing in size due to the increasing worldwide importance of optics in the energy and environment fields. In 2013 the Congress will be held in Tucson, Arizona, USA, and in 2014 it will be held in Australia. As one can see this Congress has an international scope due to the global importance of energy and environment topics.

Essentially, the need of optics in the energy and environment can be broken down into three areas:

This issue includes five key contributions on advanced light trapping for solar cells. A wide variety of promising concepts, notably based on complex nanostructures, or wavelength-scale patterns, are proposed and implemented. Gomard et al. [1] introduce an analytical method based on time-domain coupled mode theory, and address design rules for thin film solar cells including 2D photonic crystals. This contribution also illustrates the interest of such advanced devices in terms of angular acceptance. In the case of hydrogenated amorphous silicon solar cells, the absorption efficiency is only decreased from 65.7 to 60%, for angles of incidence up to 55°. The dual grating approach, consisting in patterning independently both sides of a thin film solar cell, increases the degrees of freedom available to the solar cell designer. Indeed, different functions can be combined, such as the reduction of surface reflection and the excitation of quasi-guided modes for enhanced light absorption. Schuster et al. [2] fabricated such structures, and demonstrated their impact on the absorption efficiency in silicon solar cells. As an advanced way to control light trapping, the degree of order or disorder in the photonic pattern has been investigated by Pratesi et al. [3]. These authors demonstrate that integrating a disordered pattern possessing a short-range correlation is a competitive approach with regards to photonic crystals, with a potentially lower fabrication cost.

Using 3D photonic structures, like opals, enables one to combine the potentialities of periodic and disordered structures, as discussed by Wiesendanger et al. [4]. In the case of microcrystalline silicon layers, these authors report that the collected photocurrent can then be increased by up to 16%. In order to facilitate the implementation of such 3D photonic crystals in a solar cell, Schneevoigt et al. [5] propose an approach compatible with low cost and large-scale integration. This automated spray coating process may enable the realization of opal back reflectors separately from the solar cell fabrication. With this new process, opaline films with dimensions up to 10 x 15 cm² could be generated in approximately 70 minutes.

Continuing in the development of novel solar cells, solid-state dye sensitized solar cells are a promising alternative to the photo-electrochemical cells, with potentially better stability and easier fabrication. To build such organic solar cells, Kumar Raavi et al. [6] propose the use of poly(3-hexylthiophene) (P3HT) as the hole transport material. In their spectroscopic study, the authors demonstrate the importance of the thermal annealing, which induces the formation of more crystalline P3HT, thereby increasing the conversion efficiency by 70%. Another key issue is the integration of solar cells in their environment, and their potential to operate with direct or diffuse light.

Optics also plays a major part in the design of high efficiency solar technology, with a number of proposed methods including concentrated photovoltaic systems and luminescent solar concentrators (LSCs). In the former, as discussed by Miñano et al. [7], freeform optics enable the design of concentrators that can achieve the required functionalities, such as the distribution on target and transfer efficiency, using just two optical elements, including a Fresnel lens. While for the latter, Edelenbosch et al. [8] analyze LSCs employing a fiber geometry, with a goal to reach a high level of solar concentration. Continuing with LCSs, Debije et al. [9] discuss on the operation of luminescent solar concentrators, by investigating the inclusion of dichroic dye molecules. In their calculations, they demonstrate the impact of the angular distribution of the emitted photons.

In the field of solid-state lighting, while enhancing the efficacy of LEDs is of prime importance with respect to energy saving, their color temperature should be kept as constant as possible. To reach this last objective, Wenzl et al. [10] propose to control the current driving scheme of phosphor LEDs. Their investigation is based on a combination of thermal and optical simulations. Lastly, Jiang and Lin [11] propose an overview of the field of micro-LED arrays. This is a chip-level integration scheme which tackles the issue of the compatibility of LEDs with AC power grid infrastructure. Moreover, this integration route is a competitive approach which enables the emergence of high-resolution solid-state self-emissive microdisplays.

In conclusion, the contributions in this Focus Issue offer a comprehensive selection of topics covered by the OSA Congress held in Eindhoven, with an emphasis on optics and photonics for solar cells, and LEDs. We would like to thank all the Chairs of this Congress, the Associate Editors, and the OSA staff who made this Focus Issue possible.