The emerging field of plasmonics has yielded methods for guiding and localizing light at the nanoscale, well below the scale of the wavelength of light in free space. Now plasmonics researchers are turning their attention to photovoltaics, where design approaches based on plasmonics can be used to improve absorption in photovoltaic devices, permitting a considerable reduction in the physical thickness of solar photovoltaic absorber layers, and yielding new options for solar-cell design. In this review, we survey recent advances at the intersection of plasmonics and photovoltaics and offer an outlook on the future of solar cells based on these principles.

Plasmonics for improved photovoltaic devices

The term photonic crystals appears because of the analogy between electron waves in crystals and the light waves in artificial periodic dielectric structures. During the recent years the investigation of one-, two-and three-dimensional periodic structures has attracted a widespread attention of the world optics community because of great potentiality of such structures in advanced applied optical fields. The interest in periodic structures has been stimulated by the fast development of semiconductor technology that now allows the fabrication of artificial structures, whose period is comparable with the wavelength of light in the visible and infrared ranges.

http://ieeexplore.ieee.org/iel5/6354/16969/00781867.pdf

Photonic crystals

Graham H. Carey,† Ahmed L. Abdelhady,‡ Zhijun Ning, Susanna M. Thon, Osman M. Bakr,‡ and Edward H. Sargent*,† †Department of Electrical and Computer Engineering, University of Toronto, 10 King’s College Road, Toronto, Ontario M5S 3G4, Canada ‡Division of Physical Sciences and Engineering, Solar & Photovoltaics Engineering Center, King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Saudi Arabia School of Physical Science and Technology, ShanghaiTech University, 100 Haike Road, Shanghai 201210, China Department of Electrical and Computer Engineering, Johns Hopkins University, 3400 North Charles Street, Baltimore, Maryland 21218, United States

Colloidal Quantum Dot Solar Cells.

This review article examines the current state of understanding in how metal halide perovskite solar cells can degrade when exposed to moisture, oxygen, heat, light, mechanical stress, and reverse bias. It also highlights strategies for improving stability, such as tuning the composition of the perovskite, introducing hydrophobic coatings, replacing metal electrodes with carbon or transparent conducting oxides, and packaging. The article concludes with recommendations on how accelerated testing should be performed to rapidly develop solar cells that are both extraordinarily efficient and stable.

Understanding Degradation Mechanisms and Improving Stability of Perovskite Photovoltaics.

Efficient light detection is central to modern science and technology. Current photodetectors mainly use photodiodes based on crystalline inorganic elemental semiconductors, such as silicon, or compounds such as III–V semiconductors. Photodetectors made of solution-processed semiconductors — which include organic materials, metal-halide perovskites and quantum dots — have recently emerged as candidates for next-generation light sensing. They combine ease of processing, tailorable optoelectronic properties, facile integration with complementary metal–oxide–semiconductors, compatibility with flexible substrates and good performance. Here, we review the recent advances and the open challenges in the field of solution-processed photodetectors, examining the topic from both the materials and the device perspective and highlighting the potential of the synergistic combination of materials and device engineering. We explore hybrid phototransistors and their potential to overcome trade-offs in noise, gain and speed, as well as the rapid advances in metal-halide perovskite photodiodes and their recent application in narrowband filterless photodetection. Conventional photodetectors, made of crystalline inorganic semiconductors, are limited in terms of the compactness and sensitivity they can reach. Photodetectors based on solution-processed semiconductors combine ease of processing, tailorable optoelectronic properties and good performance, and thus hold potential for next-generation light sensing.

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Solution-processed semiconductors for next-generation photodetectors

Effective light management is imperative in maintaining high efficiencies as photovoltaic devices become thinner. We demonstrate a simple and effective method of enhancing light trapping in solar cells with thin absorber layers by tuning localized surface plasmons in arrays of Ag nanoparticles. By redshifting the surface plasmon resonances by up to 200 nm, through the modification of the local dielectric environment of the particles, we can increase the optical absorption in an underlying Si wafer fivefold at a wavelength of 1100 nm and enhance the external quantum efficiency of thin Si solar cells by a factor of 2.3 at this wavelength where transmission losses are prevalent. Additionally, by locating the nanoparticles on the rear of the solar cells, we can avoid absorption losses below the resonance wavelength due to interference effects, while still allowing long wavelength light to be coupled into the cell. Results from numerical simulations support the experimental findings and show that the fraction ...

/pdf/tunable-light-trapping-for-solar-cells-using-localized-20h716y9nt.pdf

Tunable light trapping for solar cells using localized surface plasmons

The authors acknowledge the A. R. C. and NOW for
research conducted at the FOM as a part of the Joint Solar
Programme for financial support.

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Designing periodic arrays of metal nanoparticles for light-trapping applications in solar cells

We show experimentally that there is asymmetry in photocurrent enhancement by Ag nanoparticle arrays located on the front or on the rear of solar cells. The scattering cross-section calculated for front- and rear-located nanoparticles can differ by up to a factor of 3.7, but the coupling efficiency remains the same. We attribute this to differences in the electric field strength and show that the normalized scattering cross-section of a front-located nanoparticle varies from two to eight depending on the intensity of the driving field. In addition, the scattering cross-section of rear-located particles can be increased fourfold using ultrathin spacer layers.

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Asymmetry in photocurrent enhancement by plasmonic nanoparticle arrays located on the front or on the rear of solar cells

The issue of hysteresis in perovskite solar cells has now been convincingly linked to the presence of mobile ions within the perovskite layer. Here we test the limits of the ionic theory by attempting to account for a number of exotic characterization results using a detailed numerical device model that incorporates ionic charge accumulation at the perovskite interfaces. Our experimental observations include a temporary enhancement in open-circuit voltage following prolonged periods of negative bias, dramatically S-shaped current–voltage sweeps, decreased current extraction following positive biasing or “inverted hysteresis”, and non-monotonic transient behaviours in the dark and the light. Each one of these phenomena can be reproduced and ultimately explained by our models, providing further evidence for the ionic theory of hysteresis as well as valuable physical insight into the factors that coincide to bring these phenomena about. In particular we find that both interfacial recombination and carrier injection from the selective contacts are heavily affected by ionic accumulation, and are essential to explaining the non-monotonic voltage transients and S-shaped J–V curves. Inverted hysteresis is attributed to the occurrence of “positive” ionic accumulation, which may also be responsible for enhancing the stabilized open-circuit voltage in some perovskite cells.

/pdf/hysteresis-phenomena-in-perovskite-solar-cells-the-many-and-47s3lbaf7d.pdf

Hysteresis phenomena in perovskite solar cells: the many and varied effects of ionic accumulation

K.R.C. acknowledges the support of an
Australian Research Council fellowship and the EU FP7
PRIMA project.

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Fiona J. Beck

Papers

Tunable light trapping for solar cells using localized surface plasmons

Designing periodic arrays of metal nanoparticles for light-trapping applications in solar cells

Asymmetry in photocurrent enhancement by plasmonic nanoparticle arrays located on the front or on the rear of solar cells

Hysteresis phenomena in perovskite solar cells: the many and varied effects of ionic accumulation

The effect of dielectric spacer thickness on surface plasmon enhanced solar cells for front and rear side depositions