Plasmonic Concentrators for Thin-Film Photovoltaics: Enhancing Light Absorption and Efficiency of Thin-Film Solar Cells
In conventional thin-film solar cells, metallic films serve as back contacts, facilitating electrical conductivity and charge transport. However, these metallic layers often introduce optical losses by reflecting a significant portion of the incident light, preventing it from being absorbed by the active layer. This challenge is particularly pronounced in ultrathin photovoltaics, where the active dielectric material is optically thin, leading to insufficient light absorption.
Our research demonstrates that by nanoengineering the otherwise flat metal back surfaces, long-range propagating surface plasmon polaritons (SPPs) can be excited and made to interfere constructively at various wavelengths simultaneously. This interference enhances the electric field amplitude in the dielectric material above the metal, leading to a significant increase in light absorption. By leveraging this effect, even ultrathin absorber layers—where light would typically be weakly absorbed—can be transformed into efficient light-harvesting media.
By structuring the metal back contact with engineered nanohole or nanodisk arrays, we convert optical losses into optical gains, enhancing the absorption efficiency of thin-film solar cells. This approach shows significant advantages over conventional technologies, namely:
- Reduction of Optical Losses – Instead of acting as a reflective surface, the metal back contact becomes an active light-trapping medium.
- Enhancement of Absorption in Ultra-Thin Layers – Allows photovoltaic devices to maintain high efficiency even when using optically thin active layers for reduced material cost and/or increased flexibility of the solar cell.
- Broadband Absorption Enhancement – Unlike anti-reflection coatings, which work at specific wavelengths, plasmonic nanoengineering provides enhancement at multiple wavelengths simultaneously.
- Polarization Independence – Proper design of quasi-periodic arrangements of nano-scatterers on the metal surface with high degrees of rotational symmetry can lead to polarization-insensitive light absorption, a nice feature to have since sunlight is unpolarized.
Part of this work was conducted in collaboration with Prof. Nitin Padture.
Below are selected papers highlighting periodic and quasi-periodic plasmonic concentrators designed to enhance light absorption in thin-film organic and perovskite solar cells.
Nanomaterials, 2020 – Arrays of Plasmonic Nanostructures for Absorption Enhancement in Perovskite Thin Films
This study provides experimental validation of plasmonic nanostructures integrated into perovskite solar cells, demonstrating their effectiveness in enhancing optical absorption. By structuring the metallic back contact with nanohole (NH) and nanodisk (ND) arrays, we achieved up to 45.5% higher absorption efficiency in 75 nm and 110 nm-thick perovskite films. The experimental results were validated by 3D FDTD simulations. The work also suggests that these enhancements could be exploited in biosensing applications, where localized plasmonic fields could improve the detection of biochemical analytes.
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Journal of Physical Chemistry C, 2018 – Plasmon-Enhanced Thin-Film Perovskite Solar Cells
This paper explores the integration of plasmonic nanostructures with perovskite solar cells using FDTD simulations. It systematically investigates nanodisk and nanohole arrays and their impact on light trapping efficiency. The simulations reveal that optimized designs increase power conversion efficiency (PCE) by up to 52%, a major improvement over flat back contacts. These findings underscore the broader potential of plasmonic enhancement in next-generation photovoltaics and optical biosensing.
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Optics Express, 2013 – A Generalized “Cut and Projection” Algorithm for the Generation of Quasiperiodic Plasmonic Concentrators for High-Efficiency Ultrathin Film Photovoltaics
This paper introduces a novel algorithm inspired by de Bruijn’s “cut and projection” method, widely recognized for its role in generating Penrose tilings—a class of aperiodic tessellations that exhibit long-range order without translational symmetry and with five-fold rotational symmetry. This method is extended here to generate quasiperiodic arrays with varying degrees of long-range order and rotational symmetry, going beyond the well-known Penrose tile, which is referred to here as the “penta-grid.” The study presents quasiperiodic plasmonic structures (namely, subwavelength hole arrays embedded in metal films) that lack periodicity while maintaining long-range order and high rotational symmetry—as evidenced in reciprocal (Fourier-transform) space. These structures enable broadband, angle-insensitive light absorption when a thin dielectric film is deposited on the corrugated metal substrate. Results show that quasiperiodic plasmonic arrays consistently outperform both periodic and random structures in plasmonic field enhancement, leading to superior optical absorption properties. The findings are also highly relevant to biosensing applications, where precise plasmonic field distribution is critical for detecting biological molecules with high sensitivity.
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Applied Physics Letters, 2011 –Plasmonic Concentrators for Enhanced Light Absorption in Ultrathin Film Organic Photovoltaics
This pioneering study provided the first experimental proof that nanoengineered metallic surfaces enhance light absorption in thin-film photovoltaics. By introducing hole arrays into silver back contacts, we observed up to 600% enhancement in optical absorption and a corresponding increase in fluorescence emission from the absorber. This work laid the foundation for future research into plasmonic photovoltaics, demonstrating that metallic back contacts could be transformed from loss-inducing elements into active light-harvesting structures.
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Main Findings & Impact on the Field:
One of the central achievements of our research is the realization that the metal back contacts of thin-film solar cells, typically a source of optical losses, can be transformed into efficient plasmonic light concentrators. By nanoengineering these otherwise flat metallic surfaces, we have demonstrated that surface plasmon polaritons (SPPs) can be excited and controlled to interfere constructively, enhancing the local electric field intensity in the absorber layer. This effect allows for significantly higher light absorption, even in ultrathin layers where absorption would otherwise be minimal. Through a combination of experimental validation and computational modeling, we have shown that plasmonic nanostructures can be engineered to work over a broad spectral range, independent of polarization and incident angle, thus making them highly effective for real-world applications.
A key breakthrough in this research has been the identification of quasiperiodic plasmonic nanostructures as the most effective design for broadband absorption enhancement. While prior approaches relied on periodic nanostructures, we introduced a generalized “cut and projection” algorithm that enables the design and fabrication of quasiperiodic arrays with optimized long-range order and rotational symmetry. Through both theoretical simulations and experimental validation, we demonstrated that quasiperiodic arrays significantly outperform both periodic and random nanostructures, achieving higher absorption across a wider range of wavelengths. This discovery represents a major step forward in the design of nanophotonic structures, not just for photovoltaics but also for biosensing applications, where optimized plasmonic field enhancement is crucial.
In addition to exploring the fundamental mechanisms of plasmonic light enhancement, we have also systematically investigated the effects of nanostructure geometry, dielectric thickness, and metal type on optical performance. By leveraging finite-difference time-domain (FDTD) simulations, we optimized the size, shape, and arrangement of nanoholes and nanodisks, tailoring them to enhance light trapping in different photovoltaic materials. Our studies have confirmed that plasmonic concentrators are effective in both organic photovoltaics and perovskite solar cells, with perovskite devices showing a particularly strong enhancement of power conversion efficiency (PCE) by up to 52%. These findings extend the potential of plasmonics beyond traditional semiconductor-based solar cells, opening doors for high-efficiency, cost-effective thin-film solar technologies.
The innovation of this research lies not only in the optical enhancement achieved but also in establishing a scalable and integrable method for applying plasmonic concentrators in real devices. Unlike conventional approaches that require the deposition of additional optical coatings or complex photonic crystal layers, our method is fully compatible with standard solar cell fabrication processes. The ability to engineer plasmonic resonances directly into the metal back contact eliminates the need for additional layers, reducing manufacturing complexity and cost. Moreover, this approach has significant implications beyond solar energy, particularly in biosensing technologies, where localized plasmonic field enhancements can be used to improve the detection of biomolecules through optical absorption and scattering.
Looking ahead, our research has established a foundational framework for plasmonic enhancement in both energy harvesting and optical sensing applications. Future studies will focus on further optimizing plasmonic structures for multi-junction and tandem solar cells, where light management is even more critical. Additionally, there is significant potential for applying our quasiperiodic plasmonic design principles to biomedical sensing by tailoring the plasmonic response to specific molecular interactions. Another key direction will be investigating long-term stability and large-scale fabrication techniques, ensuring that these innovations can be commercially viable and integrated into next-generation photovoltaic and sensing platforms. Through continued development, our work aims to bridge the fields of plasmonic nanophotonics, renewable energy, and bio-optoelectronics, paving the way for high-efficiency, multifunctional nanostructured devices.
Summary & Future Outlook:
This body of work establishes plasmonic concentrators as a powerful tool for enhancing light absorption in thin-film photovoltaics. By nanoengineering the metal back contact, the research successfully converts optical losses into optical gains, enabling high-efficiency solar cells with reduced material costs. Furthermore, the studies hint at biosensing applications, where localized plasmonic enhancements could improve biochemical detection sensitivity, paving the way for innovative optical sensing technologies.
Looking ahead, several key research directions emerge from this work. One crucial avenue is the integration of plasmonic concentrators into multi-junction solar cells, particularly in tandem architectures such as perovskite-silicon hybrids, where efficient light management is essential for boosting power conversion efficiency. As light absorption is one of the primary limiting factors in these advanced photovoltaic devices, nanostructured back contacts could play a transformative role in optimizing their spectral response.
Another critical step is the scalability and fabrication of these plasmonic architectures for real-world applications. Future work should focus on developing cost-effective nanoimprint lithography techniques, ensuring that large-area nanostructuring can be seamlessly integrated into commercial thin-film solar panel manufacturing. Achieving high-throughput fabrication while maintaining precision in nanostructure design will be essential for industrial adoption.
Beyond photovoltaics, this research opens exciting possibilities for plasmonic biosensing. The same field-enhancement principles that drive absorption improvements in solar cells can be leveraged to develop label-free optical biosensors, enabling the detection of disease biomarkers with unprecedented sensitivity. Future work will explore how quasiperiodic plasmonic nanostructures can be tuned to specific resonance wavelengths to enhance biomolecular interactions, potentially leading to new diagnostic technologies in biomedical applications.
Finally, a major focus will be on evaluating the long-term stability and environmental durability of these nanoengineered back contacts. It will be crucial to assess their performance over extended periods under real-world operating conditions, including exposure to temperature variations, humidity, and ultraviolet radiation. Understanding and mitigating potential degradation mechanisms will ensure that these plasmonic enhancements remain effective throughout the lifespan of the devices.
By bridging photovoltaics and biosensing, this research demonstrates how nanoengineered metallic layers can revolutionize solar energy harvesting and optical sensing technologies. The continued development of plasmonic concentrators will not only improve the efficiency of next-generation solar cells but also contribute to the advancement of high-sensitivity biosensors, making a significant impact on both renewable energy and healthcare technologies.