Introduction to light trapping in solar cell and photodetector devices pdf
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- Nanostructures for Light Trapping in Thin Film Solar Cells
- Atom-to-Farm Physics of Solar Cell
- Introduction to Light Trapping in Solar Cell and Photo-detector Devices
Nanostructures for Light Trapping in Thin Film Solar Cells
Metrics details. Light manipulation has drawn great attention in photodetectors towards the specific applications with broadband or spectra-selective enhancement in photo-responsivity or conversion efficiency. In this work, a broadband light regulation was realized in photodetectors with the improved spectra-selective photo-responsivity by the optimally fabricated dielectric microcavity arrays MCAs on the top of devices. Both experimental and theoretical results reveal that the light absorption enhancement in the cavities is responsible for the improved sensitivity in the detectors, which originated from the light confinement of the whispering-gallery-mode WGM resonances and the subsequent photon coupling into active layer through the leaky modes of resonances.
In addition, the absorption enhancements in specific wavelength regions were controllably accomplished by manipulating the resonance properties through varying the effective optical length of the cavities.
This work well demonstrated that the leaky modes of WGM resonant dielectric cavity arrays can effectively improve the light trapping and thus responsivity in broadband or selective spectra for photodetection and will enable future exploration of their applications in other photoelectric conversion devices.
Photodetectors PDs are in great demand for enhancing responsivity, which is practically important to its commercial applications, such as optical communication, sensing, and imaging in our daily life. It is well acknowledged that the material extinction in active region of the devices must be high enough to allow the efficient light absorption and photocarrier generation [ 1 ].
Hence, the application of advanced light-trapping technology has been considered as the most important approach to realize the efficient photodetection in various broadband PDs [ 2 ].
Additionally, the newly raised demands for tunable selective spectral responsivity or multiple band sensing in photodetecting field also need to develop new light-manipulating methods [ 3 , 4 , 5 , 6 , 7 , 8 , 9 ].
Various optical capture strategies have been developed and employed in optical devices, e. Among these 3D light-trapping nanostructures, low Q resonant optical cavity has been considered as the most attractive medium to manipulate light in a broadband range through the multiple resonance modes [ 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 ].
The main principle is that the whispering-gallery-mode WGM resonances in the sphere can enhance the light-matter interactions in the cavity [ 16 , 19 , 23 ] or couple the light into the under-layer substrate through the waveguide mode [ 17 , 20 ]. Consequently, improved photoelectric conversion efficiency or photo-response can be realized in the corresponding optoelectronic devices [ 24 , 25 ].
This concept of light trapping in thin-film solar cells by utilizing wavelength-scale resonant dielectric nanospheres was proposed by Grandidier et al. Further, significantly enhanced light absorption and power conversion efficiency have been well demonstrated by Cui et al.
The self-assembled dielectric hollow nanospheres, embracing multiple low Q WGM resonances in the visible light region, also have been demonstrated for effective light trapping and short-circuit current density improvement on thin-film solar cells in our previous work [ 17 ]. Theoretically, different from the conventionally used optical film technology, this kind of multiple resonances should be possible for the application in PDs towards the specific wavelength manipulation or broadband light-trapping enhancement, but which has not been investigated yet.
In this work, the 3D nanostructured dielectric microcavity arrays MCAs were introduced for light-trapping engineering in broadband and specific spectral region on the silicon-based PDs. Here, the wide bandgap semiconductor ZnO was selected as the cavity material, which can be facilely prepared through varieties of physical or chemical methods [ 26 , 27 , 28 ].
The hollow spherical ZnO cavity was fabricated using the self-assembled PS nanosphere arrays as template combined with the physical depositing and thermal annealing as reported in our previous work [ 29 ].
The significant broadband light trapping was characterized in the optimized ZnO cavities, which was proved to be originated from the WGM resonances by the theoretical calculation. The employment of WGM-enhanced absorption for light management in PDs demonstrated in this work opens the door to various applications in other optoelectronic devices, such as efficient photovoltaics and light-emitting diodes LEDs. The acceptable spherical shape of the cavities except for the contact area with the substrate can be well recognized in the cross-sectional and titled SEM images of Fig.
It is well acknowledged that when cavity parameters e. Therefore, in this kind of MCA-decorated PIN PDs, the light confinement and coupling into the active layer of PD through the leaky modes [ 30 ] and the consequent light-trapping enhancement in the devices can be expected. In order to verify the light confinement and trapping properties of the fabricated ZnO MCAs, FDTD simulated transmission spectrum for the ZnO MCAs on the sapphire substrate as a simplified case was firstly examined and compared with the experimental results, as shown in Fig.
An intensified field distribution was clearly resolved around the cavity, which is known as the leaky mode [ 31 ] and would be subsequently favorable to the light radiating into the underlying active layer of the devices. These WGM resonances in the MCAs produced a broad angle scattering [ 32 ] of the incident light, exhibiting as a valley in the transmission spectra near the resonance wavelength.
This scattering effect on ZnO MCAs decorated Si substrate also can be well evidenced by the simulated reflection spectrum as shown in Fig.
Additionally, it was found that a broadband anti-reflection effect was successfully achieved on the MCA-decorated silicon substrate when compared with the bare silicon. With comparing to the reflection from the bare silicon surface, both the theoretical and experimental reflection spectra from the MCA-decorated silicon well demonstrated that the supported series of WGM resonances can be used for light trapping by utilizing the leaky modes.
However, interestingly, it was noteworthy that the mostly decreased reflection happened in the off-resonance region rather than the on-resonance peaks.
This result infers that the WGM resonance, especially the resonance with high-quality factor in some special wavelength positions, might also scatter the light back [ 35 ], which is unfavorable for the light-trapping enhancement. As shown in the typical I—V response of Fig. The wavelength-dependent photo-responsivity as shown in Fig. The enhancement ratio was calculated and is shown in Fig. Coincidentally, this wavelength region also lay at the off-resonance region as mentioned above.
The results were well consistent with the simulation results where absorption enhancement could not be enhanced under the on-resonance illumination while obviously enhanced absorption can happen in the off-resonance region, as shown in Fig. As discussed above, the actual much low resonance quality in cavities within this region should be the main reason for the broadband light trapping which is independent of the on-resonance or off-resonance.
For the shell structure cavity adopted in this work, the effective optical length can be easily increased by thickening the shell layer [ 36 ]. As shown in Fig. The experimental reflection spectra in Fig. The wavelength-dependent responsivity curves are shown in Fig. From Fig. This much stronger enhancement should have originated from the higher resonance quality for the second-order WGM of the MCAs, leading to the higher light-trapping effect through the leaky mode of WGM resonance in this wavelength region.
The much lower reflectance intensity in this wavelength region well explained this significant enhancement in light trapping, as well as the responsivity, as shown in Fig. Additionally, this enhancement also mostly happened at the off-resonance region. The background within the on-resonance and off-resonance region in b and d referring to the reflection spectra in b was highlighted in light red and light green, respectively.
In conclusion, a new strategy was proposed for light absorption improvement within broadband and specific wavelength region for photodetectors PDs by utilizing the multiple WGM resonances generated in ZnO microcavity arrays MCAs. Theoretical and experimental results indicated that the leaky mode radiation of the WGM resonances, which most effectively work in the off-resonance region, is the main enhancement mechanism for light trapping. This work well demonstrated a low-cost and good compatibility method to improve the light trapping and thus responsivity with broadband or selective spectra for photodetection by introducing the leaky mode of WGM resonant dielectric cavity arrays.
The light manipulation approach employed in this work provides an important guide for designing micro- and nanomaterial architectures to facilitate the novel applications within a specific wavelength range in optoelectronic devices. Before the decoration of the MCA structures, the PIN wafer was standardly cleaned to remove the surface residual organic matters and metal ions.
Finally, the chip-fabrication processes were carried out with the designed photosensitive region of 2. The photocurrent and IV characteristics of the devices were measured on an electrochemical workstation CHID equipped with a room-temperature probe station and LED light sources. The external quantum efficiency EQE of the devices under 0 bias were measured using an optical power meter Newport, R , which equipped with a light source Newport, 66, and a monochromator Cornerstone , Newport.
All data generated or analyzed during this study are included in this published article and its supplementary information files. Zhang J, Zhu Z, Liu W, Yuan X, Qin S Towards photodetection with high efficiency and tunable spectral selectivity: graphene plasmonics for light trapping and absorption engineering. Nanoscale — Fonash S Introduction to light trapping in solar cell and photo-detector devices.
Elsevier, Amsterdam. Adv Funct Mater — Nature Nanotech J Mater Chem C — Adv Opt Mater Garnett E, Yang P Light trapping in silicon nanowire solar cells. Nano Lett — Nat Mater — Nano Energy — Adv Energy Mater Nano Today — Adv Mater — Nat Commun Phys Chem Chem Phys — Sci Rep Wang B, Leu PW High index of refraction nanosphere coatings for light trapping in crystalline silicon thin film solar cells. Ieee J Photovolt — Cryst Growth Des — Yu J, Tian N High spectrum selectivity and enhanced responsivity of a ZnO ultraviolet photodetector realized by the addition of ZnO nanoparticles layer.
Small Huang L, Yu Y, Cao L General modal properties of optical resonances in subwavelength nonspherical dielectric structures. Phys Rev B J Photonics Energy Proc Spie S. Adv Mater J Mater Chem Download references. JY and JL conceived the idea. AY and LL carried out the experiment. AY and JY drafted the manuscript. JK gave the final approval of the version of the manuscript to be published. All authors read and approved the final manuscript.
Correspondence to Jun Yin or Jing Li. Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. Figure S1. Figure S2. Figure S3. Figure S4.
Atom-to-Farm Physics of Solar Cell
Light management plays an important role in high-performance solar cells. Nanostructures that could effectively trap light offer great potential in improving the conversion efficiency of solar cells with much reduced material usage. Developing low-cost and large-scale nanostructures integratable with solar cells, thus, promises new solutions for high efficiency and low-cost solar energy harvesting. In this paper, we review the exciting progress in this field, in particular, in the market, dominating silicon solar cells and pointing out challenges and future trends. As a light-electricity conversion device, light absorption plays a primary role in determining the achievable efficiency of a solar cell.
Introduction to Light Trapping in Solar Cell and Photo-detector Devices
Metrics details. Light manipulation has drawn great attention in photodetectors towards the specific applications with broadband or spectra-selective enhancement in photo-responsivity or conversion efficiency. In this work, a broadband light regulation was realized in photodetectors with the improved spectra-selective photo-responsivity by the optimally fabricated dielectric microcavity arrays MCAs on the top of devices.
Plasmonics can be used to improve absorption in optoelectronic devices and has been intensively studied for solar cells and photodetectors. Graphene has recently emerged as a powerful plasmonic material. It shows significantly less loss compared to traditional plasmonic materials such as gold and silver and its plasmons can be tuned by changing the Fermi energy with chemical or electrical doping.
Thin film solar cells are one of the important candidates utilized to reduce the cost of photovoltaic production by minimizing the usage of active materials. Increasing the absorption of light that can be converted into electrical current in thin film solar cells is crucial for enhancing the overall efficiency and in reducing the cost. Therefore, light trapping strategies play a significant role in achieving this goal. The main objectives of light trapping techniques are to decrease incident light reflection, increase the light absorption, and modify the optical response of the device for use in different applications. Nanostructures utilize key sets of approaches to achieve these objectives, including gradual refractive index matching, and coupling incident light into guided modes and localized plasmon resonances, as well as surface plasmon polariton modes. In this review, we discuss some of the recent developments in the design and implementation of nanostructures for light trapping in solar cells.
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New Approaches to Light Trapping in Solar Cell Devices discusses in detail the use of photonic and plasmonic effects for light trapping in solar cells. It compares and contrasts texturing, the current method of light-trapping design in solar cells, with emerging approaches employing photonic and plasmonic phenomena.