Simulation and fabrication of the c-Si solar cell using spin-on dopant

Wang LiangXing

Supervisor: Ming Lu

Although the best Si solar cells have reported a conversion efficiency of 25% [1, 2], the cost of this cell is very high because of the complex manufacturing process. In order to compete with other energy sources, the silicon solar cell cost should be brought down by at least a factor of four [3, 4]. Thus, it is essential to reduce the cost of fabrication process, including the diffusion process, anti-reflection coating, the front and rear surface passivation layers, and the contacts [5, 6].

In this work, a simple process for the Si solar cell using spin-on dopant is explored. Detailed simulation results and fabrication process are presented. The main focus in this work was on the modeling of the phosphorus profile using spin-on dopant, and the front and rear surface passivation layers. The anti-reflection coating, the front and rear contacts, and the device characterization results were also discussed.

With this simplified process using the spin-on dopant, the Si solar cell with conversion efficiency of over 16% has been achieved. The efficiency can be further enhanced by reducing the surface reflection and recombination losses.

References

[1]A.G.Martin, Progress in Photovoltaics: Research and Applications 17 (2009) 183–189.

[2]  Vikram V.Iyengar, BaradaK. Nayak, MoolC. Gupta. Solar Energy Materials & Solar Cells 94 (2010) 2205–2211.

[3]  A. Rohatgi, S. Narasimha, A.U. Ebong, P. Doshi, IEEE Transactions  on Electron Devices 46 (1999) 1970–1977.

[4]  Fa-Jun Ma Bram Hoexa, Ganesh S. Samudra, Armin G. Aberle. Energy Procedia 15 (2012) 155 – 161

[5] Yifeng Chen, HuiShen, PietroP. Altermatt. Solar Energy Materials & Solar Cells 120 (2014) 356–362.

[6] Antonios Florakis, Tom Janssens, Niels Posthuma, Joris Delmotte, Bastien Douhard, Jef Poortmans and Wilfried Vandervorst, Energy Procedia 38 ( 2013 ) 263 – 269

Ultra-sensitive and Low Detection Limit Whispering Gallery Microcavity sensor Base on Mode Coupling

Qijing Lu

Supervisor: Liying Liu

The ability to sense biomolecules (i.e., cell, DNA, virus, protein)and nanoparticle is particularly crucial for a wide range of applications[1, 2]. Optical microcavities[3], especially Whispering Gallery Microcavity, are ideal transducers for detecting biomolecules and their interactions due to their high quality factor and small mode volume.Binding of molecules or nanoparticles at the microcavitysurface causes the WGM resonance wavelength to shift. The high Q factor results in anarrow linewidth which allows the detection of minute frequency shifts due to bindingof biomolecules or nanoparticles. To achieve lower detection limit, higher Q factor is expected. However, the Q factor is limited by material absorption loss, scattering loss, diffraction loss and so on. Thus, the noises, e.g., wavelength fluctuation of a laser light source, environmentaltemperature fluctuations can be much larger than detection signal in real sensing experiment and form a bottleneck for WGM sensor.

Up to now, many methods have been proposed anddemonstrated for noise reduction.For example, temperature [4]orfrequency stabilization methods [5]are employed to improve the detection limit. Recently, mode splitting in coupled microcavity or induced by nanoparticle in single microcavity is intensively studied to resolve smaller changes in in the transmissionspectrum[6-10]. Here, we propose a single hybrid microcavity and study the mode coupling by tuning the effective radial potential of whispering gallery mode. A clear anticrossing behavior is obtained in experiment which is characteristic of strong mode coupling in photonic molecules microcavities. Furthermore, a coupled optofluidic ring laser sensor is fabricated and the laser spectralmodulation is generated by the Vernier effect, based on which the sensitivity is double enhanced.

References

1.    X. Fan, I. M. White, S. I. Shopova, H. Zhu, J. D. Suter, and Y. Sun, "Sensitive optical biosensors for unlabeled targets: A review," analytica chimica acta 620, 8-26 (2008).

2.    F. Vollmer, and S. Arnold, "Whispering-gallery-mode biosensing: label-free detection down to single molecules," Nature methods 5, 591-596 (2008).

3.    K. J. Vahala, "Optical microcavities," Nature 424, 839-846 (2003).

4.    H. Li, and X. Fan, "Characterization of sensing capability of optofluidic ring resonator biosensors," Applied Physics Letters 97, 011105 (2010).

5.    T. Lu, H. Lee, T. Chen, S. Herchak, J.-H. Kim, S. E. Fraser, R. C. Flagan, and K. Vahala, "High sensitivity nanoparticle detection using optical microcavities," Proceedings of the National Academy of Sciences 108, 5976-5979 (2011).

6.    X. Zhang, L. Ren, X. Wu, H. Li, L. Liu, and L. Xu, "Coupled optofluidic ring laser for ultrahigh-sensitive sensing," Optics express 19, 22242-22247 (2011).

7.    L. Ren, X. Wu, M. Li, X. Zhang, L. Liu, and L. Xu, "Ultrasensitive label-free coupled optofluidic ring laser sensor," Optics letters 37, 3873-3875 (2012).

8.    M. Li, X. Wu, L. Liu, X. Fan, and L. Xu, "Self-referencing optofluidic ring resonator sensor for highly sensitive biomolecular detection," Analytical chemistry 85, 9328-9332 (2013).

9.    J. Zhu, S. K. Ozdemir, Y.-F. Xiao, L. Li, L. He, D.-R. Chen, and L. Yang, "On-chip single nanoparticle detection and sizing by mode splitting in an ultrahigh-Q microresonator," Nature Photonics 4, 46-49 (2009).

10.  L. He, Ş. K. Özdemir, J. Zhu, W. Kim, and L. Yang, "Detecting single viruses and nanoparticles using whispering gallery microlasers," Nature nanotechnology 6, 428-432 (2011).

Design and construction of the infraredinterferometer

Xudong Yan

Supervisor: Min Xu

       The horizontal configuration bench actually is a precision, non-contact Fizeau FIR Interferometer. [1]The light source is a low-power 10.6m, CO2 laser. The laser beam is expanded to a 200mm diameter and exits the interferometer though the apertures by the Spatial Filter System (with 18mm focal length ZnSe Lens and 50m pinhole);ZnSe Beam Splitter and f#4 off-axis Parabola Mirror. The Transmission Flat, mounted in front of the exit aperture, is ZnSe Transmission Flat. It reflects some of the laser light back into the interferometer, thus creating a reference wavefront. The remainder of the laser light passes through the Transmission Flat to the component or assembled being tested and is referred to as the measurement wavefront. When performing IR optic quality tests, the measurement wavefront reflects back to the interferometer from the IR optics being tested. Inside the interferometer, the returning wavefront is recombined with the reference wavefront, and two wavefronts interfere with each other, the phase differences between the two wavefronts result in an image of light and dark fringes that is a direct indication of the quality of the IR optics being tested. An IR Camera A20 and a Monitor convert the IR interference pattern to visible image.[2-4]

       This test bench can meet the most demanding surface quality and transmitted wavefront distortion measurement of 8-12um IR optical systems, Can do telescope focusing alignment from infinite to 60m ranges, IR lens system aberration and IR parts surface or rough surface profile analysis. If it is equipped by a rotation stage with the unit mount, we could test unit’s boresight and evaluate the off axis aberration and image quality.[3]

       Fizeau system is Double-Pass Interferometer. When performing either transmitted wavefront or surface quality tests, the measurement wavefront is affected by the optical component twice, thus the name “double- pass interferometer”. In the interference pattern, defects in the component being tested appear to be twice as severe as they really are. The interferogram scale factor is 1 fringe spacing = /2=5.3m. Eyes reading sensitivity is 5.3/10=0.53m normally. Consider other alignment and mechanical machine error; at least we can get 0.6m alignment resolution and sensitivity. [5]

       Intelliwave Interferegram Analyzes Program is equipped with the interferometer. It quantifies measurement information obtained by the interferometer according to user-selected parameters. Measurement and analysis functions can occur automatically or can be initiated individually as desired.

Reference

[1]O.S.K.won,J.C.Wyant,C.R.Hayslett. Rough surface interferometry at 10.6um[J].Appl.Opt.,1980,19(11);1862~1869

[2]Wu Yongqian, Zhang Yudong,Zhang Juan. Design and fabrication of far-infrared Fizeau interferometer[C].SPIE,2010,7659:765919

[3]Verma K, Han B. Far-infrared Fizeauinterferometry[J]. Applied Optics, 2001, 40(28): 4981-4987.

[4]He Y, Chen L, Wang Q. Twyman-Green infrared phase-shifting interferometer and application^*[J]. Infrared and Laser Engineering, 2003, 32(4): 335-338.

[5]HE J, WANG Q, CHEN L. Alignment of Twyman-Green infrared phase-shifting interferometer[J]. Infrared and Laser Engineering, 2008, 3: 040.

Wavelength Control and Spectral Narrowing of High Power Fibre Laser Using Volume Bragg Gratings

Xiaofang Yang

Supervisor: Heyuan Zhu and Deyuan Shen

Novel fiber lasers with narrow linewidth or multi-wavelength emitting, especially those operating in the eye-safe wavelength regime at around 1.5~1.6μm, have grown rapidly due to the numerous applications including range finding, laser radar and long-haul optical transmission systems. To enable access to narrow band operation in fiber lasers, effective spectral selection and narrowing components are therefore required. Fiber Bragg gratings (FBGs), which offer a narrow linewidth and good integrity with traditional single mode gain fibers, have been widely used for spectral control in fiber lasers [1, 2]. However, they are not very effective in large mode area fibers for high-power generation. Volume Bragg gratings (VBGs), recorded in a bulk of photo-thermo-refractive (PTR) glass, have attracted great attention as appropriate external wavelength selection and spectral narrowing components in fiber lasers [3, 4], due to their excellent performance including high diffraction efficiency, narrow spectral selectivity, low insertion loss and high damage threshold.

In our experiment, the Er, Yb co-doped fiber laser system was constructed with a VBG pair to realize the specturm narrowing and dual-wavelength emitting. VBG1 and VBG2 used in the EYDFL were designed to have a central wavelength of 1610.1 nm and 1545.2 nm, with the same peak reflectivity of 99.9% and spectral selectivity of 0.38 nm, respectively. Both VBGs were anti-reflection coated for each surface (>99.6%) over the band from 1500 nm to 1700 nm to reduce cavity loss.The Bragg wavelength of a VBG is determined by λ_B=λ₀cosθ, where λ₀ is the wavelength at normal incidence and θ is the (internal) angle of incidence. Therefore, the reflecting Bragg wavelength for VBG1 could be tuned to fit the central wavelength of VBG2 by tilting it with an appropriateangle. Compare to the single VBG or the free runing laser operation, the linewidth of the laser spectra of the VBG-pair laser systems was much narrower. In the EYFL system, the measured full width at half maximum (FWHM) was ∼38 pm at 1545.3 nm, with the output power of 19.4 W; while the single VBG2-locked laser generated a broader spectrum with an exhibited FWHM of∼138 pm.

For the parallel-paired VBGs, because of the different central wavelength of the two VBGs, highly efficient and simultaneous dual-wavelengthoperation can be achieved when the resonators are properaligned and the losses for the two wavelengths are balanced. The laser oscillation cavity for the dual-wavelength tunable EYFL was first demonstrated, the wavelength splitting range of the two operating wavelengths was tuned continuously from 0.3 to 29.2 nm, with a total output power of >13 W for a wavelength separation of <20 nm.

References

1. Y. Jeong, C. Alegria, J. K. Sahu, L. Fu, M. Ibsen, C. Codemard, “A 43-W C-band tunable narrow-linewidth erbium-ytterbium co-dopedlarge-core fiber laser,” IEEE Photon. Technol. Lett. 16, 756–758 (2004).
2. J. K. Sahu, Y. Jeong, C. Codemard, J. Nilsson, M. R. Mokhtar, M. Ibsen,“Tunable narrow linewidth high power erbium:ytterbium co-dopedfiber laser,” inProc. CLEO, 2004, p. CMK1.
3. P. Jelger, P. Wang, J. K. Sahu, F. Laurell, and W. A. Clarkson, “Highpower linearly-polarized operation of a cladding-pumped Yb fibre laserusing a volume Bragg grating for wavelength selection,” Opt. Express 16, 9507–9512 (2008).
4. J. W. Kim, P. Jelger, J. K. Sahu, F. Laurell, and W. A. Clarkson, “Highpower and wavelength-tunable operation of an Er,Yb fiber laser usinga volume Bragg grating,” Opt. Lett. 33, 1204–1206 (2008).

Time: 6:30 pm, Thursday, 2014.11.13

Location:Optical Building. Room 525