This PDF file contains the front matter associated with SPIE Proceedings Volume 9358, including the Title Page, Copyright information, Table of Contents, Introduction, Authors, and Conference Committee listing.

Either nanowire or nanohole array for semiconductor were proved to be an efficient nanostructure to harvest solar light. However, for Si, the length of nanostructure about several micrometers is required to have acceptable absorption. Although this length already far less than the bulk Si in which hundred micrometers are required, the micrometers length still not feasible for Si nanostructure. High density nanostructures will cause extensive surface recombination that reduces the power conversion efficiency. Therefore, explore the dependence of light absorption to the length of Si nanostructure is very important to design an efficient solar cell. In this work, the Si nanohole array was fabricated in several depths from 110 to 960 nm. The total reflection was less than 1% at visible regime for 960 nm depth hole. The Ag nanoparticles were put at the bottom of the nanohole to explore the light absorption by plasmonic enhanced Raman scattering. A chemical, pNTP, was cover Ag nanoparticle as the prober for the plasmonic effect. As the laser light incident to the Ag nanoparticle, the surface plasmonic effect will enhance the Raman scattering of the pNTP. The enhanced Raman signal obtained from pNTP indicates the incident light could penetrate into the bottom of the Si nanohole array without significant absorption. The experiment result indicate the Raman signal decay fast after the depth of nanohole exceed 240 nm. This result indicate, the length of Si nanostructure may not need micrometers length to harvest incident solar light. This finding pave a bright route for design of Si solar cell with nanostructures.

Reflection occurs at an air-material interface. The development of antireflection schemes, which aims to cancel such reflection, is important for a wide variety of applications including solar cells and photodetectors. Recently, it has been demonstrated that a periodic array of resonant subwavelength objects placed at an air-material interface can significantly reduce reflection that otherwise would have occurred at such an interface. Here, we introduce the theoretical condition for complete reflection cancellation in this resonant antireflection scheme. Using both general theoretical arguments and analytical temporal coupled-mode theory formalisms, we show that in order to achieve perfect resonant antireflection, the periodicity of the array needs to be smaller than the free-space wavelength of the incident light for normal incidence, and also the resonances in the subwavelength objects need to radiate into air and the dielectric material in a balanced fashion. Our theory is validated using first-principles full-field electromagnetic simulations of structures operating in the infrared wavelength ranges. For solar cell or photodetector applications, resonant antireflection has the potential of providing a low-cost technique for antireflection that does not require nanofabrication into the absorber materials, which may introduce detrimental effects such as additional surface recombination. Our work here provides theoretical guidance for the practical design of such resonant antireflection schemes.

The optical and electrical properties of a photonic-plasmonic nanostructure on the back contact of thin-film solar cells were investigated numerically through the three-dimensional (3D) finite-difference time-domain method and the 3D Poisson and drift-diffusion solver. The focusing effect and the Fabry-Perot resonances are identified as the main mechanisms for the enhancement of the optical generation rate as well as the short circuit current density. However, the surface topography of certain nanopattern structures is found to reduce the internal electrostatic field of the device, thus limiting charge collection. The optimized conditions for both optics and electronics have been analyzed in this paper.

Semitransparent photovoltaics are of interest for building integration and window coatings, though demonstrate an intrinsic tradeoff between transparency and absorption / efficiency. We propose alleviating this tradeoff using light management nanostructures which selectively scatter light based on incident wavelength and angle, allowing transmission of normally incident light for window visibility and absorption of light at elevated angles. Two structures of interest are proposed and described: metal nanorods which scatter light via their localized surface plasmon resonance properties, and arrays of subwavelength nanopores in a dielectric which demonstrate coherent multiple scattering. Both structures can potentially be patterned over large areas by electrochemical oxidation of aluminum into self assembled nanoporous anodized aluminum oxide (AAO) films.

Single junction photovoltaic devices composed of direct bandgap III-V semiconductors such as GaAs can exploit the effects of photon recycling to achieve record-high open circuit voltages. Modeling such devices yields insight into the design and material criteria required to achieve high efficiencies. For a GaAs cell to reach 28 % efficiency without a substrate, the Shockley-Read-Hall (SRH) lifetimes of the electrons and holes must be longer than 3 s and 100 ns respectively in a 2 μm thin active region coupled to a very high reflective (>99%) rear-side mirror. The model is generalized to account for luminescence coupling in tandem devices, which yields direct insight into the top cell’s non-radiative lifetimes. A heavily current mismatched GaAs/GaAs tandem device is simulated and measured experimentally as a function of concentration between 3 and 100 suns. The luminescence coupling increases from 14 % to 33 % experimentally, whereas the model requires an increasing SRH lifetime for both electrons and holes to explain these experimental results. However, intermediate absorbing GaAs layers between the two sub-cells may also increasingly contribute to the luminescence coupling as a function of concentration.

We developed a straightforward method based on detailed balance relations to analyze individual subcells in multi-junction solar cells via measuring absolute electroluminescence quantum yields. This method was applied to characterization of a InGaP/GaAs/Ge 3-junction solar cell for satellite use. In addition to subcell I-V characteristics and internal luminescence yields, we derived balance sheets of energy and carriers, which revealed respective subcell contributions of radiative and nonradiative recombination losses, junction loss, and luminescence coupling. These results provide important diagnosis and feedback to fabrications. We calculated conversion-efficiency limit and optimized bandgap energy in 2-, 3-, and 4-junction tandem solar cells, including finite values of sub-cell internal luminescence quantum yields to account for realistic material qualities in sub-cells. With reference to the measured internal luminescence quantum yields, the theoretical results provide realistic targets of efficiency limits and improved design principles of practical tandem solar cells.

Optimization of non-planar antireflective coating and back- (or front-) surface texturing are widely studied to further reduce the reflection losses and increase the sunlight absorption path in solar cells. Back reflectors have been developed from perfect mirror to textured mirror in order to further increase light path, which can significantly improve the efficiency and allow for much thinner devices. A Lambertian surface, which has the most random texture, can theoretically raise the light path to 4n2 times that of a smooth surface. It’s a challenge however to fabricate ideal Lambertian texture, especially in a fast and low cost way. In this work we have developed a method to overcome this challenge that combines the use of laser interference lithography (LIL) and selective wet etching. The approach allows for a rapid wafer scale texture processing with sub-wavelength (nano)- scale control of the pattern and the pitch. The technique appears as being particularly attractive for the development of ultra-thin III-V devices, or in overcoming the weak sub-bandgap absorption in devices incorporating quantum dots or quantum wells. Preliminary results on the application of the technique for the development of back reflector for 1-1.3 eV (MQW bearing) GaAs solar cells are presented.

The high-efficiency conversion of photonic power into electrical power is of broad-range applicability to many industries due to its electrical isolation from the surrounding environment and immunity to electromagnetic interference which affects the performance and reliability of sensitive electronics. A photonic power converter, or phototransducer, can absorb several watts of infrared laser power transmitted through a multimode fiber and convert this to electrical power for remote use. To convert this power into a useful voltage, we have designed, simulated, and fabricated a photovoltaic phototransducer that generates >5 V using a monolithic, lattice-matched, vertically-stacked, single-cell device that eliminates complex fabrication and assembly steps. Experimental measurements have demonstrated a conversion efficiency of up to 60.1% under illumination of ~11 W/cm² at a wavelength of 835 nm, while simulations indicate that efficiencies reaching 70% should be realistically achievable using this novel design.

Solar concentration is using optics in order to minimize the amount of expensive photovoltaic cell material needed. For concentration factors higher than approximately 4, tracking the sun’s position is needed to keep the focal spot on the solar cell. Based on recent developments using a waveguide slab to concentrate sunlight we propose and demonstrate a light responsive, self-tracking solar concentrator. Using a phase change material acting at the focal spot, it is possible to maintain efficient coupling into the waveguide, up to an angular range of +/- 20 degrees. The system uses the unused infrared part of the solar spectrum as energy for the phase change actuator to achieve its high acceptance angle. With a spectrally matched custom silicon solar cell attached to the waveguide slab, in which light is coupled, the visible part of the solar spectrum can be efficiently converted to electricity. A proof-of-concept single lens device was demonstrated in our previous work. Here we extend the principle to a 3x3 lens array demonstration device. The current demonstration device features an acceptance angle of +/- 16 degrees and an effective concentration factor of up to 20x.

GaAsPN semiconductors are promising material for the elaboration of high efficiencies tandem solar cells on silicon substrates. GaAsPN diluted nitride alloy is studied as the top junction material due to its perfect lattice matching with the Si substrate and its ideal bandgap energy allowing a perfect current matching with the Si bottom cell. We review our recent progress in materials development of the GaAsPN alloy and our recent studies of some of the different building blocks toward the elaboration of a PIN solar cell. A lattice matched (with a GaP(001) substrate, as a first step toward the elaboration on a Si substrate) 1μm-thick GaAsPN alloy has been grown by MBE. After a post-growth annealing step, this alloy displays a strong absorption around 1.8-1.9 eV, and efficient photoluminescence at room temperature suitable for the elaboration of the targeted solar cell top junction. Early stage GaAsPN PIN solar cells prototypes have been grown on GaP (001) substrates, with 2 different absorber thicknesses (1μm and 0.3μm). The external quantum efficiencies and the I-V curves show that carriers have been extracted from the GaAsPN alloy absorbers, with an open-circuit voltage of 1.18 V, while displaying low short circuit currents meaning that the GaAsPN structural properties needs a further optimization. A better carrier extraction has been observed with the absorber displaying the smallest thickness, which is coherent with a low carriers diffusion length in our GaAsPN compound. Considering all the pathways for improvement, the efficiency obtained under AM1.5G is however promising.

Among several approaches proposed to achieve high-efficiency III-V multi-junction solar cells, the most promising approach is to incorporate a bottom junction consisting of a 1 – 1.25 eV material. In particular, several research groups have studied MBE- and MOVPE-grown 1 – 1.25 eV bulk (In)GaAsN(Sb) dilute nitride lattice matched to GaAs substrates, but it is a challenge to grow dilute nitrides without introducing a number of localized states or defects. Localized states originating from random distributions of nitrogen sites in dilute nitrides behave as highly efficient traps, leading to short minority carrier lifetimes. As our group previously reported, carrier dynamics studies are indispensable in the optimization of dilute nitride materials growth to achieve improved solar cell performance. Also, bismide QW heterostructures have recently received a great deal of attention for applications in solar cells and semiconductor lasers because theoretical studies have predicted reduction in nonradiative recombination in Bicontaining materials. For the present study, we employed time-resolved photoluminescence (TR-PL) techniques to study carrier dynamics in MOVPE-grown bulk (In)GaAsN(Sb) materials nominally lattice matched to GaAs substrates. Compared to our previous samples, our present samples grown using different metalorganic precursors at higher growth temperatures showed a significantly less background C doping density. Carrier lifetimes were measured from such dilute nitride samples with low C doping density at various temperatures between 10K and RT. We also performed preliminary TR-PL measurements on MOVPE-grown bismide QW heterostructures at low temperatures. Carrier lifetimes were measured from as-grown and annealed bismide QW structures consisting of GaAsBi(P) wells and GaAsP barriers. Lastly, TEM cross sections were prepared from both dilute nitride and bismide samples for defect and composition analysis using a high resolution TEM.

In this manuscript we carry out a comparative analysis of p-i-n junction solar cells based on 10 stacks of InAs/GaAs quantum dots (QDs) capped with GaAs(Sb)(N) capping layers (CLs). The application of such CLs allows to significantly extend the photoresponse beyond 1.3 μm. Moreover, a strong photocurrent from the CLs is observed so that the devices work as QD-quantum well solar cells. The GaAsSb CL leads to the best results, providing a strong sub-band-gap contribution, which is higher than that in a sample containing standard GaAs-capped QDs, despite giving rise to the highest accumulated strain. The use of a GaAsN CL reduces the photocurrent originating from GaAs, pointing to electron retrapping and hindered extraction and/or the introduction of point defects as possible reasons for this. Nevertheless, the addition of N helps to balance the accumulated strain, necessary to stack a higher number of QD layers. In addition, the possibility to independently tune the hole and electron confinements by the simultaneous presence of Sb and N in the CL is also confirmed for 10 stacked QD layers. This not only allows to further extend the QD ground state and, therefore, the photoresponse, but also offers the possibility to design an optimized structure facilitating carrier extraction from the QDs. Nevertheless, carrier losses seem to be stronger under the simultaneous presence of N and Sb in the CL.

Significant development work has been completed in recent years to improve experimental results reaching a record efficiency of 9.14% under one sun AM0 conditions with no anti-reflection coating. The nipi solar cell utilizes epitaxial regrowth contacts to ensure carrier selective contacts to the alternating n and p-type doped layers, forming selectively ohmic and rectifying contacts. Defects or traps formed in the rectifying contact during the epitaxial regrowth process result in injected current that contributes directly to dark current. As a result detailed characterization of the epitaxial regrowth interface is required to understand and minimize the formation of interface traps. Concentration measurements have been completed to characterize the trap states impact on efficiency as higher concentration results in state filling and a recovery in open circuit voltage. A model has been developed to gain further understanding of the measurements under concentration.

This study aims to provide an innovative insight on polycrystalline solar cells characterization. Accurate and complete information on the material's performance is achieved by probing micrometric fluctuations of its charge carriers' transport properties which might influence the global device’s performance[1][2]. Results on microcrystalline Cu(In,Ga)Se2 solar cells absorbers[3] exhibited an initial fast decay followed by a slower one . Short decay lifetimes varying between 0.4 ns and 1.8 ns, were found to be linked to recombination centers, whereas longer decay lifetimes fluctuating between 3ns and 8ns, were associated with the presence of shallow emission traps. By varying the excitation wavelength from 850nm to 450nm excitation, the authors observed a hysteresis phenomenon regarding the behavior of TRPL decays as a function of the value order of the excitation wavelength. This is related to the activation of metastable defects located at the absorber/buffer interface.

Improvements to solar cell efficiency and radiation hardness that are compatible with low cost, high volume manufacturing processes are critical for power generation applications in future long-term NASA and DOD space missions. In this paper, we provide the results of numerical simulation of the radiation effects in a novel, ultra-thin (UT), Si photovoltaic cell technology that combines enhanced light trapping (LT) and absorption due to nanostructured surfaces, separation of photogenerated carriers by carrier selective contacts (CSC), and increased carrier density due to multiple exciton generation (MEG). Such solar cells have a potential to achieve high conversion efficiencies while shown to be rad-hard, lightweight, flexible, and low–cost, due to the use of Si high volume techniques.

The time dependent transient lateral photovoltaic effect (T-LPE) has been studied with microsecond time resolution and with chopping frequencies in the kHz range, in lithographically patterned 21 nm thick, 5, 10 and 20 micron wide and 1500 micron long Co lines grown over naturally passivated p-type Si (100). We have observed a nearly linear dependence of the LPE transient response with the laser spot position. An unusual T-LPE dynamic response with a sign change in the laser-off stage has also been corroborated by numerical simulations. A qualitative explanation suggests a modification of the drift-diffusion model by including the influence of a local inductance. In addition, influence of anisotropic magnetoresistance of the Co line structure on dynamic response on T-LPE has been investigated. Specifically, we have experimentally investigated influence of the direction of the external magnetic field respect to the drift velocity of the photogenerated carriers on the T-LPE. We have observed notable dependence of the T-LPE on the magnetic field in the small field range (below 100 Oe), compatible with anisotropic magnetoresistance values. The strong influence of the magnetization alignment on the dynamic response of photogenerated carriers has been also observed through a phase sensitive lock-in experiment. These findings indicate that the microstructuring of the ferromagnetic line based position sensitive detectors (PSD) could improve their space-time resolution and add capability of magnetic field tuning of the main PSD characteristics.

High-voltage InGaAs quantum well solar cells have been demonstrated in a thin-film format, utilizing structures that employ advanced band gap engineering to suppress non-radiative recombination and expose the limiting radiative component of the diode current. In particular, multiple InGaAs quantum well structures fabricated via epitaxial lift-off exhibit one-sun open circuit voltages as high as 1.05 V. The dark diode characteristics of these high-voltage III-V photovoltaic devices are compared to the radiative current calculated from the measured external quantum efficiency using a generalized detailed balance model specifically adapted for optically-thin absorber structures. The fitted n=1 component of the diode current is found to match the calculated radiative dark current when assuming negligible photon recycling, suggesting this thin-film multiple quantum well structure is operating close to the radiative limit.

The vertically aligned Silicon nanowires are fabricated with optimized dimensions for energy applications. These nanowires are single crystalline with nanoscale diameter and micro scale length. These nanowires are fabricated in arrays for ultra wide band of absorption over all the visible domain. Unlike bulk silicon, the experimental measurements of these nanowires demonstrate maximum light absorption over ultra wide range of incident angles. Hence, these nanowires are considered as excellent candidate for cheap energy harvesting without antireflection coatings. Our experimental measurements have been also verified through electromagnetic simulations using finite difference time domain simulations.

We study excitonic energy transfer in a network of carbon nanotubes (CNTs), a promising light-absorbing material for next-generation organic solar cells. We calculate the exciton energy dispersion curves through solving the Bethe-Salpeter equation in the basis of tight-binding wave functions. Furthermore, we compute the Coulomb-coupling matrix element between bright excitonic states, in order to obtain the exciton transfer rate between similar and dissimilar carbon nanotubes with parallel or perpendicular orientations. The conservation of momentum imposes a limitation on the energy transfer rate between parallel nanotubes of different chiralities. However, there is no such limitation for transfer between misoriented CNTs, which results in transfer rates of the same order of magnitude between carbon nanotubes of similar and dissimilar chiralities. In addition, it is possible to increase the transfer rate by taking the advantage of exciton thermalization and high density of states at the bottom of excitonic subbands.

Intermediate band solar cell (IBSC) is a promising concept to achieve next generation high-efficiency solar cells by producing the gain in photocurrent via two-step photon absorption while preserving the output voltage as of the host materials. Quantum dot (QD) superlattice is a widely studied candidate to implement the IB in real devices. In this paper, a missing transition from the IB to the conduction band (CB) has been investigated by applying extreme broadband photocurrent spectroscopy extended to mid-infrared (IR) region. In both direct and delta Si-doped InAs QDSCs, photocurrent signals were observed at the short-circuit condition at low temperature solely with sub-bandgap mid-IR photo-irradiation. On the other hand, in an undoped QDSC, no significant signal was obtained. Furthermore, the mid-IR signal was reduced by decreasing the modulation frequency and turned to be zero at DC detection. We ascribe this to the displacement photocurrent by the inter-subband transition of thermal equilibrium carriers in QDs.

We have studied detailed carrier generation process in the two-step photon absorption and influence of thermal carrier escape in quantum-dot intermediate-band solar cells (QD-IBSC). The photocurrent created by the two-step photon absorption shows saturation as the inter-band excitation intensity becomes strong, and the inter-band excitation intensity showing the saturation behavior strongly depends on the inter-subband excitation intensity. To interpret this phenomenon, we carried out a theoretical simulation based on carrier dynamics considering carrier generation, energy relaxation and thermal carrier escape. The results indicate that the photocurrent saturation is caused by filling the intermediate states. The shift of the saturation point depending on the inter-subband excitation intensity is caused by the shift of the quasi-Fermi level for the intermediate states.

Multi-Quantum well solar cells (MQWSC) have been shown to present several advantages, among which are low dark currents and tunable bandgaps. They are especially suited for implementation in multi-junction cells, and are highly promising for absorbers in Hot Carrier Solar Cells (HCSC). Such applications require high concentration ratio, which arises the issue of collection efficiency. Whereas it is usually considered that collection in MQW is very close to unity at one sun, it has been shown to not be the case under high concentration at the maximum power point. We propose in this work to take advantage of the luminescence spectral variation to investigate the depth collection efficiency. In order to validate the model, a series of strain compensated InGaAs/GaAsP MQW solar cells with intentional variation of the MQW doping concentration are grown. This has the effect of switching the space charge region position and width as well as the electric field intensity. Recording the luminescence spectra at various illumination intensities and applied voltages, we show that the in-depth quasi-Fermi level splitting and thus collection properties can be probed. Other measurements (EQE, luminescence intensity variation) are shown to be consistent with these results. Regarding their use as HCSC, the luminescence of MQW solar cells has been mainly used so far for investigating the quasi-Fermi level splitting and the temperature. Our results improve our understanding by adding information on carrier transport.

InAs/AlAs_0.84Sb_0.14 quantum wells (QWs) are investigated as a potential system for applications in hot carrier solar cells. Temperature and power dependent photoluminescence (PL) measurements show evidence of carrier localization. Evidence of for the presence of hot carriers is provided through the broadening of the high-energy tail in PL with increasing excitation power. Moreover, with increasing temperature, the stability of the hot carriers appears to improve despite the increased contribution of phonons at elevated temperatures. This is attributed to the reduced radiative recombination rate driven by the type-II band offset inherent in this system; which is suggested to result in inhibited hot carrier relaxation through electron pile-up in the conduction band

Hot carrier solar cells have the promise to increase photovoltaic conversion efficiency beyond the Shockley-Quiesser limit and towards the thermodynamic maximum of 85%. The concept relies on the ability to extract photo-generated electrons from an absorber region faster than they can lose energy to the lattice in a process termed thermalisation. We have previously presented a realization of such a cell under limited operating conditions, in particular at low temperature, for narrowband illumination and with low total absorption of light. In this work we present the idea of a metallic absorber to address some of these limitations and show how such an absorber is a promising candidate to realize the hot carrier solar cell. In addition to a theoretical justification of the metallic hot carrier solar cell, we show device fabrication and experimental current-voltage characteristics of an initial cell, showing absorption of light in a thin-film metal region and a photo-current driven by this absorption.

Efficient solar energy conversion in photovoltaics and solar to chemical conversion is hindered by large band gaps and poor absorption in thin films. The easily tunable absorption and scattering cross section of localized surface plasmon resonance (LSPR) make it an ideal solution to capturing lost light. For above band edge light, scattering and light trapping can be used to increase absorption in thin semiconductor films, improving photoconversion without sacrificing recombination times. Below the band edge, plasmonic hot electrons can transfer to the semiconductor directly or resonant energy transfer can non-radiatively induce charge separation, allowing photoconversion where the semiconductor cannot absorb. In this brief review, we explore the mechanisms and efficiency of light recovery in plasmonics. Surface plasmon polaritons are used to increase light trapping in semiconductor nanowires using a metal nanohole array. Metal-semiconductor nanostructures with varying energy alignment, insulating barrier thickness, and spectral overlap are systematically varied to differentiate hot electron and resonant energy transfer. Transient absorption spectroscopy and action spectrum analysis are applied to track plasmonic charge creation and transfer, linking short and long time scale behavior. Guidelines are given for achieving optimal plasmonic light capturing and enhancement across the solar spectrum.

Standard solar cells heat up under sunlight, and the resulting increased temperature of the solar cell has adverse consequences on both its efficiency and its reliability. We introduce a general approach to radiatively lower the operating temperature of a solar cell through sky access, while maintaining its sunlight absorption. We present first an ideal scheme for the radiative cooling of solar cells. For an example case of a bare crystalline silicon solar cell, we show that the ideal scheme can passively lower the operating temperature by 18.3 K. We then show a microphotonic design based on realistic material properties, that approaches the performance of the ideal scheme. We also show that the radiative cooling effect is substantial, even in the presence of significant non-radiative heat change, and parasitic solar absorption in the cooling layer, provided that we design the cooling layer to be sufficiently thin.

GaSb thermophotovoltaic cells fabricated using Molecular Beam Epitaxy (MBE) and ion implantation techniques are studied. Challenges including different defect formation mechanisms using MBE and ion-induced defects using ion implantation were investigated by cross-sectional Transmission Electron Microscopy (XTEM), X-Ray Diffraction spectroscopy (XRD) and Scanning Electron Microscopy (SEM). For MBE grown TPVs, several approaches were used to suppress defects, including substrate preparation and using different MBE reactors. For ion-implanted TPVs, different implant doses and energies were tested to minimize the crystal damage and various Rapid Thermal Anneal (RTA) process recipes were studied to maximize the crystal recovery. Large area TPV cells with 1 × 1 cm dimensions were fabricated using these techniques, then electrically and optically characterized. Ideality factors and dark saturation currents were measured and compared for various TPVs.

Photon absorption is a primary cause of limited solar cell performance. A proposed solution is investigated in this paper through modeling and simulation of a hybrid multi-junction silicon (HMJ-Si) solar cell. HMJ-Si cells, which are stacked silicon solar cells with an insulating air gap between them, were designed with front and rear metal grating geometries that exploit interference patterns for enhanced light management. Interference patterns were investigated in MATLAB® by using the Rayleigh-Sommerfeld formula to model 31 distinct wavelengths from 800-1100nm. Also incorporated in the model were plane wave tilts from -0.005 to 0.005 radians to account for the maximum angle of light subtended by the sun. The exploration of various grating geometries showed that contact widths of 400μm spaced 900μm apart provided an optimal destructive interference pattern while maintaining a 69.2% throughput. This contact grating was selected for finite-difference time-domain (FDTD) analysis using Lumerical® FDTD Solutions. The resulting far-field projection verified that the destructive interference pattern reaches the bottom cell with negligible fringing effects. Further analysis of the data led to a nominal bottom cell front contact width of 200μm spaced 1100μm apart.

Dye-Sensitized solar cell (DSSC) is expected to be one of the next-generation photovoltaics because of its environment-friendly and low-cost properties. However, commercialization of DSSC is difficult because of the electrolyte leakage. We propose a new thermal curable base on silicon resin. The resin aimed at sealing of DSSC and gives a promising resolution for sealing of practical DSSC. Furthermore, the optimized resin was fabricated into solar cells, which exhibited best durability by retaining 97% of the initial photoelectric conversion efficiency after 1,000 hours tracking test at 80℃.

Dye-sensitized solar cells (DSSCs) via ZnO/TiO₂ nanocomposite photoanode with density-controlled abilities are presented in this paper. This nanocomposite photoanode is composed of TiO2 nanoparticles dispersed into densitycontrolled vertically aligned ZnO-TiO₂ core-shell nanorod arrays. The density-controlled ZnO-TiO₂ core-shell nanorod arrays were synthesized directly onto fluorine-doped tin oxide (FTO) substrates using an innovative two-step wet chemical route. First, the density-controlled ZnO nanorod arrays were formed by applying a ZnO hydrothermal process from a TiO₂ nanocrystals template. Second, the ZnO-TiO₂ core-shell nanorod arrays were formed by depositing a TiO₂ shell layer from a sol-gel process. The major advantages of a density-controlled ZnO/TiO₂ nanocomposite photoanode include (1) providing a better diffusion path from ZnO nanorod arrays and (2) reducing the recombination loss by introducing an energy barrier layer TiO₂ conformal shell coating. To validate the advantages of a density-controlled ZnO/TiO₂ nanocomposite photoanode, DSSCs based on a ZnO/TiO₂ nanocomposite photoanode were fabricated, in which N719 dye was used. The average dimensions of the ZnO nanorod arrays were 20 μm and 650 nm for the length and the diameter, respectively, while the designated spacing between each nanorod was around 5 μm. The performance of the solar cell was tested by using a standard AM 1.5 solar simulator from Newport Corporation. The experimental results confirmed that an open-circuit voltage, 0.93 V, was achieved, which was much higher than the conventional TiO₂ nanoparticles thin film structure for the same thickness. Thus, density-controlled ZnO/TiO₂ nanocomposite photoanodes could improve the performance of DSSCs by offering a better electron diffusion path.

Copper Indium Gallium deSelenide (Cu(In,Ga)Se₂, CIGS) is a promising material for cost-efficient solar cells. Efficiencies above 20% have already been demonstrated in laboratory, and large area CIGS solar panels are already on the market. However, it is still an interesting issue to find efficient characterization techniques that can be used to validate the quality of the different layers at any step of the process, without having to process a complete cell and measure its electrical properties. In this work, we have deposited CIGS onto Mo coated soda lime glass by co-evaporation, using the so-called three step deposition process. Then, photoluminescence (PL) measurements were made on the samples, in the range of 10K to the room temperature, and the excitation intensity was varied in a very large range, in order to reach non-linear regime. We report the first observation of stimulated emission in mechanisms are discussed. The threshold at which sample photoluminescence changes from spontaneous to stimulated is well known to be sensitive to overall sample quality, and we propose to use this measurement as a probing tool for sample quality. This opens an interesting perspective for characterization of CIGS during solar cell processing.

The laser-generation of micro-optical volume elements is a promising approach to decrease the optical shadowing of front side metal contacts of solar cells. Focusing a femtosecond laser beam into the volume of the encapsulation material causes a local modification its optical constants. Suchlike fabricated micro-optical elements can be used to decrease the optical shadowing of the front side metallization of c-Si solar cells. Test samples comprising of a sandwich structure of a glass sheet with metallic grid-lines, an Ethylene-vinyl acetate (EVA) encapsulant and another glass sheet were manufactured in order to investigate the optical performance of the volume optics. Transmission measurements show that the shadowing of the metalling grid-lines is substantially decreased by the micro-optical volume elements created in the EVA bulk right above the grid-fingers. A detailed investigation of the optical properties of these volume elements was performed: (i) experimentally on the basis of goniometric measurements, as well as (ii) theoretically by applying optical modelling and optimization procedures. This resulted in a better understanding of the effectiveness of the optical volume elements in decreasing the optical shadowing of metal grid lines on the active cell surfaces. Moreover, results of photovoltaic mini-modules with incorporated micro-optical volume elements are presented. Results of optical simulation and Laser Beam Induced Current (LBIC) experiments show that the losses due to the grid fingers can be reduced by about 50%, when using this fs-laser structuring approach for the fabrication of micro-optical volume elements in the EVA material.