Microphotoluminescence studies of Cu ₂ ZnSnS ⁴ polycrystals were performed. At room temperature, two photoluminescence (PL) bands were detected at 1.39 and 1.53 eV and attributed to band-to-tail (BT) and band-to-band (BB) recombination, respectively. At lower temperatures, band-to-impurity recombination always dominates. The results show that the model of heavily doped semiconductors applies to Cu ² ZnSnS ₄ and that, in contrast to the ternary chalcopyrites, the BT recombination in Cu ₂ ZnSnS ₄ has very low intensity. The laser power dependency of the PL intensity shows that the recombination mechanism of BT and BB bands exhibits an exciton-like behavior.

The concept of intermediate band solar cell (IBSC) is, apparently, simple to grasp. However, since the idea was proposed, our understanding has improved and some concepts can now be explained more clearly than when the concept was initially introduced. Clarifying these concepts is important, even if they are well known for the advanced researcher, so that research efforts can be driven in the right direction from the start. The six pieces of this work are: Does a miniband need to be formed when the IBSC is implemented with quantum dots? What are the problems for each of the main practical approaches that exist today? What are the simplest experimental techniques to demonstrate whether an IBSC is working as such or not? What is the issue with the absorption coefficient overlap and the Mott’s transition? What would the best system be, if any?

The field of organic photovoltaics (OPV) has progressed rapidly. With new materials and methods being briskly developed, the characterization of OPV also needs to be updated. Current-voltage (JV) analysis of poly(3-hexlythiophene) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM) OPV devices yield valuable insight into the internal physics of devices. A simple lumped circuit model, previously used to analyze various inorganic thin-film PV and more recently applied to OPV, has been used to study annealing parameters. To investigate the change in the lumped circuit model parameters, we carried out an annealing study of P3HT:PCBM blend OPV devices. We annealed devices at various temperatures and before and after evaporating the contact. We characterized and quantified the effect of thermal annealing by studying how the model parameters changed. We found that all parameters studied reacted favorably to annealing, including device resistances and parameters measuring recombination. While studying the resistances in unannealed and annealed devices, a barrier was found around the flat band voltage. This barrier disappeared upon annealing, indicating that it was due to material characteristics related to the crystallinity or the phase separation. The data were used to better characterize annealing effects.

The effect of time and temperature on the sheet resistance (R _S ) and carrier concentration (N _A ) of (100) P-type monocrystalline Si was investigated. Phosphorus-doped n ⁺ -emitters were fabricated through solid-source doping in a quartz tube furnace. The process variable values for 13 runs were proposed by response surface methodology (RSM). The optimized values for time and temperature predicted by RSM were 56 min and 1045°C, respectively, for a sheet resistance of 41.7  Ω/□ and a carrier concentration of 3.7E18  cm ⁻³ . Optimization-based fabrication was found to be in close agreement with the optimized values. Parameter optimization using RSM could be valuable in achieving predetermined dopant variables in optoelectronic devices as well as in reducing the surface recombinations and series resistance of highly efficient Si solar cells.

P-layer of a p-i-n type amorphous silicon solar cell helps in creating a built-in electric field inside the cell; it also contributes to parasitic absorption loss of incident light. Here, we report optimization of these two characteristic contributions of the p-layer of the cell. We used a highly transparent p-type hydrogenated amorphous silicon carbide (p-a-Si ₁−_x C _x :H ) window layer in an amorphous silicon solar cell. With the increased transparency of the p-type layer, the solar cell showed an improvement in short-circuit current density by 17%, along with improvement in blue response of its external quantum efficiency, although further thinner p-layer showed lower open-circuit voltage. Such a cell shows low light-induced degradation and a promise to be used in high-efficiency multijunction solar cell.

There are a great many photovoltaic (PV) modules installed around the world. Despite this, not enough is known about the reliability of these modules. Their electrical power output decreases with time mainly as a result of the effects of corrosion, encapsulation discoloration, and solder bond failure. The failure of a PV module is defined as the point where the electrical power degradation reaches a given threshold value. Accelerated life tests (ALTs) are commonly used to assess the reliability of a PV module. However, ALTs provide limited data on the failure of a module and these tests are expensive to carry out. One possible solution is to conduct accelerated degradation tests. The Wiener process in conjunction with the accelerated failure time model makes it possible to carry out numerous simulations and thus to determine the failure time distribution based on the aforementioned threshold value. By this means, the failure time distribution and the lifetime (mean and uncertainty) can be evaluated.

We fabricated highly efficient blue organic light-emitting diodes (OLEDs) by designing differing emitting layer structures with fluorescent host and dopant materials of 4,4-bis (2,2-diphenylyinyl)-1,10-biphenyl and 9,10-bis (2-naphthyl) anthracene as host materials and 4,4’-bis (9-ethyl-3-carbazovinylene)-1,1’biphenyl (BCzVBi) as a dopant material to demonstrate electrical and optical improvements. Best enhancement in luminance and luminous efficiency were achieved by a quantum well structure in device F with 8668  cd/m ² at 8 V and 5.16  cd/A at 103.20  mA/cm² , respectively. Among the blue OLED devices doped by BCzVBi, device B emits the deepest blue emission with Commission Internationale de l’É clairage coordinates of (0.157, 0.117) at 8 V.

We present a study of spectroscopic proprieties of poly(n-vinylcarbazole) (PVK) and PVK doped with iridium complexes tris[2-phenylpyridinato-C2,N]iridium(III) (Ir(ppy)₃) films prepared by spin-coating from toluene and chlorobenzene solutions. A different molecular organization of the polymer on the substrate during the spin-coating process can be produced using solvents with different boiling temperatures. The modified molecular rearrangement affects the emission properties of the PVK material and the consequent energy transfer to the doping molecules. Both static and dynamic fluorescence emissions properties have been studied, for pure PVK and PVK doped with different weight percentage of Ir(ppy)₃. Different organic light-emitting devices, using a simple architecture, have been prepared with both solvents to test the change in electroluminescence spectral shape and in electrical characteristic, and the final efficiencies of the devices have been evaluated.

A numerical optimization method (genetic algorithm) is employed to design the spherical light-emitting diode (LED) array for highly uniform illumination distribution. An evaluation function related to the nonuniformity is constructed for the numerical optimization. With the minimum of evaluation function, the LED array produces the best uniformity. The genetic algorithm is used to seek the minimum of evaluation function. By this method, we design two LED arrays. In one case, LEDs are positioned symmetrically on the sphere and the illuminated target surface is a plane. However, in the other case, LEDs are positioned nonsymmetrically with a spherical target surface. Both the symmetrical and nonsymmetrical spherical LED arrays generate good uniform illumination distribution with calculated nonuniformities of 6 and 8%, respectively.

Light trapping by means of backside diffraction gratings can strongly increase the efficiency in silicon solar cells. However, the optimization of the grating geometry involves comprehensive multiparameter scans, which necessitates an efficient simulation method. In this study, we employ a simulation approach that combines ray tracing with rigorous coupled wave analysis. As an additional benefit, this approach provides a much better physical insight into the light trapping mechanism in contrast to fully electromagnetic simulation methods. The influence of the ray tracing simulation settings in terms of recursion depth and diffraction order on the simulation results is investigated. We show that the choice of a proper recursion depth and a sufficient number of diffraction orders is essential for obtaining fully optimized grating parameters and that the minimum recursion depth required for obtaining the correct optimized grating parameters depends on the silicon thickness. Furthermore, we investigate the influence of the angle of incidence on the optimized grating parameters. As major result, we find that the optimum grating structure does not depend on the angle of incidence on the solar cell.

In order to improve the light-harvesting capability of silicon solar cells, bioinspired texturing of the exposed surface was investigated. The texture has a pit topology, which is the negative of a previously analyzed bioinspired hillock texture. Multifrequency numerical simulations of the light-coupling efficiency were carried out within the framework of the geometrical optics over a large and relevant portion of the solar spectrum. The bioinspired pit texture exhibits an efficiency significantly greater than that of a flat silicon surface, and somewhat outperforms the bioinspired hillock texture.

The optical efficiency of a holographic spectrum-splitting optical system with transmission holographic lenses is investigated. Spectrum-splitting is a promising approach to improve the efficiency of photovoltaic (PV) systems. By removing the lattice-matching constraints, it is possible to utilize low-cost thin-film PV materials and fabrication techniques. Transmission holograms are fabricated with the recording of the interference patterns of two or more coherent beams. It is also possible to use converging construction wavefronts to record holographic gratings that are matched to the focusing beam from the primary concentrator optics. Experimental holograms are fabricated in dichromated gelatin, and high diffraction efficiency is obtained. A single holographic lens is used to divide a broad spectrum into two types of PV cells. The position and orientation of the PV cells are chosen to match the dispersion properties of the holographic lens. The optical transfer efficiency of the holographic lens is measured to be ∼90% at the peak with fast transitions between the high diffraction efficiency and the high transmission spectral regions. With a GaAs solar cell and a 2.1-eV bandgap solar cell, the system efficiency is 31.0% under one-sun which is improved by 11.9% over the best single PV cell. The achievable system efficiency with the prototype filter is 96% compared to that of the ideal system.

All presently available types of solar cells transmit light with energies below their band gaps, foregoing energy. An elegant way toward overcoming these subbandgap losses and using a larger fraction of the incident light is the re‐shaping of the solar spectrum by upconversion (UC) of photons. Recently, first results on solar cells augmented by either lanthanide-based UC or triplet-triplet-annihilation UC in organic chromophores were presented. Both of these UC strategies are characterized by a nonlinear response on the illumination density under conditions relevant to solar energy conversion, opening a route for increasing the UC yield by concentrating the light. While operation of the whole cell under concentrated sunlight is in most cases undesirable, application of micro-optical focusing of the transmitted light in the upconverting layer is a promising strategy. In the present work, a more than two-fold enhancement of the current gain by UC behind an amorphous silicon solar cell through optimization of the upconverter optical design is demonstrated, including employing a focusing microstructured back reflector. The experimental data is rationalized using a simple ray tracing modeling approach, highlighting a further enhancement potential of a microstructured UC unit.

Investigating the use of prismatic lenses with cross-sectional shapes inspired by the apposition compound eyes of some dipterans, we found through numerical simulations that the exposed surfaces of silicon solar cells should be textured as arrays of bioinspired compound lenses in order to improve performance. We +used a ray-tracing algorithm to evaluate the light-coupling efficiency over a large and relevant portion of the solar spectrum and determined the array configuration that maximizes the coupling of light. Our simulation results show that the light-coupling efficiency can be significantly enhanced with respect to that of a silicon cell with a flat surface.

The intermolecular electron transfer between the carboxylic dendritic zinc(II) phthalocyanines [G ₁ -ZnPc(COOH) ₈ and G ₂ -ZnPc(COOH) ₁₆ ] and methyl viologen (MV ²⁺ ) is studied by steady-state fluorescence and UV/Vis absorption spectroscopic method. The effect of dendron generation of this series of dendritic phthalocyanines on intermolecular electron transfer is investigated. The results show that the fluorescence emission of these dendritic phthalocyanines could be greatly quenched by MV ²⁺ upon excitation at 610 nm. The Stern–Volmer constant (K _SV ) of electron transfer is decreased with increasing dendron generations. Our study suggests that these dendritic phthalocyanines are an effective new electron donor and transmission complex and could be used as a potential artificial photosynthesis system.

The design, fabrication, and characterization of an upconversion-luminescence enhancer based on a two-dimensional plasmonic crystal are described. Full-wave finite-difference time domain analysis was used for optimizing the geometrical parameters of the plasmonic crystal for maximum plasmon activity, as signified by minimum light reflection. The optimum design produced <20× enhancement in the average electromagnetic field intensity within a one-micron-thick dielectric film over the plasmonic crystal. The optimized plasmonic upconverter was fabricated and used to enhance the upconversion efficiency of sodium yttrium fluoride: 3% erbium, 17% ytterbium nanocrystals dispersed in a poly(methylmethcrylate) matrix. A thin film of the upconversion layer, 105 nm in thickness, was spin-coated on the surface of the plasmonic crystal, as well as on the surfaces of planar gold and bare glass, which were used as reference samples. Compared to the sample with a planar gold back reflector, the plasmonic crystal showed an enhancement of 3.3× for upconversion of 980-nm photons to 655-nm photons. The upconversion enhancement was 25.9× compared to the same coating on bare glass. An absorption model was developed to assess the viability of plasmonically enhanced upconversion for photovoltaic applications.

Canonical illumination control problems are studied through the calculation of an appropriate ray mapping. We show that when the problem enjoys certain symmetries, the ray mapping can be calculated independently of the lens design. Once the ray mapping is known, the lens can be constructed. Such a separation of ray mapping and lens determination greatly simplifies the design task. We provide a few examples to illustrate this concept.

This article [J. Photon. Energy. 3, , 034598 (2013)] was originally published on 6 February 2013 with an error in the denominator of Eq. (8). The value k₁ has been added as follows:

This article [J. Photon. Energy. 3, , 034599 (2013)] was originally published on 23 January 2013 with errors in the divisors of four ratios, appearing in the fifth paragraph of Sec. 4.1. In each instance the divisor and the quotient were correctly stated. In the order of appearance, the four ratios are: 0.42/0.38≈1.10 , 0.50/0.48≈1.04 , 0.42/0.33≈1.27 , and 0.50/0.43≈1.16 .