Optical Power Dissipation Research Articles

Effects of Incoherent Front Cover Glass on Current-Voltage Characteristics of Cu(In,Ga)Se2 Solar Cells: Investigation into Calculation Accuracy for Cover Glass Modeled as Optically Coherent or Incoherent

We numerically investigate the effects of an incoherent front cover glass on the current–voltage (J–V) characteristics of a Cu(In,Ga)Se2 (CIGS) solar cell using an integrated optoelectronic model. A 3-mm cover glass—the thickness of which was larger than the coherence length of sunlight—was incoherently modeled based on the equispaced thickness averaging method, where coherent simulation results of the wave equation were averaged over a set of equispaced phase thicknesses. The changes in optical power dissipation, absorptivity and electron–hole pair generation rate were calculated depending on the variation of the equispaced phase thickness. The calculation results of the J–V curves were obtained through numerical solutions of the coupled Poisson and continuity equations. By comparing the J–V curves calculated between coherently and incoherently modeled cover glass, we obtained a maximum ±0.54% deviation of the short-circuit current density. This demonstrates that the front cover glass should be modeled as optically incoherent to improve the calculation accuracy of the electrical J–V curves as well as the optical absorption characteristics in the optoelectronic modeling of CIGS solar cells.

Single- and two-qubit universal quantum gates in photonic Ti:LiNbO3 circuits

We report on the photonic Ti:LiNbO3 circuit design of single-qubit Hadamard, polarization and spatially encoded single-photon two-qubit CSIGN and CNOT quantum gates, using continuous-wave pump source and 812nm photon-pairs. The proposed circuits aim at optimizing the overall performance in terms of optical power dissipation management and accurately realizing the desired functionalities. By utilizing S-bend structures, through simulations we have obtained Electrical-field amplitudes with approximate values of ± (1/2)1/2 at the output branches of the Hadamard circuit. CSIGN modified circuit exhibits a reduction of 0.618 dB and 0.4288 dB in polarization-odd and -even modes dispersion, respectively. The modified CNOT circuit is 128.7 μm less wide than the initially designed circuit and the unwanted TM ⇄ TE polarization conversion at the applied voltage of V = 53 V is addressed.

Uniaxial Anisotropy in PEDOT:PSS Electrodes Enhances the Photocurrent at Oblique Incidence in Organic Solar Cells

PEDOT:PSS is a well studied organic conductor, commonly used as a transparent electrode material in printed organic devices such as organic solar cells. PEDOT:PSS thin films are known to be uniaxially anisotropic and exhibit a lower extinction coefficient and lower refractive index in the out of plane direction. To determine the maximum attainable photocurrent in thin film solar cells, the optical power dissipation can be calculated by the transfer matrix method. However, until now the anisotropic properties of PEDOT:PSS films have not been included in the model. In this work we have included an uniaxial anisotropic treatment of PEDOT:PSS films. We investigate reversed and semitransparent solar cells, with aluminum and PEDOT:PSS respectively as the second electrode and PEDOT:PSS as the top electrode, as compared to devices with isotropic PEDOT:PSS electrodes. For p-polarized light at large oblique incidence the inclusion of anisotropy shows a gain of over 7% for the maximum photocurrent in reversed solar cells. In semitransparent solar cells the photocurrent enhancement reaches 4–5% for p-polarized light. However, an enhancement of optical power dissipation and thus photocurrent generation of close to 40% is calculated for wavelengths close to the absorber bandgap. This work shows that for correct calculations of optical power dissipation in devices with PEDOT:PSS electrodes anisotropy should be included in the optical model. This will be especially important to determine the daily energy output of organic solar cells as their expected first markets are on building facades and indoor applications with larger fractions of diffuse light at large oblique incidence.

Unlocking Spectral Efficiency in Intensity Modulation and Direct Detection Systems

A number of inherently unipolar orthogonal frequency division multiplexing (OFDM) modulation schemes have been introduced recently in an attempt to improve the energy efficiency of OFDM-based intensity modulation and direct detection (IM/DD) systems. All such algorithms, including asymmetrically clipped optical OFDM (ACO-OFDM), pulse-amplitude-modulated discrete multitone modulation (PAM-DMT) and unipolar orthogonal frequency division multiplexing (U-OFDM), experience an inherent loss in spectral efficiency caused by the restrictions imposed on the OFDM frame structure required for the generation of a unipolar signal. The current paper presents a modified modulation approach, termed enhanced U-OFDM (eU-OFDM), which compensates the spectral efficiency loss in U-OFDM. At the same time, it still allows for the generation of an inherently unipolar modulation signal that achieves better performance in terms of both electrical power and optical power dissipation compared to the conventional state-of-the-art technique direct current (DC)-biased optical OFDM (DCO-OFDM). To the best of the authors' knowledge, the current work also presents the first experimental proof-of-concept demonstration of both U-OFDM and eU-OFDM, and clearly demonstrates the significant energy advantages that these two schemes can introduce in an optical wireless communications (OWC) system.

Effect of incidence angle and polarization on the optimized layer structure of organic solar cells

We theoretically and experimentally investigate the effect of the incidence angle and polarization of sunlight on the optimized layer structure of organic solar cells (OSCs) to obtain the best absorption efficiency in a realistic deployment situation. We use the generalized transfer matrix method with respect to the incidence angle and polarization, which can calculate the spatial distribution of the optical power dissipation in both the incoherent glass substrate and the coherent multilayer without using any indirect correction factor. The angular dependence of the short-circuit current, the open-circuit voltage, and the output electric power is calculated and compared with the experimental results. Using the simulation parameters matched with the experimental results, we calculate the generation energy density per day by considering the variation of the incidence angle during daytime and determine the optimized thickness of the active region for maximum absorption efficiency. We show that the optimized active-region thickness based on the generation energy density per day is different from that determined from the variation of the short-circuit current density in only normal incidence, which is generally used for optimizing device structure of OSCs.

Optical Modeling for Polarization-dependent Optical Power Dissipation of Thin-film Organic Solar Cells at Oblique Incidence

We present the optical models and calculation results of thin-film organic solar cells (OSCs) at oblique incidence of light, using the transfer matrix method. The simple expression for the optical power dissipation is derived at oblique incidence for s- and p-polarized light. The spatial distribution of the electric field intensity, the optical power density, and the optical power dissipation are calculated in both s- and p-polarized light with respect to the incidence angle. We identify how the light absorption efficiency for p-polarized light becomes relatively larger than that for s-polarized light as the incidence angle increases.

Universal Expression of the Optical Power Dissipation in Multilayer Structures with Complex Permittivity and Permeability

A general simple expression is derived for the time-average optical power dissipation Q in plasmonic or metamaterial-based multilayer structures, which have complex permittivity and/or complex permeability. We demonstrate that the derived general expression for Q, including the optical interference effect, is in the same form as one based on the Poynting's energy theorem, where the optical interference effect is not explicitly considered. The universal expression of Q, derived under the assumption of complex permittivity and permeability, reduces to other well-known simple forms, which are only valid when either permittivity or permeability is complex. The derived general expression of Q provides with a strong theoretical background to predict the optical absorption or loss in the design of plasmonic or metamaterial-based nanostructures.

Universal Expression of the Optical Power Dissipation in Multilayer Structures with Complex Permittivity and Permeability

A general simple expression is derived for the time-average optical power dissipation Q in plasmonic or metamaterial-based multilayer structures, which have complex permittivity and/or complex permeability. We demonstrate that the derived general expression for Q, including the optical interference effect, is in the same form as one based on the Poynting's energy theorem, where the optical interference effect is not explicitly considered. The universal expression of Q, derived under the assumption of complex permittivity and permeability, reduces to other well-known simple forms, which are only valid when either permittivity or permeability is complex. The derived general expression of Q provides with a strong theoretical background to predict the optical absorption or loss in the design of plasmonic or metamaterial-based nanostructures.