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Abstract Photo-galvanic cell is a photochemical cell device whose performance depends on the combination of several factors like dye and reductant concentrations, dye stability, pH, light intensity, electrodes used, Pt electrode area, diffusion length, etc. An entirely new and unexplored combination of platinum with Allura Red photosensitizer, d-Galactose reductant, and didecyl dimethyl ammonium chloride (DDAC) surfactant has been explored in present research to upgrade the electrical performance of these cells. Allura Red is a water-soluble azo dye which shows good absorbance in region 501–507 nm. The Allura Red and DDAC is an anionic and cationic species, respectively, and therefore, the opposite charges of dye and surfactant molecules are expected to form a stable dye-surfactant complex enhancing the dye solubility and stability. d-Galactose has been used for its good reducing properties. This unexplored combination of Pt-Allura Red-d-Galactose-DDAC with these characteristics has encouraged further enhancement of the electrical output of the photogalvanic cells. The electrical output, stability, and spectral property of the photogalvanic cells have been studied in the present work. The observed power, current, potential, efficiency, and storage capacity (as half time) are of the order of 443.8 µW, 2400 µA, 721 mV, 11.61%, and 28 min, respectively. These observed results are higher than some reported data. In the spectral study, nearly the same band intensity of the pre-illuminated and post-illuminated electrolyte solution shows quite good photo-stability of the Allura Red dye in electrolyte form. This new combination of platinum-electrolyte still has the scope to achieve the enhanced cell performance of photogalvanic cells for future development.

Photo-galvanic cell is a photochemical cell device whose performance depends on the combination of several factors like dye and reductant concentrations, dye stability, pH, light intensity, electrodes used, Pt electrode area, diffusion length, etc. An entirely new and unexplored combination of platinum with Allura Red photosensitizer, d-Galactose reductant, and didecyl dimethyl ammonium chloride (DDAC) surfactant has been explored in present research to upgrade the electrical performance of these cells. Allura Red is a water-soluble azo dye which shows good absorbance in region 501–507 nm. The Allura Red and DDAC is an anionic and cationic species, respectively, and therefore, the opposite charges of dye and surfactant molecules are expected to form a stable dye-surfactant complex enhancing the dye solubility and stability. d-Galactose has been used for its good reducing properties. This unexplored combination of Pt-Allura Red-d-Galactose-DDAC with these characteristics has encouraged further enhancement of the electrical output of the photogalvanic cells. The electrical output, stability, and spectral property of the photogalvanic cells have been studied in the present work. The observed power, current, potential, efficiency, and storage capacity (as half time) are of the order of 443.8 µW, 2400 µA, 721 mV, 11.61%, and 28 min, respectively. These observed results are higher than some reported data. In the spectral study, nearly the same band intensity of the pre-illuminated and post-illuminated electrolyte solution shows quite good photo-stability of the Allura Red dye in electrolyte form. This new combination of platinum-electrolyte still has the scope to achieve the enhanced cell performance of photogalvanic cells for future development. [ABSTRACT FROM AUTHOR]

The complete electrolyte of photogalvanic cells consists of the sensitizer, reductant, surfactant, alkali, and water solvent. In the present research, the electrochemical properties of the individual chemicals of electrolyte and complete electrolyte (including surfactant) have been studied both in the dark and illuminated conditions. Individual chemical components or combination of any two or three chemical components at low pH show very low potential (≤ 401 mV) and current (≤ 13 µA) under both pre-illuminated (dark) and illuminated conditions. For complete electrolyte (including surfactant) at high pH, the observed dark potential, photo potential, current (in dark), and current (in sunlight) is 495 mV, 720 mV, 522 µA, and 2460 µA, respectively. It has been observed that, in the case of high pH conditions of the complete electrolyte, the abrupt jump in the potential coupled with high photo-current is observed during illumination of the cell. Therefore, it is concluded that high potential and current can be obtained by combining all chemical components of the electrolyte at a time under necessary conditions including the high pH. The photogalvanics is achievable only from complete electrolyte at very high pH. The complete electrolyte (excluding surfactant) at high pH also shows photogalvanics. But, a bit low electrical output for complete electrolyte (excluding surfactant) vis-à-vis that of complete electrolyte (including surfactant) is observed and that may be attributed to the lack of role of surfactant in the dye solubility and stability. It is a reported fact that the surfactant enhances the electrical output of the photogalvanic cells. So by taking all these facts, it may be concluded that the requirement of a surfactant is not a necessary condition for photogalvanics, but its presence in the electrolyte enhances it (photogalvanics). Further, the potential and current of the cell at its initial stage and post-sensitizer degradation stage may be attributed to the polar and ionic nature of the individual chemical components of the electrolyte. [ABSTRACT FROM AUTHOR]

Enhancing photogalvanics electrical output in the sphere of solar energy is the goal of the study. The use of fossil fuels is also limitation to energy conversion. The photogalvanic (PG) cell with EDTA + TB + NaLS + CPC + Tween-80 produces superior results than a system with just one surfactant. The photopotential (PP) and photocurrent (PC) of the EDTA + TB + NaLS + CPC + Tween-80 photogalvanics were measured at 689.00 mV and 234.00 uA, respectively. The efficiency and performance of the EDTA + TB + NaLS + CPC + Tween-80 photogalvanics were determined to be 0.2811% and 109.00 min respectively. The photogalvanic system with mixed surfactants (NaLS + CPC + Tween-80) is a productive one with improved electrical characteristics. The performance of PG cells can be slightly improved by using individual surfactants as opposed to surfactant combinations. Surfactant combinations with qualities that are superior to those of the individual components can be used in PG cell applications. [ABSTRACT FROM AUTHOR]

Photo-galvanic cells are based on the diffusion of ions in the electrolyte (a mixture of sensitizer, reductant, alkali, surfactant, and solvent). The photogalvanics is characterized by the abrupt jump in the photo-potential during charging of the cell. Photo-galvanic cells have been widely studied using the complete electrolyte. The migration of current by ions gives impression that any of the ionic species individually (like sensitizer/reductant/etc.) may show current, potential, and photogalvanics. This aspect of photogalvanics of individual chemical components is missing in the literature. Therefore, the photogalvanics of the individual chemicals, mixtures of the chemicals, and complete electrolyte have been studied in present research to have insight into (i) the genesis of the current and potential generated from the cell in non-illuminated state (dark conditions), and (ii) the necessary chemical conditions required for the photogalvanics.The average open-circuit potential (Voc) and short-circuit current (Isc) in dark conditions for water, Lactic acid reductant, Cocamidopropyl betaine surfactant, Carmoisine-A dye, NaOH alkali, complete electrolyte (at low pH), and complete electrolyte (at very high pH) is 286 mV, 4 µA; 214 mV, 3 µA; 278 mV, 4 µA; 268 mV, 9 µA; 295 mV, 8 µA; 278 mV, 8 µA; and 463 mV, 253 µA, respectively. The average Voc and Isc from illuminated water, Lactic acid reductant, Cocamidopropyl betaine surfactant, Carmoisine-A dye, NaOH alkali, complete electrolyte (at low pH), and complete electrolyte (at very high pH) is 296 mV, 3 µA; 182 mV, 4 µA; 218 mV, 4 µA; 135 mV, 3 µA; 275 mV, 9 µA; 167 mV, 6 µA; and 731 mV, 2500 µA, respectively. Thus, no photogalvanics has been observed for individual chemical components, and mixtures of two or more chemical components of the electrolyte. The photogalvanics is observed only for complete electrolyte at high pH.

Summary: The technology to harness solar power has been evolving continuously with a recent focus on simultaneous power storage as well. Photogalvanic (PG) cell is a promising technology for simultaneous solar power and storage. The nature of the sensitizer, reductant, surfactant, and electrodes are the key factor determining the efficiency, stability, and power storage capacity of the PG cells. The use of a more stable dye with good diffusivity and conductivity realized through the most suitable surfactant has evaded the attention of researchers. Therefore, in the present study, the photogalvanics of the stable Quinoline Yellow (QY) dye photosensitizer in the presence of the Dodecyltrimethyl Ammonium Bromide (DTAB) surfactant, and Cellobiose reductant at an elevated pH has been studied for solar energy conversion and storage. The entirely novel and new photogalvanic system has shown abruptly enhanced electrical performance of the PG cell as potential 900 mV, current 10 000 μA, and power 989 μW. Encouraging photogalvanics may be attributed primarily to the greater QY dye‐DTAB surfactant interaction enhanced dye solubility, stability, and diffusion through the electrolyte. Spectrometric and conductometric study of the electrolyte has validated good photostability and conductivity of the electrolyte solution. Based on published literature and observed facts, a most plausible mechanism for the photogeneration of the current and power storage capacity has also been proposed. The present research does not introduce any new mechanism for the photo‐generation of the current, but a new and novel cell fabrication design with greatly enhanced electrical output in comparison to that in earlier studies. Novelty statement: The cationic Dodecyltrimethyl Ammonium Bromide surfactant and Quinoline Yellow (QY) anionic dye sensitizer has been exploited in the presence of Cellobiose reductant for enhanced dipole‐dipole interactions for further enhancing the photogalvanics. The hypsochromic and hypochromic shift of main band of QY in electrolyte may be attributed to the QY‐DTAB complex formation due to interaction between the anionic QY dye and cationic DTAB surfactant. The present study shows abruptly enhanced electrical output (potential 900 mV, current 10 000 μA, power 989 μW). [ABSTRACT FROM AUTHOR]

[Display omitted] • To evaluate the most efficient redox (dye-reductant combination) couple based on compatibility of electron donor (reductant) and acceptor (dye) species for the PG cell. • The photogalvanic study for four (BCB-fructose, BCB-AA, MB-fructose and MB-AA) redox systems has been done, simultaneously. The order for redox couple based on electrical output is: MB-AA > MB-fructose > BCB-AA > BCB-fructose. • The electrical output is high when MB is used as a photosensitizer with both fructose and AA. It may be because of the larger λ max and the low molecular weight of MB than BCB. • The literature photogalvanic data for the different dye-AA systems clearly indicate that the electrical output has a lower than MB-AA redox couple of present study. • Thus, for the PG cell, the MB-AA redox couple has highest compatibility for electron acceptor and donor out of four redox systems. There are several devices for direct conversion of solar energy to electric energy, but, all have zero storage capacity. Photogalvanic cell (PG) has both properties to convert and store (chemical form) the solar energy. Therefore, the PG cells may be playing a very important role to fulfill energy demand in the future. Here, our aim is to evaluate the most efficient redox (dye-reductant combination) couple based on the compatibility of the dnor (reductant) and acceptor (dye) species for the PG cell. For this, we have completed photogalvanics (measurement and calculation of different electrical parameters of each cell) for brilliant cresyl blue (BCB) or methylene blue (MB)-fructose/ascorbic acid (AA) redox couple for solar power conversion and storage. Here, MB/BCB and fructose/AA have been used as photosensitizers and reductants, respectively. Results show the order for redox couple based on electrical output is: MB-AA > MB-fructose > BCB-AA > BCB-fructose. The electrical output is high when MB is used as a photosensitizer with both fructose and AA. It may be because of the larger λ max and the low molecular weight of MB than BCB. Indeed, the generation of electricity in the PG cell is the outcome of the diffusion process of molecules or ions in an electrolytic solution. The results reported in the literature for the different dye-AA systems of the PG cells clearly indicate that the electrical output of every system has a lower value as compared to the MB-AA redox couple of present study. Hence, MB-AA is the most efficient and stable system out of the four redox couples. Thus, the dye and reductant having structures like MB and AA are more compatible for electron acceptor and donor power for simultaneous solar power conversion and storage in the PG cell. [ABSTRACT FROM AUTHOR]

The paper reviews the interplay of Rashba/Dresselhaus spin splittings in various two-dimensional systems made of zinc-blende III-V, wurtzite, and SiGe semiconductors. We discuss the symmetry aspects of the linear and cubic in electron wavevector spin splitting in heterostructures prepared on (001)-, (110)-, (111)-, (113)-, (112)-, and (013)- oriented substrates and address the requirements for suppression of spin relaxation and realization of the persistent spin helix state. In experimental part of the paper, we overview experimental results on the interplay of Rashba/Dresselhaus spin splittings probed by photogalvanic spectroscopy: The method based on the phenomenological equivalence of the linear-in-wavevector spin splitting and several photogalvanic phenomena. [ABSTRACT FROM AUTHOR]

The paper overviews experimental and theoretical studies of photogalvanic effects (PGEs) induced in graphene and carbon nanotubes (CNs) by polarized electromagnetic radiation. The following items are discussed: the helicity-dependent photon-drag and edge electric currents in graphene sheets, the circular PGEs in asymmetric graphene superlattices and chiral CNs, and pure valley currents generated in graphene by the interband absorption of linearly polarized light. [ABSTRACT FROM AUTHOR]

We report on the observation of photogalvanic effects in tBLG with a twist angle of 0.6°. We show that excitation of the tBLG bulk causes a photocurrent, whose sign and magnitude are controlled by the orientation of the radiation electric field and the photon helicity. The observed photocurrent provides evidence for the reduction of the point group symmetry in low twist-angle tBLG to the lowest possible one. The developed theory shows that the current is formed by asymmetric scattering in gyrotropic tBLG. We also detected the photogalvanic current formed in the vicinity of the edges. For both bulk and edge photocurrents, we demonstrate the emergence of pronounced oscillations upon variation of the gate voltage. The gate voltages associated with the oscillations correlate with peaks in resistance measurements. These are well explained by interband transitions between a multitude of isolated bands in tBLG.