Enhanced light harvesting from Först-type resonance energy transfer in the quasi-solid state dye-sensitized solar cells

The demonstrated F?rst-type resonance energy transfer (FRET) is demonstrated in quasi-solid type dye-sensitized solar cells between organic fluorescence materials as an energy donor doped in polymeric gel electrolyte and a ruthenium complex as an energy acceptor on the surface of TiO2. Strong spectral overlap of emission/absorption of the energy donor and acceptor is required to obtain high FRET efficiency. The judicious choice of the energy donor allows the enhancement of the light harvesting characters of the energy acceptor (N3) in quasi-solid dye sensitized solar cells which increases the power conversion efficiency by 25% compare to that of a pristine cell. The optimized cell architecture fabricated with the quasi-solid type electrolyte containing fluorescence materials shows a maximum efficiency of 5.08% with a short-circuit current density (J(sc)) of 12.63 mA/cm2, and an open-circuit voltage (V(oc)) of 0.70 V under illumination of simulated solar light (AM 1.5, 100 mW/cm2).     

介孔TiO2微球水热法合成及在染料敏化太阳能电池中的应用

以Ti(SO4)2为钛源,采用尿素辅助水热法合成了介孔TiO2微球,利用XRD、FESEM和比表面积分析仪对样品的晶型、形貌和比表面积进行分析,探讨了尿素加入量对TiO2微球的颗粒尺寸、比表面积、孔径和孔容的影响。采用刮涂法,用所合成的介孔TiO2微球制备了染料敏化太阳能电池(DSSC)的光阳极,结果表明,尿素用量为1.2g合成的介孔TiO2微球所组装的电池在模拟太阳光的照射下(100mW/cm2,AM1.5),光电转换效率为6.2%,明显高于商用P25纳晶所组装的电池光电转换效率(4.24%)。     

A Hybrid Solar Absorber–Electrocatalytic N‐Doped Carbon/Alloy/Semiconductor Electrode for Localized Photothermic Electrocatalysis

Converting and storing intermittent solar energy into stable chemical fuels of high efficiency depend crucially on harvesting excess energy beyond the conventional ultraviolet light spectrum. The means of applying highly efficient solar–thermal conversion on practical electricity‐driven water splitting could be a significant stride toward this goal, while some bottlenecks remain unresolved. Herein, photothermic electrocatalytic oxygen and hydrogen evolution reactions are proposed, which bestow a distinctive exothermic activation and electrochemical reactivity in a reconstructed electrolyzer system, and which are poised for efficient renewable energy production. Attributed to the synergistic in situ coupling of the N‐doped carbon, metallic alloy and oxides, in view of their broadband light absorption, high electrochemical surface area, and efficient charge transfer attributes, the hybrid photothermal electrocatalytic electrode simultaneously satisfies efficient photon‐to‐heat conversion and augmented electrochemical catalytic activity. Finally, a system level design of an appropriate photothermally mediated electrolytic cell with close‐proximity light‐illumination window along with a low‐thermal‐emittance electrolyte separator that preserve an overall large localized thermal gradient and efficient mass transport is devised. Such a photothermally mediated electrocatalytic system presented here may open up new avenues for the development of solar–thermal energy utilization in other forms.     

Highly active oxide photocathode for photoelectrochemical water reduction

A clean and efficient way to overcome the limited supply of fossil fuels and the greenhouse effect is the production of hydrogen fuel from sunlight and water through the semiconductor/water junction of a photoelectrochemical cell, where energy collection and water electrolysis are combined into a single semiconductor electrode. We present a highly active photocathode for solar H(2) production, consisting of electrodeposited cuprous oxide, which was protected against photocathodic decomposition in water by nanolayers of Al-doped zinc oxide and titanium oxide and activated for hydrogen evolution with electrodeposited Pt nanoparticles. The roles of the different surface protection components were investigated, and in the best case electrodes showed photocurrents of up to -7.6 mA cm(-2) at a potential of 0 V versus the reversible hydrogen electrode at mild pH. The electrodes remained active after 1 h of testing, cuprous oxide was found to be stable during the water reduction reaction and the Faradaic efficiency was estimated to be close to 100%.     

Electrospray preparation of hierarchically-structured mesoporous TiO₂ spheres for use in highly efficient dye-sensitized solar cells

We report a simple method to prepare hierarchically structured TiO(2) spheres (HS-TiO(2)), using an electrostatic spray technique, that are utilized for photoelectrodes of highly efficient dye-sensitized solar cells (DSSCs). This method has an advantage to remove the synthesis steps in conventional sol-gel method to form nano-sized spheres of TiO(2) nanoclusters. The fine dispersion of commercially available nanocrystalline TiO(2) particles (P25, Degussa) in EtOH without surfactants and additives is electro-sprayed directly onto a fluorine-dopoed tin-oxide (FTO) substrate for DSSC photoelectrodes. The DSSCs of HS-TiO(2) photoelectrodes show high energy conversion efficiency over 10% under illumination of light at 100 mW cm(-2), AM1.5 global. It is concluded from frequency-dependent measurements that the faster electron diffusion coefficient and longer lifetime of HS-TiO(2) than those in nonstructured TiO(2) contribute to the enhanced efficiency in DSSCs.     

One‐Step Fabrication of Unique Mesoporous NiO Hollow Sphere Film on FTO for High‐Performance P‐Type Dye‐Sensitized Solar Cells

P‐type dye sensitized solar cells (p‐DSCs) deliver much lower overall efficiency than their inverse model, n‐DSCs. However, they have fundamental and practical significance, in particular, their tandem structured solar cells with both p‐ and n‐photoelectrodes could offer great potential to significantly improve the efficiency of existing solar cells. A facile and environmentally friendly method is developed to directly one‐step grow hollow NiO spherical structures on fluorine‐doped tin oxide (FTO) substrate, in which a Ni²⁺ and polymer complex spherical structure is self‐constructed through a controlled solvent evaporation process, followed by calcination‐converting to a unique NiO hollow sphere film. The prepared material is further used as a photocathode in p‐type dye sensitized solar cells, resulting in 41% increase of an open‐circuit voltage and 18% enhancement of power conversion efficiency than NiO nanoparticles photocathode. The improved performance can be ascribed to suppressed charge recombination at the photocathode/electrolyte interface. This template‐free approach could be universally used to fabricate other nanostructured hollow spheres for a wide range of energy conversion applications such as electrochemical capacitors, chemical sensors, and electrochromic devices.     

Dual‐Hole Excitons Activated Photoelectrolysis in Neutral Solution

II–VI semiconductors exhibit unique behaviors that can generate dual‐holes (“heavy and light”), but the application in photocatalysis is still missing. Herein, an empirical utilization of light/heavy holes in a hybrid metal cluster‐2D semiconductor nanoplatelets is reported. This hybrid material can boost the hole‐transfer at the surface and suppress the recombination. Different roles are enacted by light‐holes and heavy‐holes, in which the light‐holes with higher energy and mobility can facilitate the slow kinetics of water oxidation and further reduce the onset voltage, while the massive heavy‐holes can increase the resulting photocurrent by about five times, achieving a photocurrent of 2 mA cm^?2 at 1.23 V versus RHE under AM 1.5 G illumination in nonsacrificial neutral solution. These strategies can be the solutions for photoelectrolysis and be beneficial for sustainable development in solar conversion.     

Epitaxial Bi2FeCrO6 Multiferroic Thin Film as a New Visible Light Absorbing Photocathode Material

Ferroelectric materials have been studied increasingly for solar energy conversion technologies due to the efficient charge separation driven by the polarization induced internal electric field. However, their insufficient conversion efficiency is still a major challenge. Here, a photocathode material of epitaxial double perovskite Bi₂FeCrO₆ multiferroic thin film is reported with a suitable conduction band position and small bandgap (1.9–2.1 eV), for visible‐light‐driven reduction of water to hydrogen. Photoelectrochemical measurements show that the highest photocurrent density up to ?1.02 mA cm^?2 at a potential of ?0.97 V versus reversible hydrogen electrode is obtained in p‐type Bi₂FeCrO₆ thin film photocathode grown on SrTiO₃ substrate under AM 1.5G simulated sunlight. In addition, a twofold enhancement of photocurrent density is obtained after negatively poling the Bi₂FeCrO₆ thin film, as a result of modulation of the band structure by suitable control of the internal electric field gradient originating from the ferroelectric polarization in the Bi₂FeCrO₆ films. The findings validate the use of multiferroic Bi₂FeCrO₆ thin films as photocathode materials, and also prove that the manipulation of internal fields through polarization in ferroelectric materials is a promising strategy for the design of improved photoelectrodes and smart devices for solar energy conversion.     

Front-side illuminated CdS/CdSe quantum dots co-sensitized solar cells based on TiO₂ nanotube arrays

We fabricated a front-side illuminated CdS/CdSe quantum dots co-sensitized solar cell based on TiO(2) nanotube arrays. The freestanding TiO(2) nanotube arrays were first detached from anodic oxidized Ti foils and then transferred to the fluorine-doped tin oxide to form photoanodes. An opaque Cu(2)S with high electrochemical activity was used as the counter electrode. A photovoltaic conversion efficiency as high as 3.01% under one sun illumination has been achieved after optimizing the deposition time of CdSe quantum dots and the length of the TiO(2) nanotube arrays. It is observed that the power conversion efficiency of quantum dots sensitized solar cells from the front-side illumination mode (3.01%) is much higher than that of the back-side illumination mode (1.32%) owing to the poor catalytic activity of Pt to polysulfide electrolytes and light absorption by the electrolytes for the latter.     

An optimized metal grid design to improve the solar cell performance under solar concentration using multiobjective computation

In this paper, a new multiobjective genetic algorithm (MOGA)-based approach is proposed to optimize the metal grid design in order to improve the electrical performance and the conversion efficiency behavior of the solar cells under high intensities of illumination. The proposed approach is applied to investigate the effect of two different metal grid patterns (one with 2 busbars outside the active area (linear grid) and another one with a circular busbar surrounding the active area (circular grid)) on the electrical performance of high efficiency c-Si solar cells under concentrated light (up to 150 suns). The dimensional and electrical parameters of the solar cell have been ascertained, and analytical expressions of the power losses and conversion efficiency, including high illumination effects, have been presented. The presented analytical models are used to formulate different objective functions, which are the prerequisite of the multiobjective optimization. The optimized design can also be incorporated into photovoltaic circuit simulator to study the impact of our approach on the photovoltaic circuit design.     

Visible light-induced charge retention and photocatalysis with hybrid CdSe-Au nanodumbbells

Visible light photocatalysis is a promising route for harnessing of solar energy to perform useful chemical reactions and to convert light to chemical energy. Nanoscale photocatalytic systems used to date were based mostly on oxide semiconductors aided by metal deposition and were operational only under UV illumination. Additionally, the degree of control over particle size and shape was limited. We report visible light photocatalysis using highly controlled hybrid gold-tipped CdSe nanorods (nanodumbbells). Under visible light irradiation, charge separation takes place between the semiconductor and metal parts of the hybrid particles. The charge-separated state was then utilized for direct photoreduction of a model acceptor molecule, methylene blue, or alternatively, retained for later use to perform the reduction reaction in the dark.     

Photovoltaic–Pyroelectric Coupled Effect Induced Electricity for Self‐Powered Photodetector System

Ferroelectric materials have demonstrated novel photovoltaic effect to scavenge solar energy. However, most of the ferroelectric materials with wide bandgaps (2.7–4 eV) suffer from low power conversion efficiency of less than 0.5% due to absorbing only 8–20% of solar spectrum. Instead of harvesting solar energy, these ferroelectric materials can be well suited for photodetector applications, especially for sensing near‐UV irradiations. Here, a ferroelectric BaTiO₃ film‐based photodetector is demonstrated that can be operated without using any external power source and a fast sensing of 405 nm light illumination is enabled. As compared with photovoltaic effect, both the responsivity and the specific detectivity of the photodetector can be dramatically enhanced by larger than 260% due to the light‐induced photovoltaic–pyroelectric coupled effect. A self‐powered photodetector array system can be utilized to achieve spatially resolved light intensity detection by recording the output voltage signals as a mapping figure.     

Realizing Stable Artificial Photon Energy Harvesting Based on Perovskite Solar Cells for Diverse Applications

As the fastest developing photovoltaic device, perovskite solar cells have achieved an extraordinary power conversion efficiency (PCE) of 25.3% under AM 1.5 illumination. However, few studies have been devoted to perovskite solar cells harvesting artificial light, owing to the great challenge in the simultaneous manipulation of bandgap‐adjustable perovskite materials, corresponding matched energy band structure of carrier transport materials, and interfacial defects. Herein, through systematic morphology, composition, and energy band engineering, high‐quality Cs_0.05MA_0.95PbBr_xI_3?x perovskite as the light absorber and Nb_yTi_1?yO₂ (Nb:TiO₂) as the electron transport material with an ideal energy band alignment are obtained simultaneously. The theoretical‐limit‐approaching record PCEs of 36.3% (average: 34.0 ± 1.2%) under light‐emitting diode (LED, warm white) and 33.2% under fluorescent lamp (cold white) are achieved simultaneously, as well as a PCE of 19.5% (average: 18.9 ± 0.3%) under solar illumination. An integrated energy conversion and storage system based on an artificial light response solar cell and sodium‐ion battery is established for diverse practical applications, including a portable calculator, quartz clock, and even environmental monitoring equipment. Over a week of stable operation shows its great practical potential and provides a new avenue to promote the commercialization of perovskite photovoltaic devices via integration with ingenious electronic devices.     

Formation of aligned ZnO nanotube arrays by chemical etching and coupling with CdSe for photovoltaic application

High density aligned ZnO nanotube (NT) arrays were synthesized using a facile chemical etching of electrochemically deposited ZnO nanorods (NRs). The influence of etching time and solution concentration on the ZnO NT formation was investigated. Moreover, cadmium selenide (CdSe) nanoparticles as sensitizers were assembled onto the ZnO NT and NR arrays for solar cell application. A conversion efficiency (η) of 0.44% was achieved for CdSe/ZnO NT-based solar cell under the white light illumination intensity of 85 mW/cm². An 8% enhancement in η was observed between the CdSe/ZnO NT-based and NR-based solar cell due to the enhancement of the photocurrent density. ZnO NT arrays have been proved to have a superior ability as compared with ZnO NR arrays when employed as a semiconductor film.     

Graphene/silicon nanowire Schottky junction for enhanced light harvesting

Schottky junction solar cells are assembled by directly coating graphene films on n-type silicon nanowire (SiNW) arrays. The graphene/SiNW junction shows enhanced light trapping and faster carrier transport compared to the graphene/planar Si structure. With chemical doping, the SiNW-based solar cells showed energy conversion efficiencies of up to 2.86% at AM1.5 condition, opening a possibility of using graphene/semiconductor nanostructures in photovoltaic application.     

Progress in light harvesting and charge injection of dye-sensitized solar cells

Dye-sensitized solar cells (DSSCs) based on nanocrystalline semiconductors such as TiO₂ are of great interest as an alternative to the conventional solar cells because of their high performance, low-cost production, and environmental advantages. The DSSCs consist of dye molecule coated wide bandgap semiconductor layer, electrolyte, and transparent conducting oxide (TCO) film. When the DSSCs are exposed to solar light, an incident photon creates a bound electron-hole pair in dye sensitizers. Electrons then flow into the oxide nanoparticle anode due to a difference in the energy levels. On the other hand, holes move to the counter electrode through sequential redox reactions in the electrolyte. Therefore, the cell performance is influenced by parameters such as the morphology and optical properties of nanocrystalline oxide films, the electrochemical characteristics of redox electrolytes, and the photochemical properties of molecular sensitizers. In this article, we review the major components of DSSCs such as the oxide semiconductor film, sensitizing dyes, electrolytes, and TCO and discuss their progress to maximize light harvesting and charge injection efficacy. Their electrical, optical, and chemical properties are well correlated to optimize the light harvesting and charge injection of DSSCs. We have also shown recent efforts to improve the energy conversion efficiency, long term stability, sustainability and affordability by modifying or revolutionizing the components of DSSCs. This includes a prospect on the potential commercialization of DSSCs.     

P-type Cu--Ti--O nanotube arrays and their use in self-biased heterojunction photoelectrochemical diodes for hydrogen generation

Copper and titanium remain relatively plentiful in the earth's crust; hence, their use for large-scale solar energy conversion technologies is of significant interest. We describe fabrication of vertically oriented p-type Cu-Ti-O nanotube array films by anodization of copper rich (60% to 74%) Ti metal films cosputtered onto fluorine doped tin oxide (FTO) coated glass. Cu-Ti-O nanotube array films 1 mum thick exhibit external quantum efficiencies up to 11%, with a spectral photoresponse indicating that the complete visible spectrum, 380 to 885 nm, contributes significantly to the photocurrent generation. Water-splitting photoelectrochemical pn-junction diodes are fabricated using p-type Cu-Ti-O nanotube array films in combination with n-type TiO 2 nanotube array films. With the glass substrates oriented back-to-back, light is incident upon the UV absorbing n-TiO 2 side, with the visible light passing to the p-Cu-Ti-O side. In a manner analogous to photosynthesis, photocatalytic reactions are powered only by the incident light to generate fuel with oxygen evolved from the n-TiO 2 side of the diode and hydrogen from the p-Cu-Ti-O side. To date, we find under global AM 1.5 illumination that such photocorrosion-stable diodes generate a photocurrent of approximately 0.25 mA/cm (2), at a photoconversion efficiency of 0.30%.     

Near-infrared azadipyrromethenes as electron donor for efficient planar heterojunction organic solar cells

We report the use of three solution processable azadipyrromethene (ADPM) based compounds, i.e., ADPM, B,F(2)-chelated ADPM (BF2-ADPM), and B,O-chelated ADPM (BO-ADPM), as electron donors in planar heterojunction solar cells. These small molecules possess exceptional light harvesting capability with high extinction coefficients (~1 × 10(5) M(-1) cm(-1) in solutions) and broad absorption spectra up into the near-infrared region. Planar heterojunction organic solar cells, consisting of a solution processed electron donor layer and a vapor deposited C(60) acceptor layer, have been constructed to give power conversion efficiencies of 0.56, 0.69, and 2.63% for ADPM, BF2-ADPM, and BO-ADPM, respectively, under AM 1.5G simulated 1 sun solar illumination. A high open circuit voltage (V(oc)) of ~0.8 V was achieved for the BO-ADPM/C(60) device, which is among the highest reported values for organic solar cells with photocurrent generation in the near-infrared region beyond 1.5 eV.     

Shape effect on electronic and photovoltaic properties of CdS nanocrystals

Changes in electronic and photovoltaic properties of semiconductor nanocrystals predominantly due to changes in shape are discussed here. Cadmium sulfide (CdS) semiconductor nanocrystals of various shapes (tetrapod, tetrahedron, sphere and rod) obtained using an optimized solvothermal process exhibited a mixed cubic (zinc blende) and hexagonal (wurtzite) crystal structure. The simultaneous presence of the two crystal phases in varying amounts is observed to play a pivotal role in determining both the electronic and photovoltaic properties of the CdS nanocrystals. Light to electrical energy conversion efficiencies (measured in two-electrode configuration laboratory solar cells) remarkably decreased by one order in magnitude from tetrapod --> tetrahedron --> sphere --> rod. The tetrapod-CdS nanocrystals, which displayed the highest light to electrical energy conversion efficiency, showed a favorable shift in position of the conduction band edge leading to highest rate of electron injection (from CdS nanocrystal to the wide band gap semiconductor viz. titanium dioxide, TiO2) and lowest rate of electron-hole recombination (higher free electron lifetimes).     

Ultrathin Co(Ni)-doped MoS<Subscript>2</Subscript> nanosheets as catalytic promoters enabling efficient solar hydrogen production

The design of efficient artificial photosynthetic systems that harvest solar energy to drive the hydrogen evolution reaction via water reduction is of great importance from both the theoretical and practical viewpoints.Integrating appropriate co-catalyst promoters with strong light absorbing materials represents an ideal strategy to enhance the conversion efficiency of solar energy in hydrogen production.Herein,we report,for the first time,the synthesis of a class of unique hybrid structures consisting of ultrathin Co(Ni)-doped MoS2 nanosheets (co-catalyst promoter) intimately grown on semiconductor CdS nanorods (light absorber).The as-synthesized one-dimensional CdS@doped-MoS2 heterostructures exhibited very high photocatalytic activity (with a quantum yield of 17.3％) and stability towards H2 evolution from the photoreduction of water.Theoretical calculations revealed that Ni doping can increase the number of uncoordinated atoms at the edge sites of MoS2 nanosheets to promote electron transfer across the CdS/MoS2 interfaces as well as hydrogen reduction,leading to an efficient H2 evolution reaction.