Energy Conversion Efficiency Of Cells Research Articles

Reduced Graphene Oxide-Laminated One-Dimensional TiO2-Bronze Nanowire Composite: An Efficient Photoanode Material for Dye-Sensitized Solar Cells.

A facile one-step hydrothermal method was developed to prepare reduced graphene oxide-laminated TiO2–bronze (TiO2-B) nanowire composites (TNWG), which contain two-dimensional graphene oxide nanosheets and TiO2-B nanowires. In the hydrothermal process, the functional groups of graphene oxide were reduced significantly. Dye-sensitized solar cells (DSSCs) were fabricated using TNWG as the photoanode material. The effects of different reduced graphene oxide contents in TNWG on the energy conversion efficiency of the dye-sensitized solar cells were investigated using J–V and incident photon-to-current conversion efficiency characteristics. DSSCs based on a TNWG hybrid photoanode with a reduced graphene oxide content of 8 wt % demonstrated an overall light-to-electricity conversion efficiency of 4.95%, accompanied by a short-circuit current density of 10.41 mA cm–2, an open-circuit voltage of 0.71 V, and a fill factor of 67%, which were much higher than those of DSSC made with a pure TiO2-B NW-based photoanode. The overall improvement in photovoltaic performance could be associated to the intense visible light absorption and enhanced dye adsorption because of the increased surface area of the composite, together with faster electron transport due to reduced carrier recombination.

Surface Defect Detection of Solar Cells Based on Multiscale Region Proposal Fusion Network

Manufacturing process and human operational errors may cause small-sized defects, such as cracks, over-welding, and black edges, on solar cell surfaces. These surface defects are subtle and, therefore, difficult to observe and detect. Accurate detection and replacement of defective battery modules is necessary to ensure the energy conversion efficiency of solar cells. To improve the adaptability to the scale changes of various types of surface defects of solar cells, this study proposed a multi-feature region proposal fusion network (MF-RPN) structure to detect surface defects. In such a network, region proposals are extracted from different feature layers of convolutional neural networks. Additionally, considering that multiple aspect ratios and scale settings and the use of multiple RPNs, result in an overlap of candidate regions and lead to information redundancy, we designed a multiscale region proposal selection strategy (MRPSS) to reduce the number of region proposals and improve network accuracy. Owing to the complete learning of shallow-detail texture information and deep semantic information, our multiscale RPN fusion structure can effectively improve an object’s multiscale feature extraction ability for various scales and types of surface defects of solar cells. Experimental results demonstrate that our method outperforms other methods by achieving a higher detection accuracy.

Subcutaneous Energy/Signal Transmission Based on Silk Fibroin Up-Conversion Photonic Amplification.

Transmission of energy and signals through human skin is critically important for implantable devices. Because near-infrared (NIR) light can easily penetrate through human skin/tissue, in this study we report on silk fibroin (SF) up-conversion photonic amplifiers (SFUCPAs) integrated into optoelectronic devices, which provide a practical approach for subcutaneous charging and communication via NIR lasers. SFUCPAs achieve a 4 times higher fluorescence than the control, which gives rise to a 47.3 time increase in subcutaneous NIR energy conversion efficiency of a single fibrous dye-sensitized solar cell compared with the control. Moreover, the hybrid printed electrodes exhibited reversible switching to NIR exposure with a response time of ∼1.06/1.63 s for a 3 s ON/OFF switch. Owing to the flexible, biocompatible, and cost-efficient design NIR-driven optoelectronic performance, the SFUCPAs are promising for use in applications of subcutaneous medical electronics for charging, storing information, and controlling implanted devices.

Efficiency enhancement of Si nanostructure hybrid solar cells by optimizing non-radiative energy transfer from Si quantum dots

Non-radiative energy transfer (NRET) from silicon quantum dots (SiQDs) terminated with ligands is an effective way to improve solar cell efficiency. The NRET effect can be enhanced by minimizing the distance between SiQDs and the solar cell surface. SiQDs were inserted between poly (3,4-ethylene dioxythiophene):poly (styrene sulfonate) (PEDOT:PSS) and Si nanostructures of hybrid heterojunction solar cells. To clarify dependence on ligand length, three different ligands of different lengths were investigated. 1-octene, which has the shortest ligand length, showed the greatest enhancement of NRET, resulting in the highest solar cell efficiency. The non-radiative energy transfer (NRET) effect in Si quantum dots (SiQDs) can be enhanced by shortening the ligand length, resulting in enhanced short circuit current, thus significantly improving the energy conversion efficiency of solar cells. • High-efficiency hybrid solar cells were fabricated by inserting SiQDs into hybrid solar cell with Si nanotips and PEDOT:PSS. • Non-radiative energy transfer from SiQDs terminated with ligands effectively enhanced conversion efficiency of solar cells. • SiQDs with shorter ligands had a higher conversion efficiency. • The highest conversion efficiency of 12.4% was given by hybrid solar cells with 1-octene terminated SiQDs.

Comparative study on the overall energy performance between photovoltaic and Low-E insulated glass units

A novel semi-transparent building integrated photovoltaic (BIPV) laminate was developed and introduced in this paper. It was produced by cutting standard mono-crystalline silicon solar cells into small strips and then making electrical connections between each strip before laminating the cells between two layers of glass. The overall energy performance and energy saving potential of the BIPV insulated glass unit (IGU) under real world conditions were identified through a side by side comparative study. Compared to the reference IGU, the BIPV IGU had lower solar heat gain coefficient (SHGC) but much higher U-factor. The average HVAC electricity saving of the BIPV IGU was about 10% relative to the reference IGU. Daylighting measurement and analysis were carried out to evaluate the trade-offs associated with the BIPV IGU between daylight, glare, and lighting energy use. The results indicated that the BIPV IGU is better than the reference IGU in reducing discomfort glare. However, if the most conservative viewpoint near the window is used for the assessment, a lower transmittance BIPV IGU is required to bring the overall discomfort levels below the perceptible level. Lastly, the net energy saving potential associated with the novel BIPV IGU was identified based on the power, thermal and daylighting performance. On average, the BIPV IGU saved 16.8% of the total electricity use of the room. Further studies and improvement on the energy conversion efficiency of solar cells, the optimal transmittance as well as the thermal properties would make this technology more energy-efficient and affordable.

Effect of dew and rain on photovoltaic solar cell performances

This study investigates experimentally the impact of droplets on the performance of solar photovoltaic (PV) cells due to dropwise condensation or rain falling on their cover. Dew formation occurs frequently in various climates including in semi-arid regions suitable to PV cell deployment. Then, droplets present on the cover of solar cells can negatively affect the cell power generation and efficiency due to optical effects. Here, semi-transparent glass covers were prepared without or with surface treatments and covered with acrylic droplets with contact angle ranging between 25° and 77° and surface area coverage between 19% and 49%. The current vs. voltage curves of commercial polycrystalline silicon solar cells with dry and droplet-covered glass covers were measured under simulated solar irradiation at incidence angle varying between 0° and 85°. For incident angles θi ≤ 30°, the droplets did not affect the performance of the PV cells. However, for incident angles θi > 30°, the presence of droplets caused the maximum power and energy conversion efficiency of the PV cells to decrease significantly, particularly for large droplet contact angle and/or surface area coverage. Such performance degradation was attributed to the fact that the incident light was back-scattered through the droplets instead of being trapped by total internal reflection at the cover/air interface before being eventually absorbed by the solar cell. The study also shows that the hourly energy production of PV cells can decrease significantly with dew formation, based on actual weather conditions. These results highlight the importance of selecting durable hydrophilic solar cell cover.

Liquid Thermocells Enable Low-Grade Heat Harvesting

Recently, two Science papers tackled the challenge of harvesting low-grade heat via liquid thermocells. One combines TGC and TDC to significantly enhance thermopower by an order of magnitude, and the other reveals the selectively thermosensitive crystallization/dissolution at two electrodes. These intriguing and inspiring advances in terms of materials, mechanisms, and performances are briefly introduced, and some remaining challenges and future directions are outlined for further thermopower improvement and practical implementation.

Deep-Learning Architecture in QSPR Modeling for the Prediction of Energy Conversion Efficiency of Solar Cells

The efficient and effective design of chemical processes and products heavily relies on the accurate prediction of essential properties. In this work, a deep-learning architecture integrating a bid...

Luminescent anti-reflection coatings based on down-conversion emission of Tb3+-Yb3+ co-doped NaYF4 nanoparticles for silicon solar cells applications

To improve energy conversion efficiency (Eff) of silicon solar cells, luminescent down-conversion (DC) is an effective approach to adjust solar spectrum by converting ultraviolet light to visible and near-infrared light. In this paper, Tb3+- Yb3+ co-doped NaYF4 phosphors (DCNPs) were successfully synthesized by a simple solvothermal method. It was confirmed from the strong photoluminescence excitation (PLE) and photoluminescence (PL) emission peaks that the energy transfer occured between Tb3+ and Yb3+ ions. The DCNPs were added in the SiO2 sol-gel to prepare anti-reflection coatings with DC performance, enhancing the visible and near-infrared region transmittance which matched with the band gap of silicon. An optimized short-circuit current density (Jsc) of 33.39 mA/cm2 and a relatively enhanced Eff of 6.74% were achieved in the silicon solar cells with the bi-functional film. These results indicated the availability of anti-reflection coating with DCNPs for improving energy conversion efficiency of silicon solar cells.

Influence of the Shape and Size of Ag Nanoparticles on the Performance Enhancement of CIGS Solar Cells: the Role of Surface Plasmons

The efficiency of thin-film solar cells can be increased considerably by coupling the solar cells with plasmonic nanoparticles. However, while the benefits of utilizing plasmonic nanoparticles has formerly been recognized, the physical properties of the nanoparticles at which the conversion efficiency is optimized have not yet been completely studied. Among the possible properties, this study investigates meticulously the effects of plasmonic nanoparticle shapes and size on the improvement of the energy conversion efficiency of CIGS solar cells. Two different shapes including spheres and cylinders were analyzed in this study. It was revealed that the cylindrical Ag nanoparticles with a diameter of 50 nm and a height of 125 nm placed in an array with period of 215 nm exhibited the most substantial enhancement in the optical absorption and electrical current generation. The achievements in this article have been attained through optical and electrical analysis as well as the near-field imaging studies.

Directly Determining the Interface Structure and Band Offset of a Large-Lattice-Mismatched CdS/CdTe HeterostructureSupported by the National Natural Science Foundation of China (Grant No. 11974078), the Fudan Start-up Funding (Grant No. JIH1512034), and the Shanghai Sailing Program (Grant No. 19YF1403100).

The CdS/CdTe heterojunction plays an important role in determining the energy conversion efficiency of CdTe solar cells. However, the interface structure remains unknown, due to the large lattice mismatch between CdS and CdTe, posing great challenges to achieving an understanding of its interfacial effects. By combining a neural-network-based machine-learning method and the stochastic surface walking-based global optimization method, we first train a neural network potential for CdSTe systems with demonstrated robustness and reliability. Based on the above potential, we then use simulated annealing to obtain the optimal structure of the CdS/CdTe interface. We find that the most stable structure has the features of both bulks and disorders. Using the obtained structure, we directly calculate the band offset between CdS and CdTe by aligning the core levels in the heterostructure with those in the bulks, using one-shot first-principles calculations. Our calculated band offset is 0.55 eV, in comparison with 0.70 eV, obtained using other indirect methods. The obtained interface structure should prove useful for further study of the properties of CdTe/CdS heterostructures. Our work also presents an example which is applicable to other complex interfaces.

Ultra‐Thin Poly‐Si Layers: Passivation Quality, Utilization of Charge Carriers Generated in the Poly‐Si and Application on Screen‐Printed Double‐Side Contacted Polycrystalline Si on Oxide Cells

Herein, the various measures to improve the efficiency of large‐area screen‐printed double‐side contacted polycrystalline Si on oxide (POLO)‐cells are experimentally demonstrated. The short‐circuit current density Jsc increases by 0.6 mA cm−2 upon reducing the thickness of poly‐Si from 25 to 10 nm due to the reduction of the parasitic absorption in the poly‐Si layer at the textured front side of the cell. Additionally, it is shown for the first time that the minority carriers generated by light absorbed in the poly‐Si layer can at least partially be transferred into the crystalline Si base. Remarkably high implied open‐circuit voltage Voc,impl values are achieved with n‐type cell precursors by introducing an hydrogenation step by AlxOy after reducing the poly‐Si thickness, and by an additional annealing step after sputtering of transparent conductive oxides (TCOs). All cell precursors show Voc,impl values of up to 740 mV independent of the poly‐Si thickness. A reduction in the open‐circuit voltage Voc is observed during back‐end processing to 728 mV as measured on the final cells. A certified cell energy conversion efficiency of 22.3% is reported.

Combining Photosynthesis and Photovoltaics: A Hybrid Energy-Harvesting System Using Optical Antennas.

A hybrid energy-harvesting system is proposed that combines photosynthesis and photovoltaics. First, the light passes through a spectrally selective solar cell, which absorbs almost all green light but absorbs almost no blue and red light. The blue and red light are absorbed by a photosynthesis executing plant. The solar cell is tailored in such a way that the photosynthetic process is almost unaffected by the generation of electrical energy. The spectrally selective solar cell consists of an array of inorganic optical antennas. By combining a spectrally selective solar cell and a photosynthetic executing plant, a hybrid energy system is formed, which absorbs almost 100% of the visible light, while the energy conversion efficiency of the solar cell reaches up to 50% of their nonspectrally selective counterparts. Guidelines are provided on how to realize both the highly efficient spectrally selective solar cells and hybrid energy-harvesting systems. The proposed solution allows for the realization of new greenhouses or gardens covered with spectrally selective transparent solar cells that produce chemical energy in the form of fruits and vegetables and electrical energy.

Optical Stepped Thermography of Defects in Photovoltaic Panels

Defects in photovoltaic panels can reduce the effective working area, and decrease the performance of the photovoltaic panels. Therefore, it is significant to identify such defects and to feed the fault information up to the production chain. Active infrared thermographic non-destructive testing has the advantages of non-contact, fast speed and large imaging area, and has been widely used in the detection of defects in various materials. In this article, a stepped thermography of the defects, which result in degradation of energy conversion efficiency of cells in photovoltaic panels, was proposed. The front surface of the photovoltaic panel was optically stimulated by halogen lamps in step heating way, while an infrared camera was employed to monitor the temperature evolution of the front surface and to capture infrared image sequences. The thermal image sequences were processed using data processing algorithms, focusing on enhancing the defect signatures. The techniques of background subtraction, discrete Fourier transform, polynomial fitting, first-order derivative, cross correlation coefficient and histogram equalization were mainly used. Compared to the raw thermal images, the reconstructed images using suitable algorithms are more helpful to evaluate the defects. The results show that the optical stepped thermography combined with suitable post data processing is a fast and effective technique to identify the defects in photovoltaic panels.

Experimental investigation of improving the energy conversion efficiency of PV cell by integrating with PCM

A photovoltaic panel PV's electrical output is heavily dependent upon its temperature. The electrical efficiency decreases when the temperature of a PV increases. The use of PCM material for phase change is now one of the most promising tools for reducing and regulating PV panel temperature and increasing its electrical efficiency. The current research is based on experimental studies of the effect on the thermal behavior and electrical performance of a PV panel using COPPER (Cu), SILICON CARBIDE (Sic), PARAFFIN WAX (Petroleum wax). A suitable testing setup was devised to proceed and the designs had to be designed and evaluated. A transient energy balance is also pre-sent for evaluating the thermal activity of the device and correlating it with the electrical outputs. A suitable experimental setup was devised and three prototypes were built and tested to proceed. Prototype 1 consists of a platform, a photovoltaic panel and an electrical circuit with a given charge. Prototypes 2 are designed with a container added on each PV panel's rear face which holds a combined PCM. It was shown that when using standard, the electrical output of PV panels was increased by an average of 2.8 percent and when using combined PCM by an average of 4.3 percent. These improvements as well as the corresponding behaviors were shown by a transitory energy balance approach.

Efficient polymer solar cells utilizing solution‐processed interlayer based on different conjugated backbones

AbstractThe poor energy conversion efficiency for those polymer solar cells (PSCs) creates an obstacle for their commercialization. Inspired by this issue, two cathode interlayers, PBTBTz‐TMAI and PBTzPh‐TMAI based on benzothiadiazole (BT) and benzotriazole (BTz)‐conjugated or benzene (Ph) and BTz‐conjugated alternating units (both exhibits the same tetravalent amine‐end side chain), were synthesized via Suzuki coupling polymerization and trivalent amine‐end ionization. When PBTBTz‐TMAI and PBTzPh‐TMAI were utilized as cathode interlayers in PSCs, the charge‐carrier transfer from active layer to cathode electrode was significantly improved, accompanied by an optimized exciton dissociation efficiency, primarily attributed to the introduction of tetravalent amine groups. Consequently, the device with PBTBTz‐TMAI exhibited power conversion efficiencies (PCEs) = 8.3 and 10.5% for the PTB7:PC71BM‐based and PBDB‐T:ITIC‐based PSCs, respectively. In parallel, devices with a PBTzPh‐TMAI cathode interlayer (that were established on the active layers of PTB7:PC71BM and PBDB‐T:ITIC) obtained a remarkably superior optoelectric efficiency with PCEs = 8.5 and 10.8%. These findings offer an alternative tactic toward to high efficiency PSCs to meet the increasing energy crisis.

Evaluation of Fused Aromatic-Substituted Diketopyrrolopyrrole Derivatives for Singlet Fission Sensitizers.

Singlet fission (SF) is a spin-allowed carrier multiplication process that has potential to overcome the Shockley-Queisser limit of solar energy conversion efficiency for single-junction solar cells. It is of importance to prescreen appropriate SF candidates for both basic research and practical applications of SF. Besides common polycyclic aromatic hydrocarbons (PAHs), diketopyrrolopyrrole (DPP) derivatives also undergo efficient SF. A series of DPP derivatives with fused aromatic substituents were investigated considering their conjugation length, constitution, and the introduction of terminal substituents. A comparison of SF properties between nonfused and fused aromatic-substituted DPP derivatives was carried out. Detailed analysis focused on elucidating the relationship between the frontier molecular orbital energies, multiple diradical characters, and SF-relevant excited-state energy levels. Compared to nonfused aromatic-substituted DPP derivatives, fused aromatic-substituted DPP derivatives which contain three aromatic units (thiophene or furan) still share more appropriate energy levels for SF sensitizers. Changing the five-membered aromatic units with benzene ring and introducing -F, -OMe, and -COOH as terminal substituents are both effective ways to improve their performance as SF sensitizers. The results of this research help us to understand the SF properties of DPP derivatives deeply and are beneficial for the design of new DPP-based SF sensitizers.

Interacting Ru(bpy) 3 2 + Dye Molecules and TiO2 Semiconductor in Dye-Sensitized Solar Cells

Solar energy is an alternative source of energy that can be used to replace fossil fuels. Various types of solar cells have been developed to harvest this seemingly endless supply of energy, leading to the construction of solar cell devices, such as dye-sensitized solar cells. An important factor that affects energy conversion efficiency of dye-sensitized solar cells is the distribution of dye molecules within the porous semiconductor (TiO 2 ). In this paper, we formulate a continuum model for the interaction between the dye molecule Tris(2,2 ′ -bipyridyl)ruthenium(II) (Ru(bpy) 3 2 + ) and titanium dioxide (TiO 2 ) semiconductor. We obtain the equilibrium position at the minimum energy position between the dye molecules and between the dye and TiO 2 nanoporous structure. Our main outcome is an analytical expression for the energy of the two molecules as a function of their sizes. We also show that the interaction energy obtained using the continuum model is in close agreement with molecular dynamics simulations.

Competitive role between conformational lock and steric hindrance in D-A copolymers containing 1,4-bis(thieno[3,2-b]thiophen-2-yl)benzene unit

We report the design and synthesis of two donor-acceptor (D-A) conjugated polymers based on a 2,2′-(2,5-dialkoxy-1,4-phenylene)dithieno[3,2-b]thiophene (DTTP) donor subunit having highly planar confirmation via S⋯O noncovalent bonding and electron-rich property. Introducing the DTTP subunit improves the interchain ordering and of resultant polymers, without losing solution processability. In order to promote the charge separation from photo-induced excitons at D/A interfaces, we control the position of side chain and investigate their effect on D/A phase separation in bulk-heterojunction films. We have systematically investigated the effects of noncovalent bonding and side chain position on the chain planarity and interaction packing of polymers, bulk-heterojunction thin film morphologies, and relevant photovoltaic devices. The thin film morphologies composed of conjugated polymers (PDTTP-2FBT or PDTTP-2FBTA) and with PC71BM are found to be critically dependent upon the side chain position and processing additive treatments. The resulting photovoltaic energy conversion efficiency of the polymer solar cells reached 6.79% and a comparative study on the physical, molecular modeling, and thin film characteristics was performed through DFT, GIXD, TPC, TPV, etc. The results obtained here provide an important guideline of tailoring the polymer chemical structure to optimize the molecular packing behavior and thin film morphology for high-performance organic electronics.

Lotus Leaf Derived Natural Dye as Sensitizer and Biochar as Counter Electrode for Dye-Sensitized Solar Cells

Natural dyes were obtained from lotus leaf by ethanol extraction, and biochar was prepared by one-step pyrolysis in this study. The UV-Vis spectrum of lotus leaf derived natural dye indicated that it had good light absorption performance. The energy conversion efficiency (PCE) of dye-sensitized solar cell (DSSC) with the natural dye as sensitizer and platinum as counter electrode was 0.36%, and the filling factor was as high as 0.66. Owing to its relatively rich pore structures and glassy carbon materials, the biochar showed its good catalytic performance, which made the PCE of DSSC reach 1.42% when the biochar as counter electrode and N719 as sensitizer. Meanwhile, the PCE achieved 0.15% when lotus leaf derived natural dye as sensitizer and biochar as counter electrode simultaneously. This study has realized the full utilization of biomass in dye-sensitized solar cells, providing the possibility for preparation of low-cost and high-efficiency DSSC.