Energy Conversion Efficiency Of Cells Research Articles

A novel hybrid system consisting of a dye-sensitized solar cell and an absorption refrigerator for power and cooling cogeneration

To improve the energy conversion efficiency of a dye-sensitized solar cell (DSSC), a novel hybrid system representatively consisting of a DSSC and an absorption refrigerator (APR) is put forward, in which the APR is used to thermally harness the part of high wavelength sunlight that not converted by the DSSC. The amount of heat from the DSSC is calculated, and mathematical formula for energy conversion efficiencies and output powers of the DSSC, APR and hybrid system are derived. Numerical calculations show that the maximum output power density and maximum energy conversion efficiency of hybrid system are enhanced by 9.93% and 9.92% in comparison with that of the single DSSC, respectively. Integration of APR to DSSC is a feasible route to effectively improve the energy conversion efficiency. Comprehensive sensitivity analyses are conducted to explore how the whole hybrid system performance depends on various working conditions and designing parameters, including porous nano-TiO2 film thickness, photoelectron absorption coefficient, internal irreversibility factor, heat transfer coefficient and various temperatures. The research results can provide some new understandings for further enhancing the DSSC performance.

Understanding the dropping of lithium plating potential in carbonate electrolyte

Lithium metal is an ideal anode material for high energy-density batteries owing to its high specific capacity and low redox potential. The carbonate-based electrolytes are attractive in developing high energy-density lithium metal batteries because of their wide electrochemical windows. However, the lithium deposition potential is often found dropping in the cells using the carbonate-based electrolytes, which may lead to overcharge as well as low energy conversion efficiency and low energy density of a full cell. Herein, the reason for the potential dropping in the commercial LiPF6-EC/DMC electrolyte is studied by both electrochemical evaluation and physical characterization (EC for ethylene carbonate and DMC for dimethyl carbonate). It is clarified that the repeated formation and decomposition of the organic species such as ROCO2Li and ROLi in the solid electrolyte interphase (SEI) layer during lithium plating/stripping cycling are responsible for the potential dropping. Our findings shed light on eliminating or suppressing the potential dropping to improve the energy density and the energy conversion efficiency of the secondary lithium metal batteries.

Selective Deposition of Al₂O₃ on the Upper Side-Photoelectrode to Improve Dye-Sensitized Solar Cell Efficiency.

Charge recombination at the photoelectrode/dye/electrolyte interface decreases the energy conversion efficiency of dye-sensitized solar cells (DSSCs). To suppress charge recombination at this interface in DSSCs, an aluminum oxide (Al₂O₃) film can be deposited as an insulating metal oxide layer on the photoelectrode to form an energy barrier. However, the Al₂O₃ energy barrier can also disturb the transport of injected electrons to the working electrode through the titanium dioxide (TiO₂) photoelectrode. In this study, Al₂O₃ was selectively deposited as an insulating metal oxide layer on the upper side of a TiO₂ photoelectrode, which has a high probability of charge recombination, using plasma-enhanced atomic layer deposition. Deposition of the Al₂O₃ layer by this method helped to minimize the transport rate deterioration of injected electrons. This resulted in an increase of the efficiency of DSSCs containing the Al₂O₃ layer by 42.3% compared with that of a reference DSSC without the insulating metal oxide layer.

Effect of surface modification via sol-gel spin coating of ZnO nanoparticles on the performance of WO3 photoanode based dye sensitized solar cells

In this paper, we have reported the improvement of electro-optical performance of dye sensitized solar cells based on highly porous WO3 nanoparticles as photoanode by an ultrathin coating of ZnO nanoparticles with varying precursor solution concentration over WO3 surface and the results were compared with the performance of a Dye Sensitized Solar Cell (DSSC) fabricated with bare WO3 photoanode. The semiconducting material WO3 was chosen in search of a photoanode material for DSSC alternative to TiO2. But the performance of pure WO3 based DSSC was found to be extremely poor in spite of having several advantageous properties. To improve the photovoltaic performance, we have coated the WO3 surface with varying concentrations of the ZnO precursor solution. It was observed that the concentration of the precursor solution of ZnO highly controls the performance of the DSSC. From the electrochemical measurements, it was found that the bare WO3 cell suffers high electron recombination. But the coating of an ultrathin layer of ZnO over the WO3 surface introduces an energy barrier and reduces the electron recombination and thereby enhances the cell performance. The solar cell energy conversion efficiency was found to be highest for 5 mM ZnO precursor solution concentration and it decreases with the increase in concentration further and becomes very low at a concentration of 25 mM. This may be attributed to the poor dye adsorption on the WO3 surface due to complete screening by the thicker ZnO layer.

Controlled Synthesis of Nanocrystalline Nb:SrTiO3 Electron Transport Layers for Robust Interfaces and Stable High Photovoltaic Energy Conversion Efficiency in Perovskite Halide Solar Cells

Perovskite halides are of great attraction as efficient light absorption materials for solid-state solar cells, but the stability and photovoltaic energy conversion efficiency of perovskite solar cells (PSCs) are still limited by the interface structures and defects between their light-absorbing perovskite halides and electron transport layers (ETLs). Here, we report the ultraviolet (UV) light-induced degradation mechanism at the interfaces between perovskite halide and conventional TiO2 ETL materials and provide a solution to overcome this drawback. UV-induced degradation is shown to be attributed to the formation of oxygen vacancies formed at the perovskite halide–ETL interface under UV light illumination, where the oxygen atoms released at the interface accelerate the decomposition of perovskite halide by inducing chemical reactions. Meanwhile, nanocrystalline SrTiO3 (STO) ETLs are revealed to be tunable in enabling high performance in PSCs under UV light illumination. Indeed, tuning the electronic structure of STO ETLs by Nb doping, in combination with the controllable removal of SrO phases segregated on the Nb-doped STO ETL surfaces, is exhibited to enable robust interface stability and stable high photovoltaic energy conversion efficiency for PSCs. Furthermore, we demonstrate that STO-based PSCs have no hysteresis due to low defect concentrations at the perovskite halide–STO ETL interfaces.

Atomistic approach to simulate kink migration and kink-pair formation in silicon: The kinetic activation-relaxation technique

The energy conversion efficiency of solar cells based on multicrystalline silicon is greatly deteriorated by dislocations. However, an in-depth understanding on the dislocation motion dynamics down to atomic scale is still lacking. In this paper, we propose a novel atomistic approach to simulate the kink migration and kink-pair formation which govern dislocation motion in silicon, namely the kinetic activation-relax technique (k-ART). With this method, long timescale events can be simulated and complex energy landscapes can be explored. Four mechanisms for kink migration are observed, with total activation energy of 0.16, 0.25, 0.32, and 0.25 eV. New nontrivial kink structures that participate in kink migration are identified due to the open-ended search algorithm for saddle points in k-ART. In addition, a new pathway for kink-pair formation, with a minimum activation energy of 1.11 eV is discovered. The effect of shear stress on kink migration is also investigated. It shows that shear stress shifts the energy barriers of available events to lower energies, resulting in a change of the preferred kink-migration mechanism and a reduction of kink-pair formation energy.

Highly-Conductive, Transparent Ga-Doped ZnO Nanoneedles for Improving the Efficiencies of GaN Light-Emitting Diode and Si Solar Cell

The growths of transparent, highly-conductive Ga-doped ZnO (GaZnO) nanoneedles (NNs) on the tops of GaN-based light-emitting diodes (LEDs) and Si solar cells for enhancing light extraction and reducing surface reflection, respectively, and hence increasing their efficiencies are demonstrated. The GaZnO NNs are grown based on the vapor-liquid-solid process by using surface Ag nanoparticles (NPs) as growth catalyst. In the application to LED, the residual Ag NPs can induce the surface plasmon (SP) coupling effect for increasing the LED emission efficiency. By combining the SP coupling effect, the light extraction effects of the GaZnO NNs and simultaneously deposited GaZnO thin film, and the current spreading effect of the thin film, the LED output intensity can be increased by 100%. In the solar cell application, the SP resonance of the residual Ag NPs can also enhance sunlight harvest and hence the energy conversion efficiency. By combining the effects of the residual Ag NPs, the GaZnO thin film, and the GaZnO NNs, the energy conversion efficiency of a Si solar cell can increase from 9.65 to 12.30%, corresponding to a relative enhancement of 27.5%.

Novel two-step CdS deposition strategy to improve the performance of Cu2ZnSn(S,Se)4 solar cell

Abstract Kesterite Cu2ZnSn(S,Se)4 (CZTSSe) solar cells have drawn worldwide attention for their promising photovoltaics performance and earth-abundant element composition, yet the record efficiency of this type of device is still far lower than its theoretical conversion efficiency. Undesirable band alignment and severe non-radiative recombination at CZTSSe/CdS heterojunction interfaces are the major causes limiting the current/voltage output and overall device performance. Herein, we propose a novel two-step CdS deposition strategy to improve the quality of CZTSSe/CdS heterojunction interface and thereby improve the performance of CZTSSe solar cell. The two-step strategy includes firstly pre-deposits CdS thin layer on CZTSSe absorber layer by chemical bath deposition (CBD), followed with a mild heat treatment to facilitate element inter-diffusion, and secondly deposits an appropriate thickness of CdS layer by CBD to cover the whole surface of pre-deposited CdS and CZTSSe layers. The solar energy conversion efficiency of CZTSSe solar cells with two-step deposited CdS layer approaches to 8.76% (with an active area of about 0.19 cm2), which shows an encouraging improvement of over 87.98% or 30.16% compared to the devices with traditional CBD-deposited CdS layer without and with the mild annealing process, respectively. The performance enhancement by the two-step CdS deposition is attributed to the formation of more favorable band alignment at CZTSSe/CdS interface as well as the effective decrease in interfacial recombination paths on the basis of material and device characterizations. The two-step CdS deposition strategy is simple but effective, and should have large room to improve the quality of CZTSSe/CdS heterojunction interface and further lift up the conversion efficiency of CZTSSe solar cells.

Nonlinear-response properties in a simplified time-dependent density functional theory (sTD-DFT) framework: Evaluation of excited-state absorption spectra.

The energy conversion efficiency of organic solar cells seems crucial for a clean future. The design of new light-harvesting devices needs an in-depth understanding of their optical properties, including the excited-state absorption (ESA). In biology, the optical characterization of photochemical/physical processes happening in photosynthetic pigments and proteins can be difficult to interpret due to their structural complexities. Experimentally, an ultrafast transient absorption experiment can probe the excited state interaction with light. Quantum chemistry could play an important role to model the transient absorption spectrum of excited states. However, systems that need to be investigated can be way too large for existent software implementations. In this contribution, we present the first sTDA/sTD-DFT (simplified time-dependent density functional theory with and without Tamm Dancoff approximation) implementation to evaluate the ESA of molecules. The ultrafast ESA evaluation presents a negligible extra cost with respect to sTDA/sTD-DFT original schemes for standard ground state absorption. The sTD-DFT method shows ability to assign ESA spectra to the correct excited state. We showed that in the literature, wrong assignments were proposed as for the L34/L44 mixture and N-methylfulleropyrrolidine. In addition, sTDA/sTD-DFT-xTB tight-binding variants are also available, allowing the evaluation of ESA for systems of a few thousands of atoms, e.g., the spectrum of the photoactive yellow protein composed of 1931 atoms.

Silk Fluorescence Collimator for Ultrasensitive Humidity Sensing and Light-Harvesting in Semitransparent Dye-Sensitized Solar Cells.

This work examines the self-collimation effect of silk materials on fluorescence emission/detection. A macroscopic regulation strategy, coupled with meso-reconstruction and meso-functionalization, is adopted to amplify the fluorescence emission of organic fluorescent dyes (i.e., Rhodamine 6G (R6G)) using silk photonic crystal (PC) films. The fluorescence emission can be linearly enhanced or inhibited by a PC as a result of the photonic bandgap coupling with the excitation light and/or emission light. Depending on the design of the silk fluorescence collimator, the emission can reach 49.37 times higher than the control. The silk fluorescence collimator can be applied to achieve significant benefits: for instance, as a humidity sensor, it provides good reproducibility and a sensitivity of 28.50 a.u./% relative humidity, which is 80.78 times higher than the sensitivity of the control, and as a novel curtain, it raises the energy conversion efficiency of the semitransparent dye-sensitized solar cells (DSSCs) by 16%.

Enhancing the energy conversion efficiency of low mobility solar cells by a 3D device architecture

The short circuit current and energy conversion efficiency of solar cells based on semiconductor materials with low diffusion lengths like organics and amorphous silicon can be increased by a 3D device architecture.

Dual-mode downconversion luminescence with broad near-ultraviolet and blue light excitation in Tm3+/Yb3+ codoped oxy-fluoride glasses for c-Si solar cells

In this work, we demonstrated an efficient dual-mode solar spectral converter Tm3+/Yb3+ co-doped oxy-fluoride glasses synthesized using high temperature melt-quenching method. The transmittance, photoluminescence emission (PL) and photoluminescence excitation (PLE) spectra and decay dynamics have been systematically investigated. The experimental results revealed that two distinct solar spectral converting processes, quantum cutting (QC) and down-shifting (DS) were achieved through the sensitization of Tm3+ excited multiplets and a broad band attributing to Yb3+-O2− charge transfer state (CTS), respectively. The prepared materials could convert the UV (250–370 nm) and blue (450–490 nm) photons into broad NIR emission (900–1100 nm), which coincides well with the most efficient spectral response of Si-based solar cells. The resultant Tm3+/Yb3+ co-doped oxy-fluoride glasses with dual-mode solar spectral modification indicate its potential application in improving the energy conversion efficiency of Si-based solar cells.

Enhanced light absorption in simulations of ultra-thin ZnO layers structured by a SiO2 photonic glass

Hierarchically organized nanostructures are often employed to improve the energy conversion efficiency of photovoltaic and photoelectrochemical cells. Ultra-thin semiconductors can improve the internal carrier collection yield in materials with poor carrier lifetimes by reducing the characteristic length scales of collection. However, reducing the dimension of the light absorber requires strategies to increase absorption and the overall photogeneration when the material is to be used in broadband solar energy conversion applications. Here, we explore a strategy for improving light absorption in nanometer-scale, ultra-thin film ZnO layers by integrating them into a SiO2 colloidal crystal-based photonic glass. We use three-dimensional finite-difference electromagnetic simulations to study the local and total absorption improvements on composite films of close-packed, randomized colloidal structures coated with a thin layer of ZnO. These simulations show that the near band-gap absorption in the ZnO coating is dependent on the degree of vacancies in the colloidal crystal that templates the photonic glass. With these results, we show that disordered, defective colloidal composites can potentially be used to fabricate nanostructured photoelectrodes based on ultra-thin semiconductor layers with improved light absorption characteristics.

Effect of surface texturization on minority carrier lifetime and photovoltaic performance of monocrystalline silicon solar cell

This paper presents the effect of surface texturization on the minority carrier lifetime and photoelectric conversion parameters of monocrystalline silicon solar cell. Two different wet-chemical texturization methods were employed to etch the monocrystalline silicon wafer surface. Morphology of the wafers was investigated by stylus surface profiler, field emission scanning electron microscope (FESEM) and surface reflection measurement (SRM) systems. Due to texturization pyramidal structures were formed on wafer surface as well as the surface roughness was increased by 3.07%. Untextured (S1) and textured (S2 & S3) samples were doped with phosphorus atoms with a constant flow rate of liquid phosphorus oxychloride (POCl3) in a high temperature diffusion furnace. Solar cell was fabricated using both untextured and textured silicon wafer. Maximum 1.66% decrease of optical reflectance was found in textured solar cell. The minority carrier lifetime and photoelectric parameters were investigated using surface photovoltage (SPV) and light-current-voltage (LIV) measurement system respectively. Minority carrier diffusion length and minority carrier lifetime were increased significantly in textured solar cell. Thus, surface texturization plays an important role on increasing the energy conversion efficiency of silicon solar cell.

Very high open-circuit voltage in dual-gate graphene/silicon heterojunction solar cells

Two dimensional (2D) layered materials and their heterojunctions with other materials are attracted because of their remarkable electrical and optical properties. In particular, graphene/semiconductor Schottky heterojunction is used for high performance solar cells. Here, we demonstrated very high open circuit voltage (Voc) in graphene/silicon heterojunction solar cell by dual-gate electric field application. The low density of states near Dirac point in graphene allows large modulation of graphene Fermi-level and corresponding Schottky barrier in a graphene/silicon junction. The top and bottom gate electric fields independently adjust the built-in potentials of respective upper and lower silicon energy band to induce higher band bending (1.22 eV) than the bandgap (1.12 eV). As a result, a maximum Voc of 0.94 V is achieved at the − 8 V of top-gate voltage and 10 V of bottom-gate voltage, exceeding highest known Voc for previous graphene/silicon solar cell (Voc = 0.61 V) and the S-Q Limit (0.84 V) of conventional silicon solar cell – a thermodynamic limit for the energy conversion efficiency of solar cells with a single band gap energy. The ratio of output power gain to input gate power (ΔPG/ΔPC) is approximately 1012–1014 with negligible power consumption in the gate (PC = 1 fW/cm2–10 pW/cm2), resulting in the significant advances in the power generation (PG = 40 mW/cm2).

Enhanced Efficiency of Flexible GaN/Perovskite Solar Cells Based on the Piezo-Phototronic Effect

Solar cells fabricated by piezoelectric semiconductor materials, such as GaN, AlN, and CdS, enable better performance due to piezo-phototronic modulation. Recent experiments have revealed the possibility to further improve the energy conversion efficiency of perovskite solar cells with a gallium nitride (GaN) substrate as the electron transport layer. In this study, a perovskite piezo-phototronic solar cell with a GaN layer has been investigated theoretically. The open-circuit voltage, current–voltage curves, fill factor, efficiency of power conversion, and power of maximum output under applied strains are obtained. While the applied strain is 1%, the open-circuit voltage has been improved by 3.8%. This design can offer a practical approach to produce high-efficiency perovskite solar cells.

Experimental Investigation of Enhancing the Energy Conversion Efficiency of Solar PV Cell by Water Cooling Mechanism

Solar photovoltaic cells produce electricity by receiving solar radiation. The output power of photovoltaic cells (PV) is mainly influenced by the significant increase in cell temperature during the absorption of radiation. The solar cooling system has been considered and investigated experimentally in this research paper. A passive cooling system was designed and fabricated for efficiently cool the PV module, with inlet/outlet manifold considered for uniform flow of water at the rear side of the PV module. The experimentation was performed with and without the cooling system. In this paper, a linear trend has been established between the electrical efficiency and the temperature of the photovoltaic cells. Without a cooling system, the average cell temperature reaches to 600C, and the solar panel efficiency reduced to 8 to 16%. However, when the panel was operated under the passive water system, the temperature of the PV cell was reduced to 47°C, resulting in a 10% -21% improve in the solar PV cell efficiency. Both systems, without cooling and with cooling systems are validated experimentally.

Emerging Characterizing Techniques in the Fine Structure Observation of Metal Halide Perovskite Crystal

Driven by its appealing application in the energy harvesting industry, metal halide perovskite solar cells are attracting increasing attention from various fields, such as chemistry, materials, physics, and energy-related industries. While the energy conversion efficiency of the perovskite solar cell is being investigated often by various research groups, the relationship between the surface structure and the property is still ambiguous and, therefore, becomes an urgent topic due to its wide application in the real environment. Recently, the fine structure characterization of perovskite crystals has been analysed by varying techniques, such as XRD, synchrotron-based grazing incidence XRD, XAFS, and STM, in addition to others. In this review article, we will summarize recent progresses in the monitoring of fine nanostructures of the surface and crystal structures of perovskite films, mainly by XAFS, XRD, and STM, focusing on the discussion of the relationship between the properties and the stability of perovskite solar cells. Furthermore, a prospective is given for the development of experimental approaches towards fine structure characterization.

Performance studies of ZnO and multi walled carbon nanotubes-based counter electrodes with gel polymer electrolyte for dye-sensitized solar cell

Counter electrode (CE) is one of the major component which determine the energy conversion efficiency of the dye-sensitized solar cells (DSSCs). Here in, five types of CEs using two different materials were fabricated. Three types are zinc oxide (ZnO) based while other two are multi-walled carbon nanotubes based CEs. The thickness and resistance per cm2 of each CE were measured. The gel polymer electrolyte based on polyacrylonitrile polymer, sodium iodide salt, 1-Hexyl-3-methyl-imidazolium iodide ionic liquid was also prepared. The conductivity studies revealed that the highest ionic conductivity of gel polymer electrolyte was 6.72 mS cm−1 upon incorporation of 100 wt% 1-Hexyl-3-methyl-imidazolium iodide ionic liquid. This gel polymer electrolyte was sandwiched between commercial TiO2 photo-anode and different types of CE to fabricate the DSSCs. The J-V characteristic curves of the DSSCs were obtained and the DSSC characterization parameters were determined. The efficiencies achieved using ZnO and MWCNT-based CEs were ranging from 0.46% to 7.07%. The results demonstrate that ZnO and multi-walled carbon nanotubes are good candidates of CEs for DSSC application.

Dark Field Scattering Spectroelectrochemistry of Single Au Nanoparticles at Transparent Planar and Micro-Sized Electrodes

Boron dipyrromethene (BODIPY) molecules with donor-acceptor configurations are of great interests for harvesting and converting solar energy in a solar cell. Au nanoparticles have been applied to enhance solar energy harvesting and conversion efficiency of organic solar cells because of their surface plasmon properties for increasing light absorption cross-section of an organic dye. Electrochemical properties of single BODIPY dyes and plasmonic Au nanoparticles (NPs) are studied using combined optical and electrochemical methods to reveal their structure-function relationship at the nanometer scale. Our study shows a heterogeneous half redox potential distribution for the BODIPY molecules embedded in polystyrene film because of the heterogeneity in their charge transfer rates. Single molecules adsorbed onto a TiO2 surface with ordered nanostructures show surprising fluorescence blinking activity with the shortest ON duration time in comparison to bare glass and indium-doped tin oxide (ITO) surfaces. Dark field scattering (DFS), photoluminescence (PL), and electrogenerated chemiluminescence (ECL) are used to probe local redox reactions of single Au nanoparticles at transparent planar and micro-sized electrode. Our study shows that these optical responses at individual plasmonic NPs are strongly dependent on particle size, and are affected by the local chemical and charge transfer environment of the NPs.