Increase In Photoelectric Conversion Efficiency Research Articles

Effects of TiO2 thin films on silicon nanowire arrays in heterojunction solar cells

In recent years, the energy crisis has gained increasing attention, with greater emphasis being placed on renewable energy. Currently, solar power is regarded as the most developed form of renewable energy. Many materials have been used in solar cells. Radiofrequency (RF) magnetron sputtering is an effective technique used to produce large-area, easy-to-process thin films. In this study, we fabricated p-layer silicon nanowire (SiNW) arrays by using electroless etching to replace previous multilayer films. TiO2-SiNW array heterojunctions were fabricated by preparing TiO2 as an N layer through magnetron sputtering. Subsequently, the Grey–Taguchi method was used to analyze and optimize p–n heterojunctions with TiO2 films. After the effects of the sputtering parameters (RF power, process pressure, deposition temperature, and deposition time) on surface morphology, material structure, photoelectric conversion efficiency, and reflectivity were investigated, an aluminum-doped zinc oxide (AZO) window layer was added and annealed. Grey correlation analysis revealed a decrease in reflectivity from 8.02225 % to 7.72081 % and an increase in photoelectric conversion efficiency from 0.01915 % to 0.082 %. During the confirmation runs, the TiO2 film was found to be amorphous and wrapped around an array of SiNWs. After the AZO window layer was added, reflectivity increased to 18.04712 %, and the efficiency of photoelectric conversion increased to 0.124 %. In addition, according to the results of the confirmation runs, the AZO film was polymorphic. These experimental results confirm the effectiveness of RF magnetron sputtering, which provides high reflectivity and photoelectric conversion efficiency.

Electronic structure and optical absorption property of BaTiO3/BiCoO3

In this paper, we calculated the different forms of BaTiO3/BiCoO3 composite structure, predicting their visible light absorption performance based on the electronic structure using the first principles calculations. Firstly, six possible compounds that come from BaTiO3 and BiCoO3 were constructed. By calculating the different antiferromagnetic (AFM) structures of strip, columnar, and layered composite structures, it is found that the ground state of the composite structure changes to G‐type AFM structure from C‐type AFM structure of pure BiCoO3 under the influence of BaTiO3. Energy band calculations show that band gaps of three composite structures are smaller than those of pure BaTiO3 and pure BiCoO3. Furthermore, density of states analysis shows that the conduction band minimum (CBM) and valence band maximum (VBM) of three composite structures are mainly from the contribution of Co 3d and O 2p. For the characteristic that CBM and VBM of materials come from different atoms, it would reduce the recombination opportunities of electrons and holes and is conducive to the increase of photoelectric conversion efficiency under visible light irradiation. The calculation of optical properties shows that optical absorption coefficients of three composite structures are much larger than that of BaTiO3, especially the layered composite structure. There is a high absorption peak near 500 nm of the solar spectral irradiation maximum, which is significantly important to improve the optical energy conversion efficiency of the composite materials. The work provides an effective way for the application of wide band gap ferroelectric materials in ferroelectric photovoltaic.

Design of high efficiency perovskite solar cells based on inorganic and organic undoped double hole layer

The use of organic and inorganic double hole layers allows for efficient tuning of the matching of energy levels between each layer and improve the photovoltaic performance and stability of perovskite solar cells (PSCs). However, the cost of band matching for preparing perovskite cells is huge. In this paper, the effect of double hole layer on the performance of PSCs is analyzed by theoretical calculation, and an optimized structure of PSCs is proposed. The traditional Spiro-OMeTAD and MAPbI3 absorption layers are added with copper oxide (CuO) hole layers. The Solar Capacitor One-dimensional Tool (SCAPS) is used to simulate the relationship between the energy level matching of the hole layer and the photoelectric conversion efficiency (PCE) of the cell, and then the photovoltaic conversion performance is optimized accordingly. The results show a CuO hole layer with an energy gap of 1.5 can reduce the direct recombination of electron and hole pairs in the recombination layer, thereby increasing the filling factor (FF), while Spiro-OMeTAD can reduce electron recombination in the anode, thereby increasing short circuit current (Jsc). The FF and Jsc is increased simultaneously with the addition of a 200 nm CuO layer, which results in the increase of PCE from 16.82% to 21.82%. In addition, the absorption spectra and power density distributions of the two structures were calculated, and the mechanism of high absorption under different bands was explored. The effect of different material thickness and doping concentration on the photoelectric performance was studied, and the optimal parameters of the solar cell were determined, which increases the PCE by 5.95%. The cell structure proposed in this research can provide theoretical guidance for the development of such experiments and provide a novel design idea for structural optimization of PSCs.

Highly Fluorescent Collagen-Based Quantum Dots as an Efficient Interlinkage in the 2D Perovskite Bulk for Improved Solar Cells.

A design-inexpensive, effective, and easy-to-prepare additive in the large-scale preparation of perovskite solar cells (PSCs) is urgently desired to alleviate the future energy crisis. Carbon-based quantum dots have demonstrated novel nanomaterials with excellent chemical stability and high electrical conductivity, which exhibit great potential as additives for perovskite optoelectronics. Herein, we designed novel highly fluorescent collagen-based quantum dots (Col-QDs) and thoroughly studied the micromorphological characteristics, photoluminescence properties, and the states of surface-functionalized groups on the Col-QDs. It is found that the introduction of Col-QDs in the two-dimensional (2D) perovskite precursor can be further confirmed as an efficient interlinkage via Col-Pb bands in the pure 2D perovskite heterojunction, which significantly improves the crystallinity, orientation, and interlayer coupling of perovskite crystal plates, as observed by grazing incidence X-ray diffraction (GIWAXS) and X-ray photoelectron spectroscopy (XPS). Finally, the champion Col-QD additive can efficiently modulate the photovoltaic performance of pure 2D PSCs with a significant increase of photoelectric conversion efficiency (PCE) from 8.18% up to 10.45%, which ranks among the best efficiencies of highly pure 2D PSCs. These results provide a facile and feasible approach to modulate the interlayer interaction of pure 2D perovskites and further improve their output of PSCs, which would further facilitate the burgeoning applications of the Col-QDs in various perovskite-based optical-related fields.

Effect of evaporated Sb layer on performance of flexible CZTSSe thin film solar cell

Cu2ZnSn(S,Se)4 (CZTSSe) chalcogenide with natural-abundance, environment -friendly and impressive photovoltaic performance is promising material for kesterite thin film solar cell. In this paper, the effects of evaporated Sb layer on performance of flexible CZTSSe thin film solar cell are investigated. Systematic studies show that the quasi-liquid Sb2Se3 plays productive roles in promoting grain growth, subsequently volatilizes in the elevated selenization temperature without entering into the CZTSSe lattice. Obvious improvements in crystallinity, grain size, surface roughness, hole concentration and device performance are obtained after optimizing the thickness of Sb layer. The electrostatic potential fluctuation extracted from the PL results is found to decrease from 115.9 meV to 60.7 meV after introducing 20 nm evaporated Sb layer. Finally, 20 nm evaporated Sb layer takes effect to the fullest extent which shows a 69% increase in photoelectric conversion efficiency (PCE). The incorporation of Sb opens up access to opportunity in roll-to-roll process for thin film solar cells.

The effect of thickness on the performance of CdSe:Cu2+—quantum dot-sensitized solar cells

The role of the thickness in the counter electrodes is one of the most important criteria for determining the photoelectric conversion efficiency. In this study, we report a novel strategy for optimizing the thickness of CdSe:Cu films in the quantum dot-sensitized solar cells by changing the successive ionic layer absorption and reaction cycles. The result shows that there was a sharp increase in photoelectric conversion efficiency from 1.8 to 4.23% with the SILAR cycles of CdSe:Cu films from 1 to 5 layers due to the effect of CdSe:Cu nanoparticles size on the optical and photovoltaic properties of the devices. In addition, the recombination resistances of the devices can be increased when the SILAR cycles of the counter electrodes changed from 1 layer to 5 layers. To study the above mentioned strategy, the dynamic processes were discussed in detail using the values of the dynamic resistances as: external and internal resistances (RD, Rd), series resistance (RS), shunt resistance (RSH) from one illuminatedI–V curve and resistance movement of charge at the Cu2S/electrolyte and the FTO/TiO2 interface (Rct1), resistance against the electron diffusion in the TiO2 and the charge recombination resistance at the TiO2/QDs/electrolyte interface (Rct2) from electrochemical impedance spectra.

Enhancing the ultraviolet-visible-near infrared photovoltaic responses of crystalline-silicon solar cell by using aluminum nanoparticles

We report to apply Al nanoparticles (NPs) to enhance the photovoltaic response of crystalline- or c-Si solar cell from the ultraviolet (UV) throughout the visible and near infrared (NIR) regimes. Al NPs were induced by solid thermal annealing and embedded in a SiO2 layer that was to passivate the front side of solar cell. Upon the excitation of surface plasmons (SPs) on the Al NPs under light illumination, an enhancement of broadband absorption of the solar cell was observed. The incorporation of Al NPs led to a relative 13.8% increase in photoelectric conversion efficiency of c-Si solar cell, and an external quantum efficiency enhancement from the UV throughout the visible and NIR regimes. The improvement of c-Si solar cell performance was attributed to both effects of absorption and scattering by SPs.

Characteristics of gradient-interface-structured ZnCdSSe quantum dots with modified interface and its application to quantum-dot-sensitized solar cells

Colloidal quantum dots (QDs) are attractive materials for application in photovoltaics, LEDs, displays, and bio devices owing to their unique properties. In this study, we synthesized gradient-interface-structured ZnCdSSe QDs and modified the interface based on a thermodynamic simulation to investigate its optical and physical properties. In addition, the interface was modified by increasing the molar concentration of Se. QDs at the modified interface were applied to QD-sensitized solar cells, which showed a 25.5% increase in photoelectric conversion efficiency owing to the reduced electron confinement effect. The increase seems to be caused by the excited electrons being relatively easily transferred to the level of TiO2 owing to the reduced electron confinement effect. Consequently, the electron confinement effect was observed to be reduced by increasing the ZnSe (or Zn1−xCdxSe)-rich phase at the interface. This means that, based on the thermodynamic simulation, the interface between the core QDs and the surface of the QDs can be controlled. The improvement of optical and electronic properties by controlling interfaces and surfaces during the synthesis of QDs, as reported in this work, can be useful for many applications beyond solar cells.

40% enhanced photocurrent of dye sensitized solar cells using lotus-shaped H2-treated anatase TiO2 with {0 0 1} dominated facets

After hydrogen treatment, lotus-shaped nitrogen and fluorine co-modified anatase TiO2 (NF-TiO2) with {001} facets have been synthesized and employed as photoanode materials in dye sensitized solar cells (DSSCs). In comparison with non-modified TiO2 based DSSC, we obtain a 40% enhancement of photocurrent and a 38% increase of photoelectric conversion efficiency. UV–visible absorption spectroscopy (UV–vis) and Mott-Schottky plots combined with valence band analysis are used to characterize the electronic structure variation and study the synergistic effect of hydrogen treatment. The result shows an enhanced light absorbing ability, is a positively shifted flat band potential and an increased donor density. These improvements can be mainly ascribed to the appropriate electronic structure and the effective light-scattering centers. This work provides systematic and comprehensive research on the application of hydrogenation and {001} facets dominated nitrogen and fluorine co-modified TiO2 in DSSC, and the hydrogenation treatment can lead to improved charge transport and recombination, enhanced light absorbing ability as well as elevated donor density of semiconductor. With these merits, {001} facets dominated HNF-TiO2 nanopowders in this work may find its way in enormous energy and photoelectric fields.

TiO2 Coated Graphene/ Mesoporous TiO2 Composite Layer for Perovskite Solar Cells Produced By Supramolecular Protein

[Introduction] CH3NH3PbI3 have attracted much attention as a light absorbing material for perovskite solar cells (PSCs). Owing to the compounds has better characteristics for solar cells and can be fabricated by solution process, high efficiency and inexpensive solar cells are available. Recently, PSCs have been widely researched to improve the photoelectric conversion efficiency (PCE). One of such research reported the method for mixing graphene in mesoporous TiO2 (meso-TiO2) layer. Graphene exhibits high carrier mobility and lower LUMO levels than TiO2. Therefore, the electron can be transported easily from TiO2 to graphene. However, PSCs using only graphene in electron transport layer have reported that PCE decreased because the LUMO level difference between the graphene and the CH3NH3PbI3 is large. Therefore, we propose a method to improve PCE by reducing the contact area between perovskite and graphene using a TiO2 coated graphene. In this report, CDT-1, which is a supramolecular protein composed of Dps with displaying carbon nano-horn binding peptide (NHBP-1) and Ti binding peptide (TBP-1), was used to coat TiO2 on graphene. We demonstrated the fabrication of TiO2 coated graphene using CDT-1 and the characterized the change upon PSCs using TiO2 coated graphene in meso-TiO2 layer. [Methods] The structure of CDT-1 is shown in Fig. 1. Both twelve NHBP-1s and twelve minTBP-1s are displayed on the outer surface of assembled CDT-1. Multiple NHBP-1 on the outer surface adsorbed to graphene and made graphene / CDT-1 bio-conjugates. Graphene / CDT-1 were then dipped in Titanium precursor solution. Multiple Ti binding peptides was effective to make the titanium bio-mineralization faster. Finally, precipitation of TiO2 coated graphene was obtained by ultracentrifugation. The structure of PSCs in this research is shown in Fig. 2. The compact layer of TiO2 (CL-TiO2) was prepared by spin coating on transparent conductive substrate. The meso-TiO2 layer was spin coated on the CL-TiO2 using the TiO2 coated graphene / meso-TiO2 composite paste (0, 0.1, 0.5, 1.0 wt%) and annealed at 450°C in air for 60 min. The perovskite layer was deposited onto the meso-TiO2 layer by spin-coating of PbI2 CH3NH3I precursor DMF solution, and perovskite layer was baked with 2 steps (65oC, 1 min to 100oC, 2 min) in a nitrogen filled glovebox. The hole transport layer (HTL) was spin coated on the perovskite layer using Spiro-OMeTAD, and the gold electrode was formed by thermal evaporation on HTL. The change of the photoelectric conversion characteristics on the concentration of TiO2 coated graphene were evaluated by current-voltage (I-V) measurements. [Results and discussions] The SEM images are shown in Fig. 3. The white dots in Fig. 3 are the Fe-Oxide core in CDT-1 with 4.5 nm diameter adsorbed on graphene. As a result, CDT-1 was confirmed to be adsorbed high density by NHBP-1. We analyzed TiO2 on graphene by EELS-TEM mapping. The Fig. 4 (a) shows TEM images of TiO2 coated graphene. The Fig. 4 (b) shows Ti mapping TEM-EELS images. We fabricated TiO2 coated graphene resulted from TEM-EELS images. It was successfully.The Fig. 5 (a) compares the representative I-V curves of a TiO2 coated graphene (in variable concentration)/meso-TiO2 based PSCs. The Fig. 5 (b) shows changing the PCE and Fill Factor (FF) by the TiO2 coated graphene at various concentrations in meso-TiO2. With the addition of the a TiO2 coated graphene in the meso-TiO2, PCE increased from 8.4% to 12.5% in the 0.5 wt% TiO2 coated graphene/meso-TiO2, The FF increased from 53% to 68% in the 0.5 wt% TiO2 coated graphene/meso-TiO2.These results suggest the internal resistance is reduced by using TiO2 coated graphene. [Conclusion] We successfully synthesized TiO2 coated graphene using supramolecular protein. The TiO2 coated graphene/meso-TiO2 composite based PSCs exhibited an increase in PCE and FF as compared to meso-TiO2 based PSCs. Figure 1

Improvement in performance of dye-sensitized solar cells with porous TiO2 electrodes using squid ink particles

A potentially appealing alternative to the traditional fabrication process of TiO2 film electrodes for dye-sensitized solar cells (DSSCs) was presented by utilizing water-soluble TiO2 composite pastes containing size-controlled ink particles (SIPs) isolated from the squid. The mixture ratios of SIPs in the paste formulations affected the photoelectric conversion efficiency (PCE). The highest PCE was achieved when the mixture ratio of SIPs was 20%. The process is highly reproducible and leads to a 35% increase in PCE compared with that in the DSSC without SIP addition. The utilization of SIPs in the fabrication of TiO2 film electrodes enhanced the performance of DSSCs.

Photoelectrode thin film of dye-sensitized solar cell fabricated by anodizing method and spin coating and electrochemical impedance properties of DSSC

The paper studies the photoelectrode thin film of dye-sensitized solar cell (DSSC) fabricated by anodizing method, explores the structure and properties of the fabricated photoelectrode thin film, measures the photoelectric conversion efficiency of DSSC, and finds the electrochemical impedance properties of DSSCs assembled by photoelectrode thin films in different thicknesses. Besides, in order to increase the specific surface area of nanotubes, this paper deposits TiO2 nanoparticles (TNP) on the surface of titanium oxide nanotube (TNT). As shown in experimental results, the photoelectric conversion efficiency of the DSSC fabricated by the study rises to 6.5% from the original 5.43% without TnB treatment, with an increase of photoelectric conversion efficiency by 19.7%. In addition, when the photoelectrode thin film is fabricated with mixture of TNTs and TNP in an optimal proportion of 2:8 and the photoelectrode thin film thickness is 15.5μm, the photoelectric conversion efficiency can reach 7.4%, with an increase of 36.7% from the original photoelectric conversion efficiency at 5.43%. Besides, as found in the results of electrochemical impedance analysis, the DSSC with photoelectrode thin film thickness at 15.5μm has the lowest charge-conduction resistance (Rk) value 9.276Ω of recombined electron and conduction resistance (Rw) value 3.25Ω of electrons in TiO2.

Synthesis of ZnO nanostructure films by thermal evaporation approach and their application in dye-sensitized solar cells

Zinc oxide (ZnO) films were prepared successfully by simple thermal evaporation of zinc acetate dihydrate at low temperature onto FTO (fluorine-doped tin oxide) glass substrates coated with thin ZnO seed layer. The synthetic parameter such as temperature was found to determine the morphology of nanostructures. ZnO nanorod (NR) and nanoparticle (NP) films have been synthesized at 245 and 350°C, respectively, for 6h. The dye-sensitized solar cells (DSSCs) were fabricated using the ZnO nanostructure films as photosensitized electrodes. A maximum photoelectric conversion efficiency (PCE) of 1.56%, and short-circuit photocurrent density of 5.12mA/cm2 were achieved with the ZnO NP-based DSSC. The PCE increase was ascribed to the reduced recombination loss and prolonged electron lifetime according to electrochemical impedance spectroscopy (EIS).

Effect of MWCNT Inclusion in TiO2 Nanowire Array Film on the Photoelectrochemical Performance

Rutile TiO2 nanowire array films with multi-walled carbon nanotube (MWCNT) inclusion perpendicularly grown on fluorine-doped tin oxide (FTO) substrate were prepared by a facile hydrothermal method. The absorption edges of the TiO2 nanowire array films are blue-shifted with increasing MWCNT content. The resistance of the TiO2 nanowire array film is decreased by MWCNT inclusion. The optimum TiO2/MWCNT molar ratio in the feedstock is 1:0.1. For the TiO2 nanowire array film with MWCNT inclusion served as electrode in dye-sensitized solar cell (DSSC), an overall 194% increase of photoelectric conversion efficiency has been achieved.

Key Technology on the Solar Photovoltaic & Thermal System

Using the concentrating and tracking photovoltaics generation technology, the area of photovoltaic cells is only one-fifth of the traditional one if both generate same power output, and therefore the cost of photovoltaic power generation is greatly reduced. The concentrating solar cells produced with the special construction and lamination technique have the functions of heat exchanging and temperature controlling, which prevent the solar panel from over-temperature caused by the concentrating light and the crystal silicon cell pieces will always work under 60°C, and hence the photoelectric conversion efficiency increase. The rest solar energy that cannot be converted into electrical energy by the concentrating solar cells is absorbed by water flowing through it. The flat-plate collector reheat the water flowed from the concentrating solar cells’ heat exchanger and the additional product, hot water, whose temperature is over 80°C, is got. Hence, the total efficiency of photovoltaic & thermal conversion is more than 55%. The solar photovoltaic & thermal system can high efficiently, but low costly and practicably, utilize the solar photovoltaic & thermal and practical.

Photo detection characteristics of Si/Si 1− xGe x/Si p-i-n diodes integrated with optical waveguides

Integration of Si/Si 1− x Ge x /Si and Si p-i-n diodes with Si nitride optical waveguide on silicon-on-insulator (SOI) substrates has been achieved. For light emission from Si p-i-n diode, photo current of Si/Si 1− x Ge x /Si p-i-n diode is larger than that of Si p-i-n diode, and increases with increasing Si 1− x Ge x layer thickness and Ge fraction. From the relationship between photo current and effective electroluminescence intensity, it is suggested that the enhancement of photo current due to the Si 1− x Ge x layer is caused not only by the narrowing of bandgap but also by the increase of photoelectric conversion efficiency.