Efficiency improvement of silicon solar cells enabled by ZnO nanowhisker array coating

An efficient antireflection coating is critical for the improvement of silicon solar cell performance via increased light coupling. Here, we have grown well-aligned ZnO nanowhisker (NW) arrays on Czochralski silicon solar cells by a seeding-growth two-step process. It is found that the ZnO NWs have a great effect on the macroscopic antireflection effect and, therefore, improves the solar cell performance. The ZnO NW array-coated solar cells display a broadband reflection suppression from 500 to 1,100 nm, and the minimum reflectance smaller than 3% can easily be achieved. By optimizing the time of ZnO NW growth, it has been confirmed that an increase of 3% relatively in the solar cell efficiency can be obtained. These results are quite interesting for the application of ZnO nanostructure in the fabrication of high-efficiency silicon solar cells.     

Visible to near-infrared light harvesting in Ag2S nanoparticles/ZnO nanowire array photoanodes

Pronounced absorption in the visible-NIR range of 400-1300 nm is demonstrated in the Ag(2)S nanoparticles (NPs)/ZnO nanowire (NW) array. ZnO NW arrays are grown on indium tin oxide substrates using chemical bath deposition. The Ag(2)S NPs are sequentially formed on the ZnO NWs through sonochemical synthesis. Structural characterizations indicate the slight deconstruction of surface of ZnO NWs during Ag(2)S NPs formation. By employing polysulfide electrolyte, short-circuit current (J(sc)), open-circuit voltage and therefore the efficiency of the Ag(2)S NP-sensitized ZnO NW solar cell are improved with increasing the initial sulfur concentration in the sulfur-polysulfide electrolyte. The Ag(2)S NP-sensitized ZnO NW solar cell shows a conversion efficiency of 0.49% with a superior J(sc) of ~13.7 mA cm(-2) under AM 1.5 illumination at 100 mW cm(-2). Incident photon conversion efficiency measurements reveal that Ag(2)S NPs contribute to 33.4% and 65.2% of J(sc) in the wavelength ranges of 400-700 nm and 700-1300 nm, respectively.     

Effects of dye etching on the morphology and performance of ZnO nanorod dye-sensitized solar cells

Dye-sensitized solar cells based on electrodeposited ZnO nanorod arrays were fabricated and tested. Field-emission scanning electron microscopy (FESEM) and X-ray powder diffraction (XRD) were used to identify the characters of ZnO nanorod arrays. The effects of dye etching on the morphology and performance of ZnO nanorod dye-sensitized solar cells were studied. It was found that the surfaces of ZnO nanorods were both etched by dye solutions, no matter N3 or N719. Compared with N3, N719 had a larger damage to the structure of ZnO nanorod photoanode, and the photoelectric conversion efficiency of cells decreased quickly with the sensitizing time increasing. In a certain range, the increasing length of ZnO nanorods can clearly improve the photoelectric conversion efficiency of cells.     

Efficiency improvement of InGaP/GaAs/Ge solar cells by hydrothermal-deposited ZnO nanotube structure

In this paper, a zinc oxide (ZnO) nanotube, fabricated by the hydrothermal growth method on triple-junction (T-J) solar cell devices to enhance efficiency, is investigated. Compared to those of bare T-J solar cells (without antireflection (AR) coating) and solar cells with Si₃N₄ AR coatings, the experimental results show that the T-J solar cells, which use a ZnO nanotube as an AR coating, have the lowest reflectance in the short wavelength spectrum. The ZnO nanotube has the lowest light reflection among all experimental samples, especially in the range of 350 to 500 nm from ultraviolet (UV) to visible light. It was found that a ZnO nanotube can enhance the conversion efficiency by 4.9%, compared with a conventional T-J solar cell. The Si₃N₄ AR coatings also enhance the conversion efficiency by 3.2%.The results show that a cell with ZnO nanotube coating could greatly improve solar cell performances.     

Improved dye-sensitized solar cell with a ZnO nanotree photoanode by hydrothermal method

This study investigated the influence of ZnO nanostructures on dye adsorption to increase the photovoltaic conversion efficiency of solar cells. ZnO nanostructures were grown in both tree-like and nanorod (NR) arrays on an AZO/FTO film structure by using a hydrothermal method. The results were observed in detail using X-ray diffraction, field-emission scanning electron microscopy (FE-SEM), UV-visible spectrophotometry, electrochemical impedance spectroscopy, and solar simulation. The selective growth of tree-like ZnO was found to exhibit higher dye adsorption loading and conversion efficiency than ZnO NRs. The multiple ‘branches’ of ‘tree-like nanostructures’ increases the surface area for higher light harvesting and dye loading while reducing charge recombination. These improvements result in a 15% enhancement in power conversion. The objective of this study is to facilitate the development of a ZnO-based dye-sensitized solar cell.     

Hybrid polymer/ZnO solar cells sensitized by PbS quantum dots

Poly[2-methoxy-5-(2-ethylhexyloxy-p-phenylenevinylene)]/ZnO nanorod hybrid solar cells consisting of PbS quantum dots [QDs] prepared by a chemical bath deposition method were fabricated. An optimum coating of the QDs on the ZnO nanorods could strongly improve the performance of the solar cells. A maximum power conversion efficiency of 0.42% was achieved for the PbS QDs' sensitive solar cell coated by 4 cycles, which was increased almost five times compared with the solar cell without using PbS QDs. The improved efficiency is attributed to the cascade structure formed by the PbS QD coating, which results in enhanced open-circuit voltage and exciton dissociation efficiency.     

纳米氧化锌的制备及其与MEH-PPV共混光电池器件性能研究

利用溶胶-凝胶法,以醋酸锌为前驱体,制备了纳米ZnO颗粒及纳米棒,用TEM和XRD分别研究了ZnO纳米的形貌和结构特征;用旋涂及热蒸镀的方法将纳米ZnO和聚苯乙烯撑(MEH-PPV)的混合体制成有机-无机复合光电池薄膜器件。结果表明,MEH-PPV的荧光随着ZnO含量的增加出现明显的淬灭现象,器件在标准模拟太阳光照射下,获得了1.0%的能量转化效率,和国际报道的ZnO-聚合物共混太阳能电池1.6%的能量转化效率接近。     

Substantial influence on solar energy harnessing ability by geometries of ordered Si nanowire array

The reflectance of the controlled periodic Si nanowire (NW) arrays is systematically explored, which characterizes the influence on the solar energy harnessing ability by the geometries of the NW. A unique dependence of the reflectance of the Si NW array on the diameter, the height, and the bending of the NW are disclosed. The solar energy loss caused by the reflection of the Si NW array exhibits the minimum for the NW with intermediate diameter and length. A plane-wave-based transfer-matrix method (TMM) simulation is performed, which is well consistent with the experimental results. Our results demonstrate the design principle to optimize the Si NW arrays for high-efficiency solar cells.

PACS

81.07.-b; 78.67.-n; 81.16.-c     

Effect of CdSe quantum dots on the performance of hybrid solar cells based on ZnO nanorod arrays

This paper reports the fabrication and interface modification of hybrid inverted solar cells based on ZnO nanorod arrays and poly (3-hexylthiophene). CdSe quantum dots (QDs) are grafted to the ZnO nanorod array successfully by bifunctional molecule mercaptopropionic acid to enhance the device performance. The power conversion efficiency of the device is increased by 109% from 0.11% to 0.23% under simulated 1 sun AM 1.5 solar illumination at 100 mW/cm² after the modification. The grafting of CdSe QDs effectively enhanced the excition generation and dissociation on the organic/inorganic interface. This work may provide a general method for increasing the efficiency of organic–inorganic hybrid solar cells by interface modification.     

Preparation and photoelectrochemical properties of CdS quantum dot-sensitized ZnO nanotube arrays

CdS/ZnO nanotubes (NTs) arrays were synthesized on a transparent conductive glass (FTO) substrate by hydrothermal method, chemical bath etching and successive ionic layer adsorption and reaction (SILAR) method, which were used in semiconductor-sensitized photoelectrochemical cells (PECs). The crystal structure, morphology and photoelectrochemical conversion properties of different photoanodes were investigated by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscope (TEM), high resolution transmission electron microscope (HRTEM), and electrochemical workstation. The results show a heterojunction has been formed between ZnO and CdS QDs. The ZnO NTs and CdS QDs played a remarkable controllability for PEC performances. The photoelectrochemical conversion efficiency of ZnO NTs photoanodes was 3 times that of ZnO nanorods (NRs) arrays photoanodes. After sensitization of CdS quantum dots, the photoelectrochemical conversion efficiency of CdS/ZnO NRs was improved by 7 times and the CdS/ZnO NTs was increased by 4 times. These results demonstrate that the CdS/ZnO core-shell structure can provide a facile and compatible frame for the potential applications in nanotube-based solar cells.     

Flexible Dye-Sensitized Solar Cell Based on Vertical ZnO Nanowire Arrays

Flexible dye-sensitized solar cells are fabricated using vertically aligned ZnO nanowire arrays that are transferred onto ITO-coated poly(ethylene terephthalate) substrates using a simple peel-off process. The solar cells demonstrate an energy conversion efficiency of 0.44% with good bending tolerance. This technique paves a new route for building large-scale cost-effective flexible photovoltaic and optoelectronic devices.     

ZnO photoanodes with different morphologies grown by electrochemical deposition and their dye-sensitized solar cell properties

In this article, we grew zinc oxide (ZnO) samples with different morphologies, e.g. film, nanowire and nanosheet, with electrochemical deposition (ECD) by controlling the precursor concentration and the growth mechanism was also discussed. The morphology influence on the photovoltaic conversion efficiency of the dye-sensitized solar cells (DSSC) assembled with different ZnO photoanodes was investigated by measuring current density–voltage (J–V) curve, quantum efficiency (QE) spectrum and electrochemical impedance spectrum (EIS). It was found that the DSSC constructed with ZnO nanowire array as photoanode can absorb more dye, improve the photon utilization rate and provide rapid collection channels for the photoexcited carriers. Therefore, the photovoltaic conversion efficiency of ZnO nanowire DSSC was improved.     

Performance of Cu2O/ZnO Solar Cell Prepared By Two-Step Electrodeposition

Cu₂O/ZnO solar cells with improved performance were fabricated by an inexpensive two-step process. The process involves potentiostatic deposition of ZnO on NESA glass (tin-oxide-coated glass) followed by galvanostatic deposition of Cu₂O to form Cu₂O/ZnO/NESA solar cells with a short-circuit photocurrent density of 2.08 mA cm⁻²,an open-circuit voltage of 0.19 V, a fill factor of 0.295 and conversion efficiency of 0.117%. The performance of the solar cells thus prepared is discussed in terms of the laminated structure, construction of the heterojunction, and the crystallinity and optical properties of each semiconductor.     

Solid-state dye-sensitized solar cells based on ZnO nanoparticle and nanorod array hybrid photoanodes

The effect of ZnO photoanode morphology on the performance of solid-state dye-sensitized solar cells (DSSCs) is reported. Four different structures of dye-loaded ZnO layers have been fabricated in conjunction with poly(3-hexylthiophene). A significant improvement in device efficiency with ZnO nanorod arrays as photoanodes has been achieved by filling the interstitial voids of the nanorod arrays with ZnO nanoparticles. The overall power conversion efficiency increases from 0.13% for a nanorod-only device to 0.34% for a device with combined nanoparticles and nanorod arrays. The higher device efficiency in solid-state DSSCs with hybrid nanorod/nanoparticle photoanodes is originated from both large surface area provided by nanoparticles for dye adsorption and efficient charge transport provided by the nanorod arrays to reduce the recombinations of photogenerated carriers.     

Controlled synthesis of various ZnO nanostructured materials by capping agents-assisted hydrothermal method for dye-sensitized solar cells

In this work, the morphology of ZnO materials could be controlled by changing the capping agent at constant alkali solution in hydrothermal process. ZnO nanomaterials with the structure of flowers, sheet-spheres and plates were obtained with the capping agent of ammonia, citric acid and oxalic acid, respectively. Thus prepared ZnO nanomaterials were characterized and applied as the photo-anode materials for dye-sensitized solar cell. All synthesized ZnO nanomaterials possessed high crystalline wurtzite structures grown in the (0 0 1) direction with the size of 2-4 μm, which consist of ZnO units around 20-400 nm. Among them, Sheet-sphere ZnO showed the highest crystallinity, surface area and uniform film morphology, resulting in the significantly improved PV performance with the overall conversion efficiency of 2.61% in dye-sensitized solar cell (DSSC) fabricated with sheet-sphere ZnO. It is notable that the ZnO materials with sphere structure may be the optimal photo-anode material among various ZnO nanomaterials for DSSC.     

Block copolymers as efficient cathode interlayer materials for organic solar cells

Emerging needs for the large-scale industrialization of organic solar cells require high performance cathode interlayers to facilitate the charge extraction from organic semiconductors. In addition to improving the efficiency, stability and processability issues are major challenges. Herein, we design block copolymers with well controlled chemical composition and molecular weight for cathode interlayer applications. The block copolymer coated cathodes display high optical transmittance and low work function. Conductivity studies reveal that the block copolymer thin film has abundant conductive channels and excellent longitudinal electron conductivity due to the interpenetrating networks formed by the polymer blocks. Applications of the cathode interlayers in organic solar cells provide higher power conversion efficiency and better stability compared to the most widely-applied ZnO counterparts. Furthermore, no post-treatment is needed which enables excellent processability of the block copolymer based cathode interlayer.     

The Influence of Physical Properties of ZnO Films on the Efficiency of Planar ZnO/Perovskite/P3HT Solar Cell

ZnO thin films prepared by pulsed laser deposition at low temperature are utilized as the electron transport layer in CH₃NH₃PbI_3?xCl_x‐based perovskite solar cells with a planar heterojunction structure. Oxygen pressure greatly influences the transparent and conductive properties of ZnO films, which are extremely important as electron transport layer for the perovskite solar cells. The transparent and conductive properties of the films under different oxygen pressures are studied by ultraviolet‐visible spectrophotometer and Hall effect measurement system. Through controlling the oxygen pressure, transparent ZnO films with high conductivity are grown and adopted as electron transport layer for planar perovskite solar cell with a power conversion efficiency of 6.3%. After further surface modification of ZnO electron transport layer with [6,6]‐phenyl‐C61‐butyric acid methyl ester, the efficiency of the planar solar cell increases to 7.5%.     

CdS quantum dots sensitized ZnO spheres via ZnS overlayer to improve efficiency for quantum dots sensitized solar cells

This paper reports the preparation of three-dimensional ZnO spheres by using a hydrothermal method and their application to quantum dots sensitized solar cells (QDSSCs). After achieving the desired thickness of sensitized CdS quantum dots (QDs) for ZnO spheres, ZnS overlayer was deposited on the surface of CdS/ZnO photo-anodes to further improve the photoelectric properties. CdS QDs and ZnS overlayer were deposited by successive ionic layer adsorption and reaction (SILAR) method. The surface morphology and crystal structure of the samples were verified by field-emission scanning electron microscopy (FE-SEM), Transmission electron microscopy (TEM) and X-ray diffraction (XRD). The CdS QDs sensitized solar cells were ameliorated via using ZnS as a protection-layer between quantum dots and electrolyte. As a result, the power conversion efficiency (η) has been increased from 0.60 to 1.43% after being treated by ZnS overlayer for CdS/ZnO photo-anodes.     

QUASI-SOLID-STATE DYE-SENSITIZED SOLAR CELLS BASED ON ZnO PHOTOANODE

ZnO photoanode in dye-sensitized solar cells (DSSCs) has been successfully prepared by the electro-hydrodynamic (EHD) technique. The sandwich solar cells exhibited a short-circuit photocurrent density of 7.0 mA cm^-2 and conversion efficiency of 1.65% with a quasi-solid-state electrolyte under simulated sun illumination (AM-1.5, 100 mW cm^-2). The stability and the influencing factors, such as film thickness and light intensity, on solar cell performance were discussed.     

ZnO nanosheet arrays constructed on weaved titanium wire for CdS-sensitized solar cells

Ordered ZnO nanosheet arrays were grown on weaved titanium wires by a low-temperature hydrothermal method. CdS nanoparticles were deposited onto the ZnO nanosheet arrays using the successive ionic layer adsorption and reaction method to make a photoanode. Nanoparticle-sensitized solar cells were assembled using these CdS/ZnO nanostructured photoanodes, and their photovoltaic performance was studied systematically. The best light-to-electricity conversion efficiency was obtained to be 2.17% under 100 mW/cm² illumination, and a remarkable short-circuit photocurrent density of approximately 20.1 mA/cm² was recorded, which could attribute to the relatively direct pathways for transportation of electrons provided by ZnO nanosheet arrays as well as the direct contact between ZnO and weaved titanium wires. These results indicate that CdS/ZnO nanostructures on weaved titanium wires would open a novel possibility for applications of low-cost solar cells.