Nanocrystalline silicon solar cells from excimer laser crystallization of amorphous silicon

Excimer laser crystallized nanocrystalline silicon layers were used to fabricate solar cells. The laser crystallized layers are characterized with Raman spectroscopy for structural investigations and with atomic force microscopy to study surface modifications upon crystallization. The current–voltage characteristics of the devices completed with aluminium back contacts were investigated with air mass 1.5 G solar simulations. The resulting nanocrystalline solar cells show inferior performance compared with amorphous silicon devices. The degradation of open circuit voltages and short circuit currents with the increase of crystallization energy density is explained to be due to thermal modification of the p-type/intrinsic layer interface and band gap enhancement of fine-grained nanocrystalline layers of the devices along with increased surface and grain boundary recombination of carriers.     

Nanocrystalline Ti-oxide-based solar cells made by sputter deposition and dye sensitization: Efficiency versus film thickness

Nanocrystalline TiO₂-based films with a special penniform microstructure were prepared by reactive DC magnetron sputtering followed by dye sensitization. The films were integrated in a solar cell configuration and were able to yield a higher photocurrent than sol–gel-produced Ti-oxide-based films of similar thickness. The photoelectric conversion efficiency reached 4% in 10-μm-thick sputter deposited films.     

Electrochemical solar cells

Semiconductor liquid junction solar cells reach 12 per cent solar to electrical and similar solar to chemical (hydrogen) conversion efficiency when made with single crystal semiconductors; they retain of this efficiency when made with thin, chemically formed, polycrystalline semiconductor films. The principle on which the most efficient cells are based is the neutralization (“passivation”) of damaging states, that result from weak chemical bonds at surfaces and at grain boundaries, by chemisorption of strongly bound species. The solar conversion efficiencies of cells made with chemically vapor deposited p-InP films on graphite are increased by factors between 6 and 500 upon diffusion of chemisorbed silver ions into the grain boundaries, and the efficiencies of cells made with similar films of n-GaAs, by factors between 3–4, upon diffusion of ruthenium ions.     

多晶硅太阳电池

多晶硅太阳电池由于其材料成本低于单晶硅太阳电池 ,且易于制备成方型 ,组件封装成本较低 ,目前在生产的晶体硅太阳电池中 ,其所占比例正逐渐增加。一多晶硅太阳电池的制造（１）浇铸多晶硅的制造目前应用最广的多晶硅制造方法是浇铸法 ,亦称铸造法。浇铸多晶硅在原理上有两种方式 :在一个坩埚内将多晶硅熔化 ,然后倒入另一个坩埚冷却 ;另一种是在一个坩埚内将多晶硅熔化 ,然后通过坩埚底部热交换 ,使晶体冷却。目前第一种方式已很少使用 ,普遍采用第二种方式 ,即热交换法 ,国际上著名的多晶硅生产厂商如日本的京陶、德国的拜耳、法国的伏特…     

Nanocrystalline TiO2 film with textural channels: Exhibiting enhanced performance in quasi-solid/solid-state dye-sensitized solar cells

Novel nanocrystalline TiO₂ films with the textural channels are obtained for dye-sensitized solar cells (DSSCs). The textural channels consisting of the cracks on the surface and the nanopores with average diameter of about 41 nm are produced by packaging ZnO nanowires with diameter of 30–50 nm into TiO₂ films and subsequently etching ZnO nanowires by hydrochloric acid. The performances of DSSCs based on novel TiO₂ films (with the textural channels) and traditional TiO₂ films (without the textural channels) are investigated, respectively. When two kinds of typical quasi-solid-state electrolytes and one kind of solid-state electrolyte are used, the energy conversion efficiencies of DSSCs from novel TiO₂ films are improved by 20–30% compared to that from traditional TiO₂ films. The reasons for the great improvement are investigated chiefly by UV–vis absorption spectra, field emission-scanning electron microscope (FE-SEM) and electrochemical impedance spectroscopy (EIS) technique. The results show that the introduction of the textural channels facilitates better penetration of quasi-solid/solid-state electrolytes into the nanopores of novel TiO₂ films and thus results in better interfacial/electrical contact and faster interfacial reaction.     

Monochromatic versus solar efficiencies of organic solar cells

The photovoltaic behavior in a perylene/phthalocyanine hetero-p/n-junction solar cell was investigated using intensity-dependent I/V-characteristics and short circuit photocurrent spectroscopy. It is concluded that the charge carrier generation occurs only in a very thin active region at the contact. By optimizing the light trapping, a maximum solar AM 1.5 efficiency of about 2% can be obtained. A further increase requires better material properties or new cell structures.     

Biodegradable polymer solar cells

Polymer photovoltaic devices were prepared using a biodegradable poly-l-lactic acid (PLLA) substrate loaded with nanoclay in an attempt to improve the thermal properties and possibly reduce permeation of water and oxygen. The nanoclay-loaded PLLA substrates were prepared by compounding and extrusion. The substrate thickness was 200 μm and the substrates had good transparency in the range 300–800 nm of, respectively, >80% for PLA and >60% for PLLA loaded with nanoclay. Devices were realized by application of a conducting transparent anode comprising an aluminium grid with a thin overlayer of silver and spin-coated PEDOT:PSS. The active layer consisted of microfibrillar P3HT and PCBM to encompass the low processing temperatures for PLLA and finally an evaporated aluminium cathode. It was found that PLLA as a substrate holds potential, but there are several challenges beyond the photovoltaic itself which must be met before general application within this field can be envisaged. The most important aspects are the planarity of the PLLA surface, the mechanical stresses induced by the extrusion process, the limitation in processing temperature, and the limitation in the available range of solvents for solution processing.     

Integrated tandem solar cells

The performance of integrated tandem solar cell (ITSC) devices made from pn homojunctions has been investigated. The intrinsic electrical interconnection present in an ITSC device places important restrictions on the choice of the energy gaps of the semiconductors to be used. Total conversion efficiencies are calculated and they are compared both with single solar cells and with independent tandem solar cell systems. It is concluded that ITSC devices are attractive solar energy converters provided that proper care is taken in the choice of materials used.     

Amorphous silicon solar cells

The perfectioning of the deposition techniques of amorphous silicon over large areas, in particular film homogeneity and the reproducibility of the electro-optical characteristics, has allowed a more accurate study of the most intriguing bane of this material: the degradation under sun-light illumination. Optical band-gap and film thickness engineering have enabled device efficiency to stabilize with only a 10–15% loss in the as-deposited device efficiency. More sophisticated computer simulations of the device have also strongly contributed to achieve the highest stable efficiencies in the case of multijunction devices. Novel use of nanocrystalline thin films offers new possibilities of high efficiency and stability. Short term goals of great economical impact can be achieved by the amorphous silicon/crystalline silicon heterojunction. A review is made of the most innovative achievements in amorphous silicon solar cell design and material engineering.     

Fullerene photoelectrochemical solar cells

The photoelectrochemistry of single crystal C₆₀ and fullerene photoelectrochemical solar cells is studied. Illuminated and immersed, C₆₀ is shown to drive oxidation of several solution-phase redox couples. Utilization of a photoelectrochemical solid/liquid junction, rather than solid-state photovoltaic junction, improves the observed photocurrent. Utilization of a single crystal, rather than a polycrystalline film, of C₆₀ decreases dark current to the extent that light-driven charge transfer dominates. The spectral response and current-voltage behaviour in several electrolytes is studied. A low-power fullerene photoelectrochemical solar cell, utilizing a regenerative polyiodide and ferri/ferrocyanide redox couple, is demonstrated.     

Flexible silicon solar cells

In order to be useful for certain niche applications, crystalline silicon solar cells must be able to sustain either one-time flexure or multiple non-critical flexures without significant loss of strength or efficiency. This paper describes experimental characterisation of the behaviour of thin crystalline silicon solar cells, under either static or repeated flexure, by flexing samples and recording any resulting changes in performance. Thin SLIVER cells were used for the experiment. Mechanical strength was found to be unaffected after 100,000 flexures. Solar conversion efficiency remained at greater than 95% of the initial value after 100,000 flexures. Prolonged one-time flexure close to, but not below, the fracture radius resulted in no significant change of properties. For every sample, fracture occurred either on the first flexure to a given radius of curvature, or not at all when using that radius. In summary, for a given radius of curvature, either the flexed solar cells broke immediately, or they were essentially unaffected by prolonged or multiple flexing.     

Bias-dependent high saturation solar LBIC scanning of solar cells

A light beam-induced current measurement system that uses concentrated solar radiation as a beam probe to map spatially distributed defects on a solar cell has been developed and tested [F.J. Vorster, E.E. van Dyk, Rev. Sci. Instrum., submitted for review]. The induced current response from a flat plate EFG Si solar cell was mapped as a function of surface position and cell bias by using a solar light beam induced current (S-LBIC) mapping system while at the same time dynamically biasing the whole cell with an external voltage. This paper examines the issues relating to transient capacitive effects as well as the electrical behaviour of typical solar cell defect mechanisms under spot illumination. By examining the bias dependence of the S-LBIC maps, various defect mechanisms of photovoltaic (PV) cells under concentrated solar irradiance may be identified. The techniques employed to interpret the spatially distributed IV curves as well as initial results are discussed.     

Plated contacts for solar cells with superior adhesion strength to screen printed solar cells

The improvement of adhesion strength and durability of plated contacts is required for cell manufacturers to gain confidence for large-scale manufacturing. To overcome weak adhesion at the metal/Si interface, new approaches were developed. These involve the formation of laser-ablated anchor points, or grooves in the extreme case of overlapping anchor points, in the heavily doped silicon surface. When plated, these features greatly strengthen the mechanical adhesion strength of the metal. A stylus-based adhesion tester was developed specifically for evaluating the effectiveness of plated contacts to smooth silicon surfaces. The use of such a tester was also extended in this work to textured and roughened surfaces to allow evaluation of different metal contacting approaches. The adhesion strengths for various metal contacting schemes were evaluated, including screenprinted silver contacts, nickel/copper (Ni/Cu) lightinduced plated (LIP) contacts for laser-doped selective emitter (LDSE) cells, buried-contact solar cells (BCSCs), and Ni/Cu LIP contacts formed with laser-ablated anchoring points in selective emitter (LAASE) cells. The latter has superior adhesion strength. The standard “peel test” of the industry was compared to the stylus-based adhesion testing, with the latter shown value for testing metal contacts on smooth surfaces but with caution needed for use with textured or roughened surfaces.     

Monograin materials for solar cells

This paper reviews results of studies on different materials and technologies for monograin layer (MGL) solar cells conducted at Tallinn University of Technology. The MGL consists of monograin powder crystals embedded into an organic resin. The MGL combines the superior photoelectrical parameters of single crystals with the advantages of polycrystalline materials, such as the low cost and simple technology of materials and layers preparation and the possibility of making devices of practically unlimited area. A main technological advantage is the separation between absorber and cell formations. The developments in the field of monograin materials of CuInSe₂, Cu₂ZnSnS₄ and Cu₂ZnSnSe₄ and technical parameters of MGL solar cells are summarized.     

非晶硅太阳电池的原理

非晶硅太阳电池是２０世纪７０年代中期发展起来的一种新型薄膜太阳电池，与其他太阳电池相比，非晶硅电池具有以下突出特点：（１）制作工艺简单，在制备非晶硅薄膜的同时就能制作pin结构。（２）可连续、大面积、自动化批量生产。（３）非晶硅太阳电池的衬底材料可以是玻璃、不锈钢等，因而成本小。（４）可以设计成各种形式，利用集成型结构，可获得更高的输出电压和光电转换效率。（５）薄膜材料是用硅烷（SiH４）等的辉光放电分解得到的，原材料价格低。１非晶硅太阳电池的结构、原理及制备方法非晶硅太阳电池是以玻璃、不锈钢及特种…     

High-efficiency silicon space solar cells

SHARP's activities on Si solar cells developments and features of Si solar cells for space use in comparison with GaAs solar cells are presented. Two types of high-efficiency silicon solar cells and the same kinds of high-efficiency solar cells with integrated bypass function (IBF cells) were developed and qualified for space applications. The NRS/LBSF cells and NRS/BSF cells showed an average of 18% and 17% efficiencies, respectively, at AMO and 28°C conditions. The IBF cells have P⁺N⁺ diodes on the front surface to protect itself from reverse voltage due to shadowing. The designs and features of these solar cells are presented. The radiation tests results of these solar cells are also presented. The NRS/BSF cells showed lower degradation rate compared to conventional BSFR cells with the same thickness (100 μm). But the NRS/LBSF cells showed a higher degradation rate than the BSFR cells. The IBF cells showed almost the same radiation characteristics as the same kinds of cells without IBF. The results of radiation tests on these high-efficiency solar cells and the discussions about the radiation characteristics of them are presented. In the last section, the future silicon solar cell development plan is discussed.     

Solvent-free ZnO dye-sensitised solar cells

Dye-sensitised solar cells (DSSC) based on commercial nanostructured zinc oxide combined with imidazolium-based room temperature ionic-liquid electrolytes are characterized. The electrolytes are based on a binary mixture of two ionic liquids, one of them used as source of iodide ions. The composition of this solvent-free electrolyte is optimized with respect to the concentration of iodine and iodide and the effect of additives such as lithium and tert-butylpyridine (TBP) on the photovoltaic performance and the recombination rate is analyzed and discussed. A maximum photoconversion efficiency of 3.4% at 1 sun illumination has been obtained for cells of 0.64 cm² active area with the best performing compositions. Diffusion limitations due to slow transport processes are analyzed and discussed.     

Electrolyte modified photoelectrochemical solar cells

Rationale electrolyte modification of photoelectrochemical systems can be used to (i) enhance facile charge transfer, (ii) suppress competing reactions and suppress both (iii) electrode and (iv) electrolyte decomposition products, as well as (v) substantially effect the open-circuit photovoltage. Studies on polysulfide, ferrocyanide, polyselenide and polyiodide electrolyte modification of photoelectrochemical solar cells are discussed. Electrolyte modification of semiconductor/electrolyte systems entails investigation of the primary photo-redox species, the nature of the counter ion, the distribution of species in solution, and related competing reactions. The examples presented emphasize the fundamental and practical importance of probing the active electrolytic constituents pertinent to overall photoelectrochemical energy conversion.     

Colloidal quantum dot solar cells

In recent years colloidal quantum dots solar cells have been the subject of extensive research. A promising alternative to existing silicon solar cells, quantum dot solar cells are among the candidates for next generation photovoltaic devices. Colloidal quantum dots are attractive in photovoltaics research due to their solution processability which is useful for their integration into various solar cells. Here, we review the recent progresses in various quantum dot solar cells which are prepared from colloidal quantum dots. We discuss the preparation methods, working concepts, advantages and disadvantages of different device architectures. Major topics discussed in this review include integration of colloidal quantum dots in: Schottky solar cells, depleted heterojunction solar cells, extremely thin absorber solar cells, hybrid organic-inorganic solar cells, bulk heterojunction solar cells and quantum dot sensitized solar cells. The review is organized according to the working principle and the architecture of photovoltaic devices.