Passivation and antireflection AZO:H layer in AZO:H/p-Si heterojunction solar cells

In this work, aluminum-doped zinc oxide (AZO)/p-Si heterojunction solar cells were prepared by sputtering of ~120 nm AZO thin films in Ar or Ar–H₂ atmosphere on textured p-Si wafers, and the effects of hydrogen incorporation on the solar cell performance were investigated. Results showed that the performance of AZO/p-Si heterojunction solar cells was improved with the increase of hydrogen volume concentration from 0 to 23 %. The AZO:H/p-Si heterojunction solar cells prepared in Ar–23 % H₂ exhibited a short-circuit current density of 29 mA/cm² and a conversion efficiency of 2.84 %. The reflectance measurement indicated that the reflectance of p-Si surface in the range of 400–1,100 nm decreased from 13 to 4 % after AZO:H films coating; and the capacitance–voltage measurement indicated that the density of defect states at AZO/p-Si interface was decreased after hydrogen incorporation. Passivation and antireflection functions can be realized in AZO:H films deposited in Ar–H₂, which opens a novel route to prepare cost-effective AZO/p-Si heterojunction solar cells.     

Atmospheric pressure chemical vapour deposition of F doped SnO2 for optimum performance solar cells

The potential of thin film photovoltaic technologies in supporting sustainable energy policies has led to increasing interest in high performance transparent conducting oxides (TCOs), and in particular doped SnO₂, as electrical contacts for solar cells. We have developed an advanced atmospheric pressure chemical vapour deposition process, by applying fast experimentation and using a combinatorial chemistry approach to aid the studies. The deposited films were characterised for crystallinity, morphology (roughness) and resistance to aid optimisation of material suitable for solar cells. Optical measurements on these samples showed low absorption losses, less than 1% around 500 nm for 1 pass, which is much lower than those of industrially available TCOs. Selected samples were then used for manufacturing single amorphous silicon (a-Si:H) solar cells, which showed high solar energy conversion efficiencies up to 8.2% and high short circuit currents of 16 mA/cm². Compared with (commercially available) TCO glasses coated by chemical vapour deposition, our TCO coatings show excellent performance resulting in a high quantum efficiency yield for a-Si:H solar cells.     

Enhanced performance of SubPC/C60 solar cells by annealing and modifying surface morphology

The performance effect of organic solar cells with subphthalocyanine (SubPC)/fullerene (C60) bilayer was investigated with thermal treatment while changing the vacuum deposition rate of SubPC. The thermal annealing at 100 degrees C increases the optical absorption intensity of SubPC film at the spectral range of 550-630 nm. The X-ray diffraction (XRD) patterns indicates that the thermally annealed film formed the much-ordered morphology, as compared to the non-annealed film. Consequently, thermally treated solar cell exhibited almost 10% higher power conversion efficiency (PCE) compared to the non-annealed device. The fill factor (FF) and PCE of the devices were increased as the deposition rate of SubPC was increased up to 5 A/s and then saturated at higher deposition rates (> 5 A/s). The surface roughness of SubPC films, measured with an atomic force microscope, increased from 1.1 to 5 nm as the deposition rate increased from 1 to 7 A/s. These results imply that rough surface increases the interfacial area between SubPC and C60 and thereby improves the separation of photogenerated electron and hole pairs at the SubPC/C60 interface.     

利用金属辅助化学腐蚀法在硅表面获得纳米绒面结构以提升多晶硅太阳电池效率

在硅片表面制备绒面结构能够有效降低太阳光在硅片表面的反射损失,是提高太阳能电池转换效率的一条重要途径。通过真空热蒸发法在多晶硅片上沉积纳米银颗粒,利用金属辅助化学腐蚀(MACE)法,制备了不同腐蚀时间下的纳米绒面结构,其中,腐蚀时间为60s的纳米绒面的平均反射率低至4.66%(300~1100nm)。同时,对腐蚀时间为60s的纳米绒面用KOH溶液进行优化处理,将KOH处理前后的多晶硅片采用常规电池工艺进行电池制备研究。对比发现,经过KOH处理后的电池效率比未经KOH处理的电池效率提高了0.43%。     

Carbon nanotube films by filtration for nanotube-silicon heterojunction solar cells

Carbon nanotube films with high nanotube loading were prepared using a vacuum filtration method and their photovoltaic properties as semi-transparent conducting electrodes in nanotube-silicon heterojunction solar cells were investigated. The correlation between the power conversion efficiency of the solar cells and the figure of merit (FM) of the films were obtained. The maximum efficiencies (up to 1.5%) were found for those cells using the films with highest FMs and transmittances. For comparison, the photovoltaic performance of a self-assembled nanotube thin film of high transmittance (91%) was tested and the corresponding solar cell showed a conversion efficiency of ∼4%. This work provides guidance for future improvement on the photovoltaic properties of nanotube films as window electrode materials.     

ZnO纳米四脚状阵列电极染料敏化太阳能电池

采用化学气相沉积(CVD)法制备了不同尺寸的四脚状纳米ZnO和ZnO纳米棒。采用X射线粉末衍射(XRD)、扫描电子显微镜(SEM)对纳米ZnO的晶型结构和形貌进行表征,研究结果表明CVD法制备的四脚状纳米ZnO具有三维空间结构,其最小平均臂宽约为70nm,臂长约300nm,制备的纳米棒直径约为84nm,长约2μm,且都为六方纤锌矿晶型结构。将ZnO纳米四脚状及纳米棒利用滚涂法在FTO导电玻璃上形成ZnO光阳极,经N719染料敏化后组装成染料敏化太阳能电池,光电性能结果表明,染料敏化小尺寸的四脚状纳米ZnO太阳能电池光电转换效率(η=1.88%)高于染料敏化大尺寸的四脚状纳米ZnO太阳能电池光电转换效率(η=1.18%),远高于染料敏化ZnO纳米棒太阳能电池的光电转换效率(η=0.7%)。     

Hierarchical structured TiO2 photoanodes for dye-sensitized solar cells

A novel approach has been developed to fabricate hills-like hierarchical structured TiO2 photoanodes for dye-sensitized solar cells (DSSCs). The appropriately aggregated TiO2 clusters in the photoanode layer could cause stronger light scattering and higher dye loading that increases the efficiency of photovoltaic device. For detailed light-harvesting study, different molecular weights of polyvinyl alcohol (PVA) were used as binders for TiO2 nanoparticles (P-25 Degussa) aggregation. A series of TiO2 films with dissimilar morphology, the reflection of TiO2 films, absorbance of attached dye, amount of dye loading, and performance of fabricated DSSC devices, were measured and investigated. An optimized device had energy conversion efficiency of 4.47% having a higher dye loading and good light harvesting, achieving a 23% increase of short-circuit current J(sc) in DSSCs.     

Thermal oxidation properties of titanium nitride and titanium-aluminum nitride materials — A perspective for high temperature air-stable solar selective absorber applications

Air-stable high temperature solar selective surfaces have the advantages of simplifying the design, and reducing the cost of solar thermal energy conversion systems. Previous studies on the properties of titanium nitride (TiN) or titanium-aluminum nitride (TiAlN) films suggested that these materials could be a candidate for solar energy applications. In this paper, we report that oxidation occurs at 450 °C, and an oxide layer of about 20-30 nm was formed after only a few minutes of heat treatment with oxygen. The thickness of the oxide layer is comparable to the thickness of the absorbing layer of the solar thermal selective absorbers, which can affect significantly the solar thermal performance. TiN produced at higher nitrogen pressure (2.1 Pa with 40% nitrogen in argon) could absorb oxygen more easily into bulk and was less oxidation resistant during the heat treatment than that produced at 0.4 Pa of 40% nitrogen in argon. The hardness after the oxidation treatment was slightly increased by approximately 10%, consistent with reported oxidation resistant properties of this material for mechanical protection applications. As a result of this study, TiN or TiAlN as an element may not be suitable candidates for use as solar selective absorbers in air-stable high temperature applications.     

Influence of TiO2 nanofiber additives for high efficient dye-sensitized solar cells

TiO2 nanofibers were prepared from a mixture of titanium-tetra-isopropoxide and poly vinyl pyrrolidone by applying the electrospinning method. The samples were characterized by XRD, FE-SEM, TEM and BET analyses. The diameter of electrospun TiO2 nanofibers is in the range of 70 approximately 160 nm. To improve the short-circuit photocurrent, we added the TiO2 nanofibers in the TiO2 electrode of dye-sensitized solar cells (DSSCs). TiO2 nanofibers added in DSSCs can make up to 20% more conversion energy than the conventional DSSC with only TiO2 films only.     

A study on the correlation between the grain size and the conversion efficiency of Mc-Si solar cells

For grain size estimation, a prototype system was developed by integrating a vision-acquiring hardware and a vision-assistant-processing module based on the platform software package of LabVIEW, to systematically estimate the average grain size of solar-grade multicrystalline (mc)-Si wafers. Three groups of 156 x 156 mm mc-Si wafers were selected to produce the average grain sizes of 3.4 mm (Group 1), 3.8 mm (Group II), and 4.6 mm (Group III), and were used for the fabrication of mc-Si solar cells by employing the standard mc-Si cell fabrication procedure of the 30 MW mass production line. The conversion efficiency including Jsc and Pmax, showed a quasi linear dependence on the mean grain size, with a correlation factor of 0.525%/mm. By combining the EL image and the grain size/position-dependent EQE spectra in a wavelength range of 400-1100 nm, the conversion efficiency of uniformly-surface-texturized mc-Si solar cells with larger grain sizes can be made much higher as a result of the much-reduced spatial density of the nano/microscope grain boundaries acting as recombination centers or traps.     

高效本征薄层异质结(HIT)太阳电池技术研究进展

高效本征薄层异质结(HIT)是由本征钝化层沉积在a-Si/c-Si界面处组成,这种硅异质结(SHJ)结构由于钝化性能好,实际效率值往往比同质结电池更高。本文首先介绍了HIT高效电池发展现状、电池基本结构的特点,然后从制备工艺、钝化原理、能带带阶等几个方面对衬底层、非晶硅层(本征/掺杂)、TCO薄膜以及金属格栅电极展开讨论,并对未来高效HIT电池的工业化发展趋势做了展望。     

Comparison of the in vitro release characteristics of mucosal freeze-dried wafers and solvent-cast films containing an insoluble drug

Drug release characteristics of freeze-dried wafers and solvent-cast films prepared from sodium carboxymethylcellulose have been investigated and compared. In vitro drug dissolution studies were performed using an exchange cell and drug release was measured by UV spectroscopy at 272?nm using distilled water. The dissolution profiles of hydrochlorothiazide from the wafers and films were compared by determining the rates of drug release, estimated from the % release versus time profiles and calculating their difference (f(1)) and similarity (f(2)) factors. The effects of drug loading, polymer content and amount of glycerol (GLY) (films) on the drug release characteristics of both formulations were investigated. Both the wafers and films showed sustained type release profiles that were best explained by the Korsmeyer-Peppas equation. Changes in the concentration of drug and GLY (films) did not significantly alter the release profiles whilst increasing polymer content significantly decreased the rate of drug release from both formulations. The rate of release was faster from the wafers than the corresponding films which could be attributed to differences in the physical microstructure. The results show the potential of employing both formulations in various mucosal drug delivery applications.     

Automatic vision-based grain optimization and analysis of multi-crystalline solar wafers using hierarchical region growing

Solar power has become an attractive alternative source of energy. The multi-crystalline solar cell has been widely accepted in the market because it has a relatively low manufacturing cost. Multi-crystalline solar wafers with larger grain sizes and fewer grain boundaries are higher quality and convert energy more efficiently than mono-crystalline solar cells. In this article, a new image processing method is proposed for assessing the wafer quality. An adaptive segmentation algorithm based on region growing is developed to separate the closed regions of individual grains. Using the proposed method, the shape and size of each grain in the wafer image can be precisely evaluated. Two measures of average grain size are taken from the literature and modified to estimate the average grain size. The resulting average grain size estimate dictates the quality of the crystalline solar wafers and can be considered a viable quantitative indicator of conversion efficiency.     

Combined power of perovskites and silicon solar cells

The photovoltaic (PV) or solar cells technology can be categorised into two main groups, the wafer‐based and thin‐film based PVs. The wafer‐based PVs include the commonly known crystalline silicon (c‐Si) and gallium arsenide (GaAs) cells. The GaAs cells exhibit higher efficiency compared to crystalline silicon (c‐Si) cells but it is the later that dominates the commercial market. Thin‐film based (2nd Generation) PVs, including cadmium telluride (CdTe), amorphous silicon (a‐Si:H) and copper‐indium‐gallium‐selenide (CIGS), generally absorb light more efficiently than wafer‐based cells and can allow the use of materials in very thin films form. CdTe PVs have proven to be highly efficient but holds only a few percentage share of the market. There is still a need for more R&D before further commercialisation. An emerging and relatively new class of thin‐film based photovoltaics (3rd Generation) technology that has the potential to overcome the current energy conversion efficiencies and performance by making use of novel materials. This class of PVs include organic photovoltaic (OPV), dye‐synthesised solar cells (DSSC), quantum‐dot (QD) and last but not least, the perovskite PV. Perovskite PVs can offer a low cost energy generation solution with the best device conversion efficiencies have shot from lower than 4% in 2009 to more than 21% in 2016. Perovskite based devices can be fabricated using vacuum thermal evaporation or by solution processing of the active layers. Although most recent perovskite solar cells with record efficiencies (>20%) are prepared via solution processing, the early breakthrough in perovskite solar cells was made with vacuum processed perovskites thin films. Vacuum thermal evaporation offers the ability and flexibility to prepare solar cell devices in various configuration. Recent developments in the field of perovskite demonstrates its compatibility with both, first and second generation PV technologies, and is therefore likely to be embraced by the conventional PV industry and make its way into utility‐scale power generation.     

Effect of nanoporous silicon coating on silicon solar cell performance

The surface modification of silicon solar cells was used for improvement of photovoltaic characteristics of silicon solar cells. A screen-printed solar cell technology is used to fabricate n⁺-p silicon solar cell. Nanoporous silicon (PS) layer on n⁺-type Si wafers or on the frontal surface of (n⁺-p)Si solar cell was formed by electrochemical etching in HF-containing solution. The surface morphology, porosity, spectra of photoluminescence and reflectance of PS layers were analyzed. The photovoltaic characteristics of two silicon solar cell type with and without PS layer (PS/(n⁺-p)Si and (n⁺-p)Si cell) were measured and compared. The spectra of photosensitivity of cells were measured in the wavelength range of 300-1100 nm. An average reflection of the porous silicon layer, fabricated on a polished silicon surface, is decreased to 4%. A remarkable increment of the conversion efficiency by 20% have been achieved for PS/(n⁺-p)Si solar cell comparing to (n⁺-p)Si solar cell without PS layer. The results, related with improving of the performance of PS/(n⁺-p)Si solar cell, have been attributed to the effective antireflection and the wide-gap window role of nanoporous silicon on the silicon solar cell.     

Toward efficient carbon nanotube/P3HT solar cells: active layer morphology, electrical, and optical properties

We demonstrate single-walled carbon nanotube (SWCNT)/P3HT polymer bulk heterojunction solar cells with an AM1.5 efficiency of 0.72%, significantly higher than previously reported (0.05%). A key step in achieving high efficiency is the utilization of semiconducting SWCNTs coated with an ordered P3HT layer to enhance the charge separation and transport in the device active layer. Electrical characteristics of devices with SWCNT concentrations up to 40 wt % were measured and are shown to be strongly dependent on the SWCNT loading. A maximum open circuit voltage was measured for SWCNT concentration of 3 wt % with a value of 1.04 V, higher than expected based on the interface band alignment. Modeling of the open-circuit voltage suggests that despite the large carrier mobility in SWCNTs device power conversion efficiency is governed by carrier recombination. Optical characterization shows that only SWCNT with diameter of 1.3-1.4 nm can contribute to the photocurrent with internal quantum efficiency up to 26%. Our results advance the fundamental understanding and improve the design of efficient polymer/SWCNTs solar cells.     

Simultaneous plasma and thermal treatments of ITO surfaces for organic solar cells

Organic solar cells' power conversion efficiency was improved by combined thermal and CF4 plasma surface treatments of indium tin oxide (ITO). This was further enhanced by adding O2 to the CF4 plasma, which increased atomic fluorine concentration. Organic solar cells were produced with layered structures of ITO, spin-cast thin film of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) mixture (100 nm), and Al (100 nm) as top electrode. While CF4 plasma surface treatment alone significantly improved power conversion efficiency (PCE), from 0.34% to 1.99%, further enhancements occurred with the combined thermal treatment, up to 2.24%. 20% O2 addition to the CF4 plasma resulted in greatest improvement (up to 2.34%) due to optimized surface fluorination. Measured work functions of surface treated ITO increased from 4.80 to 5.17 eV with the plasma and thermal treatments. Such treatments reduce the energy barrier for hole injection at the ITO surface by increasing ITO's work function.     

醋酸铜辅助催化刻蚀制备金刚线切割多晶硅片绒面

金刚线切割多晶硅片表面减反射结构难以制备的问题阻碍着多晶硅光伏的进步。银辅助的酸腐蚀是解决这一问题的较好方法,但银的消耗和废液处理等增加了成本。本研究提出了醋酸铜辅助催化刻蚀金刚线切割多晶硅片方案,考察了刻蚀反应温度和时间对硅片表面形貌的影响,确定了最优的反应温度和时间分别为25℃和5 min。在此条件下,所获得的多晶硅在300～1100 nm波段的平均反射率为15.1%。按照标准太阳电池制备工艺流片后,所获太阳电池的光电转换效率为19.4%。     

Synthesis of high quality zinc-blende CdSe nanocrystals and their application in hybrid solar cells

Oleic acid (OA) modified zinc-blende cadmium selenium nanocrystals (NCs) with different diameters, 3-5?nm, have been prepared. We find that the morphology and fluorescent properties of the samples are related to the preparation conditions such as the chain-length and concentration of the cadmium precursor as well as the concentration of OA. The hybrid solar cells based on the obtained spherical CdSe NCs as an acceptor and Poly(2-methoxy-5-(2'-ethylhexoxy)-p-phenylenevinylene) (MEH-PPV) as a donor show an energy conversion efficiency (ECE) as high as 0.85%, three times higher than that reported before for spherical CdSe NCs/conjugated polymer hybrid solar cells. When poly(3-hexylthiophene) (P3HT) is used as the donor phase instead of MEH-PPV, the energy conversion efficiency increases up to 1.08%. The solar cell based on CdSe NCs/conjugated polymer has the potential to open up new production technologies for hybrid solar cells based on semiconductor NCs.     

Progress in a-Si:H/c-Si heterojunction emitters obtained by Hot-Wire CVD at 200 °C

In this work, we investigate heterojunction emitters deposited by Hot-Wire CVD on p-type crystalline silicon. The emitter structure consists of an n-doped film (20 nm) combined with a thin intrinsic hydrogenated amorphous silicon buffer layer (5 nm). The microstructure of these films has been studied by spectroscopic ellipsometry in the UV-visible range. These measurements reveal that the microstructure of the n-doped film is strongly influenced by the amorphous silicon buffer. The Quasy-Steady-State Photoconductance (QSS-PC) technique allows us to estimate implicit open-circuit voltages near 700 mV for heterojunction emitters on p-type (0.8 Ω·cm) FZ silicon wafers. Finally, 1 cm² heterojunction solar cells with 15.4% conversion efficiencies (total area) have been fabricated on flat p-type (14 Ω·cm) CZ silicon wafers with aluminum back-surface-field contact.