Effect of porous silicon layer on the performance of Si/oxide photovoltaic and photoelectrochemical cells

Photovoltaic and photoelectrochemical systems were prepared by the formation of a thin porous film on silicon. The porous silicon layer was formed on the top of a clean oxide free silicon wafer surface by anodic etching in HF/H₂O/C₂H₅OH mixture (2:1:1). The silicon was then covered by an oxide film (tin oxide, ITO or titanium oxide). The oxide films were prepared by the spray/pyrolysis technique which enables doping of the oxide film by different atoms like In, Ru or Sb during the spray process. Doping of SnO₂ or TiO₂ films with Ru atoms improves the surface characteristics of the oxide film which improves the solar conversion efficiency.The prepared solar cells are stable against environmental attack due to the presence of the stable oxide film. It gives relatively high short circuit currents (I_sc), due to the presence of the porous silicon layer, which leads to the recorded high conversion efficiency. Although the open-circuit potential (V_oc) and fill factor (FF) were not affected by the thickness of the porous silicon film, the short circuit current was found to be sensitive to this thickness. An optimum thickness of the porous film and also the oxide layer is required to optimize the solar cell efficiency. The results represent a promising system for the application of porous silicon layers in solar energy converters. The use of porous silicon instead of silicon single crystals in solar cell fabrication and the optimization of the solar conversion efficiency will lead to the reduction of the cost as an important factor and also the increase of the solar cell efficiency making use of the large area of the porous structures.     

Experimental and simulation study for ultrathin (∼100 μm) mono crystalline silicon solar cell with 156×156 mm2 area

A reduction in silicon material consumption in the photovoltaic industry is required for cost reduction. Using crystalline silicon wafers of less than 120 microns of thickness is a promising way for cost and material reduction in the solar cell production. The standard thickness of crystalline silicon solar cells is currently around 180 microns. If the wafers are thinner than 100 microns in the silicon solar cells, the amount of silicon will be reduced by almost half, which should result in prominent cost reduction. With this aim, many groups have worked with thin crystalline silicon wafers. However, most of them have studied with small size substrates. In this paper, we present the electrical characteristics for thin single crystalline silicon solar cells of 100 and 115 μm thickness and 156×156 mm² area manufactured through a conventional process. We have achieved 17.2% conversion efficiency with a 115 μm silicon substrate and 16.8% with a 100 μm substrate. This enables the commercialization of the thin crystalline silicon solar cells with high conversion efficiency. We also suggest issues to be solved in thin crystalline silicon solar cell manufacturing.     

Effect of hydrogen annealing on characteristics of polycrystalline silicon

The characteristics of mc-Si used for solar cells during H2 ambient annealing at 800-1200 ℃ were investigated by means of FTIR and QSSPCD. The results reveal that grain boundaries or defects in mc-Si may facilitate the formation of oxygen precipitates, and the formation of oxygen precipitates has deleterious effect on the lifetime of mc-Si. Decreasing lifetime could result from the formation of new recombination during annealing. Additionally, It is found that hydrogen may facilitate the formation of oxygen precipitates in mc-Si. On the other hand, the diffusion of hydrogen may passivate the defects/boundaries and it is beneficial to the lifetime of mc-Si.     

Aluminum fire-through with different types of the rear passivation layers in crystalline silicon solar cells

Aluminum penetration during dielectric layer annealing on silicon was studied for solar cell application. The thickness and uniformity of the aluminum-doped region was examined in variously annealed dielectric layers. Three types of silicon wafers were used with (1) bare Si, (2) SiO₂ layer (80 nm)/Si, and (3) SiN_X layer (80 nm)/Si. Local metal contacts were made through laser-drilled holes, and annealing was tested at four different temperatures. Reactions between aluminum and silicon were observed by cross-sectional scanning electron microscopy. Reactions occurred at 660 °C on bare Si and at ca. 690 °C on the SiO₂ layer. However, the SiO₂ did not withstand annealing at higher temperatures. The SiN_X layer showed no Al-BSF region in samples annealed at up to 760 °C, making it a suitable material for rear passivation layers in local contact Si solar cells. A Si solar cell fabricated by laser drilling and screen printing showed an efficiency of 12.41% without optimization.     

RF magnetron sputtered ITO:Zr thin films for the high efficiency a-Si:H/c-Si heterojunction solar cells

ITO and ITO:Zr films with various thicknesses were prepared on glass substrates by RF magnetron sputtering. We observed a decrease in sheet resistance with increasing film thickness that in good agreement with Fuchs-Sondheimer theory. The ITO films doped with ZrO₂ (～0.2 wt%) showed improvement in some of the electrical and optical properties of ITO films. The surface roughness of ITO:Zr films increased with increasing film thickness. ITO:Zr films with thickness of 120 nm showed highest work function of 5.13 eV, as estimated from XPS data. The ITO:Zr films were employed as front electrodes in HIT solar cells; the best device performance was found to be: V_oc = 710 mV, J_sc = 34.44 mA/cm², FF = 74.8%, η = 18.30% at a thickness of 120 nm. A maximum quantum efficiency (QE) of 89% was recorded for HIT solar cells at a wavelength of 700 nm for 120 nm thick ITO:Zr films.     

一种太阳能高效多晶硅铸锭用坩埚底部引晶涂层的制备方法

介绍一种太阳能电池用高效多晶硅片生产过程中,铸锭用坩埚底部引晶涂层的制备方法。此方法是在坩埚底部分别制备两个涂层:第一层是硅粉和无机陶瓷胶的混合物,第二层是氮化硅粉和无机硅溶胶、去离子水的混合物。此方法的创新点是将硅粉替代传统的石英砂作为引晶晶核来制作引晶层。结果表明,与传统石英砂引晶层相比,此方法产生的多晶硅锭晶体均匀、位错少,制成的太阳能电池转换效率高(平均达到17.8%)。     

a-Si/c-Si heterojunction solar cells on SiSiC ceramic substrates

Silicon thin-film solar cells are considered to be one of the most promising cells in the future for their potential advantages, such as low cost, high efficiency, great stability, simple processing, and none-pollution. In this paper, latest progress on poly-crystalline silicon solar cells on ceramic substrates achieved by our group was reported. Rapid thermal chemical vapor deposition (RTCVD) was used to deposited poly-crystalline silicon thin films, and the grains of as-grown film were enlarged by Zone-melting Recrystallization (ZMR). As a great changein cell's structure, traditional diffused pn homojunction was replaced by a-Si/c-Si heterojunction, which lead is to distinct improvement in cell's efficiency.A conversion efficiency of 3.42% has been achieved on 1cm2 a-Si/c-Si heterojunction solar cell ( Isc =16.93 mA, Voc =310.9 mV, FF =06493, AM =1.5 G,24 ℃), while the cell with diffused homojunction only gotan efficiency of 0.6%. It indicates that a-Si emitter formed at low temperature might be more suitable for thin film cell on ceramics.     

涂覆稀土配合物掺杂薄膜硅太阳能电池的光伏特性

研究了涂覆稀土有机配合物掺杂薄膜硅太阳能电池的光伏特性.当(0.5 mol%TTFAEu3 0.5 mol%PHBATb3 )共掺薄膜涂覆在硅太阳能电池表面时,硅太阳能电池的光电转换效率可提高15%.     

冶金硅定向凝固法制备太阳能级多晶硅及其微观组织与位错(英文)

以冶金硅为原料,探索采用具有高温度梯度的真空定向凝固技术制备低成本太阳能级多晶硅,并研究其在不同生长条件下的微观组织特征、晶界与晶粒大小、固液界面形貌以及位错结构。结果表明,当凝固速率低于60μm/s时,能获得具有高密度和良好取向的定向凝固多晶硅棒状试样,硅晶粒大小随凝固速率的增大而减小;在控制凝固过程,获得平的固液界面形貌是获得沿凝固方向排列柱状晶的关键;由于硅的小平面生长特性,微观组织中出现了位错生长台阶和孪晶结构;在晶粒中,位错分布呈现不均匀性,并且位错密度随凝固速率的增加而增加;在此基础上,讨论了多晶硅的生长行为以及位错形成机制。     

Influence of texture feature size on spherical silicon solar cells

The effects of surface texturing on spherical silicon solar cells were investigated. Surface texturing for spherical Si solar cells was prepared by immersing p-type spherical Si crystals in KOH solution with stirring. Two kinds of texture feature sizes (1 and 5μm pyramids) were prepared by changing stirring speed. After fabrication through our baseline processes, these cells were evaluated by solar cell performance and external quantum efficiency. The cell with 1 and 5μm pyramids shows the short circuit current density ( Jsc ) value of 31.9 and 33.2 mA·cm-2 , which is 9% and 13% relative increase compared to the cell without texturing. Furthermore, the cell with 5 μm pyramids has a higher open-circuit voltage (0.589 V) than the cell with 1 μm pyramids (0.577 V). As a result, the conversion efficiency was improved from 11.4% for the cell without texturing to 12.1% for the cell with 5 μm pyramids.     

Effect of the thickness of the Ru-coating on a counter electrode on the performance of a dye-sensitized solar cell

A ruthenium (Ru) catalytic layer was assessed as the counter electrode (CE) in dye sensitized solar cells (DSSCs) by examining the effect of the Ru thickness on the DSSC performance. Ru films with different thicknesses (34, 46, 69 and 90 nm) were deposited on glass/fluorine-doped tin oxide (FTO) substrates as the CE by atomic layer deposition (ALD) at 250 °C using RuDi as the precursor and O₂ as the reaction gas. Finally, a 0.45 cm² DSSC of glass/FTO/TiO₂/dye(N719)/electrolyte(C6DMII, GSCN)/Ru CE structure was prepared. The properties of the DSSCs were examined by field emission scanning electron microscopy (FESEM), four-point-probe, cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), current-voltage (I–V), incident photon-to-current conversion efficiency (IPCE), and dark current measurements. FESEM showed that the crystallized Ru films had been deposited quite uniformly and conformally on the glass/FTO surface. The sheet resistance of the Ru film decreased with increasing Ru thickness. CV profiling revealed an increase in catalytic activity with increasing film thickness. The charge transfer resistance at the interface between the Ru-coated CE and electrolyte decreased with increasing Ru thickness. I–V profiling showed that the energy conversion efficiency was increased up to 3.40 % by increasing the Ru thickness. Moreover, the IPCE and dark current results showed the efficiency of the Ru-coated CE was comparable to that of a conventional platinum (Pt) CE.     

铸造多晶硅中氧的热处理行为研究

研究了铸造多晶硅中不同温度单步退火下氧沉淀的形成规律。实验发现，单步热处理工艺下铸造多晶硅中氧沉淀的形成规律和单晶硅的基本相似，但是在铸造多晶硅中形成氧沉淀的量明显高于直拉单晶硅中氧沉淀的量；在含高密度位错的单晶硅中形成氧沉淀的量远高于无位错单晶硅中氧沉淀的生成量，而有晶界的多晶硅中形成氧沉淀生成量仅稍微高于无晶界单晶硅中氧沉淀生成量。以上结果表明，铸造多晶硅中位错对氧沉淀的形成有明显的促进作用，而晶界则对氧沉淀的促进作用不是很显著。最后，基于实验结果讨论了铸造多晶硅中初始氧浓度，位错和晶界对氧沉淀影响的机理。     

Effect of monodisperse Cu2S nanodisks on photovoltaic performance of P3HT/PCBM polymer solar cells

Hybrid solar cells using monodisperse Cu₂S nanodisks compositing with the mixture of poly (3-hexylthiophene):1-(3-methoxycarbonyl) propyl-1-pheny [6,6] C61 (P3HT:PC₆₀BM) as the active layer have been fabricated and characterized. The hybrid solar cells exhibit the highest efficiency of 1.35% when the weight ratio of P3HT:PC₆₀BM:Cu₂S is 1:0.8:0.224. The power conversion efficiency (PCE) of nanocomposite device is increased 22.7% comparing with that of the device based on pure P3HT/PC₆₀BM. It is due to that the effect of high-quality Cu₂S nanodisks with good dispersity contributes the increased electronic transportation in the active layer and results in the enhancement in photovoltaic performance. We also investigated the morphology of photoactive layer by microscope; it is found that the dispersity of nanomaterial in active layer is very important for device performance and improvement of carrier mobility.     

Low-reflective surface texturing for large area multicrystalline silicon using NaOH-NaClO solution

Multicrystalline silicon surface texturing using the mixed etching solution of the sodium hydroxide (NaOH) and of the sodium hypochlorite (NaClO) has been investigated. The reaction rate during the texturing process is easier to control due to the presence of NaOCl as an oxidizing agent in NaOH solution. The advantage of this etching is that the uniform mc-Si surface texturing with a low step height and less grain boundary delineation can be obtained. The Mc-Si surface after NaOH-NaOCl mixed etching with the 1: 4 ratio in the case of 20% NaOH has the optimum light trapping effect. In the case of the optimum etching condition, the average reflectivity for the textured surface of a large area (156 × 156 mm²) mc-Si can be reduced to less than 10%.     

双电源低温渗氮工艺在316不锈钢上的应用

通过正交试验研究了交流脉冲电压、直流脉冲偏压和温度对316不锈钢表面硬度和渗层厚度的影响,获得了双电源低温渗氮最佳工艺参数。通过光学显微镜(OM)、X射线衍射仪(XRD)、显微硬度计、电化学工作站以及摩擦磨损试验机等研究了最佳工艺下渗氮试样的性能。结果表明,影响渗氮试样性能因素的顺序为:交流脉冲电压＞温度＞直流脉冲偏压。最佳工艺参数为交流脉冲电压360 V,直流脉冲偏压270 V,温度380 ℃。对最佳工艺制备的试样与单电源进行对比:渗层厚度为43.4 μm,是单电源的8.5倍;表面硬度为1350 HV0.025,是单电源的3.1倍;自腐蚀电位由－256 mV(vs SCE,下同)提高到－180 mV;自腐蚀电流密度从13.90 μA/cm² 降低到0.45 μA/cm²;摩擦因数从0.55降低到0.42。双电源渗氮速率的提高是由于高能离子轰击引起的表面结构缺陷和渗氮气体的高度离解。     

Effect of oxygen precipitates in solar grade silicon on minority carrier lifetime and efficiency of solar cells

The effect of oxygen precipitates on minority carrier lifetime and performance of solar cell was studied by means of Fourier Transform Infrared Spectroscopy (FTIR), quasi-steady state photoconductance (QSSPCD), optical microscope, spectrumresponse and solar cell efficiency test. The minority carrier lifetime and performance of solar cell reduced depend on oxygen precipitates. A few of oxygen precipitates have formed after single-step annealing; and they do not impact the efficiency dramatically. Pre-annealing at 650 ℃ for 4 h enhances the oxygen precipitation when it is subjected to middle temperature annealing. The solar cells performance decayed sharply. Especially annealing at 950 ℃ for 3 h, the V os and I sc of cells decrease 12% and 25% respectively. Few oxygen precipitates have formed in silicon after high temperature annealing at about 1050 ℃ whether pre-annealing is used or not, and the performance of cells is notbe affected.     

晶硅衬底参数对太阳电池输出特性的影响

利用晶硅电池模拟软件PC1D研究晶硅衬底的厚度、少子寿命及掺杂浓度对电池输出特性的影响规律。结果表明:晶硅衬底的厚度对电池输出特性的影响与其少子的扩散长度有关,衬底厚度的减小有利于其开路电压的提高,存在一最佳厚度值使其转换效率、短路电流及填充因子最高;当少子的扩散长度远大于衬底厚度时,电池的输出特性几乎与衬底厚度无关;当衬底少子扩散长度与衬底厚度的比值为2.5~3.0时,电池的转换效率最高;晶硅衬底的掺杂浓度在5×1015~1×1017cm 3之间,即电阻率在0.2~3.0.cm范围内时,晶硅电池能获得良好的输出特性。     

Influence of TiCl4 treatment on performance of dye-sensitized solar cell assembled with nano-TiO2 coating deposited by vacuum cold spraying

Titanium tetrachloride (TiCl4) treatment was employed to TiO2 coating deposited on fluoride-doped tin oxide (FTO) conducting glass and indium oxide doped tin oxide (ITO) conducting glass, respectively. The nano-crystalline TiO2coating was deposited using a composite powder composed of polyethylene glycol (PEG) and 25 nm TiO2 particles by vacuum cold spraying (VCS) process. A commercial N-719 dye was used to adsorb on the surface of TiO2 coating to prepare TiO2 electrode, which was applied to assemble dye-sensitized solar cell (DSC).The cell performance was measured under simulated solar light at an intensity of 100 mW·cm-2.Results show that with an FTO substrate the DSC composed of a VCS TiO2 electrode untreated by TiCl4 gives a short-circuit current density of 13.1 mA·cm-2 and an open circuit voltage of 0.60 V corresponding to an overall conversion efficiency of 4.4%. It is found that after TiCl4 treatment to the VCSTiO2 electrode with an FTO substrate, the short circuit current density of the cell increases by 31%, the open-circuit voltage increases by 60 mV and a higher conversion yield of 6.5% was obtained. However, when an ITOsubstrate is used to deposit TiO2 coating by VCS, after TiCl4 treatment, the conversion efficiency of the assembled cell reduces slightly due to corrosionof the conducting layer on the ITO glass by TiCl4.     

点杂多晶太阳能硅片电解磨削多线切割试验研究

提出了一种电解磨削多线切割点杂多晶太阳能硅片的新方法。电源的正极接硅锭,负极接切割线网,电解过程中硅锭发生微区钝化反应,形成硬度较小的钝化膜,使点杂多晶太阳能硅片更易切割。试验结果表明:该技术具有切割效率高、切片合格率高等优点。进一步检测发现,硅片宏观表面线痕浅、隐裂少,微观表面平整性好。该技术的应用降低了硅片加工的成本,提高了硅材料的利用率,也为太阳能电池的运用拓宽了空间。     

Enhanced efficiency of polymer:fullerene bulk-heterojunction solar cells with the insertion of thin CdS layer near the Al electrode

The insertion layer of cadmium sulfide (CdS) between polymer–fullerene blend and Al electrode is used to enhance the short-circuit current (I_sc) and the power conversion efficiency (PCE). The solar cells based on the blend of poly[2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) and C₆₀ with the function layer of CdS (∼10 nm) shows the open-circuit voltage (V_oc) of ∼0.7 V, short-circuit current (I_sc) of ∼4.6 mA/cm², filling factor (FF) of ∼0.28, and the power conversion efficiency (PCE) of ∼5.3% under monochromatic light (532 nm) photoexcitation of about 16.7 mW/cm². Compared to cells without the CdS layer, the power conversion efficiency increases about an order of magnitude. The thickness of CdS layer was varied from 10 to 40 nm using e-beam deposition, and we obtained optimum current density–voltage characteristics for 10 nm thick CdS layer.