Research on the boron contamination at the p/i interface of microcrystalline silicon solar cells deposited in a single PECVD chamber

This paper studies boron contamination at the interface between the p and i layers of μ c-Si:H solar cells deposited in a single-chamber PECVD system. The boron depth profile in the i layer was measured by Secondary Ion Mass Spectroscopy. It is found that the mixed-phase μ c-Si:H materials with 40% crystalline volume fraction is easy to be affected by the residual boron in the reactor. The experimental results showed that a 500-nm thick μ c-Si:H covering layer or a 30-seconds of hydrogen plasma treatment can effectively reduce the boron contamination at the p/i interface. However, from viewpoint of cost reduction, the hydrogen plasma treatment is desirable for solar cell manufacture because the substrate is not moved during the hydrogen plasma treatment.     

Significant Improvement of Passivation Performance by Two-Step Preparation of Amorphous Silicon Passivation Layers in Silicon Heterojunction Solar Cells

The key feature of amorphous/crystalline silicon heterojunction solar cells is extremely low surface recombination,which is related to superior passivation on the crystalline silicon wafer surface using thin hydrogenated amorphous silicon(a-Si:H)layers,leading to a high open-circuit voltage.In this work,a two-step method of a-Si:H passivation is introduced,showing excellent interface passivation quality,and the highest effective minority carrier lifetime exceeds 4500 μs.By applying a buffer layer deposited through pure silane plasma,the risk of film epitaxial growth and plasma damage caused by hydrogen diluted silane plasma is effectively reduced.Based on this,excellent passivation is realized through the following hydrogen diluted silane plasma process with the application of high density hydrogen.In this process,hydrogen diffuses to a-Si/c-Si interface,saturating residual dangling bonds which are not passivated by the buffer layer.Employing this two-step method,a heterojunction solar cell with an area of 239 cm~2 is prepared,yielding to open-circuit voltage up to 735 mV and total-area efficiency up to 22.4%.     

The n-type Si-based materials applied on the front surface of IBC-SHJ solar cells

Interdigitated back contact silicon hetero-junction(IBC-SHJ) solar cells exhibit excellent performance owing to the IBC and SHJ structures.The front surface field(FSF) layer composed of electric field passivation and chemical passivation has been proved to play an important role in IBC-SHJ solar cells.The electric field passivated layer n~+-a-Si: H, an n-type Si alloy with carbon or oxygen in amorphous phase, is simulated in this study to investigate its effect on IBC-SHJ.It is indicated that the n~+-a-Si: H layer with wider band gap can reduce the light absorption on the front side efficaciously,which hinders the surface recombination of photo-generated carriers and thus contributes to the improvement of the short circuit current density J_(sc).The highly doped n~+-a-Si: H can result in the remakable energy band bending, which makes it outstanding in the field passivation, while it makes little contribution to the chemical passivation.It is noteworthy that when the electric field intensity exceeds 1.3 × 10~5 V/cm, the efficiency decrease caused by the inferior chemical passivation is only 0.16%.In this study, the IBC-SHJ solar cell with a front n~+-a-Si: H field passivation layer is simulated, which shows the high efficiency of 26% in spite of the inferior chemical passivation on the front surface.     

Water sorption thermodynamics in glassy polymers endowed with hydrogen bonding interactions

In this contribution, we review and critically compare the results of the analyses we have previously performed on water sorption thermodynamics in a series of polyimides. The experimental investigation was performed by combining gravimetric tests and in situ vibrational spectroscopy. A non-equilibrium theory, based on a compressible lattice framework accounting for the glassy state of the polymer and for the occurrence of hydrogen bonding interactions, has been used to interpret data. Information at a molecular level gained by vibrational spectroscopy has been used to tailor the model equations. The main features of water sorption thermodynamics are well captured, qualitatively and quantitatively, by the adopted model which displays a remarkable agreement with experimental results.     

Theoretical analysis and numerical simulation of the impulse delivering from laser-produced plasma to solid target

A plasma is produced in air by using a high-intensity Q-switch Nd：YAG pulsed laser to irradiate a solid target, and the impulses delivering from the plasma to the target are measured at different laser power densities. Analysing the formation process of laser plasma and the laser supported detonation wave （LSDW） and using fluid mechanics theory and Pirri＇s methods, an approximately theoretical solution of the impulse delivering from the plasma to the target under our experimental condition is found. Furthermore, according to the formation time of plasma and the variation of pressure in plasma in a non-equilibrium state, a physical model of the interaction between the pulse laser and the solid target is developed. The plasma evolutions with time during and after the laser pulse irradiating the target are simulated numerically by using a three-dimensional difference scheme. And the numerical solutions of the impulse delivering from the plasma to the target are obtained. A comparison among the theoretical, numerical and experimental results and their analyses are performed. The experimental results are explained reasonably. The consistency between numerical results and experimental results implies that the numerical calculation model used in this paper can well describe the mechanical action of the laser on the target.     

Research on the optimum hydrogenated silicon thin films for application in solar cells

Hydrogenated silicon (Si:H) thin films for application in solar cells were deposited by using very high frequency plasma enhanced chemical vapour deposition (VHF PECVD) at a substrate temperature of about 170℃. The electrical, structural, and optical properties of the films were investigated. The deposited films were then applied as i-layers for p-i-n single junction solar cells. The current--voltage (I-V) characteristics of the cells were measured before and after the light soaking. The results suggest that the films deposited near the transition region have an optimum properties for application in solar cells. The cell with an i-layer prepared near the transition region shows the best stable performance.     

Atomistic simulation of topaz:Structure,defect,and vibrational properties

The clay force field(CLAYFF) was supplemented by fluorine potential parameters deriving from experimental structures and used to model various topazes. The calculated cell parameters agree well with the observed structures. The quasi-linear correlation of the b lattice parameter to different F/OH ratios calculated by changing fluorine contents in OH-topaz supports that the F content can be measured by an optical method. Hydrogen bond calculations reveal that the hydrogen bond interaction to H1 is stronger than that to H2, and the more fluorine in the structure, the stronger the hydrogen bond interaction of hydroxyl hydrogen. Defect calculations provide the formation energies of all common defects and can be used to judge the ease of formation of them. The calculated vibrational frequencies are fairly consistent with available experimental results, and the 1080-cm-1frequency often occurring in natural OH-topaz samples can be attributed to Si–F stretching because of the F substitution to OH and the Al–Si exchange.     

Long-lived population of the metastable 2s state in muonic hydrogen

Preliminary experimental results of the search for long-lived metastable μp(2s) are presented. The μp(2s) are identified via muon transfer to neon in a gas mixture of hydrogen and several percent of neon at mbar pressures. An energy-dependent 1s transfer rate to neon has been observed. The time spectra can only be explained assuming a nonzero μp(2s) population. This revised version was published online in August 2006 with corrections to the Cover Date.     

Light trapping characteristics of glass substrate with hemisphere pit arrays in thin film Si solar cells

In this paper, the light trapping characteristics of glass substrate with hemisphere pit(HP) arrays in thin film Si solar cells are theoretically studied via a numerical approach. It is found that the HP glass substrate has good antireflection properties. Its surface reflectance can be reduced by ～ 50% compared with planar glass. The HP arrays can make the unabsorbed light return to the absorbing layer of solar cells, and the ratio of second absorption approximately equals 30%.Thus, the glass substrate with the hemisphere pit arrays(HP glass) can effectively reduce the total reflectivity of a solar cell from 20% to 13%. The HP glass can also prolong the optical path length. The numerical results show that the total optical path length of the thin film Si solar cell covered with the HP glass increases from 2ω to 4ω. These results are basically consistent with the experimental results.     

Plasma parameter diagnosis using hydrogen emission spectra of a quartz-chamber 2.45 GHz ECRIS at Peking University

A quartz-chamber 2.45 GHz electron cyclotron resonance ion source(ECRIS) was designed for diagnostic purposes at Peking University [Patent Number: ZL 201110026605.4]. This ion source can produce a maximum 84 m A hydrogen ion beam at 50 k V with a duty factor of 10%. The root-mean-square(RMS) emittance of this beam is less than 0.12π mm mrad. In our initial work,the electron temperature and electron density inside the plasma chamber had been measured with the line intensity ratio of noble gases. Based on these results, the atomic and molecular emission spectra of hydrogen were applied to determine the dissociation degree of hydrogen and the vibrational temperature of hydrogen molecules in the ground state, respectively. Measurements were performed at gas pressures from 4×10~(-4) to 1×10~(-3) Pa and at input peak RF power ranging from 1000 to 1800 W. The dissociation degree of hydrogen in the range of 0.5%-10% and the vibrational temperature of hydrogen molecules in the ground state in the range of 3500-8500 K were obtained. The plasma processes inside this ECRIS chamber were discussed based on these results.     

Surface passivation of crystalline silicon by sputter deposited hydrogenated amorphous silicon

This letter shows that intrinsic hydrogenated amorphous silicon (a‐Si:H) films deposited by RF magnetron sputtering can provide outstanding passivation of crystalline silicon surfaces, similar to that achieved by plasma enhanced chemical vapour deposition (PECVD). By using a 2% hydrogen and 98% argon gas mixture as the plasma source, 1.5 Ω cm n‐type FZ silicon wafers coated with sputtered a‐Si:H films achieved an effective lifetime of 3.5 ms, comparable to the 3 ms achieved by PECVD (RF and microwave dual‐mode). This is despite the fact that Fourier transform infrared spectroscopy measurements show that sputtering and PECVD deposited films have very different chemical bonding configurations. We have found that film thickness and deposition temperature have a significant impact on the passivation results. Self‐annealing and hydrogen plasma treatment during deposition are likely driving forces for the observed changes in surface passivation. These experimental results open the way for the application of sputtered a‐Si:H to silicon heterojunction solar cells. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

钙钛矿/硅叠层太阳电池中平面a-Si:H/c-Si异质结底电池的钝化优化及性能提高

最近,旋涂法制备的钙钛矿/平面硅异质结高效叠层太阳电池引起人们广泛关注,主要原因是相比于绒面硅衬底制备的钙钛矿/硅叠层太阳电池,其制备工艺简单、制备成本低且效率高.对于平面a-Si:H/c-Si异质结电池, a-Si:H/c-Si界面的良好钝化是获得高转换效率的关键,进而决定了钙钛矿/硅异质结叠层太阳电池的性能.本文主要从硅片表面处理、a-Si:H钝化层和P型发射极等方面展开研究,通过对硅片表面的氢氟酸(HF)浸泡时间和氢等离子体预处理气体流量、a-Si:H钝化层沉积参数、钝化层与P型发射极(I/P)界面富氢等离子体处理的综合调控,获得了相应的优化工艺参数.对比研究了p-a-Si:H和p-nc-Si:H两种缓冲层材料对I/P界面的影响,其中高电导、宽带隙的p-nc-Si:H缓冲层既能够降低I/P界面的缺陷态,又可以增强P型发射层的暗电导率,提高了前表面场效应钝化效果.通过上述优化,制备出最佳的P-type emitter layer/aSi:H(i)/c-Si/a-Si:H(i)/N-type layer (inip)结构样品的少子寿命与implied-Voc分别达到2855μs和709 mV,表现出良好的钝化效果.应用于平面a-Si:H/c-Si异质结太阳电池,转换效率达到18.76%,其中开路电压达到681.5 mV,相对于未优化的电池提升了34.3 mV.将上述平面a-Si:H/c-Si异质结太阳电池作为底电池,对应的钙钛矿/硅异质结叠层太阳电池的开路电压达到1780 mV,转换效率达到21.24%,证明了上述工艺优化能够有效地改善叠层太阳电池中的硅异质结底电池的钝化及电池性能.     

Large-scale black multi-crystalline silicon solar cell with conversion efficiency over 18 %

In this paper, large area multi-crystalline silicon (mc-Si) solar cells of 156 mm × 156 mm were fabricated by the combination of Ag-assisted etching and sodium hydroxide (NaOH) treatment. Scanning electron microscope, UV–Vis–NIR spectrophotometer, external quantum efficiency measurement system, and current–voltage test were used to characterize the etched black silicon wafers and the fabricated solar cells. It was found that, though the black mc-Si without NaOH treatment showed a lowest reflectance of 2.03 % in the wavelength of 400–900 nm, the maximum conversion efficiency came from the mc-Si solar cells produced by combination of Ag-assisted etching and NaOH treatment. Though the solar cell with additional NaOH treatment for 30 s presented a reflectance of 5.45 %, it presented the highest conversion efficiency of 18.03 %, which is 0.64 % higher than the traditional mc-Si solar cell (17.39 %) and much higher than that of the black mc-Si solar cell without NaOH treatment (16.24 %).     

表面钝化对多晶硅绒面形貌的影响

多晶硅表面制绒技术是太阳能光伏产业亟待突破的一个关键技术.本文根据多晶硅强酸制绒的基本原理,提出了表面活性剂钝化多晶硅表面以降低硅原子与酸反应速度从而改善多晶硅绒面形貌的方法.实验研究了不同含量的添加剂对酸液刻蚀多晶硅绒面形貌的影响,用扫描电镜观察对应的绒面结构,用积分反射仪测量其绒面的表面反射率.实验结果表明:加入活性剂后酸液能使多晶硅表面陷阱坑分布更加均匀,并且能有效消除产生漏电流的缺陷性深沟槽,样品表面反射率比较低,其表面反射率降低到21.5%.与传统酸液腐蚀的多晶硅绒面结构相比,陷阱坑密度明显增加,这种方法在多晶硅太阳电池的生产中是有价值的.     

Mass production technology for multicrystalline Si solar cells

The worldwide shipments of the PV modules in the last 10 years show an increase of about 20% per year. The worldwide PV modules shipments were 201 MW in 1999. About 85% modules have made from crystalline silicon. The multicrystalline silicon (mc-Si) modules shipments have showed substantial increase. PV market would be expected to increase by the development of low cost and high technologies of mc-Si solar cells. This paper reviews recent progress in mass production technologies of mc-Si solar cells.     

Quantum Transport across Amorphous-Crystalline Interfaces in Tunnel Oxide Passivated Contact Solar Cells: Direct versus Defect-Assisted Tunneling

Tunnel oxide passivated contact solar cells have evolved into one of the most promising silicon solar cell concepts of the past decade,achieving a record efficiency of 25%.We study the transport mechanisms of realistic tunnel oxide structures,as encountered in tunnel oxide passivating contact(TOPCon) solar cells.Tunneling transport is affected by various factors,including oxide layer thickness,hydrogen passivation,and oxygen vacancies.When the thickness of the tunnel oxide layer increases,a faster decline of conductivity is obtained computationally than that observed experimentally.Direct tunneling seems not to explain the transport characteristics of tunnel oxide contacts.Indeed,it can be shown that recombination of multiple oxygen defects in a-SiO_x can generate atomic silicon nanowires in the tunnel layer.Accordingly,new and energetically favorable transmission channels are generated,which dramatically increase the total current,and could provide an explanation for our experimental results.Our work proves that hydrogenated silicon oxide(SiO_x:H) facilitates high-quality passivation,and features good electrical conductivity,making it a promising hydrogenation material for TOPCon solar cells.By carefully selecting the experimental conditions for tuning the SiO_x:H layer,we anticipate the simultaneous achievement of high open-circuit voltage and low contact resistance.     

Effective surface passivation of crystalline silicon by rf sputtered aluminum oxide

In recent years, excellent surface passivation has been achieved on both p‐type and n‐type surfaces of silicon wafers and solar cells using aluminum oxide deposited by plasma‐assisted atomic layer deposition. However, alternative deposition methods may offer practical advantages for large‐scale manufacturing of solar cells. In this letter we show that radio‐frequency magnetron sputtering is capable of depositing negatively‐charged aluminum oxide and achieving good surface passivation both on p‐type and n‐type silicon wafers. We thus establish that sputtered aluminum oxide is a very promising method for the surface passivation of high efficiency solar cells. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

氧化随机织构硅表面对单晶硅太阳电池性能的影响研究

热氧化生长的SiO\-2 薄膜经常在高效单晶硅太阳电池中被用作扩散掩膜,化学镀掩膜,钝化层或者基本的减反射层.在这些高效太阳电池中,经常使用碱性溶液对单晶硅表面进行处理,得到随机分布的正金字塔结构的织绒表面,减少表面的光反射.表面氧化后的正金字塔太阳电池暗反向电流-电压呈现"软击穿"现象,并联电阻明显下降.研究结果表明引起这些现象的原因在于氧化正金字塔表面会导致在体内形成位错型缺陷,这些缺陷能够贯穿整个pn 结,导致太阳电池的并联电阻下降,同时载流子在位错型缺陷在能隙中引入的能级处发生复合,导致空间电荷区 关键词： 热氧化 随机织构 位错 太阳电池