The p recombination layer in tunnel junctions for micromorph tandem solar cells

A new tunnel recombination junction is fabricated for n–i–p type micromorph tandem solar cells. We insert a thin heavily doped hydrogenated amorphous silicon (a-Si:H) p + recombination layer between the n a-Si:H and the p hydrogenated nanocrystalline silicon (nc-Si:H) layers to improve the performance of the n–i–p tandem solar cells. The effects of the boron doping gas ratio and the deposition time of the p-a-Si:H recombination layer on the tunnel recombination junctions have been investigated. The current-voltage characteristic of the tunnel recombination junction shows a nearly ohmic characteristic, and the resistance of the tunnel recombination junction can be as low as 1.5 ·cm 2 by using the optimized p-a-Si:H recombination layer. We obtain tandem solar cells with open circuit voltage V oc = 1.4 V, which is nearly the sum of the V oc s of the two corresponding single cells, indicating no V oc losses at the tunnel recombination junction.     

Effect of emitter layer doping concentration on the performance of a silicon thin film heterojunction solar cell

A novel type of n/i/i/p heterojunction solar cell with a-Si:H(15nm)/a-Si:H(10nm)/ epitaxial c-Si(47μm)/epitaxial c-Si(3μm) structure is fabricated by using the layer transfer technique, and the emitter layer is deposited by hot wire chemical vapour deposition. The effect of the doping concentration of the emitter layer S d (Sd =PH3 /(PH3 +SiH4 +H2 )) on the performance of the solar cell is studied by means of current density-voltage and external quantum efficiency. The results show that the conversion efficiency of the solar cell first increases to a maximum value and then decreases with S d increasing from 0.1% to 0.4%. The best performance of the solar cell is obtained at S d = 0.2% with an open circuit voltage of 534 mV, a short circuit current density of 23.35mA/cm2 , a fill factor of 63.3%, and a conversion efficiency of 7.9%.     

β-FeSi2 as the bottom absorber of triple-junction thin-film solar cells: A numerical study

Using β-FeSi2 as the bottom absorber of triple-junction thin-film solar cells is investigated by a numerical method for widening the long-wave spectral response. The presented results show that the β-FeSi2 subcell can contribute 0.273 V of open-circuit voltage to the a-Si/μc-Si/β-FeSi2 triple-junction thin-film solar cell. The optimized absorber thicknesses for a- Si, μ-Si, and/3-FeSi2 subcells are 260 nm, 900 nm, and 40 nm, respectively. In addition, the temperature coefficient of the conversion efficiency of the a-Si/μc-Si//3-FeSi2 cell is -0.308 %/K, whose absolute value is only greater than that of the a-Si subcell. This result indicates that the a-Si/μc-Si/β-FeSi2 triple-junction solar cell has a good temperature coefficient. As a result, using β-FeSi2 as the bottom absorber can improve the thin-film solar cell performance, and the a-Si/μc-Si/β-FeSi2 triple-junction solar cell is a promising structure configuration for improving the solar cell efficiency.     

Influence of p-layer on the performance of n-i-p μc-Si:H thin film solar cells

The high pressure radio frequency plasma enhanced chemical vapor deposition (RF-PECVD) process was adopted to prepare the n-i-p microcrystalline silicon solar cells,the influence of p-type layers on the performance of the solar cells was investigated,and the optimum p layer suited to the n-i-p microcrystalline silicon solar cells was obtained.The experimental results demonstrate that the performance of the solar cells can be highly affected by the structural and optical properties of the p-layers,and the performance of solar cells can be greatly improved by optimizing p layers.We have achieved an initial active-area efficiency of 8.17% (V oc =0.49 V,J sc =24.9 mA/cm 2 ,FF=67%) for the μc-Si:H single-junction n-i-p solar cells and an initial active-area efficiency of 10.93% (V oc =1.31 V,J sc =13.09 mA/cm 2 ,FF=64%) for the a-Si:H/μc-Si:H tandem n-i-p solar cells.     

Microstructure evolution and passivation quality of hydrogenated amorphous silicon oxide(a-SiOx:H) on〈100〉- and 〈111〉-orientated c-Si wafers

Hydrogenated amorphous silicon oxide(a-SiOx:H) is an attractive passivation material to suppress epitaxial growth and reduce the parasitic absorption loss in silicon heterojunction(SHJ) solar cells. In this paper, a-SiOx:H layers on different orientated c-Si substrates are fabricated. An optimal effective lifetime(τ(eff)) of 4743 μs and corresponding implied opencircuit voltage(iV(oc)) of 724 mV are obtained on〈100〉-orientated c-Si wafers. While τ(eff) of 2429 μs and iV_oc of 699 mV are achieved on 111-orientated substrate. The FTIR and XPS results indicate that the a-SiOx:H network consists of SiOx(Si-rich), Si–OH, Si–O–SiHx, SiO2 ≡ Si–Si, and O3 ≡ Si–Si. A passivation evolution mechanism is proposed to explain the different passivation results on different c-Si wafers. By modulating the a-SiOx:H layer, the planar silicon heterojunction solar cell can achieve an efficiency of 18.15%.     

Fabrication of c-Si：H（p）/c-Si（n） Heterojunction Solar Cells with Microcrystalline Emitters

The p-type microcrystalline silicon （μc-Si：H） on n-type crystalline silicon （c-Si） heterojunction solar cells is fabricated by radio-frequency plasma enhanced chemical vapour deposition （rf-PECVD）. The effect of the μc- Si：Hp-layers on the performance of the heterojunction solar cells is investigated. Optimum μc-Si：H p-layer is obtained with hydrogen dil u tion ratio of 99.65 %, rf-power of 0. 08 W/cm^2 , gas phase doping ratio of 0. 125 %, and the p-layer thickness of 15nm. We fabricate μc-Si：H（p）/c-Si（n） heterojunction solar cells without texturing and obtained an efficiency of 13.4%. The comparisons of the solar-cell performances using different surface passivation techniques are discussed.     

Indium–tin oxide films obtained by DC magnetron sputtering for improved Si heterojunction solar cell applications

The indium–tin oxide(ITO) film as the antireflection layer and front electrodes is of key importance to obtaining high efficiency Si heterojunction(HJ) solar cells. To obtain high transmittance and low resistivity ITO films by direct-current(DC) magnetron sputtering, we studied the impacts of the ITO film deposition conditions, such as the oxygen flow rate,pressure, and sputter power, on the electrical and optical properties of the ITO films. ITO films of resistivity of 4×10-4?·m and average transmittance of 89% in the wavelength range of 380–780 nm were obtained under the optimized conditions:oxygen flow rate of 0.1 sccm, pressure of 0.8 Pa, and sputtering power of 110 W. These ITO films were used to fabricate the single-side HJ solar cell without an intrinsic a-Si:H layer. However, the best HJ solar cell was fabricated with a lower sputtering power of 95 W, which had an efficiency of 11.47%, an open circuit voltage(V oc) of 0.626 V, a filling factor(FF) of 0.50, and a short circuit current density(J sc) of 36.4 m A/cm2. The decrease in the performance of the solar cell fabricated with high sputtering power of 110 W is attributed to the ion bombardment to the emitter. The V oc was improved to 0.673 V when a 5 nm thick intrinsic a-Si:H layer was inserted between the(p) a-Si:H and(n) c-Si layer. The higher V oc of 0.673 V for the single-side HJ solar cell implies the excellent c-Si surface passivation by a-Si:H.     

Improved performance of microcrystalline silicon solar cell with graded-band-gap silicon oxide buffer layer

Microcrystalline silicon(μc-Si:H) solar cell with graded band gap microcrystalline silicon oxide(μc-Si Ox:H) buffer layer is prepared by plasma enhanced chemical vapor deposition and exhibits improved performance compared with the cell without it. The buffer layer moderates the band gap mismatch by reducing the barrier of the p/i interface, which promotes the nucleation of the i-layer and effectively eliminates the incubation layer, and then enhances the collection efficiency of the cell in the short wavelength region of the spectrum. The p/i interface defect density also decreases from 2.2 × 1012cm-2to 5.0 × 1011cm-2. This graded buffer layer allows to simplify the deposition process for the μc-Si:H solar cell application.     

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%.     

非晶Si1-xGex:H薄膜太阳能电池研究

The AMPS-ID program is used to investigate electrical and optical properties of the thin film solar cell of a-SiC:H/a-Si1-xGex:H/a-Si:H. The short circuit current density, open circuit voltage, fill factor and efficiency of the solar cell are investigated. The efficiency of the solar cell is 9.19% as thickness of a-Si1-xGex:H is 340 nm with Ge content x=0.1. In addition, we also discuss the factors which affect solar cell efficiency.     

Effects of deposition pressure and plasma power on the growth and properties of boron-doped microcrystalline silicon films

Using diborane as doping gas, p-doped μc-Si：H layers are deposited by using the plasma enhanced chemical vapour deposition （PECVD） technology. The effects of deposition pressure and plasma power on the growth and the properties of μc-Si：H layers are investigated. The results show that the deposition rate, the electrical and the structural properties are all strongly dependent on deposition pressure and plasma power. Boron-doped μc-Si：H films with a dark conductivity as high as 1.42 Ω^-1·cm^-1 and a crystallinity of above 50% are obtained. With this p-layer, μc-Si：H solar cells are fabricated. In addition, the mechanism for the effects of deposition pressure and plasma power on the growth and the properties of boron-doped μc-Si：H layers is discussed.     

提高非晶硅/微晶硅叠层太阳电池光稳定性的研究

如何提高硅基薄膜太阳电池的光稳定性是硅基薄膜太阳电池研究和产业化过程中非常重要的问题. 为了提高非晶硅/微晶硅叠层电池的光稳定性, 本文首先给出了良好光稳定性非晶硅顶电池的结果, 然后重点研究了N/P隧穿结和微晶硅底电池本征层硅烷浓度梯度对叠层电池光稳定性的影响. 经过初步优化, 连续光照1000 h后非晶硅/微晶硅叠层电池的最小光致衰退率只有7%.     

a-Si:H/c-Si 异质结太阳电池 J-V 曲线的 S-Shape 现象

通过异质结界面分析与 AMPS 模拟计算研究了 a-Si:H/c-Si 异质结太阳电池在低温工作、a-Si:H 层低掺杂、高价带补偿以及高界面态时光态 J-V 曲线出现 S-Shape 现象的物理过程,总结了 S-Shape 现象的物理原因.分析结果表明,当空穴输运受到界面势垒的限制时,空穴在 c-Si 界面附近聚集,能带重新分配,c-Si 耗尽区的电场减小,更多的电子从 c-Si 准中性区反转至 c-Si 界面及耗尽区与空穴复合,复合速率显著增大,光电流的损失显著增大,光态 J-V< 关键词： 模拟 异质结太阳电池 a-Si:H/c-Si 异质结     

Influence of the total gas flow rate on high rate growth microcrystalline silicon films and solar cells

This paper reports that high-rate-deposition of microcrystalline silicon solar cells was performed by very-highfrequency plasma-enhanced chemical vapor deposition.These solar cells,whose intrinsic μc-Si:H layers were prepared by using a different total gas flow rate (F total),behave much differently in performance,although their intrinsic layers have similar crystalline volume fraction,opto-electronic properties and a deposition rate of ～ 1.0 nm/s.The influence of F total on the micro-structural properties was analyzed by Raman and Fourier transformed infrared measurements.The results showed that the vertical uniformity and the compact degree of μc-Si:H thin films were improved with increasing F total.The variation of the microstructure was regarded as the main reason for the difference of the J-V parameters.Combined with optical emission spectroscopy,we found that the gas temperature plays an important role in determining the microstructure of thin films.With F total of 300 sccm,a conversion efficiency of 8.11% has been obtained for the intrinsic layer deposited at 8.5 A/s (1 A=0.1 nm).     

The role of hydrogen in hydrogenated microcrystalline silicon film and in deposition process with VHF-PECVD technique

The role of hydrogen in hydrogenated microcrystalline silicon （μc-Si：H） thin films in deposition processes with very high frequency plasma-enhanced chemical vapour deposition （VHF-PECVD） technique have been investigated in this paper. With in situ optical emission spectroscopy （OES） diagnosis during the fabrication of μc-Si：H thin films under different plasma excitation frequency Ve （60MHz-90MHz）, the characteristic peak intensities （IsiH＊, IHα＊ and IHβ＊ ） in SiH4＋H2 plasma and the ratio of （IHα＊ ＋ IHβ＊ ） to IsiH＊ were measured; all the characteristic peak intensities and the ratio （IHα＊ ＋ IHβ＊ ）/IsiH＊ are increased with plasma excitation frequency. It is identified that high plasma excitation frequency is favourable to promote the decomposition of SiH4＋H2 to produce atomic hydrogen and SiHx radicals. The influences of atomic hydrogen on structural properties and that of SiHx radicals on deposition rate of μc-Si：H thin films have been studied through Raman spectra and thickness measurements, respectively. It can be concluded that both the crystalline volume fraction and deposition rate are enhanced with the increase of plasma excitation frequency, which is in good accord with the OES results. By means of FTIR measurements, hydrogen contents of μc-Si：H thin films deposited at different plasma excitation frequency have been evaluated from the integrated intensity of wagging mode near 640 cm^-1. The hydrogen contents vary from 4% to 5%, which are much lower than those of μc-Si：H films deposited with RF-PECVD technique. This implies that μc-Si：H thin films deposited with VHF-PECVD technique usually have good stability under light-soaking.     

纳米硅(nc-Si:H )/晶体硅(c-Si)异质结太阳电池的数值模拟分析

运用美国宾州大学发展的AMPS程序模拟分析了n-型纳米硅（n+-nc-Si:H）/p-型晶体硅(p-c-Si)异质结太阳电池的光伏特性.分析表明，界面缺陷态是决定电池性能的关键因素，显著影响电池的开路电压（VOC）和填充因子（FF），而电池的光谱响应或短路电流密度（JSC）对缓冲层的厚度较为敏感.对不同能带补偿（bandgap offset）的情况所进行的模拟分析表明，随着ΔEc的增大，由于界面态所带来的开路电压和填充因子的减小逐渐被消除，当ΔEc达到05eV左右时界面态的影响几乎完全被掩盖.界面层的其他能带结构特征对器件性能的影响还有待进一步研究.最后计算得到了这种电池理想情况下（无界面态、有背面场、正背面反射率分别为0和1）的理论极限效率ηmax=3117% (AM15，100mW/cm2，040—110μm波段).     

原位等离子体逐层氧化a-Si:H/SiO2多层膜的光致发光研究

采用在等离子体增强化学汽相沉积系统中沉积a-Si:H和原位等离子体逐层氧化的方法制备a-Si:H/SiO2多层膜.改变a-Si:H层的厚度，首次在室温下观察到来自a-Si:H/SiO2多层膜较强的蓝色光致发光和从465到435nm的蓝移.x射线能谱证明，SiO2层是化学配比的SiO2；C-V特性表明，a-Si:H/SiO2界面得到了很好的钝化；透射电子显微镜表明，样品形成了界面陡峭的多层结构.结合光吸收谱和光致发光谱的研究，对其发光机理进行了讨论.用一维量子限制模型对光致发光峰随着a-Si:H层厚度的减小 关键词： a-Si:H/SiO2多层膜 光致发光     

非晶硅界面缓冲层对非晶硅锗电池性能的影响

针对非晶硅锗电池本征层高锗含量时界面带隙失配以及高界面缺陷密度造成电池开路电压和填充因子下降的问题,通过在PI界面插入具有合适带隙的非晶硅缓冲层,不仅有效缓和了带隙失配,降低界面复合,同时也通过降低界面缺陷密度改善内建电场分布,从而提高了电池的收集效率. 进一步引入IN界面缓冲层以及对非晶硅锗本征层进行能带梯度设计,在仅采用Al背电极时,单结非晶硅锗电池转换效率达8.72%. 关键词： 非晶硅缓冲层 非晶硅锗薄膜太阳电池 带隙 界面     

The high deposition of microcrystalline silicon thin film by very high frequency plasma enhanced chemical vapour deposition and the fabrication of solar cells

This paper reports that the intrinsic microcrystalline silicon ($\mu $c-Si:H) films are prepared with plasma enhanced chemical vapour deposition from silane/hydrogen mixtures at 200\du\ with the aim to increase the deposition rate. An increase of the deposition rate to 0.88\,nm/s is obtained by using a plasma excitation frequency of 75\,MHz. This increase is obtained by the combination of a higher deposition pressure, an increased silane concentration, and higher discharge powers. In addition, the transient behaviour, which can decrease the film crystallinity, could be prevented by filling the background gas with Hchemical vapour deposition, plasma deposition, solar cells, crystallinityProgram supported by the State Key Development Program for Basic Research of China (Grant No 2006CB202601), and Basic Research Project of Henan Province in China (Grant No 072300410140).7280N, 7830G, 8115HThis paper reports that the intrinsic microcrystalline silicon ($\mu $c-Si:H) films are prepared with plasma enhanced chemical vapour deposition from silane/hydrogen mixtures at 200\du\ with the aim to increase the deposition rate. An increase of the deposition rate to 0.88\,nm/s is obtained by using a plasma excitation frequency of 75\,MHz. This increase is obtained by the combination of a higher deposition pressure, an increased silane concentration, and higher discharge powers. In addition, the transient behaviour, which can decrease the film crystallinity, could be prevented by filling the background gas with Hchemical vapour deposition, plasma deposition, solar cells, crystallinityProgram supported by the State Key Development Program for Basic Research of China (Grant No 2006CB202601), and Basic Research Project of Henan Province in China (Grant No 072300410140).7280N, 7830G, 8115HThis paper reports that the intrinsic microcrystalline silicon ($\mu $c-Si:H) films are prepared with plasma enhanced chemical vapour deposition from silane/hydrogen mixtures at 200\du\ with the aim to increase the deposition rate. An increase of the deposition rate to 0.88\,nm/s is obtained by using a plasma excitation frequency of 75\,MHz. This increase is obtained by the combination of a higher deposition pressure, an increased silane concentration, and higher discharge powers. In addition, the transient behaviour, which can decrease the film crystallinity, could be prevented by filling the background gas with Hchemical vapour deposition, plasma deposition, solar cells, crystallinityProgram supported by the State Key Development Program for Basic Research of China (Grant No 2006CB202601), and Basic Research Project of Henan Province in China (Grant No 072300410140).7280N, 7830G, 8115HThis paper reports that the intrinsic microcrystalline silicon ($\mu $c-Si:H) films are prepared with plasma enhanced chemical vapour deposition from silane/hydrogen mixtures at 200\du\ with the aim to increase the deposition rate. An increase of the deposition rate to 0.88\,nm/s is obtained by using a plasma excitation frequency of 75\,MHz. This increase is obtained by the combination of a higher deposition pressure, an increased silane concentration, and higher discharge powers. In addition, the transient behaviour, which can decrease the film crystallinity, could be prevented by filling the background gas with Hchemical vapour deposition, plasma deposition, solar cells, crystallinityProgram supported by the State Key Development Program for Basic Research of China (Grant No 2006CB202601), and Basic Research Project of Henan Province in China (Grant No 072300410140).7280N, 7830G, 8115HThis paper reports that the intrinsic microcrystalline silicon ($\mu $c-Si:H) films are prepared with plasma enhanced chemical vapour deposition from silane/hydrogen mixtures at 200\du\ with the aim to increase the deposition rate. An increase of the deposition rate to 0.88\,nm/s is obtained by using a plasma excitation frequency of 75\,MHz. This increase is obtained by the combination of a higher deposition pressure, an increased silane concentration, and higher discharge powers. In addition, the transient behaviour, which can decrease the film crystallinity, could be prevented by filling the background gas with H$_{2}$ prior to plasma ignition, and selecting proper discharging time after silane flow injection. Material prepared under these conditions at a deposition rate of 0.78\,nm/s maintains higher crystallinity and fine electronic properties. By H-plasma treatment before i-layer deposition, single junction $\mu $c-Si:H solar cells with 5.5{\%} efficiency are fabricated.