One-step Fabrication of Nanoporous Black Silicon Surfaces for Solar Cells using Modified Etching Solution

Currently, a conventional two-step method has been used to generate black silicon （BS） surfaces on silicon substrates for solar cell manufacturing. However, the performances of the solar cell made with such surface generation method are poor, because of the high surface recombination caused by deep etching in the conventional surface generation method for BS. In this work, a modified wet chemical etching solution with additives was developed. A homogeneous BS layer with random porous structure was obtained from the modified solution in only one step at room temperature. The BS layer had low reflectivity and shallow etching depth. The additive in the etch solution performs the function of pH-modulation. After 16-min etching, the etching depth in the samples was approximately 200 nm, and the spectrum-weighted-reflectivity in the range from 300 nm to 1200 nm was below 5%. BS solar cells were fabricated in the production line. The decreased etching depth can improve the electrical performance of solar cells because of the decrease in surface recombination. An efficiency of 15.63% for the modified etching BS solar cells was achieved on a large area, p- type single crystalline silicon substrate with a 624.32-mV open circuit voltage and a 77.88% fill factor.

Realization of conformal doping on multicrystalline silicon solar cells and black silicon solar cells by plasma immersion ion implantation

Emitted multi-crystalline silicon and black silicon solar cells are conformal doped by ion implantation using the plasma immersion ion implantation （PⅢ） technique. The non-uniformity of emitter doping is lower than 5 %. The secondary ion mass spectrometer profile indicates that the PⅢ technique obtained 100-rim shallow emitter and the emitter depth could be impelled by furnace annealing to 220 nm and 330 nm at 850 ℃ with one and two hours, respectively. Furnace annealing at 850 ℃ could effectively electrically activate the dopants in the silicon. The efficiency of the black silicon solar cell is 14.84% higher than that of the mc-silicon solar cell due to more incident light being absorbed.

Preparation, microstructure and dislocation of solar-grade multicrystalline silicon by directional solidification from metallurgical-grade silicon

A vacuum directional solidification with high temperature gradient was performed to prepare low cost solar-grade multicrystalline silicon （mc-Si） directly from metallurgical-grade mc-Si. The microstructure characteristic, grain size, boundary, solid-liquid growth interface, and dislocation structure under different growth conditions were studied. The results show that directionally solidified multicrystalline silicon rods with high density and orientation can be obtained when the solidification rate is below 60 μm/s. The grain size gradually decreases with increasing the solidification rate. The control of obtaining planar solid-liquid interface at high temperature gradient is effective to produce well-aligned columnar grains along the solidification direction. The growth step and twin boundaries are preferred to form in the microstructure due to the faceted growth characteristic of mc-Si. The dislocation distribution is inhomogeneous within crystals and the dislocation density increases with the increase of solidification rate. Furthermore, the crystal growth behavior and dislocation formation mechanism of mc-Si were discussed.

Sunlight loss for femtosecond microstructured silicon with two impurity bands

Black silicon, produced by irradiating the surface of a silicon wafer with femtosecond laser pulses in the presence of a sulfur-bearing gas, is widely believed to be a potential material for efficient multi-intermediate-band silicon solar cells. Taking chalcogen as an example, we analyse the loss of sunlight for silicon with two impurity bands and we find that loss of the sunlight can be minimized to 0.332 when Te^0（0.307 eV） and Te＋（0.411 eV） are doped into microstructured silicon. Finally, problems needed to be resolved in analysing the relationship between conversion efficiency of the ideal four-band silicon solar cell and the position of the introduced two intermediated bands in silicon according to detailed balance theory are pointed out with great emphasis.

Characterization of the nanosized porous structure of black Si solar cells fabricated via a screen printing process

A silicon（Si） surface with a nanosized porous structure was formed via simple wet chemical etching catalyzed by gold（Au） nanoparticles on p-type Cz-Si（100）.The average reflectivity from 300 to 1200 nm was less than 1.5%.Black Si solar cells were then fabricated using a conventional production process.The results reflected the output characteristics of the cells fabricated using different etching depths and emitter dopant profiles.Heavier dopants and shallower etching depths should be adopted to optimize the black Si solar cell output characteristics. The efficiency at the optimized etching time and dopant profile was 12.17%.However,surface passivation and electrode contact due to the nanosized porous surface structure are still obstacles to obtaining high conversion efficiency for the black Si solar cells.

Influence of atomic layer deposition Al_2O_3 nano-layer on the surface passivation of silicon solar cells

A stack of Al2O3/SiNx dual layer was applied for the back side surface passivation of p-type multi-crystalline silicon solar cells, with laser-opened line metal contacts, forming a local aluminum back surface field （local Al-BSF） structure. A slight amount of Al2O3, wrapping around to the front side of the wafer during the thermal atomic layer deposition process, was found to have a negative influence on cell performance. The different process flow was found to lead to a different cell performance, because of the Al2O3 wrapping around the front surface. The best cell performance, with an absolute efficiency gain of about 0.6% compared with the normal full Al-BSF structure solar cell, was achieved when the Al2O3 layer was deposited after the front surface of the wafer had been covered by a SiNx layer. We discuss the possible reasons for this phenomenon, and propose three explanations as the Ag paste, being hindered from firing through the front passivation layer, degraded the SiNx passivation effect and the Al2O3 induced an inversion effect on the front surface. Characterization methods like internal quantum efficiency and contact resistance scanning were used to assist our understanding of the underlying mechanisms.

黑硅与黑硅太阳电池的研究进展

黑硅材料的特殊结构能够极大地降低硅表面的光反射,有效地提高硅基太阳能电池转换效率。本文介绍了国内外黑硅制备技术的进展,黑硅的制备方法主要包括飞秒激光法、化学腐蚀法、反应离子刻蚀法和电化学腐蚀法。还概述了黑硅太阳电池的研究进展,并展望了黑硅及其应用的发展趋势。

圆化处理法制备高效大尺寸多晶黑硅太阳电池

采用金属辅助化学腐蚀法制备了多晶黑硅,并研究了极低浓度NaOH溶液对扩孔后黑硅结构的圆化作用及其对多晶黑硅太阳电池性能的影响。用扫描电镜（Scanning electron microscope,SEM）和量子效率（Quantum efficiency,QE）测试仪对黑硅表面形貌及黑硅电池性能进行了表征。结果表明,利用极低浓度的NaOH圆化扩孔后黑硅的尖端及棱角可以减少表面复合的影响。处理后的黑硅表面孔洞均匀且平滑,黑硅太阳电池400~900nm可见光波段平均反射率为4.15%,批量生产的电池平均转换效率达到17.94%,比常规酸制绒工艺制备的电池平均转换效率提高了0.35%。

硅基太阳电池用黑硅材料的研究进展

介绍了黑硅材料在硅基太阳电池中的广角宽光谱吸收特性、主要制备方法等研究现状,并指出所面临的问题和今后的研究趋势。

高效多晶黑硅电池的产线技术

在产线工艺的基础上，研发金属催化化学刻蚀技术，制备出具有微米／纳米复合绒面结构的多晶黑硅太阳电池。通过对黑硅纳米结构的修正刻蚀，实现电池光学性能和电学性能的同步提高；通过系统的优化，黑硅电池的性能特圳是其短路电流提高rI50～300mA，这主要得益于电池蓝光响应特性的改善。

基于倒金字塔减反射结构的多晶黑硅及其高效太阳电池

采用酸体系的纳米重构(Nano structure rebuilding,NSR)溶液对黑硅纳米结构进行重构,得到不同尺寸的倒金字塔减反射微结构,实现了低成本纳米减反射微结构多晶黑硅(Multicrystalline-black silicon,mc-bSi)太阳电池的量产。先用Ag金属催化腐蚀(Metal assisted chemical etching,MACE)对砂浆切割(Multi wire slurry sawn,MWSS)多晶硅片(Multicrystalline silicon,mc-Si)进行了研究,发现倒金字塔结构的面夹角均为54.7°,且500nm尺寸大小的倒金字塔结构黑硅太阳电池的转换效率达到了18.62%,电池的表面反射率降低至3.29%。研究了Ag/Cu双原子催化腐蚀法对金刚线切割(Diamond wire sawn,DWS)多晶硅片的制绒效果,发现多晶硅片表面金刚线切割痕几乎消失不见,采用倒金字塔尺寸为600nm的DWS片样品制备出了性能最佳的太阳电池,其开路电压Voc为640mV,短路电流密度Jsc为37.35A/cm2,填充因子FF为79.91%,最高效率为19.10%,高于同结构的MWSS多晶黑硅太阳电池。

黑硅制备及应用进展

黑硅作为一种新型低反射率的硅材料,有良好的广谱吸收特性,在光电领域将有很好的应用前景。概括地介绍了黑硅的各种制备方法(飞秒激光扫描、化学腐蚀法和等离子体处理),以及黑硅在太阳能电池、光电二极管、场发射、太赫兹发射等领域的应用。

多晶黑硅材料及其太阳电池应用研究

利用等离子体浸没离子注入技术（PⅢ）成功制备了多晶黑硅材料。通过原子力显微镜（AFM）观测分析多晶黑硅材料的表面形貌和粗糙度，黑硅材料表面呈小山峰结构，表面粗糙度约为50nm。利用紫外．可见一红外分光光度计测量黑硅的反射率，结果表明黑硅材料在300—1100nm的平均反射率为7．9％，远低于酸制绒硅片反射率。利用制备的多晶黑硅材料制备太阳电池器件，其光电转换效率可达15．88％，开路电压为605mV，短路电流密度为33．7mA／cm2。最后研究了扩散工艺对黑硅太阳电池性能的影响。

基于BiFeO_3/ITO复合膜表面钝化的黑硅太阳电池性能研究

采用金属银辅助化学刻蚀法在制绒的硅片表面刻蚀纳米孔形成微纳米双层结构,以期获得高吸收率的太阳能电池用黑硅材料.鉴于微纳米结构会在晶硅表面引入大量的载流子复合中心,利用磁控溅射技术在黑硅太阳电池表面制备了BiFeO_3/ITO复合膜,并对其表面性能和优化效果进行了探索.实验制备的具有微纳米双层结构的黑硅纳米线长约180—320 nm,在300—1000 nm波长范围内入射光反射率均在5%以下.沉积BiFeO_3/ITO复合薄膜后的黑硅太阳能电池反射率略有提高,但仍然具有较强的光吸收性能;采用BiFeO_3/ITO复合膜的黑硅太阳能电池开路电压和短路电流密度分别由最初的0.61 V和28.42 mA/cm^2提升至0.68 V和34.57 mA/cm^2,相应电池的光电转化效率由13.3%上升至16.8%.电池综合性能的改善主要是因为沉积BiFeO_3/ITO复合膜提高了电池光生载流子的有效分离,从而增强了黑硅太阳电池短波区域的光谱响应,表明具有自发极化性能的BiFeO_3薄膜对黑硅太阳能电池的表面性能可起到较好的优化作用.

超薄柔性黑硅太阳电池研究

通过PC1D模拟软件分析了硅片厚度对电池性能的影响,结果表明:随着硅片厚度减薄,硅片对光的吸收效率逐渐减弱。为了强化硅片表面的陷光能力,弥补硅衬底减薄对光吸收的损失,采用化学刻蚀法制备获得了具有纳米绒面的黑硅太阳电池。通过模拟对比厚度为80μm的黑硅电池和常规电池性能,结果表明:硅纳米长度为0.85μm的黑硅表面平均反射率从常规制绒的12.65%降低至4.06%,黑硅电池短路电流从常规的8.693 A增加至9.104 A,黑硅电池效率从常规的18.87%提高至19.74%。

太阳电池用非晶碳薄膜在黑硅衬底上的生长

利用微波等离子体化学气相沉积(MPCVD)法在黑硅和抛光单晶硅片衬底上生长非晶碳薄膜,其中变量为CH4流量,分别为10sccm、14sccm、18sccm、22sccm、26sccm。通过扫描电子显微镜(SEM)、X射线衍射分析(XRD)、原子力显微镜(AFM)、拉曼光谱表征了非晶碳薄膜的结构和形貌特征。结果表明,在650℃时随着CH4流量的逐渐增加,在平整的非晶碳薄膜上C-C的sp2相团簇颗粒的直径逐渐变大。AFM测试结果显示,非晶碳薄膜表面的平均粗糙度(Ra)为0.494nm。

多晶黑硅表面微结构对电池效率的影响

采用Ag离子辅助化学刻蚀法制备了多晶黑硅薄片,使用NaOH溶液处理多晶黑硅表面,增大其表面纳米孔直径,使SiN_x薄膜能够均匀覆盖整个黑硅表面,提高黑硅的钝化效果,进而提高多晶黑硅电池光电转化效率。通过反射谱仪、扫描电子显微镜(SEM)、太阳电池测试系统等测试和表征不同扩孔时间对多晶黑硅各方面性能的影响。结果表明:未被NaOH扩孔处理的多晶黑硅的反射率最低,为5.03%,多晶黑硅太阳电池的光电转化效率为16.51%。当多晶黑硅被NaOH腐蚀40 s时,反射率为10.01%,电池的效率为18.00%,比普通多晶硅太阳电池的效率高2.19%,比未被扩孔处理的多晶黑硅太阳电池的效率高1.49%。

微纳混合结构黑硅的制备及其关键工艺技术讨论

黑硅是一种能大幅提高器件光电转换效率的新型电子材料,微纳混合结构黑硅是一种比普通黑硅材料更高效的新型黑硅材料,如何制备出大面积、形貌特征好、表面洁净度高的黑硅材料是制备高效的黑硅太阳能电池的前提。首先,利用湿法腐蚀方法,通过设计合适的反应固体装置和良好的工艺控制手段,在金字塔硅表面制备了大面积的微纳混合结构黑硅;然后,对其制备的关键工艺技术进行了研究讨论。实验结果表明,该方法制备的微纳混合结构黑硅具有形貌特征好、表面洁净度高和低表面反射率等特征。有效去除表面银沉积物后,该黑硅在300~1 100 nm范围内的加权平均反射率低至4.06%。该制备工艺方法适用于大面积高效微纳混合结构黑硅的规模制备,在高效黑硅太阳能电池领域具有重要的应用价值。

晶体硅表面Ag纳米颗粒形貌控制及其对黑硅性能的影响

采用湿法化学法在太阳能级Si（100）表面沉积Ag纳米颗粒，并对Ag颗粒进行了退火处理。利用扫描电子显微镜研究了不同沉积时间及退火工艺对硅片表面Ag纳米颗粒形貌的影响规律。在此基础上采用退火前后的鲰纳米颗粒辅助化学腐蚀法制备了黑硅减反射结构，并用扫描电子显微镜观察了所制备黑硅的微结构，用紫外．可见分光光度计研究了所制备黑硅的反射率。研究表明，制备的Ag颗粒为不规则片状结构，并且随鲰沉积时间的延长，Ag颗粒逐渐长大。通过对样品退火处理，Ag颗粒收缩成球状纳米颗粒。利用未退火的舷颗粒制备的黑硅呈不规则纳米线状微结构，在300～1100nm范围内平均反射率为2．7％；而利用退火后球状Ag纳米颗粒制备的黑硅则呈多孔状微结构，同样波长范围内平均反射率为14．2％。