The effect of etching time of porous silicon on solar cell performance

Porous silicon (PS) layers based on crystalline silicon (c-Si) n-type wafers with (1 0 0) orientation were prepared using electrochemical etching process at different etching times. The optimal etching time for fabricating the PS layers is 20 min. Nanopores were produced on the PS layer with an average diameter of 5.7 nm. These increased the porosity to 91%. The reduction in the average crystallite size was confirmed by an increase in the broadening of the FWHM as estimated from XRD measurements. The photoluminescence (PL) peaks intensities increased with increasing porosity and showed a greater blue shift in luminescence. Stronger Raman spectral intensity was observed, which shifted and broadened to a lower wave numbers of 514.5 cm⁻¹ as a function of etching time. The lowest effective reflectance of the PS layers was obtained at 20 min etching time. The PS exhibited excellent light-trapping at wavelengths ranging from 400 to 1000 nm. The fabrication of the solar cells based on the PS anti-reflection coating (ARC) layers achieved its highest efficiency at 15.50% at 20 min etching time. The I-V characteristics were studied under 100 mW/cm² illumination conditions.     

Fabrication and characterization of zinc oxide anti-reflective coating on flexible thin film microcrystalline silicon solar cell

This paper studies the fabrication and characterization of 80 nm zinc oxide anti-reflective coating (ARC) on flexible 1.3 μm thin film microcrystalline silicon (μc-Si) solar cell. High resolution X-ray diffraction (HR-XRD) shows a c-axis oriented ZnO (0 0 2) peak (hexagonal crystal structure) at 34.3° with full width at half maximum (FWHM) of 0.3936°. Atomic force microscope (AFM) measures high surface roughness root-mean-square (RMS) of the layer (50.76 nm) which suggests scattering of the incident light at the front surface of the solar cell. UV–vis spectrophotometer illustrates that ZnO ARC has optical transmittance of more than 80% in the visible and infra-red (IR) regions and corresponds to band gap (E_g) of 3.3 eV as derived from Tauc equation. Inclusion of ZnO ARC successfully suppresses surface reflectance from the cell to 2% (at 600 nm) due to refractive index grading between the Si and the ZnO besides quarter-wavelength (λ/4) destructive interference effect. The reduced reflectance and effective scattering effect of the incident light at the front side of the cell are believed to be the reasons why short-circuit current (I_sc) and efficiency (η) of the cell improve.     

In_2O_3:Sn中间层改善B掺杂ZnO薄膜的性能及其应用研究

金属有机化学气相沉积(MOCVD)法生长的掺硼氧化锌(BZO)薄膜,具有天然的"类金字塔"绒面结构,作为硅基薄膜太阳电池的前电极具有良好的陷光效果.但直接获得的BZO薄膜表面形貌过于尖锐,影响后续硅基薄膜材料生长质量及太阳电池的光电转换效率.本文设计了以一层超薄In2O3:Sn(ITO)薄膜(～4 nm厚度)作为中间层的多层膜,并通过对顶层BZO薄膜的厚度调制,改善BZO薄膜的表面特性,薄膜结构为:glass/底层BZO/ITO/顶层BZO.合适厚度的顶层BZO薄膜有助于获得类似"菜花状"形貌特征,尖锐的表面趋于"柔和",而较厚的顶层BZO薄膜仍然保持"类金字塔状"结构."柔和"的BZO薄膜表面结构有助于提高后续生长薄膜电池的结晶质量.将获得的新型"三明治"结构多层膜应用于p-i-n型氢化微晶硅(μc-Si:H)薄膜太阳电池,相比传统的BZO薄膜,电池的量子效率QE在500—800 nm波长范围提高了～10%,并且电池的Jsc和Voc均有所提高.     

高压射频等离子体增强化学气相沉积制备高效率硅薄膜电池的若干关键问题研究

报道了采用高压射频等离子体增强化学气相沉积(RF-PECVD) 制备高效率单结微晶硅电池和非晶硅/微晶硅叠层电池时几个关键问题的研究结果, 主要包括: 1)器件质量级本征微晶硅材料工艺窗口的确定及其结构和光电性能表征; 2)孵化层的形成机理以及减小孵化层的有效方法; 3)氢稀释调制技术对本征层晶化率分布及其对提高电池性能的作用; 4)高电导、高晶化率的微晶硅p型窗口层材料的获得, 及其对减小微晶硅电池p/i界面孵化层厚度和提高电池性能的作用等. 在解决上述问题的基础上, 采用高压RF-PECVD制备的单结微晶硅电池效率达8.16%, 非晶硅/微晶硅叠层电池效率11.61%.     

Nanocrystalline ZnO film deposited by ultrasonic spray on textured silicon substrate as an anti-reflection coating layer

A ZnO thin film was successfully synthesized on glass, flat surface and textured silicon substrates by chemical spray deposition. The textured silicon substrate was carried out using two solutions (NaOH/IPA and Na₂CO₃). Textured with Na₂CO₃ solution, the sample surface exhibits uniform pyramids with an average height of 5 μm. The properties and morphology of ZnO films were investigated. X-ray diffraction (XRD) spectra revealed a preferred orientation of the ZnO nanocrystalline film along the c-axis where the low value of the tensile strain 0.26% was obtained. SEM images show that all films display a granular, polycrystalline morphology. The morphology of the ZnO layers depends dramatically on the substrate used and follows the contours of the pyramids on the substrate surface. The average reflectance of the textured surface was found to be around 13% and it decreases dramatically to 2.57% after deposition of a ZnO antireflection coating. FT-IR peaks arising from the bonding between Zn–O are clearly represented using a silicon textured surface. A very intense photoluminescence (PL) emission peak is observed for ZnO/textured Si, revealing the good quality of the layer. The PL peak at 380.5 nm (UV emission) and the high-intensity PL peak at 427.5 nm are observed and a high luminescence occurs when using a textured Si substrate.     

Metal oxide buffer layer for improving performance of polymer solar cells

We report the application of aluminum doped ZnO (ZnO:Al) layer as a buffer on ITO glass for fabrication of non-inverted polymer solar cells. The ZnO:Al thin film was deposited using DC magnetron sputtering, with the thickness being varied from 23 to 100 nm. The devices showed most discernible improvements in their efficiencies when a thin layer of ZnO:Al film of thickness ∼40 nm was introduced. The observed enhancement in short circuit current density and open circuit voltage is likely attributed to the role of the ZnO:Al film as an optical tuner and an interfacial diffusion barrier. The result suggests that a metal oxide layer inserted between ITO and polymer layers can be a route for improving both efficiency and stability of polymer solar cells.     

Efficient antireflective downconversion Er3+ doped ZnO/Si thin film

This study is an investigation of the potential of Er doped ZnO thin films for downconversion photons and an antireflective layer when placed in front of the silicon solar cells. We optimized the properties of the film with appropriate deposition conditions on Si (111) substrate by aerosol assisted chemical vapor deposition (AACVD) process. An enhancement of both crystallinity and optical response was achieved in the case of film doped with 2.504 at.% Er³⁺. A low reflectance and high refractive index of the film were obtained at around 632 nm. Downconversion process was also reached for this film under visible excitation to near-infrared (NIR) 980 nm photons useful for Si solar cell.     

Low-porosity porous silicon nanostructures on monocrystalline silicon solar cells

In this work we present a study of low-porosity porous silicon (PS) nanostructures stain etched on monocrystalline silicon solar cells. The PS layers reduce the reflectance, improve the diffusion of dopants by rapid thermal processes, and increase the homogeneity of the sheet resistance. Some samples were subjected to chemical oxidation in HNO₃ to reduce the porosity of the surface layer. After the diffusion process, deposition of a SiN_x antireflection layer, and screen printing of the samples, an efficiency of 15.5% is obtained for low-porosity PS solar cells, compared with an efficiency of 10.0% for standard PS cells and 14.9% for the reference Cz cells.     

Influence of H2O/DEZ ratio on LPCVD ZnO:B films for application in a-Si:H/μc-Si:H tandem solar cells

In this study, boron doped zinc oxide (ZnO:B) films were prepared at different water to diethyl zinc (H₂O/DEZ) flow ratios from 0.6 to 1.4 by a low pressure chemical vapor deposition (LPCVD) technique. It is found that the morphology of ZnO:B films varies from small leaf-like to pyramidal surface structures with the increasing H₂O/DEZ flow ratio. The rough ZnO:B films deposited at a relatively H₂O/DEZ flow ratio such as 1.2 or 1.4 show a high haze value of up to 28 % at 600 nm and $\mathrm{a} (11\overline{2}0)$ preferential crystallographic orientation. All ZnO:B films were applied in hydrogenated amorphous silicon/microcrystalline silicon tandem solar cells (a-Si:H/μc-Si:H) as front electrodes. The efficiency of the solar cells increases with the increasing H₂O/DEZ flow ratio, which is attributed to a high spectral response mainly in the long-wavelength range and the consequent enhancement of short-circuit current. A high-efficiency a-Si:H/μc-Si:H tandem solar cell of 10 % was achieved. The H₂O/DEZ ratio is an important process parameter to tune the material properties of LPCVD ZnO:B films and the performances of corresponding silicon thin film solar cells.     

Fabrication and characterization of nanocrystalline n-CdO/p-Si as a solar cell

A nanocrystalline CdO/Si solar cell was fabricated via deposition of a CdO thin film on p-type silicon substrate with approximately 370 nm thickness using solid–vapor deposition for Cd powder at 1274 K with argon and oxygen flow. Scanning electron microscopy revealed that the product was a Cadmium oxide nanocrystalline. X-ray diffraction and energy dispersive X-ray analysis were used to characterize the structural properties of the solar cell. The nanocrystalline thin film had a grain size of 38 nm. The solar cell yielded a minimum effective reflectance that exhibited excellent light-trapping at wavelengths ranging from 400 to 1000 nm. Photoluminescence spectroscopy was conducted to investigate the optical properties. The direct band gap energy of the nanocrystalline CdO thin film was 2.46 eV. CdO/Si solar cell photovoltaic properties were examined under 100 mW/cm² solar radiation. The cell showed an open circuit voltage (V_oc) of 457 mV, a short-circuit current density (J_sc) of 18.5 mA/cm², a fill factor (FF) of 0.652, and a conversion efficiency (η) of 5.51%.     

An effective reflectance method for designing broadband antireflection films coupled with solar cells

The solar spectrum covers a broad wavelength range, which requires that antireflection coating (ARC) is effective over a relatively wide wavelength range for more incident light coming into the cell. In this paper, we present two methods to measure the composite reflection of SiO₂/ZnS double-layer ARC in the wavelength ranges of 300-870 nm (dual-junction) and 300-1850 nm (triple-junction), under the solar spectrum AM0. In order to give sufficient consideration to the ARC coupled with the window layer and the dispersion effect of the refractive index of each layer, we use multi-dimensional matrix data for reliable simulation. A comparison between the results obtained from the weighted-average reflectance (WAR) method commonly used and that from the effective-average reflectance (EAR) method introduced here shows that the optimized ARC through minimizing the effective-average reflectance is convenient and available.     

非晶硅太阳电池BZO/p-a-SiC:H接触特性改善的研究

采用重掺杂的p型微晶硅来改善前电极掺硼氧化锌 (ZnO:B) 和窗口层p型非晶硅碳 (p-a-SiC) 之间的非欧姆接触特性. 通过优化插入层p型微晶硅的沉积参数 (氢稀释比H₂/SiH₄、硼掺杂比B₂H₆/SiH₄) 获得了较薄厚度下 (20 nm) 暗电导率高达4.2 S/cm的p型微晶硅材料. 在本征层厚度约为150 nm, 仅采用Al背反射电极的情况下,获得了效率6.37%的非晶硅顶电池(V_oc=911 mV, FF=71.7%, J_sc=9.73 mA/cm²), 开路电压V_oc和填充因子FF均较无插入层的电池有大幅提升. 关键词： 氧化锌 p型微晶硅 非晶硅顶电池 非欧姆接触     

Influence of the semiconductor/metal rear contact on the performance of n(a-Si:H)/i(a-Si:H)/p(c-Si) heterojunction solar cells

The aim of this work is to analyze on the results of using of Al/Ag layer as a rear contact to improve the performance of heterojunction silicon solar cells. An analytical method is presented to extract the physical parameters of the equivalent circuit. These parameters are extracted to simulate the I(V) characteristic of heterojunction silicon solar cells, with Al and Al/Ag rear-metal contact. A good agreement between our analytical method and experimental measurement of electrical characteristics is obtained which show clearly how the Al/Ag rear contact can improve the characteristics of silicon solar cells. The influence of the rear-metal contact on the performance of the c-Si(p)-based bifacial HIT solar cell, i.e., the ZnO/Al/a-Si:H(n)/a-Si:H(i)/c-Si(p)/metal solar cell, is investigated in detail by computer simulation using the AFORS-HET software. Accordingly, the design optimization of the bifacial HIT solar cells on c-Si(p) substrates is provided. These simulation show an optimal conversion efficiency of 23% when the rear-metal contact is perfectly ohmic.     

An effective reflectance method for designing broadband antireflection films coupled with solar cells

The solar spectrum covers a broad wavelength range,which requires that antireflection coating(ARC) is effective over a relatively wide wavelength range for more incident light coming into the cell.In this paper,we present two methods to measure the composite reflection of SiO2/ZnS double-layer ARC in the wavelength ranges of 300-870 nm(dualjunction) and 300-1850 nm(triple-junction),under the solar spectrum AM0.In order to give sufficient consideration to the ARC coupled with the window layer and the dispersion effect of the refractive index of each layer,we use multidimensional matrix data for reliable simulation.A comparison between the results obtained from the weighted-average reflectance(WAR) method commonly used and that from the effective-average reflectance(EAR) method introduced here shows that the optimized ARC through minimizing the effective-average reflectance is convenient and available.     

椭圆偏振光谱表征单晶硅衬底上生长的非晶硅和外延硅薄膜

本文采用射频等离子体增强化学气相沉积(rf-PECVD)技术在单晶硅衬底上沉积了两个系列的硅薄膜. 通过对样品进行固定角度椭圆偏振测试, 结果表明第一个系列硅薄膜为非晶硅, 形成了突变的a-Si:H/c-Si异质结构, 此结构在HIT电池中有利于形成好的界面特性, 对于非晶硅薄膜采用通常的Tauc-Lorentz摇摆模型(Genosc)拟合结果很好; 第二个系列硅薄膜为外延硅, 对于外延硅薄膜, 随着膜厚增加晶化率降低, 当外延硅薄膜厚度为46 nm时开始非晶硅生长. 对于外延硅通常采用EMA模型(即将硅薄膜体层看成由非晶硅和c-Si构成的混合层)拟合结果较好, 当硅薄膜中出现非晶硅生长时, 将体层分成混合层和非晶硅两层, 采用三层模型拟合结果很好. 本文证实了椭偏光谱分析采用不同的模型可对单晶硅衬底上不同结构的硅薄膜进行有效表征.     

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.     

Optical Analysis of Nanocrystalline ZnO Films Coated on Porous Silicon by Radio Frequency (RF) Magnetron Sputtering

Zinc oxide thin films have been deposited onto porous silicon (PSi) substrates at high growth rates by radio frequency (RF) sputtering using a ZnO target. The advantages of the porous Si template are economical and it provides a rigid structural material. Porous silicon is applied as an intermediate layer between silicon and ZnO films and it contributed a large area composed of an array of voids. The nanoporous silicon samples were adapted by photo electrochemical (PEC) etching technique on n-type silicon wafer with (111) and (100) orientation. Micro-Raman and photoluminescence (PL) spectroscopy are powerful and non-destructive optical tools to study vibrational and optical properties of ZnO nanostructures. Both the Raman and PL measurements were also operated at room temperature. Micro-Raman results showed that the A₁(LO) of hexagonal ZnO/Si(111) and ZnO/Si(100) have been observed at around 522 and 530 cm^–1, re- spectively. PL spectra peaks are distinctly apparent at 366 and 368 cm^–1 for ZnO film grown on porous Si(111) and Si(100) substrates, respectively. The peak luminescence energy in nanocrystalline ZnO on porous silicon is blue-shifted with regard to that in bulk ZnO (381 nm). The Raman and PL spectra pointed to oxygen vacancies or Zn interstitials which are responsible for the green emission in the nanocrystalline ZnO.     

Top PV market solar cells 2016

Photovoltaic (PV) technologies which play a role in PV market are divided into basic two types: wafer-based (1st generation PV) and thin-film cell (2nd generation PV). To the first category belong mainly crystalline silicon (c-Si) cells (both mono- and multi-crystalline). In 2015 around 90% of the solar market belonged to crystalline silicon. To the 2nd generation solar cells belongs thin film amorphous silicon (a-Si) or a combination of amorphous and microcrystalline silicon (a-Si/μc-Si), compound semiconductor cadmium telluride (CdTe), compound semiconductor made of copper, indium, gallium and selenium (CIS or CIGS) and III–V materials. The PV market for thin film technology is dominated by CdTe and CIGS solar cells. Thin film solar cells’ share for all thin film technologies was only 10% in 2015. New emerging technologies, called 3rd generation solar cells, remain the subject of extensive R&D studies but have not been used in the PV market, so far.In this review the best laboratory 1st and 2nd generation solar cells that were recently achieved are described. The scheme of the layer structure and energy band diagrams will be analyzed in order to explain the boost of their efficiency with reference to the earlier standard designs.     

ps-laser scribing of CIGS films at different wavelengths

Continuous growth of the thin-film electronics market stimulates the development of versatile technologies for large-scale patterning of thin-film materials on rigid and flexible substrates, and laser technologies are a promising method to accomplish the scribing processes. Lasers with picosecond pulse duration were applied in scribing of complex multilayered CuIn _x Ga_(1−x)Se₂ (CIGS) solar cells deposited on a polyimide substrate. The ablative properties of the films were examined as a function of the wavelength of laser radiation, pulse energy, and the irradiation dose. The selective removal of ITO and CIGS layers was achieved with 355 nm irradiation without any significant damage to the underlying layers in the ITO/CIGS/Mo/PI solar cell system. The 355 nm wavelength was also found to be favorable for scribing of absorber layer in a ZnO/CIGS/Mo/PI solar cell system. 266 nm radiation significantly modified the film structure due to high absorption. Extensive melt formation in the CIGS layer was found when 532 nm radiation was applied, though the trenches were smooth and crack-free.     

Superstrate p-i-n a-Si:H solar cells on textured ZnO:Al front transparent conduction oxide

Superstrate p-i-n amorphous silicon thin-film (a-Si:H) solar cells are prepared on SnO₂:F and ZnO:Al transparent conducting oxides (TCOs) in order to see the effect of TCO/p-layers on a-Si:H solar cell operation. The solar cells prepared on textured ZnO:Al have higher open circuit voltage V_oc than cells prepared on SnO₂:F. The presence of a thin microcrystalline p-type silicon layer (μc-Si:H) between ZnO:Al and p a-SiC:H plays a major role by causing an improvement in the fill factor as well as in V_oc of a-Si:H solar cells prepared on ZnO:Al TCO. Without any treatment of the p-i interface, we could obtain a high V_oc of 994 mV while keeping the fill factor (72.7%) and short circuit current density J_sc at the same level as for the cells on SnO₂:F TCO. This high V_oc value can be attributed to modification in the current transport in this region due to creation of a potential barrier.