Design Analysis of Heterojunction Solar Cells with Aligned AZO Nanorods Embedded in p-type Si wafer

Higher price-per-watt of silicon (Si) solar cells is still the main bottleneck in their widespread use for power generation due to their expensive manufacturing process. The n-type zinc oxide (n-ZnO) and p-type Si (p-Si) based single heterojunction solar cell is one of the several methods being tried to replace conventional Si single homojunction solar cell technology. In this work, we have explored the possibility of producing photovoltaic materials by employing RF sputtering and hydrothermal technologies. Conductivity of ZnO nanorods has been increased by aluminium (Al) doping. The advantages of using Al doped ZnO (AZO) nanorods (NRs) have been investigated. The integrated reflectance (IR) has been found to be only ~2.86%. Hence, the short circuit current density (Jsc) has been increased by minimizing the reflection loss of solar cells. AZO NR array have been developed over several large area (3″ × 3″) textured p-Si wafers to confirm the repeatability. The maximum efficiency of AZO NRs/Si solar cell of 0.8 cm2 area has been found to be 6.25% for textured p-type Si wafer which is much higher than reported hitherto for this type of solar cell. A simple, low temperature, low cost procedure is thus being proposed, which has the potential of attaining lower cost of production of heterojunction silicon solar cells.     

Hybrid solar cells from MDMO-PPV and silicon nanocrystals

Solution-processed bulk heterojunction solar cells from silicon nanocrystals (Si NCs) and poly(3-hexylthiophene) (P3HT) have shown promising power conversion efficiencies. Here we report on an attempt to enhance the performance of Si NC-polymer hybrid solar cells by using poly[2-methoxy-5-(3',7'-dimethyloctyloxy)-1,4-phenylenevinylene] (MDMO-PPV) as a hole conductor, which is expected to yield a higher open circuit voltage than P3HT due to its lower highest occupied molecular orbital (HOMO). Bulk heterojunction solar cells consisting of 3-5 nm silicon nanocrystals (Si NCs) and poly[2-methoxy-5-(3',7'-dimethyloctyloxy)-1,4-phenylenevinylene] (MDMO-PPV) have been fabricated. The properties of the hybrid Si NC/MDMO-PPV devices were studied as a function of the Si NC/MDMO-PPV weight ratio. Cells of 58 wt% 3-5 nm Si NCs showed the best overall performance under simulated one-sun AM 1.5 global illumination (100 mW cm(-2)). Compared to composite films of Si NCs and poly(3-hexylthiophene), we indeed observed an improved open circuit voltage but a lower power conversion efficiency from the Si NC/MDMO-PPV devices. The lower efficiency of Si NC/MDMO-PPV is correlated to the lower hole mobility and narrower absorption spectrum of MDMO-PPV compared to P3HT.     

Impacts of Post-metallisation Processes on the Electrical and Photovoltaic Properties of Si Quantum Dot Solar Cells

As an important step towards the realisation of silicon-based tandem solar cells using silicon quantum dots embedded in a silicon dioxide (SiO₂) matrix, single-junction silicon quantum dot (Si QD) solar cells on quartz substrates have been fabricated. The total thickness of the solar cell material is 420 nm. The cells contain 4 nm diameter Si quantum dots. The impacts of post-metallisation treatments such as phosphoric acid (H₃PO₄) etching, nitrogen (N₂) gas anneal and forming gas (Ar: H₂) anneal on the cells’ electrical and photovoltaic properties are investigated. The Si QD solar cells studied in this work have achieved an open circuit voltage of 410 mV after various processes. Parameters extracted from dark I–V, light I–V and circular transfer length measurement (CTLM) suggest limiting mechanism in the Si QD solar cell operation and possible approaches for further improvement.     

TiO2光诱导制备超小绒面太阳电池的性能

介绍了一种新型 TiO2光诱导制备超小绒面的方法。结果表示,在光照条件下利用 TiO2的光催化特性加快了腐蚀液与 Si 的反应速度,使得表面反射率能够由原来的 30%降低为现在的 5%,提高了陷光作用。该方法制备的太阳电池表面复合现象仍然较为严重,但有所改善。在最终的太阳电池上开路电压 Voc和短路电流密度 Jsc都有较为明显的提高。同时也证明了利用 TiO2同样可以在高阻的抛光 Si 源片上制备出较为均匀的绒面,虽然 TiO2光诱导制备的超小绒面没有 Ag 诱导的纳米柱绒面那么低的反射率,但是避免了引进金属杂质等问题。因此,TiO2光诱导制绒作为制备超小绒面太阳电池的新方法有着良好的发展前景。     

Nanorainforest solar cells based on multi-junction hierarchical p-Si/n-CdS/n-ZnO nanoheterostructures

Solar cells based on one-dimensional nanostructures have recently emerged as one of the most promising candidates to achieve high-efficiency solar energy conversion due to their reduced optical reflection, enhanced light absorption, and enhanced carrier collection. In nature, the rainforest, consisting of several stereo layers of vegetation, is the highest solar-energy-using ecosystem. Herein, we gave an imitation of the rainforest configuration in nanostructure-based solar cell design. Novel multi-layer nanorainforest solar cells based on p-Si nanopillar array/n-CdS nanoparticles/n-ZnO nanowire array heterostructures were achieved via a highly accessible, reproducible and controllable fabrication process. By choosing materials with appropriate bandgaps, an efficient light absorption and enhanced light harvesting were achieved due to the wide range of the solar spectrum covered. Si nanopillar arrays were introduced as direct conduction pathways for photon-generated charges' efficient collection and transport. The unique strategy using PMMA as a void-filling material to obtain a continuous, uniform and low resistance front electrode has significantly improved the overall light conversion efficiency by two orders of magnitude. These results demonstrate that nanorainforest solar cells, along with wafer-scale, low-cost and easily controlled processing, open up substantial opportunities for nanostructure photovoltaic devices.     

An Efficient Dual‐Mode Solar Spectral Modification for c‐Si Solar Cells in Tm3+/Yb3+ Codoped Tellurite Glasses

A series of Tm³⁺/Yb³⁺ codoped tellurite glasses, which demonstrate an interesting dual‐mode solar spectral converting for c‐Si solar cells, have been successfully prepared by conventional high‐temperature melt‐quenching technique. The photoluminescence (PL), photoluminescence excitation (PLE) spectra along with the decay curves have been studied systematically. The results indicate that the transparent glasses show two distinguishable near infrared (NIR) spectral converting behaviors, that is, quantum cutting (QC) and downshifting (DS) processes, sensitized by narrow f–f transition absorption of Tm³⁺:³H₆ → ¹G₄ at 465 nm and broad absorption band due to charge‐transfer state (CTS) of Yb³⁺‐O^2? at 320 nm, respectively. The Tm³⁺/Yb³⁺ codoped tellurite glasses convert ultraviolet (240–400 nm) and blue (450–490 nm) photons into NIR (920–1100 nm) ones, which well match the optimal spectral response of silicon (Si) solar cells. The prepared tellurite glass can be potentially utilized as spectral converter to improve the photovoltaic conversion of c‐Si solar cells. The dual‐mode solar spectrum converting material might explore a novel approach to realize UV‐Vis to NIR downconversion for Si solar cells application.     

Substantial influence on solar energy harnessing ability by geometries of ordered Si nanowire array

The reflectance of the controlled periodic Si nanowire (NW) arrays is systematically explored, which characterizes the influence on the solar energy harnessing ability by the geometries of the NW. A unique dependence of the reflectance of the Si NW array on the diameter, the height, and the bending of the NW are disclosed. The solar energy loss caused by the reflection of the Si NW array exhibits the minimum for the NW with intermediate diameter and length. A plane-wave-based transfer-matrix method (TMM) simulation is performed, which is well consistent with the experimental results. Our results demonstrate the design principle to optimize the Si NW arrays for high-efficiency solar cells.

PACS

81.07.-b; 78.67.-n; 81.16.-c     

Fabrication and characterization of silicon wire solar cells having ZnO nanorod antireflection coating on Al-doped ZnO seed layer

In this study, we have fabricated and characterized the silicon [Si] wire solar cells with conformal ZnO nanorod antireflection coating [ARC] grown on a Al-doped ZnO [AZO] seed layer. Vertically aligned Si wire arrays were fabricated by electrochemical etching and, the p-n junction was prepared by spin-on dopant diffusion method. Hydrothermal growth of the ZnO nanorods was followed by AZO film deposition on high aspect ratio Si microwire arrays by atomic layer deposition [ALD]. The introduction of an ALD-deposited AZO film on Si wire arrays not only helps to create the ZnO nanorod arrays, but also has a strong impact on the reduction of surface recombination. The reflectance spectra show that ZnO nanorods were used as an efficient ARC to enhance light absorption by multiple scattering. Also, from the current-voltage results, we found that the combination of the AZO film and ZnO nanorods on Si wire solar cells leads to an increased power conversion efficiency by more than 27% compared to the cells without it.     

薄膜太阳能电池研究进展

薄膜太阳能电池是缓解能源危机的新型光伏器件。综述了硅基薄膜太阳能电池、CdTe薄膜太阳能电池、CIS（CIGS）薄膜太阳能电池、TiO2薄膜太阳能电池、ZnO薄膜太阳能电池和有机薄膜太阳能电池的研究现状,展望了太阳能电池的发展趋势。     

High-efficiency Silicon Solar Cells: A Review

Over the past few decades, crystalline silicon solar cells have been extensively studied due to their high efficiency, high reliability, and low cost. In addition, these types of cells lead the industry and account for more than half of the market. For the foreseeable future, Si will still be a critical material for photovoltaic devices in the solar cell industry. In this paper, we discuss key issues, cell concepts, and the status of recent high-efficiency crystalline silicon solar cells.     

Optical simulations of P3HT/Si nanowire array hybrid solar cells

An optical simulation of poly(3-hexylthiophene) (P3HT)/Si nanowire array (NWA) hybrid solar cells was investigated to evaluate the optical design requirements of the system by using finite-difference time-domain (FDTD) method. Steady improvement of light absorption was obtained with increased P3HT coating shell thickness from 0 to 80 nm on Si NWA. Further increasing the thickness caused dramatic decrease of the light absorption. Combined with the analysis of ultimate photocurrents, an optimum geometric structure with a coating P3HT thickness of 80 nm was proposed. At this structure, the hybrid solar cells show the most efficient light absorption. The optimization of the geometric structure and further understanding of the optical characteristics may contribute to the development for the practical experiment of the promising hybrid solar cells.     

Silicon Solar Cell with Nanoporous Structure Formed on a Textured Surface

A nanoporous silicon (Si) surface was formed on monocrystalline silicon solar cells by electrochemical etching. The galvanostatic mode was applied to conventional n–p–p⁺ solar cells, which were fabricated by pyramidal texturing, phosphorous diffusion, screen-printing, rapid thermal firing, and laser isolation (effective area of 144.7 cm²). Without an additional antireflection layer such as SiN _x , the anodic reaction of the Si wafer could provide uniform porous layers on a pyramidal surface (111) with relatively low reflectance, and it would improve the photovoltaic performance.     

Periodic nano/micro-hole array silicon solar cell

In this study, we applied a metal catalyst etching method to fabricate a nano/microhole array on a Si substrate for application in solar cells. In addition, the surface of an undesigned area was etched because of the attachment of metal nanoparticles that is dissociated in a solution. The nano/microhole array exhibited low specular reflectance (<1%) without antireflection coating because of its rough surface. The solar spectrum related total reflection was approximately 9%. A fabricated solar cell with a 40-μm hole spacing exhibited an efficiency of 9.02%. Comparing to the solar cell made by polished Si, the external quantum efficiency for solar cell with 30 s etching time was increased by 16.7%.     

Recent Progress of Innovative Perovskite Hybrid Solar Cells

Recently, innovative perovskite hybrid solar cells have attracted great interest in solar cell research fields, such as dye-sensitized solar cells, organic photovoltaics, thin-film solar cells, and silicon solar cells, because their device efficiencies are gradually approaching those of crystalline Si solar cells, and they can be fabricated by cheap low-temperature solution processes. Here, we review the recent progress of innovative perovskite hybrid solar cells. The introduction includes the general concerns about solar cells and why we need innovative solar cells. The second part explains the structure and the material properties of hybrid perovskite materials. We focus on why the hybrid perovskite materials can exhibit excellent solar cell properties, such as high open-circuit voltage. The third part introduces recent progress in innovative perovskite hybrid solar cells, in terms of device architecture and deposition methods for dense perovskite thin films with full surface coverage. The device architecture is important in attaining high power conversion efficiency; the device operating mechanism is dependent on the device structure; and the pinhole-free dense perovskite thin films with full surface coverage are crucial for achieving high efficiency. Finally, we summarize the recent progress in perovskite hybrid solar cells, and the issues to be solved, in the summary and outlook section.     

Si/PEDOT:PSS core/shell nanowire arrays for efficient hybrid solar cells

A solution filling and drying method has been demonstrated to fabricate Si/PEDOT:PSS core/shell nanowire arrays for hybrid solar cells. The hybrid core/shell nanowire arrays show excellent broadband anti-reflection, and resulting hybrid solar cells absorb about 88% of AM 1.5G photons in the 300-1100 nm range. The power conversion efficiency (PCE) of the hybrid solar cell reaches 6.35%, and is primarily limited by direct and indirect interfacial recombination of charge carriers.     

Sb2S3太阳能电池的研究进展

Sb₂S₃太阳能电池相比于其他太阳能电池如铜铟镓硒、碲化镉和有机-无机钙钛矿等,具有成本低、无毒性、稳定性高的优点,并且Sb₂S₃材料本身拥有优良的光学性能,如带隙宽度为1.5～2.2eV、光吸收系数高达105cm–1,因此在太阳能转化方面具有良好的应用前景。但目前Sb₂S₃太阳能电池的光电转化效率仍然不高,其最高光电转化效率仅有7.5%,远低于发展成熟的单晶硅太阳能电池、铜铟镓硒、碲化镉太阳能电池。本文简要介绍了Sb₂S₃太阳能电池的工作原理,从光阳极、吸光层Sb₂S₃、空穴传输层3个方面阐述了其发展现状及存在的问题。随后针对限制光电转化效率的因素,阐述了现有的优化电池性能的方法及其研究进展。最后对Sb₂S₃太阳能电池的未来发展方向进行了展望,基于对现有研究分析认为,在未来的研究中需要进一步探索新型的光阳极半导体的种类和结构,研究简单低耗、结晶性良好的Sb₂S₃薄膜的制备方法,研究具有高电子传导率、与Sb₂S₃和对电极接触良好的空穴传输层以及发展高效界面修饰以及金属离子掺杂的方法,以提高Sb₂S₃太阳能电池的性能。     

Enhancing light harvesting in planar halide perovskite film solar cells by silicon nanorods

The introduction of nanostructures is an effective method to boost the photovoltaic performance of hybridized organic-inorganic halide perovskite-film solar cells. Taking into account their excellent light-scattering in the ultraviolet–visible range and their chemical inertness, silicon (Si) nanorods can be incorporated into the perovskite-film solar cells to enhance the light harvesting of the devices. By depositing Si nanorods between the prepared film and the substrate, the light scattering induced by the Si nanorods significantly promoted light absorption of the films. Moreover, resulting from the incorporation of Si nanorods, the enlarged grain size and compact structure of the films prolonged the lifetime of the carriers, which promoted the photoelectric properties of the perovskite films. By the appropriate incorporation of Si nanorods, the photovoltaic conversion efficiency of the CH₃NH₃Pb(Br_0.25I_0.75)₃-film-based solar cell was increased from 12.6% to 14.9% and the relative stability of the devices under dark humidity was improved. This strategy of employing low-cost and easily prepared Si nanorods to enhance the light harvesting of perovskite photovoltaic devices could be applied to photovoltaic devices based on perovskite films with other compositions.     

A novel method for crystalline silicon solar cells with low contact resistance and antireflection coating by an oxidized Mg layer

One of the key issues in the solar industry is lowering dopant concentration of emitter for high-efficiency crystalline solar cells. However, it is well known that a low surface concentration of dopants results in poor contact formation between the front Ag electrode and the n-layer of Si. In this paper, an evaporated Mg layer is used to reduce series resistance of c-Si solar cells. A layer of Mg metal is deposited on a lightly doped n-type Si emitter by evaporation. Ag electrode is screen printed to collect the generated electrons. Small work function difference between Mg and n-type silicon reduces the contact resistance. During a co-firing process, Mg is oxidized, and the oxidized layer serves as an antireflection layer. The measurement of an Ag/Mg/n-Si solar cell shows that V _oc, J _sc, FF, and efficiency are 602 mV, 36.9 mA/cm², 80.1%, and 17.75%, respectively. It can be applied to the manufacturing of low-cost, simple, and high-efficiency solar cells.     

Ultrathin microcrystalline hydrogenated Si/Ge alloyed tandem solar cells towards full solar spectrum conversion

Thin film solar cells have been proved the next generation photovoltaic devices due to their low cost, less material consumption and easy mass production. Among them, micro-crystalline Si and Ge based thin film solar cells have advantages of high efficiency and ultrathin absorber layers. Yet individual junction devices are limited in photoelectric conversion efficiency because of the restricted solar spectrum range for its specific absorber. In this work, we designed and simulated a multi-junction solar cell with its four sub-cells selectively absorbing the full solar spectrum including the ultraviolet, green, red as well as near infrared range, respectively. By tuning the Ge content, the record efficiency of 24.80% has been realized with the typical quadruple junction structure of a-Si:H/a-Si_0.9Ge_0.1:H/µc-Si:H/µc-Si_0.5Ge_0.5:H. To further reduce the material cost, thickness dependent device performances have been conducted. It can be found that the design of total thickness of 4 mm is the optimal device design in balancing the thickness and the PCE. While the design of ultrathin quadruple junction device with total thickness of 2 mm is the optimized device design regarding cost and long-term stability with a little bit more reduction in PCE. These results indicated that our solar cells combine the advantages of low cost and high stability. Our work may provide a general guidance rule of utilizing the full solar spectrum for developing high efficiency and ultrathin multi-junction solar cells.     

Controllable synthesis of single- and double-walled carbon nanotubes from petroleum coke and their application to solar cells

Single- and double-walled carbon nanotubes (SWCNTs and DWCNTs) have been controllably synthesized by an arc discharge in different atmosphere using petroleum coke as carbon source. The morphology and properties of two kinds of carbon nanotubes (CNTs) synthesized with Fe as catalyst were characterized by scanning electron microscopy, high-resolution transmission electron microscopy, Raman spectroscopy, energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, UV–visible spectroscopy, inductively coupled plasma optical emission spectrometer, thermogravimetric analysis and infrared spectroscopy. In the He gas atmosphere only SWCNTs were found to be synthesized by arc discharge in contrast to the case in Ar gas atmosphere in which only DWCNTs were formed, In addition, properties of solar cells based on both kinds of CNTs and n-type Si are examined under illumination of light emission diode (LED). It is found that the performance of solar cells depends significantly on the type of CNTs, i.e., SWCNTs-based solar cells show better performance under LED illumination with wavelengths in the range of 400–940 nm than the case of DWCNTs which exhibit high performance under illumination of the 1310 nm infrared light.