A novel low cost texturization method for large area commercial mono-crystalline silicon solar cells

Texturization of mono-crystalline silicon for solar cell fabrication is still a key issue due to consumption of large amount of costly isopropyl alcohol (IPA) in conventional NaOH/KOH solution. The need of IPA arises due to the improvement in the uniformity of pyramidal structures and elimination of spots caused by bubbles sticking on the wafer surface during the texturization process. We investigated a new texturization technique for mono-crystalline silicon solar cells with tribasic sodium phosphate (Na₃PO₄, 12H₂O) solution with much less amount of IPA. The proposed texturization method of this paper is cost effective due to reduction in the consumption of expensive IPA. The cost comparison of our novel texturization approach with conventional NaOH texturization has also been reported in this paper. We are reporting for the first time such a novel approach of using tribasic sodium phosphate for texturization of mono-crystalline silicon surface with which solar cells of efficiency 14–14.8% are fabricated with more than 90% yield.     

Amorphous silicon/p-type crystalline silicon heterojunction solar cells with a microcrystalline silicon buffer layer

Undoped hydrogenated amorphous silicon (a-Si:H)/p-type crystalline silicon (c-Si) structures with and without a microcrystalline silicon (μc-Si) buffer layer have been investigated as a potential low-cost heterojunction (HJ) solar cell. Unlike the conventional HJ silicon solar cell with a highly doped window layer, the undoped a-Si:H emitter was photovoltaically active, and a thicker emitter layer was proven to be advantageous for more light absorption, as long as the carriers generated in the layer are effectively collected at the junction. In addition, without using heavy doping and transparent front contacts, the solar cell exhibited a fill factor comparable to the conventional HJ silicon solar cell. The optimized configuration consisted of an undoped a-Si:H emitter layer (700 Å), providing an excellent light absorption and defect passivation, and a thin μc-Si buffer layer (200 Å), providing an improved carrier collection by lowering barrier height at the interface, resulting in a maximum conversion efficiency of 10% without an anti-reflective coating.     

Improved fill-factor for the double-sided buried-contact bifacial silicon solar cell

Despite the commercial success of buried-contact solar cells, the performance of early generations of these devices has been limited by an effective high rear-surface recombination velocity. For a number of years, the double-sided buried-contact bifacial (DSBCB) solar cells have demonstrated improved rear-surface passivation with corresponding improvements in current and voltage. In the past, however, the fill factors of these devices have been significantly degraded due to shunting of the rear floating junction. These limitations have been overcome through the use of much higher sheet resistivities for the rear n-type layer. Experimental devices based on this new approach have achieved fill factors approaching 82% while simultaneously achieving open-circuit voltages in the vicinity of 670 mV. Efficiencies in the range 17–18% without texturing, anti-reflection coatings, any form of light trapping, or even rear reflector have ben achieved on float-zone material.     

Material properties of microcrystalline silicon for solar cell application

The paper reviews the material requirements of microcrystalline silicon (μc-Si) in terms of the device operation and configuration for thin film solar cells and thin film transistors (TFTs). We investigated the material properties of μc-Si films deposited by using 13.56 MHz plasma-enhanced chemical vapor deposition (PECVD) from a conventional H₂ dilution in SiH₄. Two types of intrinsic μc-Si films deposited at the high pressure narrow electrode gap and the low pressure wide electrode gap were studied for the solar cell absorption layers. The material properties were characterized using dark conductivity, Raman spectroscopy, and transmission electron microscope (TEM) measurements. The μc-Si quality and solar cell performance were mainly determined by microstructure characteristics. Solar cells adopting the optimized μc-Si film demonstrated high stability with no significant changes in solar cell performance after air exposure for six months and subsequent illumination for over 300 h. The results can be explained that low ion bombardment and high atomic hydrogen density under the PECVD condition of the high pressure narrow electrode gap produce high-quality μc-Si films for solar cell application.     

Recent progress of amorphous silicon solar cell applications and systems

Fifteen years have passed since the first industrial use of amorphous silicon (a-Si) solar cells for consumer products. At present, a-Si solar cells are entering a new age of use in power generating systems at private residences and other outdoor applications. This paper reviews recent advances in amorphous silicon (a-Si) solar cells and their applications. Technological developments in the field of a-Si solar cells are discussed. Various applications and systems that take advantage of the a-Si solar cell are then introduced. Finally, future prospects are discussed, including a new concept of GENESIS system for worldwide energy generation and transmission.     

非晶硅太阳能路灯系统的设计

介绍太阳能路灯系统的组成,各部分的工作原理、工作特点,并以沈阳汉锋工厂内安装的太阳能路灯为例,来说明非晶硅太阳能路灯系统的设计方法。具有弱光性、低成本的非晶硅太阳能电池与高亮度、长寿命的LED光源相结合将是未来照明工程的发展趋势。     

单晶硅太阳电池在槽式聚光与普通光照条件下伏安特性的对比研究

为进一步对开发聚光热电联供系统提供依据与指导,在槽式聚光器中,设计了槽式单晶硅太阳能电池热电联供测试系统,并在太阳聚光条件下对单晶硅太阳电池进行了伏安特性的测试.测试结果表明,普通单晶硅太阳能电池在聚光10倍左右的情况下,开路电压变化不大,开路电流放大了4.1倍左右,伏安特性曲线基本满足线性关系.     

Fabrication of buried contact silicon solar cells using porous silicon

We report the fabrication of buried contact solar cells using porous silicon as sacrificial layer to create well-defined channels (for buried contacts) in silicon. In this paper, the salient features of the technology have been presented. No detrimental effect was found in the performance of buried contact solar cell with partially filled contact area compared to the solar cells having conventional planar contacts. However, a marked difference in the short circuit current density was seen when channel was fully filled with metal by screen printing, without degradation in the open-circuit voltage. It is expected that improved processing in combination with optimized buried metallic contact parameters may yield higher efficiencies that may result in substantial decrease in solar cell cost.     

Performance of p-type silicon-oxide windows in amorphous silicon solar cell

a-SiO_x films have been prepared using silane and pure oxygen as reactive gases in plasma CVD system. Diborane was introduced as a doping gas to obtain p-type conduction silicon oxide. Infrared absorption spectra show the incorporation of Si–O stretch mode around 1000 cm⁻¹. The optical bandgap increases with the oxygen to silane gas ratio, while the electrical conductivity decreases. Hydrogenated amorphous silicon solar cells have been fabricated using p-type a-SiO_x with around 1.85 eV optical bandgap and conductivity greater than 10⁻⁷ S/cm. The measured current–voltage characteristics of the solar cells under 100 mW/cm² artificial light are V_oc=0.84 V, J_sc=14.7 mA/cm², FF=0.635 with a conversion efficiency of 7.84%.     

An optimum design of antireflection coating for spherical silicon solar cells

Antireflection (AR) coatings for spherical crystalline silicon solar cells are theoretically optimized from the viewpoint of achieving the largest photon densities in the spherical crystalline silicon solar cells. Because the AR film thickness is optimized with regard to the photon densities in the spherical crystalline silicon solar cells, tolerance in the film thickness can be evaluated. Also, the optimized AR film thicknesses for the spherical crystalline silicon solar cells and planar crystalline silicon solar cells are compared, and analytic expressions for the optimized AR film thicknesses are derived as a function of a quarter-wavelength film thickness.     

Effect of silicon solar cell processing parameters and crystallinity on mechanical strength

Silicon wafer thickness reduction without increasing the wafer strength leads to a high breakage rate during subsequent handling and processing steps. Cracking of solar cells has become one of the major sources of solar module failure and rejection. Hence, it is important to evaluate the mechanical strength of solar cells and influencing factors. The purpose of this work is to understand the fracture behavior of silicon solar cells and to provide information regarding the bending strength of the cells. Triple junctions, grain size and grain boundaries are considered to investigate the effect of crystallinity features on silicon wafer strength. Significant changes in fracture strength are found as a result of metallization morphology and crystallinity of silicon solar cells. It is observed that aluminum paste type influences the strength of the solar cells.     

Optimization of fabrication process of high-efficiency and low-cost crystalline silicon solar cell for industrial applications

The process conditions for a high-efficiency and low cost crystalline silicon solar cell were optimized. Novel approaches such as wafer cleaning and saw -damage removal using 0.5 wt% of 2,4,6-trichloro-1,3,5-triazine, silicon surface texturing with optimized pyramid heights (∼5 μm), and a third step of drive-in after phosphosilicate glass (PSG) removal followed by oxide removal were investigated. A simple method of chemical etching adopted for edge isolation was optimized with edge etching of 5-10 μm, without any penetration of chemicals between the stacked wafers. The conversion efficiency, open-circuit voltage, short-circuit current, and fill factor of the cell fabricated with the optimized process were a maximum of 17.12%, 618.4 mV, 5.32 A, and 77% under AM1.5 conditions, respectively.     

Omnidirectional light absorption in thin film silicon solar cell with dual anti-reflection coatings

A theoretical model for an all-in-one thin film silicon solar cell (TFSSC) design with the anti-reflection (AR) coatings, the transparent electrodes, the silicon and the back reflective coatings all deposited on one piece of glass is proposed and the optical performance for the design is numerically simulated. The calculated average reflectance over the wavelength range of 0.4–1.0 μm and incident angles from 0° to 75° for the optimized dual-AR coatings as a whole is 3.67% – ranking among the lowest values for current AR coatings on silicon solar cells. Furthermore, the spectrum-averaged absorptance (SAA) in the 5-μm-thick cell in the 0.3–1.2 μm wavelength range decreases only by 2.58% when the incident angle varies from 0° to 75°, clearly showing the omnidirectional characteristics of the dual-AR coatings. With reasonable assumption of the internal quantum efficiency (near unity), the 5-μm cell produces a spectrum averaged external quantum efficiency (EQE) of 81.4% at 75° angle of incidence – 6.7% larger than the experiment result of the best planar bulk cell. Under equal sunshine conditions, TFSSCs generally give higher output voltages than their bulk counterpart if equal light absorption is assumed, so the 5-μm cell has the potential to reach the highest experimental conversion efficiency of the best planar bulk cell. By using a special mathematical technique, we are able to prove the angle-dependent absorption curves in the longer wavelength region tend to converge to a small neighborhood of the upper limit irrespective of significant differences between the transmission profiles. This indicates the AR requirement in the longer wavelength region can be significantly relaxed.     

Thickness dependence of microcrystalline silicon solar cell properties

This paper addresses the performance of pin and nip solar cells with microcrystalline silicon (μc-Si:H) absorber layers of different thickness. Despite the reverse deposition sequence, the behavior of both types of solar cells is found to be similar. Thicker absorber layers yield higher short-circuit currents, which can be fully attributed to an enhanced optical absorption. Open-circuit voltage V_OC and fill factor FF decrease with increasing thickness, showing limitations of the bulk material. As a result of these two contrary effects the efficiency η varies only weakly for absorber layers of 1 to 4 μm thickness, yielding maximum values up to 8.1 %. For a-Si:H/μc-Si:H stacked solar cells an initial efficiency of 12% has been obtained.     

Advanced cost-effective crystalline silicon solar cell technologies

An overview is given concerning current industrial technologies, near future improvements and medium-term developments in the field of industrially viable crystalline silicon terrestrial solar cell fabrication (without concentration).     

Interface effects on the carrier transport and photovoltaic properties of hydrogenated amorphous silicon/crystalline silicon solar cells

Current-voltage-temperature (I-V-T) characteristics evaluated near 150K and 300K were used to study the photovoltaic property variations in hydrogenated amorphous silicon (a-Si:H)/crystalline silicon (c-Si) solar cells. The possible carrier transport mechanisms in such devices were examined from the I-V-T data which indicated a significant influence of the amorphous /crystalline interface on the short-circuit current density (J_sc) and open-circuit voltage (V_oc) of the solar cells. Carrier transport near 300K for forward biases was by a multi-tunneling mechanism and became space charge limited with increasing bias. For devices having low J_sc and V_oc an additional region was seen in both forward and reverse biases, at low temperatures, where the current simply varied linearly with the applied bias. This characteristic manifested in both high and low temperatures region for devices with still lower photovoltaic properties, which has been reasoned to be due to a higher interface density. Passivating the c-Si surface with HF just prior to the amorphous layer deposition resulted in a large improvement in the properties. The most significant effect was on the J_sc which improved by an order of magnitude. The treatment also affected the lower temperature I-V-T data in that the current fell to very low levels. The spectral response of the treated solar cells showed enhanced blue/violet response compared with the unpassivated devices. The interface passivation plus reducing a-Si thickness has improved the solar cell efficiency from 0.39% to 9.5%.     

Modelling of material properties influence on back junction thin polycrystalline silicon solar cells

The influence of polycrystalline silicon properties on the performances of thin back junction solar cells has been investigated by means of a 3-dimensional model taking into account grain size, grain boundary recombination, volumic recombination, and surface recombination. The drastic influence of front surface recombination has been confirmed. The grain size has been shown to be of minor importance provided the grain size is not too small and the grain boundaries are correctly passivated. An optimal base thickness has been determined which is all the smaller that the material is more imperfect.     

工业化薄晶体硅太阳电池背电极浆料

对薄晶体硅太阳电池的生产工艺和材料进行了试验.通过调整背电极浆料和电池基片厚度,探索了减少太阳电池弯曲度的途径.试验显示,使用薄片铝浆对电池弯曲度的影响有明显改善,弯曲度可降低52%,电池片弯曲度最小为0.55 mm.     

Chemical bath deposition for the fabrication of antireflective coating of spherical silicon solar cells

A CdS film as an antireflective (AR) coating has been successfully deposited on spherical silicon solar cells by chemical bath deposition, which is a novel deposition method of AR coatings for spherical silicon solar cells. The CBD method is a growth method in an aqueous solution and enables film formation for electronic devices with arbitrary shapes. The solar cell performance of the cell with the CdS film showed a 16% increase in short circuit current compared to that without an ARC. The result confirms that the CBD method is useful for the ARC fabrication of spherical silicon solar cells.     

硅太阳电池材料的研究进展

目前各种太阳电池材料中，硅是最主要的材料。文章简要介绍单晶硅、多晶硅、带状硅、非晶硅以及多晶硅薄膜材料的研究状况，并对有关问题和太阳电池材料的发展趋势进行了讨论。