Category II-VI and I-III-VI compound semiconductor solar cells

Talking about the future development of CIGS thin film solar cells

Talking about the future development of CIGS thin film solar cells

In the future, thin-film solar cell products will be similar to today’s computer CPUs, and the demand for products can also be stimulated by the ever-improving energy conversion efficiency. Judging from a certain area. The roof of the house, the exterior of the building, the surface of the clothes bag, etc. Some possible application and installation places of thin-film solar cells. Needless to say, its power output increases proportionally with efficiency. How to further improve the energy conversion efficiency of the product is a major challenge, and it is also the key to the decisive victory of the product. Although reducing the manufacturing cost of the product is another factor, compared with the two, the former also has the effect of reducing costs. should be given more attention.

The more traditional method to improve the efficiency of CIGS solar cells is to use a tandem structure, that is, PN junctions made of different materials are stacked in order from top to bottom according to the size of the energy gap. According to theoretical calculations, the series connection of three cells can achieve the most economical Affordable results, see Figure 1. The light-transmitting conductive layers can be connected in series between the cells, each responsible for the absorption of sunlight in different bands, which can improve the efficiency to more than 30%. Taking the Hybrid V compound semiconductor as an example, the current maximum has reached 40%. The IHB VI family also has different material combinations with adjustable energy gaps for device design. The related material data is shown in the series structure of the compound, as shown in Figure 2.

Figure 1 - Calculated energy conversion efficiency of tandem solar cells, Figure 2 - IHB group VI compounds can change the energy gap through the adjustment of different material compositions to meet the design of tandem solar cell devices
Figure 1 – Calculated energy conversion efficiency of tandem solar cells, Figure 2 – IHB group VI compounds can change the energy gap through the adjustment of different material compositions to meet the design of tandem solar cell devices

Another research direction to improve the efficiency of CIGS solar cells is to deposit an ultra-thin absorber layer (ETA cell for short) in nanostructures, as shown in Figure 3. Its operation principle is similar to that of dye-sensitized TiO2 solar cells. similar. If quantum dots can be deposited and formed, using their light absorption characteristics different from those of bulk materials, when the size of the material is reduced to the point where the particle size is lower than the mean free path of carriers. It can reduce the carrier recombination generated by light, and can control the energy gap value of nanocrystals by adjusting the size, improve the utilization rate of sunlight energy, and also allow photons with more energy than the energy gap to generate more than one pair of electrons. and holes to improve battery efficiency. This new type of design is called a third-generation solar cell. Since it is an emerging technology, there are still problems to be overcome. If the efficiency can be effectively improved to more than 10% in the future, it may become one of the market mainstreams of thin-film solar cells. To read more about batteries click here to open.

Figure 3 ETA cell compares with crystalline silicon solar cells up to 200µm thick, and thin film solar cells can build their product features on flexible substrates. Figure 4 is a comparison of the measured efficiency values ​​of flexible CIGS solar cells fabricated on different substrates. High-efficiency CIGS solar cells are usually prepared at temperatures above 500 °C,

Figure 4-(a) Efficiency comparison of CIGS solar cells fabricated on various flexible substrates; (b) Polyimide is the efficiency of CIGS solar cells fabricated on substrates at different temperatures
Figure 4-(a) Efficiency comparison of CIGS solar cells fabricated on various flexible substrates; (b) Polyimide is the efficiency of CIGS solar cells fabricated on substrates at different temperatures

It is feasible to use metals such as stainless steel as the substrate. However, if the mass is to be greatly reduced in order to facilitate the use of personal power sources or to facilitate the application of power sources in outer space, lightweight polymer substrates are often used. From Figure 4(b), it can be seen that the efficiency value of CIGS solar cells fabricated at different substrate temperatures starts to drop when the temperature is above 450 °C [19], because this type of substrate has cracking phenomenon at this temperature, so a low-temperature process is required. Preparation of CIGS films. The German company Solarion has developed a roll-to-roll process to manufacture CIGS solar cells on flexible polymer substrates. As shown in Fig. 5, the device structure is fabricated by Polyimide/Mo/CIGS/CdS/ZnO stack, in which the CIGS film is fabricated by ion beam assisted evaporation, but the cell efficiency is only about 8%. Defects will affect the film properties. resulting in low power generation efficiency. In our laboratory, high-quality CIS epitaxial films can be grown at 300°C by UV-assisted evaporation. This method should be a better choice for the research and development of low-temperature processes.

Figure 5 - Solarion's roll-to-roll process using flexible polymers as substrates
Figure 5 – Solarion’s roll-to-roll process using flexible polymers as substrates

There is a worrying question in the mass production of CIGS solar cells, that is, whether In will run out of material when there is a lot of demand. Although some arguments suggest that In mineral stocks are sufficient, they are not necessarily credible. When planning ahead, there is indeed a research on the idea of ​​replacing In with Zn and Sn, but the method is successful because of the concomitant generation of three phases. It can be tried to use CuGaTe2 with similar energy gap. In addition, reducing the amount of use is also one of the solutions. If you can seek a breakthrough in the design of the device structure, try to make use of the extremely high light absorption coefficient of CIGS to reduce the thickness of CIGS by half or even to a quarter, which is another solution. Way. These may be the focus of future research and development.

Due to the significant increase in demand for crystalline silicon solar cells in recent years, raw material manufacturers of silicon materials strategically do not cooperate with the simultaneous expansion of production, resulting in the dilemma of material shortages. Those who are eager to catch a ride and participate in the investment and establishment of factories are discouraged. Turning to the production of thin-film solar cells, because the mass production technology of amorphous silicon solar cells is mature and easy to obtain, several amorphous silicon solar cell manufacturing plants were established around the beginning of 2007. However, the efficiency of amorphous silicon solar power modules Low, it can meet the demand of the towel field in the short term, but it is not optimistic in the long term. Another option on the tabletop of static film solar cells is CIGS, whose power and module efficiency is close to that of products made of polysilicon materials. More turn-key mass production equipment manufacturers with a full set of technologies came to Taiwan to sell.

The above information and development have made this industry attract attention. We can see that in the field of solar cells, there can be different materials, different processes, and different products. Higher efficiency and lower cost are the keys to winning, and there is no clear answer at present. Research in this area is still worthy of further exploration, and we have noticed that new ideas are advancing with the times, and new combinations of technologies and materials are constantly being introduced. Today, the research and development of solar cells has escaped the old framework and is heading for a new future, which has the opportunity to become a cheap and clean energy source in human daily life.

Read more: What are semiconductor solar cells and blackbody radiation

Device Structure of CIGS High Efficiency Solar Cells

Device Structure of CIGS High Efficiency Solar Cells

The device structure commonly used in high-efficiency CIS solar cells is shown in Figure 1(a). The energy gap values ​​of each layer material are Zn(): 3.30eV, CdS: 2.42eV, CulnSe2: 1.02eV, decreasing from top to bottom , which can cover a broad absorption range of the solar spectrum. Usually, the P-type Cu-rich CIS film is firstly plated on the indium-coated glass substrate to form a good ohmic contact, and then the In evaporation temperature is increased to continue plating the Intrin sic In-rich CIS film. At this time, its grain structure inherits the underlying CuCIS-rich film, which is also a large grain and a rough surface. The N-type CdS buffer layer on the CIS is designed for the best matching of the heterojunction electrical properties, and a chemical bath deposition method is used to cover the slightly rough surface intact. Finally, ZnO and Al/Ni beer films were grown successively by sputtering to complete the entire device structure. The energy conversion efficiency of solar cells with CIS as the main absorber layer is currently up to 15.4%; while the efficiency of the recent CIGS solar cells is close to 20%, and its device structure is shown in Figure 1(b).

Figure 1 (a) High-efficiency CIS solar cell structure, (b) high-efficiency GIGS solar cell structure
Figure 1 (a) High-efficiency CIS solar cell structure, (b) high-efficiency GIGS solar cell structure

The combination of materials in the device structure of the above-mentioned high-efficiency CIS solar cells has been in the same vein since the publication of the first CIS solar cell in 1976, but it is the same as the 10% breakthrough of the CIS solar cell structure by Piyin in the 1980s. compared to the material. However, there have been some important changes, including the use of uranium glass for the Jin glass substrate, the replacement of CIS with CIGS, and the slight changes in the anti-reflection layer and light-transmitting layer. The selection and characteristics of materials for each layer are briefly described below.

In the selection of glass substrates, borosilicate glass was initially used, and later, lower-cost uranium glass was used. Nano-atoms have strong diffusion ability in solid-state materials, and can pass through the aluminum layer into the CIS coating during the CIS evaporation process. The temperature at that time was about 500 °C and the time was about 60 min. Uranium has some unexpected but very positive effects in the growth of CTS films, and some preliminary understandings have been obtained in related studies: ① it inhibits the formation of crystalline defects; ② it contributes to the P-type conductivity. Although clear experimental evidence has not yet been obtained, indirect experimental results indicate that these effects and cell efficiency have been significantly improved. In this experiment, a thin NaF-containing film was deliberately plated on the indium layer to regenerate the CIS and complete the above device structure. , Table 2 shows that the cell efficiency value is improved by about 3%.

Figure 2 - The electrical improvement of the completed CIGS solar cell after plating a very thin NaF film on top of the Mo layer
Figure 2 – The electrical improvement of the completed CIGS solar cell after plating a very thin NaF film on top of the Mo layer

In terms of the ohmic contact of the back electrode, it has been experimentally confirmed that there is only a few atomic layers of M0Se2 between CIS and Mo when the CIS film is grown, which improves the CIS/Mo interface with Schottky contact characteristics. quality, while showing good ohmic contact characteristics.

For a long time, CdS is considered to be the best match to form a PN junction with CIS, and the energy band structures formed by the two have been discussed in many papers. Some believe that Cd will diffuse into CIS and replace Cu to become N-type dopant, causing the position of the PN junction to move inward to the CIS, so that the internal electric field formed by the PN junction is separated from the original CdS/CIS heterojunction due to the lattice. Defects due to lattice mismatch create regions of carrier recombination.

Originally in the 1980s. The role of N-CdS is mainly a light-transmitting layer (window layer). But because Cd is a heavy metal element, the thickness of the layer is greatly reduced, and now it is often called a buffer layer (buffer layer). Because the surface of the CIGS thin film is slightly uneven, the preparation of the CdS thin layer is often carried out by chemical bath deposition (CBD) to ensure that the thin film can cover the CIGS surface continuously and completely. Recent studies have found that discontinuous CdS The thin film will make the efficiency of CIGS solar cells not higher than 18% [1:. The relevant data is shown in Figure 3. This buffer layer also has the effect of blocking the atomic impact of ZnO and reducing the generation of defects. The current research also tends to use Cd-free buffer layer materials. Based on the current research results, a direct comparison under the same conditions is shown in Figure 4. Some materials such as ZnS and other buffer layers are matched with CIGS. For solar cells, their efficiency is already on par.

Figure 3 - Discontinuous CdS films prevent CIGS solar cells from reaching efficiencies higher than 18%
Figure 3 – Discontinuous CdS films prevent CIGS solar cells from reaching efficiencies higher than 18%
Figure 4 - Comparison of CIGS cell efficiency using various Cd-free materials versus CdS for the buffer layer
Figure 4 – Comparison of CIGS cell efficiency using various Cd-free materials versus CdS for the buffer layer

In the previous CIS solar cell structure, ZnO is the anti-reflection layer (anti-reflection layer), but in the high-efficiency CIGS solar cell structure, it has multiple roles, so the i-ZnO, which is an electrical near-intrinsic semiconductor, is Light-transmitting layer, doped with Al, ZnO:AlC with good conductivity, also known as AZO) is the outermost layer with multiple functions such as light-transmitting conductivity and anti-reflection.

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原文 I - Ⅲ -Ⅵ 2 族半导体太阳能电池/CuInSe2 的薄膜工艺 自 20 世纪 50 年代以来 ,I - Ⅲ -Ⅵ 2 族化合物开始被研究以了解其结晶相和材 料性质 ,Shay 和Wernick 在 1975 年将这些研究成果结集出版。以 CulnSe2 搭配 CdS 所制作的 PN 结太阳能电池的器件特性也随后在 1976 年发表 。之后 CIS 太阳能电地效率随着持续地改良工艺与搭配的材料而逐步提高,目前最高效率的I - Ⅲ -Ⅵ 2 薄膜太阳能电池 ,其主吸收层,其 Ga/ In 的比值必须维 持在0.3以内。若高 于 0.3 ,则导致 太阳能电池效率 大幅降低 。以三元化合 物 CulnSe2 制成的太阳能电池效率稍低 ,这是因为虽然该材料拥有相当高的光吸收 系数,但是 CulnSe2 的能隙仅约 1.O eV 。Ga 的加入使材料成为四元化合物 ,可 增 大CulnSe2 的能隙 ,也使得电池的开路电压( open circuit voltage ) 得以提升并降低 电流减少电阻损失 ,进而获得更高的电池效率 。之前我无意中浏览到一篇文章,作者在对电池效率影响的各个因素写的很细,很全面。如果您感兴趣,请访问。 CulnSe2是所有的 I - Ⅲ -Ⅵ 2 族化合物当中被研究得最多的 ,当然也获得很好 的成果。然而即使加入 Ga 成为来增大能隙以提升电池效率 ,但如前所述,当 x 值超过 0. 3 时就无法得 到 预期的效果 ,而 :r = 0. 3 时,其能隙仅 达 1. 15 eV 。曾经有一些努力 试图借助四元化合物,甚至五元化合物的组成调配来改变能隙 ,以尝试提升电池效率 ,但结果并非 如此 ,反而使得效率降低 L 叫 。似乎长时间以来 ,在CulnSe2 和Se2 所获 得的材料匹配和改良的成功经验无法直接被应用到其他I - Ⅲ -Ⅵ 2 系列的化合物 上,尤其是CulnSe2 ,它是除了CulnSe2 之外 ,另外通过组成调配可得到N 型和 P 型 的 I - Ⅲ -Ⅵ 2 族化合物 ,见表 1 ,它的能隙大约为 1. 5 eV ,如前所述 ,它是一种具有适当能隙值的太阳能电池材料 。往往这些材料特性的变化包括界面和内在缺陷等。 加总之后的影响足以导致可观的负面结果,显然针对这些 I - Ⅲ -Ⅵ 2 系列的化合 物仍需要投入足够的研究力量,以呈现其该有的器件表现 。因此以下即针对高效率太阳能电池的器件结构以及工艺等进行介绍 。 1. CuInSe2 的薄膜工艺 高效率 CIS 太阳能电池都是使用共蒸发 ( co-evaporation ) 或晒化 ( selenization) 反应法镀制 CIS 薄膜。其他如共溅射方式则存在因较高能量的薄膜 表面撞击而产生缺陷 ,以及In 排斥现象造成对薄膜组成的控制有所不足等缺憾 ,目前尚无法以此工艺产出高效率太阳能 电池;另外,如低成本的电化学沉积法 (electro­ deposition ) 所镀制的薄膜则因质量不佳也不适用于高效率太阳能电池的制作。 三源( CIS) 或四源 ( CIGS) 的共蒸发工艺是使用元素态蒸发源 ,在450 ~600℃的基板温 度下蒸发 。因为 Se 元素的蒸 气压高 ,所以常 在 Se 维持过量 ( over pressure) 的情况下来调整 Cu 与第三族元素 1) 时,晶粒约有几百甚至上千纳米的大小 ,薄膜呈现粗糙的 表面 ;而富 In 薄膜的晶粒小于几十纳米 ,故薄膜表面平滑光亮。CIS 薄膜蒸镀的 过程中 ,先形成 Cu2Se 和 In2Se3 两个二元相 ( binary phase ) ,再进一步反应生成 CuInSe2 三元相 ( ternary phase) 。 在 20 世纪 80 年代 ,美国波音公司实验室所制作的 CIS 太阳能电池突破 10 % 的能量转换效率 ,达到12% ,其 CIS 薄膜是先后分别在富 Cu 和富 In 的蒸发条 件下制备的 。在富 Cu 的条件下可得到大晶粒的 CJS 薄膜但却含有 Cu2Se 二次 相 ,在多晶薄膜的生 长过程中 ,Cu2Se 为 液 态并 呈 现 在 表面 和晶界 面 ( grain boundary ) ,此有助于晶粒长大 ;紧接着富In 的生长条件将可让多余的 In2Se3 二 元相跟富 Cu CIS 膜中的 Cu2Se 二次相完全反应而被消除 ,最后得到的是大晶粒且单一相的 CIS 薄膜 ,当然薄膜中先形成的组分含稍多的铜而呈现 P 型导电特 性 ,而稍后形成的部分则为In 偏多的组分,因而具高电阻率N 型接近本征 ( in­ trinsic) 半导体的导电特性 。 同时期 ,ARCO solar 公司亦发展 CIS 的晒化工艺 ,以该工艺制作的 CIS 太 阳能电池,其效率虽略逊于以蒸发工艺所制作的太阳能电池,但紧随其后。晒化 工艺是先分别镀制特定厚度的 Cu 和 In 金属膜以达成特定的原子数配比 ,再置于 H2Se 气体或 Se 蒸气之中 ,以 400 ℃以上的温度让其反应成 Cu2Se 。以晒化法 制备的薄膜 ,其组成均匀度略逊于蒸发者,但仍能满足高效率太阳能电池的要 求 ,其好处在于可使用大面积溅射工艺,甚至低成本的墨印( ink printing ) 工 艺 ,适合量产的规划 。另外 ,新式的晒化法采用快速退火 ( rapid thermal ling ,升温速率至少10℃/s 以上),将萃板上 Cu/ In/Se 三元素预镀层 ( precursor film ) 以 400~500℃的温度在极短时间 (1~5 min ) 内完成晒化反应显然此工艺更具产量大与戚本低的优势 。 晒化法若以逐渐升温的方式为之其成膜过程是一系列的反应先后在进行 ,亦 即先有铜化耐和锢化晒等多神二元中间相的形成 ,最后合成三元的 CIS 单一相。 如果使用快速升温即可跳过中间相的形成 .直接合成CIS 化合物 ,以此方式 所制备的材料并不会造成电池效率减损 ,至于薄膜形成的机制则因合成速度太快 而难以得知 ,但仍可利用间接的方式寻求更好的材质 。 目前以 CIGS 为主要吸收层的太阳能电池 ,其最高转换效率已达19. 2 % ,是 由美国 NREL 于 2003 年提出 。NREL 使用改良式的蒸发 法 称 为 三 阶段工艺 ( three-stage process ) ,顾名思义,此法是将整个工艺分为三个阶段来调变基板温 度与控制不同的元素源及其蒸发温度。 第一阶段是将已 镀上 铝 ( Mo ) 金属的铀玻璃加热至 260℃,井同时提供元素 In 、Ga 和 Se 生长 On ,Ga)先驱物 ;第二阶段则关闭元素 In 和 Ga ,改提供元素Cu 和 缸,井加热 基板至 560°c ,此时四元化合物Cu On , Ga)开始形成 ,并伴随产生二次相于薄膜表面 ,该二次相呈液态,有助于产生大晶粒且致密的柱状结晶;第三阶段即关闭元素 Cu 并保持基板温度在 560℃,再继续提供In 、Ga 和 Se 一小段时间后也关闭 In 和 Ga ,使足够的元素 In 和 Ga 与二次相再次反应 ,在表面形成Cu2(In,Ga)4 Se7或Cu1(In,Ga)3 Se5 薄膜 ,故最后会 形成铜稍微不足 ( Cu-poor ) 的 Cu(In,Ga)4 Se2薄膜 ,其组成比值为o. 93< Cu/ ( In十Ga)≤O. 97 ,最后在元素 Se 气氛下 ,做 5~10 min 的高温退火进行再结晶 。 以三阶段蒸镀工艺生长的 CIGS 薄膜的剖面品粒结构 以此法制备的 CIGS 薄膜,其组成元素纵深分布如图1 所示 0 借着加 入 Ga 形成四元化合物 ,可增大主 吸收层的能隙值 ,如此能使开路电压增加 20~30 mV 。至于 Ga 的浓度分布梯度则运用了 a-SiGe 太阳能电池的 能带设计概念 ,使导带形成V 形双斜率,此设计带有背向电场用来推动电子向 PN 结移动 ,有助于减少在背面金属接触界面处复合 ( recombination ) 的机会并 加强电荷的收集 ,而光入射方向则得益于能隙渐减的斜率设计,扩大光吸收波段 的涵盖植围 。整体而言,可增加短路电流 。 上述的材料 和器件设计理念的成功运用是 将 CIGS 太阳能电池效率推向15 % 以上 的主要原因 。事实上 ,以硫取代部分晒成 为四元化合物也可 以使能隙增加而得到像 CIGS 一样的效果 ,只是硫的蒸气压比晒高许多,若使用蒸发法在控制上需使用特殊的蒸发 源设计以特制阀门调节硫蒸气的输出。目前在 CIG 晒化量产工艺中 ,也可以同时置入晒 和硫合成 CIGSS 五元化合物。 阅读更多:你对多晶硅太阳能电池了解多少? I - Ⅲ -Ⅵ 2 zú bàndǎotǐ tàiyángnéng diànchí/CuInSe2 de bómó gōngyì zì 20 shìjì 50 niándài yǐlái,I - Ⅲ -Ⅵ 2 zú huàhéwù kāishǐ bèi yánjiū yǐ liǎojiě qí jiéjīng xiāng hé cáiliào xìngzhì,Shay hé Wernick zài 1975 nián jiāng zhèxiē yánjiū chéngguǒ jiéjí chūbǎn. Yǐ CulnSe2 dāpèi CdS suǒ zhìzuò de PN jié tàiyángnéng diànchí de qìjiàn tèxìng yě suíhòu zài 1976 nián fābiǎo. Zhīhòu CIS tàiyángnéng diàn dì xiàolǜ suízhe chíxù dì gǎiliáng gōngyì yǔ dāpèi de cáiliào ér zhúbù tígāo, mùqián zuìgāo xiàolǜ de I - Ⅲ -Ⅵ 2 bómó tàiyángnéng diànchí, qí zhǔ xīshōu céng, qí Ga/ In de bǐzhí bìxū wéichí zài 0.3 Yǐnèi. Ruò gāo yú 0.3, Zé dǎozhì tàiyángnéng diànchí xiàolǜ dàfú jiàngdī. Yǐ sān yuán huàhéwù CulnSe2 zhì chéng de tàiyángnéng diànchí xiàolǜ shāo dī, zhè shì yīnwèi suīrán gāi cáiliào yǒngyǒu xiāngdāng gāo de guāng xīshōu xìshù, dànshì CulnSe2 de néng xì jǐn yuē 1.O eV.Ga de jiārù shǐ cáiliào chéngwéi sì yuán huàhéwù, kě zēng dà CulnSe2 de néng xì, yě shǐdé diànchí de kāilù diànyā (open circuit voltage) déyǐ tíshēng bìng jiàngdī diànliú jiǎnshǎo diànzǔ sǔnshī, jìn'ér huòdé gèng gāo de diànchí xiàolǜ. Zhīqián wǒ wúyì zhōng liúlǎn dào yī piān wénzhāng, zuòzhě zài duì diànchí xiàolǜ yǐngxiǎng de gège yīnsù xiě de hěn xì, hěn quánmiàn. Rúguǒ nín gǎn xìngqù, qǐng fǎngwèn tycorun.Com. CulnSe2 shì suǒyǒu de I - Ⅲ -Ⅵ 2 zú huàhéwù dāngzhōng bèi yánjiū dé zuìduō de, dāngrán yě huòdé hěn hǎo de chéngguǒ. Rán'ér jíshǐ jiārù Ga chéngwéi lái zēng dà néng xì yǐ tíshēng diànchí xiàolǜ, dàn rú qián suǒ shù, dāng x zhí chāoguò 0. 3 Shí jiù wúfǎ dédào yùqí de xiàoguǒ, ér:R = 0. 3 Shí, qí néng xì jǐn dá 1. 15 EV. Céngjīng yǒu yīxiē nǔlì shìtú jièzhù sì yuán huàhéwù, shènzhì wǔ yuán huàhéwù de zǔchéng diàopèi lái gǎibiàn néng xì, yǐ chángshì tíshēng diànchí xiàolǜ, dàn jiéguǒ bìngfēi rúcǐ, fǎn'ér shǐdé xiàolǜ jiàngdī L jiào. Sìhū cháng shíjiān yǐlái, zài CulnSe2 hé Se2 suǒ huòdé de cáiliào pǐpèi hé gǎiliáng de chénggōng jīngyàn wúfǎ zhíjiē bèi yìngyòng dào qítā I - Ⅲ -Ⅵ 2 xìliè de huàhéwù shàng, yóuqí shì CulnSe2, tā shì chúle CulnSe2 zhī wài, lìngwài tōngguò zǔchéng diàopèi kě dédào N xíng hé P xíng de I - Ⅲ -Ⅵ 2 zú huàhéwù, jiàn biǎo 1, tā de néng xì dàyuē wèi 1. 5 EV, rú qián suǒ shù, tā shì yī zhǒng jùyǒu shìdàng néng xì zhí de tàiyángnéng diànchí cáiliào. Wǎngwǎng zhèxiē cáiliào tèxìng de biànhuà bāokuò jièmiàn hé nèizài quēxiàn děng. Jiā zǒng zhīhòu de yǐngxiǎng zúyǐ dǎozhì kěguān de fùmiàn jiéguǒ, xiǎnrán zhēnduì zhèxiē I - Ⅲ -Ⅵ 2 xìliè de huàhéwù réng xūyào tóurù zúgòu de yánjiū lìliàng, yǐ chéngxiàn qí gāi yǒu de qìjiàn biǎoxiàn. Yīncǐ yǐxià jí zhēnduì gāo xiàolǜ tàiyángnéng diànchí de qìjiàn jiégòu yǐjí gōngyì děng jìnxíng jièshào. 1. CuInSe2 de bómó gōngyì gāo xiàolǜ CIS tàiyángnéng diànchí dōu shì shǐyòng gòng zhēngfā (co-evaporation) huò shài huà (selenization) fǎnyìng fǎ dù zhì CIS bómó. Qítā rú gòng jiàn shè fāngshì zé cúnzài yīn jiào gāo néngliàng de bómó biǎomiàn zhuàngjí ér chǎnshēng quēxiàn, yǐjí In páichì xiànxiàng zàochéng duì bómó zǔchéng de kòngzhì yǒu suǒ bùzú děng quēhàn, mùqián shàng wúfǎ yǐ cǐ gōngyì chǎn chū gāo xiàolǜ tàiyángnéng diànchí; lìngwài, rú dī chéngběn de diàn huàxué chénjī fǎ (electro­ deposition) suǒ dù zhì de bómó zé yīn zhìliàng bù jiā yě bù shìyòng yú gāo xiàolǜ tàiyángnéng diànchí de zhìzuò. Sān yuán (CIS) huò sì yuán (CIGS) de gòng zhēngfā gōngyì shì shǐyòng yuánsù tài zhēngfā yuán, zài 450 ~600℃de jībǎn wēndù xià zhēngfā. Yīnwèi Se yuánsù de zhēngqì yā gāo, suǒyǐ cháng zài Se wéichí guòliàng (over pressure) de qíngkuàng xiàlái tiáozhěng Cu yǔ dì sān zú yuánsù 1) shí, jīng lì yuē yǒu jǐ bǎi shènzhì shàng qiān nàmǐ de dàxiǎo, bómó chéngxiàn cūcāo de biǎomiàn; ér fù In bómó de jīng lì xiǎoyú jǐ shí nàmǐ, gù bómó biǎomiàn pínghuá guāngliàng.CIS bómó zhēng dù de guòchéng zhōng, xiān xíngchéng Cu2Se hé In2Se3 liǎng gè èr yuán xiāng (binary phase), zài jìnyībù fǎnyìng shēngchéng CuInSe2 sān yuán xiāng (ternary phase). Zài 20 shìjì 80 niándài, měiguó bōyīn gōngsī shíyàn shì suǒ zhìzuò de CIS tàiyángnéng diànchí túpò 10% de néngliàng zhuǎnhuàn xiàolǜ, dádào 12% , qí CIS bómó shì xiānhòu fēnbié zài fù Cu hé fù In de zhēngfā tiáojiàn xià zhìbèi de. Zài fù Cu de tiáojiàn xià kě dédào dà jīng lì de CJS bómó dàn què hányǒu Cu2Se èr cì xiāng, zài duō jīng bómó de shēngzhǎng guòchéng zhōng,Cu2Se wèi yètài bìng chéngxiàn zài biǎomiàn hé jīng jièmiàn (grain boundary), cǐ yǒu zhù yú jīng lì zhǎng dà; jǐn jiēzhe fù In de shēng cháng tiáojiàn jiāng kě ràng duōyú de In2Se3 èr yuán xiāng gēn fù Cu CIS mó zhōng de Cu2Se èr cì xiāng wánquán fǎnyìng ér bèi xiāochú, zuìhòu dédào de shì dà jīng lì qiě dānyī xiàng de CIS bómó, dāngrán bómó zhōng xiān xíngchéng de zǔ fèn hán shāo duō de tóng ér chéngxiàn P xíng dǎodiàn tèxìng, ér shāo hòu xíngchéng de bùfèn zé wèi In piān duō de zǔ fèn, yīn'ér jù gāo diànzǔ lǜ N xíng jiējìn běn zhēng (in­ trinsic) bàndǎotǐ de dǎodiàn tèxìng. Tóngshí qí,ARCO solar gōngsī yì fāzhǎn CIS de shài huà gōngyì, yǐ gāi gōngyì zhìzuò de CIS tàiyángnéng diànchí, qí xiàolǜ suī lüè xùn yú yǐ zhēngfā gōngyì suǒ zhìzuò de tàiyángnéng diànchí, dàn jǐn suí qí hòu. Shài huà gōngyì shì xiān fēnbié dù zhì tèdìng hòudù de Cu hé In jīnshǔ mó yǐ dáchéng tèdìng de yuánzǐ shù pèi bǐ, zài zhìyú H2Se qìtǐ huò Se zhēngqì zhī zhōng, yǐ 400 ℃yǐshàng de wēndù ràng qí fǎnyìng chéng Cu2Se. Yǐ shài huà fǎ zhìbèi de bómó, qí zǔchéng jūnyún dù lüè xùn yú zhēngfā zhě, dàn réng néng mǎnzú gāo xiàolǜ tàiyángnéng diànchí de yāoqiú, qí hǎochù zàiyú kě shǐyòng dà miànjī jiàn shè gōngyì, shènzhì dī chéngběn de mò yìn (ink printing) gōngyì, shìhé liàng chǎn de guīhuà. Lìngwài, xīnshì de shài huà fǎ cǎiyòng kuàisù tuìhuǒ (rapid thermal ling, shēngwēn sùlǜ zhìshǎo 10℃/s yǐshàng), jiāng cuì bǎn shàng Cu/ In/Se sān yuánsù yù dùcéng (precursor film) yǐ 400~500℃de wēndù zài jí duǎn shíjiān (1~5 min) nèi wánchéng shài huà fǎnyìng xiǎnrán cǐ gōngyì gèng jù chǎnliàng dà yǔ qī běn dī de yōushì. Shài huà fǎ ruò yǐ zhújiàn shēngwēn de fāngshì wéi zhī qí chéng mó guòchéng shì yī xìliè de fǎnyìng xiānhòu zài jìnxíng, yì jí xiān yǒu tóng huà nài hé gù huà shài děng duō shén èr yuán zhōngjiān xiàng de xíngchéng, zuìhòu héchéng sān yuán de CIS dānyī xiāng. Rúguǒ shǐyòng kuàisù shēngwēn jí kě tiàoguò zhōngjiān xiàng de xíngchéng. Zhíjiē héchéng CIS huàhéwù, yǐ cǐ fāngshì suǒ zhìbèi de cáiliào bìng bù huì zàochéng diànchí xiàolǜ jiǎnsǔn, zhìyú bómó xíngchéng de jīzhì zé yīn héchéng sùdù tài kuài ér nányǐ dé zhī, dàn réng kě lìyòng jiànjiē de fāngshì xúnqiú gèng hǎo de cáizhì. Mùqián yǐ CIGS wéi zhǔyào xīshōu céng de tàiyángnéng diànchí, qí zuìgāo zhuǎnhuàn xiàolǜ yǐ dá 19. 2% , Shì yóu měiguó NREL yú 2003 nián tíchū.NREL shǐyòng gǎiliáng shì de zhēngfā fǎ chēng wèi sān jiēduàn gōngyì (three-stage process), gùmíngsīyì, cǐ fǎ shì jiāng zhěnggè gōngyì fēn wéi sān gè jiēduàn lái tiáo biàn jībǎn wēndù yǔ kòngzhì bùtóng de yuánsù yuán jí qí zhēngfā wēndù. Dì yī jiēduàn shì jiāng yǐ dù shàng lǚ (Mo) jīnshǔ de yóu bōlí jiārè zhì 260℃, jǐng tóngshí tígōng yuánsù In,Ga hé Se shēngzhǎng On,Ga) xiānqū wù; dì èr jiēduàn zé guānbì yuánsù In hé Ga, gǎi tígōng yuánsù Cu hé gāng, jǐng jiārè jībǎn zhì 560°c, cǐ shí sì yuán huàhéwù Cu On, Ga) kāishǐ xíngchéng, bìng bànsuí chǎnshēng èr cì xiāng yú bómó biǎomiàn, gāi èr cì xiāng chéng yètài, yǒu zhù yú chǎnshēng dà jīng lì qiě zhìmì de zhùzhuàng jiéjīng; dì sān jiēduàn jí guānbì yuánsù Cu bìng bǎochí jībǎn wēndù zài 560℃, zài jìxù tígōng In,Ga hé Se yī xiǎoduàn shíjiān hòu yě guānbì In hé Ga, shǐ zúgòu de yuánsù In hé Ga yǔ èr cì xiāng zàicì fǎnyìng, zài biǎomiàn xíngchéng Cu2(In,Ga)4 Se7 huò Cu1(In,Ga)3 Se5 bómó, gù zuìhòu huì xíngchéng tóng shāowéi bùzú (Cu-poor) de Cu(In,Ga)4 Se2 bómó, qí zǔchéng bǐzhí wèi o. 93< Cu/ (In shí Ga)≤O. 97, Zuìhòu zài yuánsù Se qìfēn xià, zuò 5~10 min de gāowēn tuìhuǒ jìnxíng zài jiéjīng . Yǐ sān jiēduàn zhēng dù gōngyì shēngzhǎng de CIGS bómó de pōumiàn pǐn lì jiégòu yǐ cǐ fǎ zhìbèi de CIGS bómó, qí zǔchéng yuánsù zòngshēn fēnbù rú tú 1 suǒ shì 0 jièzhe jiārù Ga xíngchéng sì yuán huàhéwù, kě zēng dà zhǔ xīshōu céng de néng xì zhí, rúcǐ néng shǐ kāilù diànyā zēngjiā 20~30 mV. Zhì yú Ga de nóngdù fēnbù tīdù zé yùnyòngle a-SiGe tàiyángnéng diànchí de néng dài shèjì gàiniàn, shǐ dǎo dài xíngchéng V xíng shuāng xiélǜ, cǐ shèjì dài yǒu bèi xiàng diànchǎng yòng lái tuīdòng diànzǐ xiàng PN jié yídòng, yǒu zhù yú jiǎnshǎo zài bèimiàn jīnshǔ jiēchù jièmiàn chù fùhé (recombination) de jīhuì bìng jiāqiáng diànhè de shōují, ér guāng rùshè fāngxiàng zé dé yì yú néng xì jiàn jiǎn de xiélǜ shèjì, kuòdà guāng xīshōu bōduàn de hángài zhí wéi. Zhěngtǐ ér yán, kě zēngjiā duǎnlù diànliú. Shàngshù de cáiliào hé qìjiàn shèjì lǐniàn de chénggōng yùnyòng shì jiāng CIGS tàiyángnéng diànchí xiàolǜ tuī xiàng 15% yǐshàng de zhǔyào yuányīn. Shìshí shàng, yǐ liú qǔdài bùfèn shài chéng wèi sì yuán huàhéwù yě kěyǐ shǐ néng xì zēngjiā ér dédào xiàng CIGS yīyàng de xiàoguǒ, zhǐshì liú de zhēngqì yā bǐ shài gāo xǔduō, ruò shǐyòng zhēngfā fǎ zài kòngzhì shàng xū shǐyòng tèshū de zhēngfā yuán shèjì yǐ tèzhì fámén tiáojié liú zhēngqì de shūchū. Mùqián zài CIG shài huà liàng chǎn gōngyì zhōng, yě kěyǐ tóngshí zhì rù shài hé liú héchéng CIGSS wǔ yuán huàhéwù. Yuèdú gèng duō: Nǐ duì duōjīngguī tàiyángnéng diànchí liǎojiě duōshǎo? 展开 3,754 / 5,000 翻译结果 I-III-VI Group 2 Semiconductor Solar Cell/CuInSe2 Thin Film Process

I-III-VI Group 2 Semiconductor Solar Cell/CuInSe2 Thin Film Process

Since the 1950s, I-III-VI 2 compounds have been studied to understand their crystalline phases and material properties, and Shay and Wernick published the results of these studies in 1975. The device characteristics of PN junction solar cells fabricated with CulnSe2 and CdS were also published in 1976. After that, the electrical efficiency of CIS solar energy has been gradually improved with the continuous improvement of the process and matching materials. The current highest efficiency I-III-VI 2 thin film solar cell, its main absorber layer, its Ga/In ratio must be maintained within 0.3. . If it is higher than 0.3, the solar cell efficiency will be greatly reduced. The efficiency of solar cells made with the ternary compound CulnSe2 is slightly lower because although the material has a rather high light absorption coefficient, the energy gap of CulnSe2 is only about 1.0 eV. The addition of Ga makes the material a quaternary compound, which can increase the energy gap of CulnSe2, and also increase the open circuit voltage of the battery and reduce the current to reduce the resistance loss, thereby achieving higher battery efficiency. Before I accidentally browsed an article, the author wrote very detailed and comprehensive on the various factors affecting battery efficiency. If you are interested, please visit

CulnSe2 is the most studied of all I-III-VI 2 compounds, and of course good results have been obtained. However, even if Ga is added to increase the energy gap to improve the cell efficiency, as mentioned above, when the value of x exceeds 0.3, the expected effect cannot be obtained, and when r = 0.3, the energy gap can only reach 1.15 eV. There have been some attempts to change the energy gap by means of the composition of quaternary compounds, or even pentads, in an attempt to improve cell efficiency, but this has not been the case, but has reduced the efficiency. It seems that for a long time, the successful experience of material matching and improvement obtained in CulnSe2 and Se2 cannot be directly applied to other I-III-VI 2 series compounds, especially CulnSe2, which is in addition to CulnSe2, additionally by composition. The I-III-VI 2 compounds of N-type and P-type can be obtained by formulating, as shown in Table 1, its energy gap is about 1.5 eV, as mentioned above, it is a kind of solar cell with appropriate energy gap value Material. Often these changes in material properties include interfacial and intrinsic defects.

Table 1-Energy gap and electrical properties after annealing of I-III-VI group 2 compounds
Table 1-Energy gap and electrical properties after annealing of I-III-VI group 2 compounds

The combined effect is enough to lead to considerable negative results, and it is clear that enough research efforts are still needed for these I-III-VI 2 series compounds to show their proper device performance. Therefore, the following is an introduction to the device structure and process of high-efficiency solar cells.

  1. Thin film process of CuInSe2

High-efficiency CIS solar cells use co-evaporation (co-evaporation) or solarization (selenization) reaction method to coat CIS thin films. Other methods, such as co-sputtering, have defects such as defects caused by high-energy film surface impact, and insufficient control of film composition due to In repulsion. At present, high-efficiency solar cells cannot be produced by this process; For example, the thin films plated by low-cost electrochemical deposition (electro deposition) are not suitable for the fabrication of high-efficiency solar cells due to their poor quality.

The three-source (CIS) or four-source (CIGS) co-evaporation process uses an elemental evaporation source to evaporate at a substrate temperature of 450 to 600 °C. Because the vapor pressure of the Se element is high, the ratio of Cu to Group III elements 1), the grain size is about several hundreds or even thousands of nanometers, and the film has a rough surface; while the grain size of the In-rich film is less than tens of nanometers, so the surface of the film is smooth bright. In the process of CIS thin film evaporation, two binary phases (Cu2Se and In2Se3) are formed first, and then the CuInSe2 ternary phase is formed by further reaction.

In the 1980s, the CIS solar cell produced by the Boeing laboratory in the United States broke through 10% of the energy conversion efficiency, reaching 12%, and its CIS thin film was successively prepared under Cu-rich and In-rich evaporation conditions. CJS films with large grains can be obtained under Cu-rich conditions but contain Cu2Se secondary phases. During the growth of polycrystalline films, Cu2Se is liquid and appears on the surface and grain boundaries, which helps Grain growth; followed by In-rich growth conditions, the excess In2Se3 binary phase will completely react with the Cu2Se secondary phase in the Cu-rich CIS film and be eliminated, resulting in a large-grain and single-phase CIS The film, of course, the component formed first in the film contains a little more copper and exhibits P-type conductivity, while the part formed later is a component with more In, so it has a high resistivity N-type close to intrinsic (in trinsic) ) Conductivity properties of semiconductors.

At the same time, ARCO solar company also developed the CIS solarization process. Although the efficiency of CIS solar cells produced by this process is slightly lower than that of solar cells produced by evaporation process, it is close behind. The tanning process is to first coat Cu and In metal films with specific thicknesses to achieve a specific atomic number ratio, and then place them in H2Se gas or Se vapor, and react them into Cu2Se at a temperature above 400 °C. The composition uniformity of the thin film prepared by the solarization method is slightly inferior to that of the vaporizer, but it can still meet the requirements of high-efficiency solar cells. Process, suitable for mass production planning. In addition, the new tanning method adopts rapid thermal annealing (rapid thermal ling, the heating rate is at least 10°C/s or more), and the Cu/In/Se three-element pre-plating layer (precursor film) on the extraction plate is heated at a temperature of 400~500°C. The drying reaction is completed in a very short time (1~5 min), obviously this process has the advantages of large output and low cost.

If the solarization method is gradually heated, the film formation process is a series of reactions that are carried out successively, that is, the formation of polythematic binary mesophases such as copper resistance and induration, and finally the synthesis of ternary. CIS single phase.

The formation of intermediate phases can be skipped if rapid heating is used. Directly synthesizing CIS compounds, the materials prepared in this way will not cause loss of cell efficiency. As for the mechanism of film formation, it is difficult to know because the synthesis speed is too fast, but indirect methods can still be used to find better materials.

At present, the highest conversion efficiency of solar cells with CIGS as the main absorber layer has reached 19.2%, which was proposed by NREL in the United States in 2003. NREL uses an improved evaporation method called a three-stage process. As the name suggests, this method divides the entire process into three stages to modulate the substrate temperature and control different element sources and their evaporation temperatures.

The first stage is to heat the uranium glass plated with aluminum (Mo) metal to 260°C, and to provide the elements In, Ga and Se to grow On, Ga) precursors at the same time; in the second stage, the elements In and Ga are turned off and replaced to provide Elemental Cu and vat, well heat the substrate to 560°C, at this time the quaternary compound Cu On, Ga) begins to form, accompanied by the formation of a secondary phase on the film surface, which is liquid and helps to generate large grains And dense columnar crystals; the third stage is to turn off the element Cu and keep the substrate temperature at 560 ° C, and then continue to provide In, Ga and Se for a short period of time and also turn off In and Ga, so that enough elements In and Ga are combined with the secondary phase. Reaction again to form Cu2(In,Ga)4Se7 or Cu1(In,Ga)3Se5 film on the surface, so Cu(In,Ga)4Se2 film with slightly insufficient copper (Cu-poor) will eventually be formed. Its composition The ratio is 0.93<Cu/(In+Ga)≤0.97. Finally, in the elemental Se atmosphere, do high temperature annealing for 5~10 min for recrystallization.

Cross-sectional grain structure of CIGS thin films grown by three-stage evaporation process
The depth distribution of the constituent elements of the CIGS thin film prepared by this method is shown in Figure 1. By adding Ga to form a quaternary compound, the energy gap value of the main absorber layer can be increased, so that the open circuit voltage can be increased by 20-30 mV. As for the concentration distribution gradient of Ga, the energy band design concept of a-SiGe solar cells is used to make the conduction band form a V-shaped double slope. The opportunity for recombination at the back metal contact interface enhances the collection of charges, and the light incident direction benefits from the design of the slope of the energy gap, which expands the coverage of the light absorption band. Overall, the short-circuit current can be increased.

Figure 1-Depth distribution of constituent elements of CIGS thin films
Figure 1-Depth distribution of constituent elements of CIGS thin films

The successful application of the above-mentioned material and device design concepts is the main reason for pushing the efficiency of CIGS solar cells above 15%. In fact, replacing part of the tanned with sulfur into a quaternary compound can also increase the energy gap to obtain the same effect as CIGS, but the vapor pressure of sulfur is much higher than that of tanning. If the evaporation method is used, a special evaporation source design is required for control. The output of sulfur vapour is regulated by a special valve. At present, in the mass production process of CIG tanning, it is also possible to simultaneously insert tanning and sulfur to synthesize CIGSS five-membered compounds.

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CdTe Thin Film Technology and Development Trend of CdTe Thin Film Solar Cells

CdTe Thin Film Technology and Development Trend of CdTe Thin Film Solar Cells

  1. CdTe thin film process

In order to reduce the cost of CdTe films, polycrystalline structures are often the mainstay, which can be prepared by various methods, including evaporation, close-spaced sublimation (CSS), and vapor transport deposition (vapor transport deposition). , VTD ) , chemical vapor deposition ( chemical vapor deposition , CVD ) , electrochemical deposition ( electro deposition . ED ) , screen printing ( screen printing ) , thermal plate spraying ( spray pyrolysis ) , sputtering ( sputtering ), etc. has been used [7]. Figure 7.4 organizes various CdTe coating processes and related process conditions for reference and comparison [8]. Because CdTe has ionic bonds. It is easy to form Cd and Te bonds during the film formation process, and different coating methods are used. It is not difficult to control the stoichiometric composition. Even elemental films of Cd and Te can be plated separately at room temperature and then heated up. to form compounds.

It is worth mentioning that CdTe solar cells often require an additional heat treatment procedure. Also CdCl2 is usually mixed into the air with a partial pressure of 0.04 and heat treatment at a temperature of 425 ℃ for 20 min. This promotes the growth of CdTe grains and the passivation of the crystal interface, so that the high resistance at the crystal interface disappears, and at the same time, it promotes the mutual diffusion of materials between PN heterojunctions, forming ternary compounds (such as CdS/CdTe near the interface. Produces CdTe1, S,) with a graded composition, thereby reducing the interface defect density caused by the lattice mismatch between CdTe and CdS. This procedure helps to greatly improve the efficiency of solar cells; while 0 in the air has The effect of increasing the P-type conductivity of CdTe and promoting CdS/CdTe interdiffusion. There is also a saying: Since this is a necessary follow-up process. It does not matter which method is used for the CdTe coating, as much as possible using the low-cost method.

  1. Electrical properties and device technology of CdTe

The combination of N-CdS/P-CdTe in II-VI solar cells can reach 16.5% energy conversion efficiency. The large-area CdTe solar cell module has entered the mass production stage in recent years, and its energy conversion efficiency has exceeded 10%. Different companies use different preparation methods for the P-CdTe film in the device structure, which are coating technologies such as close-range volatilization, electrochemistry, and vapor transport.

The P-type doping of CdTe is dominated by P or As, and it is usually doped under Cd overpressure, that is, Cd-rich conditions. The hole concentration of 2 × 101; cm – 3 can be obtained for the CdTe epitaxial film prepared by CVD or MOCVD, while the polycrystalline film is only 6 × 101 cm . As doped CdTe prepared by photo-assisted molecular beam epitaxy (PAMBE) has the highest hole concentration of 6. 2 × 1018 cm – 3, which is conducive to the activity of atoms on the surface under illumination , and also makes Te more easily desorbed, and the effect on the doping amount is not obvious. In the MBE process, some people have also used low-energy ion beam doping, and its hole concentration is only 2 × 1017 cm3, but the material defects caused by the ion beam impact make its electrical properties worse, and it often needs to be regrown on it. A layer of undoped CdTe to avoid reducing the short-circuit current of the solar cell.

In terms of ohmic contact, because the work function of P-CdTe is as high as 5.7 eV, no metal can form an ideal ohmic contact with it, so the metal alloy containing Cuo.12Au0.88 is rich in Te after treatment. The surface of CdTe is diffused from Cu into the lattice position where CdTe replaces Cd, which promotes the formation of high content of P-type doping on the surface of CdTe, and holes are conducted through strong electric field tunneling. In the module mass production process, the 1-contact resistance contact of the P-CdTe polycrystalline film is often fabricated by electron beam evaporation on the surface of CdTe after CdCl2 annealing treatment → Cu thin layer, and then heated to promote the diffusion of Cu into CdTe, achieve surface doping.

In summary, the fabrication of high-efficiency N-CdS/P-CdTe solar cells should be based on the following designs and steps: ① Coating the CdTe film on the transparent CdS/TCO/Glass substrate; ② The thinner the CdS light-transmitting layer, the more It can improve the spectral response of short wavelength; ③ After the CdTe coating, a heat treatment procedure is required in the atmosphere of CdCl2 and O2 to improve the grain structure and P-type conductivity of CdTe, and also promote the interaction between CdTe and CdS. The interdiffusion of CdTeS is formed to reduce the number of interface defects; ④ The CdTe layer is chemically treated to make its surface rich in Te, then plated with Cu and heated to diffuse into CdTe to increase the amount of P-type doping, and finally plated on Conductive materials such as Ni or graphite.

  1. Future development of CdTe thin film solar cells

CdTe solar cells are mass-produced by one or two companies in the United States and Germany. The energy conversion efficiency of large-area CdTe modules can currently reach 10.5% and the service life is as long as 25 years. Its unit cost has the opportunity to be $1 per watt. The following are the thin-film solar cells with the lowest cost at present. Furthermore, Cd and Te elements can be obtained from the smelting process of basic metals such as copper and iron ore. However, a negative factor in the application of this product is that the Cd contained in the material is a heavy metal element, and the environmental protection problems caused by its process and disposal have attracted much attention. Although the industry emphasizes that the pollution of Cd compounds is very different from that of elemental Cd, and that the process and waste recycling treatment procedures can meet strict requirements, a company in the United States even takes long-term samples of its employees in the production line. Examination of the Cd content in the body has not detected higher than usual results, but it is still worrying. Under the competition of other materials, although the EU’s restrictions on the Cd content of most electronic products have not yet included solar cells, the manufacturers of CdTe solar cells mass-produced in the short term have fewer competitors to produce the same products, and the products are more expensive. This is lower than solar cells made of other materials, thus making profits. Manufacturers even give a plan to pay the cost of recycling solar panels in the future, but in the long run, under the stricter environmental protection requirements in the future, it is not conducive to CdTe solar cells. development of.

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What are the characteristics of II-VI and I-III-VI compound semiconductor materials?

What are the characteristics of II-VI and I-III-VI compound semiconductor materials?

one II-VI compounds

As shown in the periodic table of elements in Fig. 1, group E elements (including Zn, CD, Hg) and group H elements (i.e. s, Se, Te, etc.) constitute group II and VI compounds with semiconductor properties, Its basic properties are shown in Fig. 1[5l. Except that CdTe and ZnSe have n-type and p-type conductive properties, other II-VI compounds can only obtain a single conductive form, such as p-type ZnTe and n-type CDs, CdSe, ZnS, etc. Therefore, there are some restrictions on the matching of materials. According to theoretical calculation, PN homojunction (Homo J function) The energy conversion efficiency of solar cell is the highest, and its energy gap is 1 About 5 EV, so CDT has naturally become the most suitable material for solar cells in h-group compounds.

periodic table of ele ments
periodic table of ele ments

II-VI compounds have stronger ionic bonds than V group. In addition, the vapor pressure of group II and VI elements is similar and their value is not low. Therefore, in the preparation of materials, it is easy to form compounds by self interactive coordination. For the growth of thin films, if the substrate temperature is set so that the same atoms (ii-ii or vi-vi) cannot form valence bonds, the elements of group H and group m only have interactive valence bonds to form group II-VI compounds; Under normal coating conditions, the temperature is not high, about 300 ℃.

Some of the crystalline structures of II-VI compounds are cubic sphalerite structures, such as ZnSe, ZnTe, CdTe, etc., while others are hexagonal structures, such as CdSe; CDs and ZnS have one or both of the above two structures according to the material preparation conditions. Different structures have different properties.

In semiconductor materials, the strength of valence bond is directly related to the energy gap. From the periodic table in Fig. 1, those with small atomic numbers of constituent elements in II-VI compounds have strong ionic bonds. For example, Zn Se is stronger than Zn te, and CD-s is also stronger than CD te; Their energy gap also reflects the strength of bidding bond. Compared with CD te, Zn te has stronger valence bond and larger energy gap.

  1. I-ill-vi group 2 compounds

Group I VI 2 compounds can be regarded as three element compounds derived from group II VI, that is, the elements of group H are replaced by group I (Cu, Ag) and group I (al, GA, in) and combined with group VI (CS, Se, TE). Because there are two kinds of atoms arranged alternately and orderly in the lattice position occupied by cations, the unit cell seems to be formed by stacking the unit cells of two amphibolites. However, the unit length ratio of c-axis and a-axis is different due to the valence bond strength of two different cations and anions, which is not equal to 2. Such a crystalline structure is called chalcopyrite structure, as shown in Figure 2.

crystal structure of I-III-VI compounds
crystal structure of I-III-VI compounds

As can be seen from the periodic table of Fig. 1, this series of compounds include 18 compounds such as group I elements Cu and Ag, group IV elements Al, in and GA and group M elements s, Se and te. Like other compound semiconductors, their energy gaps can form quaternary or even quinary compounds through the mutual substitution of homologous elements in a certain range. The biggest difference between it and tianv or HVI compounds is that there is no composition very close to the chemical ratio. The composition stability range of single phase can reach 3% ~ 5%, and the degree of deviation from the fixed ratio composition of 1:1:2 is considerable. The above situation can be seen from the pseudo binary phase diagram of Fig. 2. The situation of deviating from the fixed specific composition will produce intrinsic point defects in the material. There are 12 kinds of ternary compounds of III-VI group, and the distribution of the number of various point defects is closely related to the chemical composition and the formation energy of defects.

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