Cadmium telluride film Solar cell Development overview of
1、 Overview & }6 _" ~7 R$ K: U5 P4 r
CdTe is a Ⅱ - Ⅵ compound semiconductor with a band gap of 1.5eV, which is very compatible with the solar spectrum. * It is suitable for photoelectric energy conversion. It is a good PV material [1], has a high theoretical efficiency (28%) [2], has stable performance, has been valued by the photovoltaic industry, and is a kind of thin film battery with rapid technological development. Cadmium telluride is easy to deposit into large area films, and the deposition rate is also high. CdTe thin film solar cells are usually based on CdS/CdTe heterojunction. Although the difference between CdS and CdTe and lattice constant is 10%, the heterostructure composed of them has excellent electrical performance, and the filling factor of the solar cell made of them is as high as F F=0.75 [3]. ! |. s. f) I0 W `3 K
Various processes and technologies for preparing CdTe polycrystalline films have been developed, such as near space sublimation, electrodeposition, PVD, CVD, CBD, screen printing, sputtering, vacuum evaporation, etc. [4]. Screen printing sintering method: screen printing CdTe and CdS films with CdTe and CdS slurry, and then heat treating them for 1h in a controlled atmosphere at 600-700 ℃ Near space sublimation method: glass is used as the substrate, the substrate temperature is 500~600 ℃, and the deposition rate is 10 μ m/min. Vacuum evaporation method: CdTe is sublimated from a heating crucible at about 700 ℃ and condensed on a substrate at 300~400 ℃, with a typical deposition rate of 1 nm/s. The typical structure of semiconductor heterojunction battery with CdTe absorption layer and CdS as window layer: antireflection film/glass/(SnO2: F)/CdS/P-CdTe/back electrode. The laboratory efficiency of the battery keeps rising, * up to 16%. At the beginning of 1990s, CdTe battery has realized large-scale production, but the market development is slow, and the market share has been hovering around 1%. The average efficiency of commercial batteries is 8% - 10% [5]. / L2 d: c/ B4
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In order to better and more systematically study CdTe solar cells, this paper briefly introduces CdTe Thin film solar cell The research progress and industrial development at home and abroad, as well as the existing problems and constraints.
#{+]% Q7 X, I "q * W II. Development status and trend of CdTe thin film solar cell industry abroad ( r. w- e+ z. Q9 N" [
CdTe thin film solar cell is a kind of photovoltaic device that develops rapidly in thin film solar cells. In 1993, the University of South Florida in the United States used the sublimation method to make a solar cell with an efficiency of 15.8% on an area of 1cm2 [6]. Subsequently, Japan's Matsushita Battery reported that the CdTe based cell uses CdTe as the absorption layer, The typical structure of n-CdS/P - CdTe semiconductor heterojunction cell with CdS as the window layer is MgF2/glass/SnO2 ∶ F/n-CdS/P - dTe/back electrode. The small area cell * has a high conversion efficiency of 16% [7], which became the * high record of CdTe thin film solar cells at that time. In recent years, the research direction of solar cells is high conversion efficiency, low cost and high stability Therefore, thin film solar cells represented by CdTe have attracted much attention. Siemens reported that the conversion efficiency of cells with an area of 3600cm2 has reached the level of 11.1%. The National Renewable Energy Laboratory of the United States provided the test results of a 6879cm2 CdTe thin film solar cell with Solar Cells lnc, and the conversion efficiency reached 7.7%; Bp Solar's CdTe thin film solar cell, with an area of 4540cm2, has an efficiency of 8.4%, and the solar cell with an area of 706cm2 has a conversion efficiency of 10.1%; Goldan Photon's CdTe solar cell has an area of 3528cm2 and a conversion efficiency of 7.7%. See Table 1 [7-11] for details. ( g$ q) s9 L/ S$ I( g0 [4 K; Z$ G
Table 1 Parameters of CdTe thin film solar cells [7-11] , o0 K7 F # a* o( L/ ?' y; {
Small area single battery 6 ^& c0 l8 ^+ U7 m: C! e6 V
Area of research institution/cm2 Open circuit voltage/V conversion efficiency/%
) ]# } {; a9 E3 v$ k/ @Matsushita 1.0 16
9 g' }, C |/ F6 s! aUSF 0.928 0.845 15.8
1 r$ b# Z% Q* fSCI 0.27 0.839 13.3
2 @- p- d3 C; z2 i5 sCSM 0.10 0.778 12.9 1 H( H! W8 X& K/ @5 d8 v6 W
NREL 0.69 0.823 12.8 2 |9 i _, n( C9 u( a# j* A/ @! g
. j& Q3 c) w {) N# ?, ?1 c$ {
Large area single battery
7 k2 a8 E9 q; g. O+c Research facility area/cm2 Conversion efficiency/% power/W
2 a/ A/ B7 a* z ]+ V& sBP Solar 4540 8.4 38.2 2 Y2 H- o! j) j/ Z9 F
SCI 6728 9.1 61
9 T4 x0 e( ~) n& ^; e" `GP 3528 7.7 27.2
) e. \" F. R: ^% B" qMatsushita 1200 8.7 10
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It is believed that CdTe thin film solar cells are easy to manufacture among solar cells, so they are making rapid progress towards commercialization To improve efficiency is to optimize the cell structure and the material process of each layer. Properly reducing the thickness of the window layer CdS can reduce the loss of incident light, thus increasing the short wave response of the cell to improve the short circuit current density. CdTe cells with higher conversion efficiency use a thinner CdS window layer, which has set a record. To reduce costs, it is necessary to reduce the deposition temperature of CdTe to below 550 ℃, Use cheap glass as the substrate; When laboratory achievements go into industry, they must go through the process of design, research and optimization of components and production modes In recent years, not only research groups in many countries have been able to produce CdTe solar cells with a conversion efficiency of more than 12% at low substrate temperature, but also have made gratifying progress in large-area modules. Many companies are carrying out pilot tests of CdTe thin film solar cells and building production plants, some of which have been put into production
"^. x * b $f9? $O On the basis of extensive and in-depth application research, the CdTe thin film solar cells in many countries around the world have begun to move from laboratory research to large-scale industrial production. In 1998, the output of CdTe batteries in the United States was 0.2MW. At present, the production capacity of CdTe thin film batteries in Golden Photo of the United States is 2MW [12], and the output of CdTe batteries in Japan is 2.0MW. German ANTEC will build a 10MW CdTe thin film solar cell module manufacturing plant in Rudisleben, and its production cost is expected to be less than $1.4/w. The module not only has excellent performance, but also has advanced production technology, which makes the PV module It has a * * shape and can be used in buildings, which not only broadens the application range, but also can replace some building materials to further reduce the cost of batteries. BP Solar plans to produce CdTe thin film solar cells in Fairfield. Solar Cells will also further expand the production of CdTe thin film solar cells.
# k3 X6 m$ ]- O9 i! 5) _ III. Development status and trend of domestic CdTe thin film solar cell industry
f. G1 C$ @; The {9K "f CdTe thin film solar cell has low manufacturing cost. At present, the obtained * efficiency is 16%, which is a new type of solar cell with good application prospects. It has become the main object of research and development in the United States, Germany, Japan, Italy and other countries.
B k (h! @ 7 Q The research work of CdTe thin film batteries in China began in the early 1980s. Inner Mongolia University used evaporation technology, and Beijing Solar Energy Research Institute used electrodeposition technology (ED) to research and prepare CdTe thin film batteries. The latter developed a battery efficiency of 5.8% [13]. From the mid-1980s to the mid-1990s, research work was at a standstill. In the late 1990s, the Institute of Solar Materials and Devices of Sichuan University, under the leadership of Professor Feng Lianghuan, carried out research on cadmium telluride thin film solar cells in China. During the "Ninth Five Year Plan" period, it undertook the scientific and technological research project funded by the Ministry of Science and Technology: "Development of Ⅱ - Ⅵ compound semiconducting polycrystalline thin film solar cells". The CdTe thin film battery was studied by using the near space sublimation technology and achieved good results* The near battery efficiency has exceeded 13.38% [14], entering the world's advanced ranks. During the "Tenth Five Year Plan" period, the research on CdTe thin film batteries was included in the "863" key project of the national high-tech research and development plan.
%| - i8 O 'w "O&S9 I $L After years of unremitting efforts of several generations of scientific workers, China is in the rapid development stage from laboratory basic research to application industrialization, and plans to establish a pilot production line with an annual output of 0.5MW. The research on CdTe thin film solar cells will last for two years, from the original basic research carried out by several scientific research institutes, such as Inner Mongolia University, Sichuan University, Xinjiang University, to the industrialization of new film CdTe/CdS solar cell core materials of Sichuan Apollo Solar Technology Development Co., Ltd. This year, a production line with an annual output of 50 tons of cadmium telluride will be built The 10 ton production line of cadmium sulfide will enable the industrialization of CdTe thin film solar cells in China to develop rapidly and move towards the level of * * * *. 5 v. E; ~; C- l! b* B8 p* U
4、 Existing problems and constraints / K+ o# T& Y, J
CdTe thin-film solar cells are easier to manufacture than other thin-film batteries, so it has made rapid progress towards commercialization. It has moved from laboratory research stage to large-scale industrial production. The next research and development focus is to further reduce costs, improve efficiency and improve production processes. CdTe solar cells have many factors conducive to competition, but its global market share was only 0.42% in 2002. At present, the efficiency of commercial products of CdTe solar cells has exceeded 10%. The reasons why it cannot become the mainstream of the market are as follows: 1 modular The cost of the substrate material is too high. The overall CdTe solar cell material accounts for 53% of the total cost, of which the semiconductor material only accounts for about 5.5%. 2、 The natural transportation and storage of tellurium is limited, and its total amount is bound to be unable to meet the needs of a large number of overall power generation relying on such photocells. 3、 The toxicity of cadmium makes people unable to accept such photocells at ease. $ {$ f [: U& {9 h
As a large-scale production and application of photovoltaic devices, the problem of environmental pollution deserves attention. The pollution of toxic element Cd to the environment and the harm to the health of operators cannot be ignored. We can not obtain clean energy, but also cause new harm to human body and human living environment. It is technically simple to effectively dispose of abandoned and damaged CdTe components. But Cd is a heavy metal, which is highly toxic. Its compounds are as toxic as Cd. The main impacts are: first, the harm of dust containing Cd to humans and other animals through the respiratory tract; The second is the pollution caused by the discharge of production wastewater and waste. Therefore, Cd and Te on broken glass sheets should be removed and recycled, damaged and abandoned components should be properly treated, and wastewater and waste discharged in production should be treated in accordance with environmental standards. At present, all countries are making great efforts to study and solve the factors for the development of CdTe thin film solar cells. It is believed that the above problems will be solved one by one soon, so that CdTe thin film solar cells will become one of the new energy components in the future society.
