1 Introduction

　　New and renewable energy is one of the most decisive technological fields in the 21st century. t Solar photovoltaic (PV) panels are an important renewable energy source, which can be used as a stand-alone energy source and can also be grid-connected to generate electricity with zero pollution emission. Due to the cost of silicon solar cells, they were initially only used in space, but with the development of technology and the maturity of the production process, their costs are decreasing and their applications are gradually expanding. In the face of today's energy supply situation and the increasingly serious environmental pollution, which endangers the survival of mankind itself, the concept of developing new and renewable energy sources has been widely accepted around the world. Very large photovoltaic power plants with a generating capacity of more than 100 MW are being built all over the world, and there are few large photovoltaic power plants with a generating capacity of several tens of MW (under construction and completed). The large-scale development has made the upstream raw material production in short supply, the problem is becoming more and more prominent, many solar cell chip manufacturers and module manufacturers have to be often in a state of shutdown due to the problem of raw materials, the supply and price of raw materials has become a bottleneck to restrict the current solar cell production.

　　The thickness of thin film cells is generally 0.5 to several microns, which is less than 1/100 of that of crystalline silicon solar cells, greatly reducing the consumption of raw materials and thus the cost. Thin film cells can be deposited on inexpensive substrates such as glass, stainless steel sheets or mylar films, and can be bent or even rolled up for portability.

　　The research on thin film solar cells started in the 1960s, and the current international trends are mainly amorphous silicon (a-Si:H) thin film solar cells, micro(multi)-crystalline silicon thin film solar cells, copper indium selenium (CuInSe,CIS) thin film solar cells, cadmium telluride (CdTe) thin film solar cells, dye sensitized thin film solar cells (DSSC), and organic thin film solar cells. The development of each type of thin-film solar cells is summarized below.

(1) Light weight, high specific power

　　Amorphous silicon thin film cells prepared on stainless steel substrates and mylar film substrates are light, soft and have high specific power. The specific power on the stainless steel substrate can reach 1000W/Kg, and the specific power on the polyester film can reach 2000W/Kg. The specific power of crystalline silicon is generally only 40-100W/Kg. Since the substrate is very thin, it can be curled and cut, which is convenient to carry, which is very beneficial for reducing transportation costs, especially for space applications.

(2) Good anti-irradiation performance

　　As crystalline silicon solar cells and GaAs solar cells are irradiated by cosmic rays, the lifetime of oligon decreases significantly. For example, at 1Mev electron radiation flux of 1&TImes;1016e/cm2 , the output power drops by 60%, which is a serious problem for space applications. In contrast, amorphous silicon solar cells exhibit good radiation resistance because the radiation of cosmic ray particles does not (or very little) affect the carrier mobility in amorphous silicon solar cells, but can greatly reduce the diffusion length of oligons in crystalline silicon solar cells and GaAs solar cells, resulting in a decrease in the internal quantum efficiency of the cells. At the same particle irradiation flux, the radiation resistance of amorphous silicon solar cells (10% efficiency, AM0 condition) is 50 times higher than that of monocrystalline silicon solar cells, which has good stability. Multi-junction amorphous silicon solar cells have higher radiation resistance than single-junction ones.

(3) High temperature resistance

　　The energy band width of monocrystalline silicon is 1.1 eV, the energy band width of GaAs is 1.35 eV, while the optical band gap of amorphous silicon is greater than 1.65 eV, which has a relatively wide band gap. At the same operating temperature, the saturation current of amorphous silicon solar cells is much smaller than that of monocrystalline silicon solar cells and GaAs solar cells, while the temperature coefficient of short-circuit current is one times higher than that of crystalline silicon cells, which is very favorable to maintain high open-circuit voltage (Voc) and curve factor (FF) at higher temperatures. Good temperature characteristics are very important in the summer when the surface temperature of solar cells often reaches 60-70 degrees.

　　It is reported that in space applications, amorphous silicon solar cells with an initial stabilization efficiency of 9% outperform monocrystalline silicon solar cells with an initial efficiency of 14% due to irradiation and high temperatures.

　　After more than 30 years of development, amorphous silicon solar cells have made great technological progress, mainly by replacing amorphous silicon films with amorphous silicon carbide films or microcrystalline silicon carbide films as window materials to improve the spectral response of the cell in the short-wave direction; using gradient interface layers to improve the transport characteristics of the heterogeneous interface; using microcrystalline silicon films as n-type layers to reduce the series resistance of the cell; using fluffy tin dioxide instead of planar indium tin oxide; using multilayer backside solar cells; and using multi-layer indium tin oxide. The use of multilayer back-reflective electrodes to reduce light reflection and transmission losses and improve short-circuit current; the use of laser etching technology to achieve integrated cell processing; the use of stacked cell structure to extend the spectral response range of the cell and improve the photoelectric conversion efficiency; the use of continuous deposition technology in separate chambers to eliminate cross-contamination of reactive gases and improve the performance of the cell. The adoption of the above technologies has increased the photovoltaic conversion efficiency of amorphous silicon thin film solar cells from 2% to 13.7%.

With the improvement of the photovoltaic efficiency of amorphous silicon solar cells, the industrialization of amorphous silicon solar cells has also made remarkable progress. Due to the superior short-wave response characteristics of amorphous silicon materials, they occupy a great advantage in micro-power electronic products such as calculators and watches, which work under fluorescent lights, and not only made billions of dollars in profits in the decade of the 1980s, but also still have a large consumer market. From calculators, watches and other low light applications to a variety of consumer products and even power applications, such as radios, sun hats, garden lights, microwave relay stations, aviation and marine signals, weather monitoring, photovoltaic water pumps and small independent power supply applications continue to expand, production is rising rapidly. Several MW-class production lines and many amorphous silicon thin-film solar cell companies emerged in the world. By the mid-1980s, the annual sales volume of amorphous silicon thin film solar cells was growing rapidly, forming a three-way system of amorphous silicon thin film, polycrystalline silicon and monocrystalline silicon.