Thin film solar cells can be made of low-cost glass, plastic, ceramics, graphite, metal sheets and other different materials as substrates. It only takes a few μ m to form a film thickness that can generate voltage. Therefore, under the same light receiving area, the amount of raw materials can be significantly reduced compared with silicon wafer solar cells (the thickness can be more than 90% lower than that of silicon wafer solar cells), At present, the laboratory conversion efficiency * has reached more than 20%, and the stable efficiency of large-scale mass production * is about 13% higher. In addition to being planar, thin film solar cells can also be made into non planar structures because of their flexibility. They can be combined with buildings or become part of buildings. In the manufacturing of thin film solar cells, various deposition technologies can be used to grow p-type or n-type materials layer by layer. Common thin film solar cells include amorphous silicon CuInSe2 (CIS), CuInGaSe2 (CIGS), and CdTe Etc.
Thin film solar cells * Classification
Amorphous Silicon (a-Si)
Nanocrystalline Silicon, nc-Si，Microcrystalline Silicon，mc-Si)
Compound semiconductor II-IV family (CdS, CdTe, CuInSe2)
Dye sensitized Solar Cell
Organic/polymer solid cells
Thin film solar cell * principle
The essence of photoelectric conversion In organic heterojunction solar cells, the essence of photoelectric conversion is that the donor molecule (D) is oxidized by the receptor molecule (A) under the excitation of light. The whole photoelectric conversion process can be divided into three steps:
1) Photon energy absorption by donor molecules;
2) Energy is transferred to the donor molecule by diffusion;
3) The high-energy donor molecules on the interface transfer electrons to the receptor molecules to complete the redox reaction.
Thin film solar cells * Features
1. Small power loss under the same shielding area (good power generation under weak light)
2. The power loss under the same illuminance is less than that of wafer solar cells
3. Better power temperature coefficient
4. Better optical transmission
5. High cumulative power generation
6. Only a small amount of silicon raw materials are needed
7. There is no internal circuit short circuit problem (online has been built in during series battery manufacturing)
8. The thickness is thinner than the wafer solar cell
9. Material supply is secure
10. BIPV
Thin film solar cell * performance parameters
The main performance of the battery includes rated capacity, rated voltage, charge discharge rate, impedance, life and self discharge rate.
Rated capacity
Under the conditions specified in the design (such as temperature, discharge rate, termination voltage, etc.), the battery shall be able to discharge * low capacity, in ampere hours, represented by the symbol C. The capacity is greatly affected by the discharge rate, so the discharge rate is often marked with Arabic numerals in the lower right corner of the letter C, such as C20=50, indicating that the capacity at the rate of 20 hours is 50 A · h. The theoretical capacity of the battery can be calculated according to the amount of electrode active substance in the battery reaction formula and the electrochemical equivalent of the active substance calculated according to Faraday's law. The actual capacity of the battery is often lower than the theoretical capacity due to the possible side effects in the battery and the special needs of the design.
Rated voltage
The typical working voltage of battery at normal temperature is also called nominal voltage. It is a reference for selecting different types of batteries. The actual working voltage of the battery varies with different service conditions. The open circuit voltage of the battery is equal to the difference between the balance electrode potential of the positive and negative electrodes. It is only related to the type of active substance of the electrode, and has nothing to do with the amount of active substance. Battery voltage is essentially DC voltage, but under some special conditions, the phase change of metal crystals or some phase forming films caused by electrode reaction will cause small fluctuations in voltage, which is called noise. The fluctuation amplitude is very small but the frequency range is very wide, so it can be distinguished from the self-excited noise in the circuit.
Charge discharge rate
Sometimes, there are two kinds of representation: rate and multiple. The hourly rate is the charging and discharging rate expressed by the charging and discharging time, which is numerically equal to the number of hours obtained by dividing the rated capacity (ampere hour) of the battery by the specified charging and discharging current (ampere hour). Multiplication is another representation of charge discharge rate, and its value is the reciprocal of time rate. The discharge rate of the primary battery is expressed by the time from discharge through a fixed resistance to the termination voltage. The discharge rate has a great influence on the battery performance.
impedance
The battery has a large electrode electrolyte interface area, so it can be equivalent to a series circuit with large capacitance, small resistance and inductance. However, the actual situation is much more complicated, especially the impedance of the battery changes with time and DC level, and the measured impedance is only valid for the specific measurement state.
life
The storage life refers to the * long time allowed to store the battery from its manufacture to its use, in years. The total period, including storage period and service life, is called the validity period of the battery. The storage battery life can be divided into dry storage life and wet storage life. The cycle life refers to the number of large charging and discharging cycles that the battery can achieve under the specified conditions. When specifying the cycle life, the system of charge discharge cycle test must be specified at the same time, including charge discharge rate, discharge depth and ambient temperature range.
Self discharge rate
The rate at which the battery capacity is lost during storage. It is expressed as the percentage of the capacity lost by self discharge in unit storage time to the capacity before storage. Chemical battery Chemical battery refers to a kind of device that converts the chemical energy of positive and negative active substances into electrical energy through electrochemical reaction. After long-term research and development, chemical batteries have ushered in a wide variety of applications. It can be as large as a huge device that can be accommodated in a building, and as small as a variety in millimeters. We are always serving our good life. The development of modern electronic technology has put forward high requirements for chemical batteries. Every breakthrough in chemical battery technology has brought about the development of electronic equipment. People in modern society are increasingly inseparable from chemical batteries in their daily life. Now many electrochemical scientists in the world focus their interests on the field of chemical batteries as the power of electric vehicles. The distinction between dry battery and liquid battery dry battery and liquid battery dates back to the period of early battery development* The early battery consists of a glass container filled with electrolyte and two electrodes. Later, batteries based on paste electrolyte, also known as dry batteries, were introduced.
There are still "liquid" batteries. Generally, they are very large varieties. For example, those large fixed types as uninterruptible power supply Lead acid battery Or the lead-acid battery used together with the solar cell. For mobile equipment, some use fully sealed, maintenance free lead-acid batteries, which have been used successfully for many years. The electrolyte sulfuric acid is fixed by silicon gel or absorbed by glass fiber partition. Disposable batteries and rechargeable batteries Disposable batteries are commonly referred to as "disposable" batteries, because they cannot be recharged and used after their power is exhausted, so they can only be discarded. Common disposable batteries include alkaline manganese dioxide batteries, zinc manganese dioxide batteries lithium battery , zinc battery, zinc air battery, zinc mercury battery, mercury battery, hydrogen oxygen battery and magnesium manganese battery.
The common rechargeable batteries are Lead acid battery Nickel cadmium battery, nickel iron battery, nickel hydrogen battery, lithium ion battery. Its advantage is long cycle life. They can be fully charged and discharged for more than 200 times. Some rechargeable batteries have higher load capacity than most disposable batteries. In the use of ordinary nickel cadmium and nickel hydrogen batteries, due to the memory effect, it is inconvenient to use them, which often causes premature failure.
Thin film solar cell * theoretical charging time
Theoretical charging time of the battery: the power of the battery divided by the output current of the charger.
For example, if the output current of the charger is 500MA, the charging time is equal to 800MAH/500MA=1.6 hours. When the charger displays that the charging is complete, it will take about half an hour to recharge the battery. fuel cell Fuel cell is a device that converts the chemical energy of fuel directly into electrical energy through electrochemical reaction. The fuel cell uses hydrogen to carry out an oxidation reaction at the anode to oxidize hydrogen into hydrogen ions, while oxygen carries out a reduction reaction at the cathode to combine with hydrogen ions from the anode to generate water. The current can be generated during the redox reaction. Fuel cell technologies have emerged: alkaline fuel cell (AFC), phosphoric acid fuel cell (PAFC), proton exchange membrane fuel cell (PEMFC), molten carbonate fuel cell (MCFC), solid oxide fuel cell (SOFC), and direct methanol fuel cell (DMFC), It is more optimistic and positive development by the industry.
Thin film solar cell * has problems
V 1. About organic thin film solar cells
V organic thin film solar cells have the characteristics of low cost, light weight, soft product, high degree of freedom of design and large area preparation. However, compared with silicon based thin film solar cells, they have lower conversion efficiency and stability. The specific problems are as follows:
The generation process of carriers in v_ (1) organic solar cells is quite different from that in inorganic solar cells. The photogenerated carriers of organic polymers are not generated directly by absorbing photons, but first generate excitons, and then generate free carriers through the dissociation of excitons. The carriers formed in this way are easy to compound in pairs, and then reduce the photocurrent
The doping of v_ (2) conjugated polymer is of high concentration, which can ensure that the material has high conductivity, but the carrier life is inversely proportional to the doping concentration. With the increase of doping concentration, the photogenerated carrier increases, and the photoelectric conversion efficiency of the battery is very low.
V 2. Questions about the physical operation stage
Although we have initially made solid organic thin film solar cells, there are still many imperfections, such as high process costs, poor stability, and many improvements. Since we have never had similar laboratory experience before, let alone similar experience, we once felt that we had no way to start. Later, we went to the teacher's laboratory for exercise to see how the graduate students' seniors and sisters worked in the laboratory, and gradually improved their hands-on ability in learning. After the hands-on stage of the laboratory, we should also strengthen our learning and strive for further improvement.
Thin film solar cell * Preparation of organic film
Preparation of polymer film If the organic layer is a polymer, the following can be used:
1. Scalpel or line knife
2. Screen printing
3. Ink jet printing
Thin film solar cells * sub packaging
Battery slice cutting machine: cut the whole battery into the required size. Links between battery slices: ultrasonic welding machine. Laminate: crimp the prepared battery substrate (sail cloth) with the Tedlar laminating packaging machine. Install the connector or junction box. The junction box is mainly used to connect wires. The box is equipped with reverse diodes, Prevent the current between the solar cells and the strings. The other one should also be matched with the solar cells, which is beautiful, practical and convenient for wiring
Thin film solar cell * use
Translucent solar cell module: building integrated solar energy application (BIPV) Application of thin-film solar energy: portable folding charging power supply, * *, application of travel thin-film solar module: roof, building integrated, remote power supply, national defense.
Thin film solar cells * application cases
1. BIPV
Building Integrated Photovoltaics (BIPV) refers to a power generation method that uses the photoelectric effect of solar cells installed on the surface of buildings or combined with buildings to directly convert renewable radiant energy such as solar energy into electrical energy. The electric energy generated by it is converted by its matched inverter controller to directly meet the power demand of the building. If the generated electric energy is surplus, it will be transmitted to the municipal power grid. If the electric energy is not enough for the use of the building, it will be fed directly from the municipal power grid.
According to statistics, building energy consumption accounts for at least 30% of the world's total energy consumption. 60% of the world's solar cells are used in grid connected power generation systems, and are mainly used for the combination of urban buildings and photovoltaic systems, that is, photovoltaic building integration. It can be predicted that BIPV will be a big market for photovoltaic power generation in the future. The combination of solar power system and buildings will make solar power transition to alternative energy and become an important part of the world energy structure, thus fundamentally changing the subordinate position of solar power in the world energy.
China launched the "Golden Sun Project" in 2009 to promote the technological progress and development of domestic photovoltaic power generation industry. For the application of translucent thin film solar cells on the external glass curtain wall of buildings, China launched the standard preparation kick-off meeting of the industry standard Code for Electrical Design of Solar Photovoltaic Glass Curtain Walls on September 14, 2010. This standard will greatly promote the development of the combination of thin film solar cell industry and the construction industry.
2. Portable folding charging power supply, field travel
For example, flexible thin film solar cells can be used on backpacks, tents and life jackets to provide necessary power. Future concept backpack designed by designer Karan Singh Gandhi: Androcell high-tech backpack
3. Stratospheric airship
Thin film solar cells play an important role in stratospheric airships. Since stratospheric airships work at an altitude of about 20km above sea level, and they usually have to carry out fixed point stay or cruise missions for months or even years, it is impossible to provide energy and power through cables, let alone by carrying aviation kerosene. At present, a good solution is to use solar energy. The airship itself is a flexible body, so it must use thin film solar cells which are also flexible bodies. The concept map of the US HAA stratospheric airship using thin-film solar cells to provide most of the energy.
