Perovskite is named after the Russian mineralogist Perovski. It originally referred to the mineral calcium titanate (CaTiO3). Later, the structure ABX3 and similar crystals were collectively called perovskite minerals. After that, the excellent properties of perovskite were fully studied and explored, becoming a third-generation photovoltaic technology with obvious advantages. After continuous research, the efficiency of perovskite cells is also rising rapidly, and a variety of technical routes have emerged, giving it the strength to challenge the dominance of crystalline silicon photovoltaic cells in the future.
Next, we will start from the concept of perovskite materials , understand their functions, advantages and working principles, and analyze the industrial chain of the perovskite battery industry, sorting out the raw materials, technical routes, preparation processes and production of perovskite batteries in detail Equipment and application scenarios, etc., provide an in-depth analysis of the development of the perovskite industry.
01 Industry Overview
1. Perovskite materials
Perovskite is a general term for a type of crystal with an ABX3 molecular structure, which can be used to prepare perovskite solar cells. In the general chemical formula of the perovskite structure, the A position is generally a cation with a smaller atomic radius (such as Cs+, MA+, FA+, etc.), the B position is a transition metal ion with a larger atomic radius (such as Sn2+, Pb2+, etc.), and X is Halogen anions (I-, Br-, Cl-, etc.). Perovskite materials have superior charge transport properties, long carrier diffusion distance, full spectrum absorption and high light absorption coefficient, so they can effectively absorb sunlight and efficiently generate photogenerated carriers while reducing energy in the photoelectric conversion process. Loss, it is an ideal optoelectronic material.
2. Perovskite is the third generation photovoltaic technology with obvious advantages
Since the birth of the world's first solar cell in 1954, photovoltaic cell technology has gone through three generations:
(1) The first generation is based on crystalline silicon solar cells. The main application scenario is centralized photovoltaic power stations. The technology is currently the most mature, but the photoelectric conversion efficiency is close to the upper limit. The space for improving efficiency and reducing costs is relatively limited, and the marginal cost has increased significantly high.
(2) The second generation is mainly based on thin-film solar cells. Typical representatives are copper indium gallium selenide (CIGS) and cadmium telluride (CdTe) solar cells. The main application scenarios are distributed photovoltaics, and the photoelectric conversion efficiency of small-area laboratory specimens Higher than crystalline silicon cells, but in actual applications the photoelectric conversion efficiency is lower than crystalline silicon, and the cost is relatively expensive.
(3) The third generation is new solar cells, which mainly include: perovskite cells, dye-sensitized cells and quantum dot cells. The third generation of perovskite cells is a new type of compound thin film solar cell. It has the advantages of fast efficiency improvement, low cost and strong material designability of the second generation thin film cells. At the same time, with the advancement of commercialization, it is expected to make up for the problems faced by the second generation. There is a big gap between mass production performance and theoretical advantageous conditions.
3. Working principle of perovskite battery
Perovskite cells are mainly composed of the following five functional layers: transparent conductive oxide (TCO), electron transport layer (ETL), perovskite layer, hole transport layer (HTL) and back electrode. As a semiconductor material, perovskite produces a photovoltaic effect, that is, the semiconductor generates an electromotive force when exposed to light. Under illumination conditions, the perovskite compound absorbs photons. After absorbing the photons, its valence band electrons will jump to the conduction band. The conduction band electrons are then injected into the conduction band of TiO2 and then transferred to FTO. At the same time, holes are transferred. to the organic hole transport layer (HTL), whereby the electron-hole pairs are separated. When the external circuit is turned on, the movement of electrons and holes generates current.
The functions of each film layer in a perovskite battery
Principle of perovskite battery power generation
4. Perovskite has obvious advantages and full industrialization potential.
In the third generation of new batteries, perovskite has the advantages of long carrier lifetime, adjustable band gap (the lowest energy that a semiconductor can absorb), and wide light absorption unit. The applications of perovskite batteries include single junction and stacked layers. a technical direction.
Perovskite cells have a higher efficiency limit than crystalline silicon cells. Perovskite cells have high light absorption coefficients, are less affected by temperature differences, and have less photoelectric loss. The typical band gap of methylamine lead iodine (CH3NH3PbI3) perovskite is 1.55eV, which is close to the optimal band gap. The single-junction efficiency laboratory efficiency has exceeded 25%, and the upper limit of the efficiency can reach more than 30%. The upper limit of crystalline silicon cell efficiency is difficult to exceed 30%. Moreover, the perovskite material has an adjustable band gap and is stacked with crystalline silicon to achieve higher theoretical efficiency. Using a 1.12eV bandgap crystalline silicon cell in series with a 1.73eV perovskite cell can ensure optimal distributed absorption of solar spectrum irradiation, and the theoretical efficiency exceeds 43%.
02 Policy to stimulate perovskite industrialization
Major breakthroughs in perovskite photovoltaics in academia in the past decade have promoted the industrialization of perovskites. Since perovskite photovoltaics are quite different from the existing photovoltaic industry chain dominated by crystalline silicon photovoltaics, the rise of perovskite photovoltaics is bound to reshape the entire industry chain. At present, not only the industrial side is actively promoting the commercialization of perovskite, but the policy side is also constantly stimulating the industrialization of perovskite.
03 Industry chain analysis
The perovskite battery industry chain has been significantly shortened, with only 45 minutes from raw materials to components. The upstream of perovskite batteries includes materials and auxiliary materials. The midstream battery manufacturers select technical paths, preparation processes and equipment to make battery components, and finally apply them to downstream power stations and new applications. Crystalline silicon cells require processing of silicon materials, silicon wafers, cells, and components in four different factories. This process takes at least three days. The production process of perovskite solar cells is simple. Upstream glass, film, targets, and chemical raw materials can be processed into components in a single factory within 45 minutes. The industrial chain is significantly shortened and the value is highly concentrated.
1. Raw materials
(1) Conductive layer
The substrate is made of flexible materials, stainless steel plates, glass, etc. The conductive oxides on the substrate are generally indium tin oxide (ITO conductive glass) and fluorine doped SnO2 (FTO transparent conductive glass). TCO glass refers to glass deep processed products that are uniformly coated with a transparent conductive oxide film on the surface of flat glass through physical or chemical coating methods, achieving high transmittance and conductivity of visible light. TCO conductive glass includes ITO, FTO, and AZO coated glass, which use tin doped indium oxide (In2O3), fluorine doped tin oxide (SnO2), and aluminum doped zinc oxide (ZnO) as targets, respectively. FTO has slightly inferior conductivity compared to ITO, but it has advantages such as relatively low cost, easy laser etching, and suitable optical performance. It has become the mainstream product of thin film photovoltaic cells. At present, Jinjing Technology's TCO conductive film glass has been successfully produced and has established business relationships with some domestic cadmium telluride and perovskite battery enterprises, which have been recognized and started supplying. In addition to Jinjing Technology, TCO glass companies also include Amazon, Yaopi Glass, South Glass A, Qibin, and others.
(2) Hole transport layer
At present, the common hole transport materials (HTMs) are mainly three types: organic small molecules, organic polymers, and inorganic semiconductors. The commonly used organic small molecules mainly include Spiro OMeTAD and its modified materials; Common organic polymers include PEDOT: PSS (solution film-forming, suitable for flexible substrates), PTAA, P3HT (poly-3-hexylthiophene), among which P3HT is the mainstream; The commonly used inorganic HTMs include CuI, CuSCN, CuOx, NiOx, MoOx, and VOx. Compared with polymers, organic small molecules have good fluidity, but their preparation is difficult and expensive; Organic polymers have better film-forming properties and higher migration rates. Compared to organic HTMs, inorganic HTMs have higher hole mobility, better conductivity and stability, and lower cost.
(3) Perovskite absorbing layer
The basic material is a precursor solution of perovskite, which is generally composed of alkali metal halide perovskite and organic metal halide perovskite. Organic inorganic mixed crystalline materials, such as organic metal trihalide CH3NH3PbX3 (X=Cl Br I), are generally used as light absorbing materials. The most common one is CH3NH3PbI3 (methylamine lead iodine). The production of metal halide perovskite requires abundant raw material reserves, low prices, and the preparation of precursor solution does not involve any complex processes, with low purity requirements. The subsequent components also do not have high requirements for the processing environment.
(4) Electronic transport layer
Electronic transfer materials (ETM) can mainly be divided into metal oxides (commonly used TiO2, ZnO, etc.) and composite materials, mainly involving materials such as titanium 60, BCP, PCDM, selenium dioxide, titanium dioxide, etc. The most commonly used and researched ETM currently is TiO2, but due to the mismatch between the electron mobility and diffusion distance of TiO2 and the hole mobility and diffusion distance of perovskite materials and commonly used HTMs, it has become a bottleneck in charge capture efficiency in battery structures. At present, researchers have achieved a conversion efficiency of 15.6% under low temperature conditions (less than 150 ℃) using mesoporous Al2O3 as the skeleton, TiO2 nanoparticles and graphene composites instead of TiO2 as the ETM.
(5) Electrode layer
Metal electrodes (Al, Au, Ag), transparent conductive electrodes, TCO, etc. are generally used, and the materials involved are mainly titanium, copper foil, and stainless steel foil. The selection of electrode materials results in different technical routes and preparation methods.
2. Technical path
The structure of perovskite batteries is mainly divided into single junction and multi junction stacked batteries. Single junction battery structures are divided into mesoporous structures and planar formal or trans structures. Currently, the industrialization of single junction batteries mainly involves planar trans structures. The current mainstream perovskite stacking technologies for stacked batteries include: perovskite/crystalline silicon stacking, perovskite/perovskite stacking, and perovskite/CIGS stacking. Due to the mature and stable advantages of bottom cell (crystalline silicon battery) technology, perovskite/crystalline silicon stacking has the fastest research progress among many layers and leads the laboratory efficiency. The double-end stacking method refers to the sub battery being connected in series through an interconnection interface, requiring only one transparent electrode, which is low-cost and has development prospects in terms of technology.
(1) Single junction battery
Single junction battery structures are mainly divided into mesoporous structures and planar structures, which are further divided into formal structures (n-i-p) and trans structures (p-i-n). Distinguish between mesoporous and planar structures based on the presence or absence of a mesoporous skeleton electron transport layer; Distinguish between formal and reverse structures based on whether the electron transport layer or the hole transport layer is first placed on the transparent conductive electrode.
1) Mesoporous structure
The mesoporous structure is similar to a sandwich layered structure, with a simple structure, mainly divided into five layers: transparent conductive electrode, mesoporous electron transport layer, perovskite absorption layer, hole transport layer, and metal electrode. The mesoporous electron transport layer extracts electrons from perovskite excited by photons, while blocking the migration of holes towards the cathode direction; It has a high light transmittance, making it easier for more photons to shine on the perovskite absorption layer; The role of mesopores as a skeletal support for the perovskite absorption layer; The main material is TiO2.
Mesopores can serve as a framework to support perovskites, but high-temperature preparation poses significant technological challenges. The mesoporous perovskite supports the framework, increasing the contact area between the perovskite absorption layer and the electron transport layer, effectively improving the electron transfer efficiency; The preparation of mesoporous layers usually requires high-temperature annealing treatment at 400-500 ℃, which increases the difficulty of the process.
2) Planar structure
Compared to mesoporous structures, planar structures have fewer mesoporous layers and can be prepared at low temperatures. The planar structure is directly spin coated with perovskite on the dense TiO2 electron transport layer, which is relatively simple compared to the mesoporous structure and can be prepared by low-temperature solution method, which is more conducive to the development of flexible batteries, stacked batteries, and large-area batteries.
The main difference between formal and trans structures is whether light first passes through the electron transport layer or the hole transport layer. For the formal structure, there is an electron transport layer on the transparent electrode. After the sunlight passes through the transparent electrode, it passes through the electron transport layer and then to the absorption layer; For the trans structure, there is a hole transport layer on the transparent electrode, and after the sunlight passes through the transparent electrode, it passes through the hole transport layer and then to the absorption layer.
Although the efficiency of the trans structure is lower than that of the formal structure, it has smaller hysteresis, higher filling rate, and better stability, making it suitable for mass production. At present, the highest efficiency of perovskite is 25.7% for the formal structure, and the efficiency of the trans structure has also reached 24.3% after years of development, reducing the gap with the formal structure. The main advantage of the trans structure is that light passes through the hole transport layer first, which can reduce the hysteresis of the battery and increase the filling rate. In addition, the formal structural hole transport materials are mostly organic compounds Spiro OMeTAD, and in order to increase conductivity, it is usually necessary to add Li salts, Co salts, etc. that are sensitive to water and oxygen. Although high efficiency is achieved, the stability of the device is also sacrificed; The trans structured hole transport layer materials are mostly inorganic metal oxides (such as NiOx, CuO, etc.), which have good device stability.
(2) Stacked battery
The stacked structure is divided into three parts: narrow-band gap bottom battery, interconnect/tunneling junction, and broadband gap top battery. Broadband gap batteries act as top cells to absorb high-energy photons, while narrowband gap batteries act as bottom cells to absorb lower energy photons, achieving segmented utilization of the solar spectrum by sub cells, thereby avoiding thermal losses of high-energy photons and improving solar energy utilization and photovoltaic conversion efficiency of the battery. The bandgap width of perovskite ABX3 can be adjusted from 1.17 to 2.8 eV by changing the A, B, and X components, which can be matched with other medium and narrow bandgap bottom batteries.
Two junction stacked batteries are the main application direction, and perovskite/crystalline silicon stacked batteries currently have the highest efficiency. The more layers there are, the theoretically higher efficiency can be achieved. However, considering cost, currently, two junction stacked batteries are the main application direction; The battery efficiency of perovskite/crystalline silicon stack and perovskite/perovskite stack is relatively high, at 32.5% and 28%, respectively, making them the focus of current research on stacked batteries. The efficiency of perovskite/CIGS stacked batteries has also been greatly improved, making them a promising competitor for the next generation of photovoltaic cells.
1) Perovskite/crystalline silicon layer
Perovskite/crystalline silicon layer is a type of battery that uses crystalline silicon as the base. The bandgap of crystalline silicon batteries is relatively narrow, only 1.12eV. As a stacked bottom battery, the wide bandgap (1.67eV-1.75eV) perovskite serves as the top battery.
Perovskite can form stacked batteries with crystalline silicon cells such as HJT and TOPCon, among which HJT is most suitable for perovskite stacking. The process of crystalline silicon battery is mature, and as a bottom battery, it is relatively stable, which has the potential for low manufacturing costs compared to other types of stacked cells; HJT is most suitable for perovskite layers due to its excellent amorphous silicon passivation layer, symmetrical structure, and transparent conductive oxide (TCO).
The structure and material of the interconnection layer can cause photoelectric losses. 1) In terms of interconnection layer structure, it can be divided into planar and trap structures. Planar structures emit strong light, which is not conducive to light transmission; Trapped light structure, weak light reflection, but uneven surface, uniform application of perovskite is a major challenge. 2) In terms of interconnect layer materials, TCO is commonly used, among which the most common TCO is indium doped tin oxide (ITO), which has excellent conductivity and light transmittance. However, the refractive index of ITO does not match the silicon substrate, resulting in light reflection loss in the wavelength band above 800nm.
The layered structure of perovskite/crystalline silicon has a maximum efficiency of 32.5%, and improving the material of the interconnection layer and the stability of the perovskite top battery is a breakthrough. Due to the stability of crystalline silicon bottom batteries, perovskite/crystalline silicon has the strongest overall stability and is one of the closest technological paths to industrialization. The highest efficiency reaches 32.5%; A-Si: H and nc Si: H materials have the characteristics of low transverse conductivity, parasitic loss, and reflection loss, making them ideal materials for interconnection layers in stacked batteries; In addition, like single junction batteries, improving the photoelectric performance of perovskite batteries is also the core point of stacked batteries, such as reducing non radiative recombination through additive engineering.
2) Perovskite/Perovskite Layered
Perovskite/perovskite stacking is achieved by artificially synthesizing wide bandgap and narrow bandgap perovskites. Due to the adjustable bandgap of perovskite, narrow bandgap (about 1.25eV) perovskite is used as the base cell, and wide bandgap (about 1.75eV) perovskite is used as the top cell.
The efficiency of perovskite/perovskite layering is gradually catching up with that of perovskite/crystalline silicon layering, with lower cost per kilowatt hour and simpler process. Perovskite/perovskite stacking allows for flexible adjustment of the bandgap between both sub cells, maximizing the efficient utilization of the solar spectrum, resulting in an open circuit voltage higher than that of perovskite/crystalline silicon stacked cells. Currently, the highest laboratory efficiency of perovskite/perovskite stacking is 29%. The cost of electricity per kilowatt hour for perovskite/crystalline silicon stack is 5.22 cents/KWh, while the cost of electricity per kilowatt hour for perovskite/perovskite stack is 4.22 cents/KWh, which is lower than that of crystalline silicon stack. Perovskite/perovskite layering is a process of coating top cells on glass, which is simpler than applying perovskite on the surface of crystalline silicon velvet compared to perovskite/crystalline silicon layering.
Compared to perovskite/crystalline silicon layering, full perovskite layering not only needs to improve the performance of wide bandgap perovskite and interconnect layers, but also needs to solve the instability problem of narrow bandgap perovskite. Narrow bandgap perovskites mainly contain tin, and tin ions are prone to oxidation, leading to instability of perovskites; There is a risk of solvent degradation of wide bandgap perovskite batteries during the deposition process of narrow bandgap batteries. At present, the improvement of the stability of narrow bandgap perovskites mainly relies on additive engineering similar to that of wide bandgap perovskites.
Perovskite/perovskite stack structure diagram
Cost of electricity cost comparison
3) Perovskite/CIGS stacking
CIGS has an adjustable narrow bandgap width and a high light absorption coefficient. By using narrow bandgap CIGS as the bottom cell and wide bandgap perovskite as the top cell, CIGS can theoretically achieve higher optoelectronic performance than perovskite/crystalline silicon stacked structures due to its adjustable narrow bandgap width and high light absorption coefficient.
There is a shunt effect in the perovskite/CIGS stacking process, which affects the efficiency of the battery. The structure of CIGS batteries limits the top perovskite to only have a p-i-n (trans) structure; CIGS battery structures are usually deposited through vacuum methods such as sputtering or co evaporation, which often result in high surface roughness. Generally, the root mean square height of the surface can reach up to 200nm. Although the thickness of the perovskite absorption layer ranges from 500-1000nm, the thickness of the hole transport layer does not exceed 100nm, which is not enough to fully cover the nano rough surface, leading to potential shunt effects.
The current highest laboratory efficiency of perovskite/CIGS stacking is 24.2%, which is relatively backward among the three stacking technologies.
(3) Selection of mass production routes
Different technological routes have their own advantages and disadvantages. Currently, large crystalline silicon factories tend to choose the perovskite/crystalline silicon stacking route, while the full perovskite route is more suitable for startups. 1) In terms of efficiency, the development of perovskite/crystalline silicon layers is the fastest and the highest; 2) In terms of photoelectric loss, single junction batteries have the smallest loss; 3) In terms of stability, all perovskite batteries have the worst stability; 4) In terms of cost, all perovskite batteries have the lowest cost per kilowatt hour; 5) Mainstream manufacturer selection route: In the mass production stage, the number of single junction and stacked battery manufacturers is similar. In the strategic planning stage, most manufacturers choose stacked batteries. In stacked batteries, large crystalline silicon manufacturers prefer perovskite/crystalline silicon stacked batteries to leverage their technological advantages. Renshuo Solar has made a unique choice of fully layered perovskite, providing a reference for the selection of technology routes for startups.
3. Preparation process and process
The top electrode layer (TCO) is usually the responsibility of glass production companies, and battery companies directly purchase TCO glass to complete the subsequent process. The preparation of perovskite batteries can usually be divided into five steps: treatment of TCO glass → preparation of electron transport layer → preparation of perovskite layer → preparation of hole transport layer → preparation of back electrode. The production of the absorbing layer is a key step in the assembly of perovskite solar cells, and its film quality is influenced by multiple factors such as environmental temperature, humidity, oxygen content, annealing temperature, annealing time, and operating methods, which greatly affect the performance of the final device.
Specifically: 1) Treatment of TCO glass: First, cut the TCO glass into small pieces of appropriate area, then use solution or laser etching, and then clean and dry. 2) Preparation of electron transport layer: usually achieved by vapor deposition techniques such as magnetron sputtering or solution spin coating, followed by annealing after magnetron sputtering or spin coating to obtain the electron transport layer. 3) Preparation of perovskite layer: There are various techniques for preparing perovskite absorbing layers, which can be roughly divided into five categories: solution coating method, spin coating method, spray coating method and inkjet printing method, soft film covering method, and vapor deposition method. The commonly used methods are spin coating method and gas-phase method. 4) Preparation of hole transport layer: Usually, solution spin coating method is used to prepare, and after spin coating, annealing is performed to obtain HTL. 5) Preparation of back electrode: Fix the device on a mask board, place it in a coating machine for evaporation, cool it down, and complete the preparation.
(1) Spin coating method
The spin coating method mainly involves dropping a solution of perovskite precursor onto a drip plate, relying on the centrifugal force of high-speed rotation of the workpiece to complete the coating and thin film deposition. It has the advantages of high film quality and precise control of thin film thickness, and is generally used for preparing small area batteries in the laboratory. According to the different steps, it can be further divided into one-step and two-step methods.
(2) Solution coating method
Mainly through the coating device, the perovskite precursor solution completes relative motion on the substrate surface, relying on the surface tension of the liquid and substrate contact to form a film. According to the different coating equipment, it can be further divided into scraper coating method, slit coating method, and screen printing method. Among them, the slit coating method has the advantages of fast printing speed, high slurry utilization rate, and more refined film quality control, and is currently the mainstream method used in the industrialization of perovskite batteries.
(3) Spray and inkjet printing methods
Spray painting and inkjet printing are techniques that apply pressure inside the nozzle to extrude a solution of perovskite precursor from the nozzle and form a film on the substrate. The commonly used nozzles in spray painting include high-pressure gas nozzles and ultrasonic nozzles. Unlike spray painting, inkjet printing utilizes the deformation of the piezoelectric material inside the nozzle to extrude the solution and perform relative motion according to the preset program. It can prepare different patterns according to requirements, avoiding the process of plate making and improving the utilization rate of perovskite raw materials. Both spraying methods can adjust the perovskite film formation morphology by adjusting the concentration of the perovskite solution, the distance between the nozzle and the substrate, and the spraying speed.
(4) Soft film covering method
This method utilizes PI (polyimide) film coverage in a pressure environment to achieve the conversion of amine complex precursors into perovskite films. This method effectively prevents the solvent from evaporating into the air, making it easy to obtain a perovskite film with no pinholes and high uniformity. In addition, this deposition method does not require a vacuum environment and can be carried out under low-temperature processes.
(5) Vapor deposition method
1) Vacuum coating method
The steam plating method generally uses co evaporation as the main method. Compared to the solution method, the perovskite thin film obtained by vacuum coating method is more uniform and flat, but it requires precise control of the composition of the evaporation source, which is extremely difficult to operate. This method still needs to be carried out in a vacuum environment, with a long film preparation time and high equipment cost.
2) Gas assisted solution method
This method first uses liquid-phase coating technology to coat the precursor film on the substrate, and then transfers it to the vapor of organic amine halides (MAIs), which is completely converted into perovskite films, combining the advantages of solution and vacuum coating methods.
4. Production equipment
The production of perovskite battery modules requires four types of equipment: coating equipment, laser equipment, coating equipment, and packaging equipment. The coordination of materials, processes, and equipment in the production of perovskite components forms the core competitiveness of perovskite enterprises. At present, some of the four types of equipment have been selected for localization. The total core investment of the 100 MW production line is about 120 million yuan, of which the investment ratio of coating equipment: laser equipment: coating equipment: packaging equipment is 50%: 25%: 15%: 10%.
(1) Coating equipment: Coating equipment has the highest value and is the main way to reduce costs in the future
The coating equipment mainly involves three types: PVD, PRD, and ALD. PVD technology is further divided into vacuum evaporation method, sputtering method, and ion plating method. The back electrode is mainly used for vapor deposition of PVD, which is currently quite mature and can also be made using PRD plasma reaction equipment. The mainstream electronic transport layer uses RPD devices, or first uses RPD or ALD devices to create barrier layers, and then uses sputtered PVD as the transport layer. The mainstream use of the hole transport layer is sputtering PVD, and vapor deposition PVD can also be used; Glass substrate substrate: Using sputtered PVD to form a conductive layer, the technology is relatively mature. Production of 100 MW level perovskite requires 3 coating equipment, including 2 PVDs, with a unit price of 10 million yuan per unit; 1 PRD, priced at 20 million yuan per unit.
Corresponding equipment companies include Jiejia Weichuang, Maiwei Shares, Jingshan Light Machinery, Zhongneng Optoelectronics, Shengcheng Photovoltaics, etc. Among them, Jiejia Weichuang mass-produced the key production equipment RPD for perovskite solar cells in July 2022 and successfully shipped the GW level HJT battery production line equipment. Shengcheng Photovoltaic launched a development strategic cooperation with a leading enterprise in the perovskite battery industry in May 2021. Currently, the company's developed perovskite battery cluster type multi cavity evaporation equipment has been put into mass production and successfully applied to multiple clients.
(2) Coating equipment: The mainstream method uses a slit coating mechanism for preparation
The coating equipment is mainly used to make perovskite absorbing layers. At present, the preparation process of perovskite layers in China mainly uses slit coating machines, with several companies including Xinxin Optoelectronics, Xianna Optoelectronics, Infinite Optoelectronics, Polar Optoelectronics, and Wandu Optoelectronics having layouts; Manufacturers such as GCL Optoelectronics, Fiber Optics, Infinite Optoelectronics, and Polar Optoelectronics are simultaneously laying out spin coating machines and PVD evaporation processes; Scraper coating, spraying, CVD, and screen printing machines are among the few technical options.
The industrialization process of German Shanghai coating film is leading, with a market share of over 70% in the market for large-sized electronic narrow seam coating equipment in 2022. The company is currently the largest supplier of core slit coating equipment for perovskite battery manufacturing in China, with a market share of over 70% in the field of large-sized electronic slit coating equipment, and technical indicators comparable to similar global enterprise products; And supply large scale core narrow seam coating equipment to the 100MW calcium titanium mineral production line of GCL.
(3) Laser equipment: The industrialization process is fast, and domestic manufacturers have achieved mass production
The laser process involves the entire preparation process of perovskite thin film batteries, with a slicing effect. The perovskite battery requires three parallel laser etchings (P1-P3) and P4 edge cleaning, with an overall value of about 10-20%. In the etching process of P1-P3, laser equipment is mainly used for laser marking, engraving the perovskite absorption layer, perovskite layer, and electrode layer, removing the TCO layer, and performing edge cleaning insulation.
The industrialization process of laser enterprises is fast. Di Er Laser's laser equipment has been applied in the production process of TCO layer, oxide layer, and electrode layer in perovskite solar cells. Currently, there are small batch orders and delivery has been completed. Maiwei Group has delivered laser equipment for single junction perovskite batteries in 2021, and will increase equipment layout for single junction perovskite batteries in the future. Delong Laser launched a complete production equipment for perovskite thin film solar energy in 2020, including P1, P2, P3 laser marking equipment, and P4 laser edge cleaning equipment. The equipment has been put into use on customer production lines and has achieved large-scale production at the level of 100 megawatts.
(4) Packaging equipment: Photovoltaic module suppliers are expected to benefit
To avoid damage to the perovskite structure or other functional layers caused by external environmental factors and decomposition leaks, encapsulation is the most effective solution. At present, there are two common packaging technologies for perovskite solar cells: the first generation packaging technology uses evaporative metal injectors and welded metal strips to conduct current from the battery to the outside and seal the edges of the metal strips. The second generation packaging technology separates the perovskite electrode from the metal electrode through a transparent indium tin oxide electrode to ensure a certain horizontal gap between the electrode and the printed circuit board. The packaging surface is directly the ITO electrode, which can better seal the entire device.
Perovskite is commonly packaged with POE instead of EVA. Due to the sensitivity of perovskite materials, the packaging requirements for perovskite batteries are higher than those for crystalline silicon batteries. Generally, POE film is used instead of EVA film
Photovoltaic module suppliers are expected to benefit: Fushimian can provide full line solutions for leading perovskite module manufacturers, mainly providing precision cutting and laminating equipment, insulation tape machines, conductive tape machines, busbar pasting machines, laminating machines and other packaging equipment. Zhongneng Optoelectronics has a laminating machine and ALD equipment for passivation of optoelectronic devices. Jingshan Light Machinery has reached a cooperation agreement with Huazhong University of Science and Technology to jointly develop photovoltaic atomic coating equipment.
5. Application
(1) BIPV perovskite batteries are ideal materials
BIPV is an important scenario for the future application of photovoltaics: Building Integrated Photovoltaics (BIPV) is a distributed power generation system that integrates photovoltaic modules into buildings. Its main application scenarios include roofs, curtain walls, windows, fences, etc. Among them, facades and photovoltaic roofs are the main application directions.
Perovskite is an ideal material for BIPV applications: 1) Perovskite components are lighter and thinner, have better flexibility, high plasticity, and can be bent arbitrarily, making them more widely used in BIPV; 2) Compared to crystalline silicon batteries, they have stronger transparency and can meet the requirements of buildings for different light intensities; 3) Perovskite components have the characteristic of adjustable color, which can produce components of different colors according to needs, with stronger aesthetics; 4) It also has high conversion efficiency and stable power generation in cloudy and artificial light environments.
(2) CIPV is currently in its early stages
CIPV is still in its early stages: In vehicle photovoltaic power generation system (CIPV) is a complete set of off grid photovoltaic power generation systems installed on vehicles. This field is currently in its early stages, and only a few models are equipped with photovoltaic integrated panoramic sunroof; At the same time, startup EV Solar Kits is developing an in car photovoltaic design solution for Tesla, which can be installed on the roof of Model 3 and Model Y cars at a cost of 5000 yuan. After installation, the car can run an additional 100 kilometers per day.
(3) The dawn of industrialization of ground power stations is emerging
The gradual maturity of technology will help promote large-scale applications, and the future application space of perovskite is vast. Perovskite has a high efficiency upper limit, optical and electrical performance, and a cost of about 5% of traditional photovoltaics. It is expected to promote photovoltaic grid parity after large-scale application. However, due to its poor stability and low lifespan, large-scale application poses technical difficulties. On February 15, 2023, the first phase of the centralized perovskite photovoltaic power station project in Qujiang District, Quzhou City, started construction with an installed capacity of 12MW and a planned investment of 60 million yuan. It is the world's first perovskite ground photovoltaic power station, and the dawn of industrial application is emerging. The application space of perovskite ground power stations is broad.
(4) Flexible photovoltaics, wearable photovoltaics, etc
The absorption layer of perovskite has a strong absorption coefficient, and visible spectrum absorption can be achieved with only a very thin layer. In addition to being used in centralized and distributed power plants, flexible, wearable, and foldable preparations can also be made. Flexible solar cells have broad application space in mobile objects, portable devices, and aerospace fields due to their advantages of light weight, flexibility, and low installation cost.
04 The advantages and constraints of industrialization of perovskite batteries
1. Industrialization advantages
The industrial advantage of perovskite lies in its efficiency improvement and cost reduction, which far exceeds that of crystalline silicon. From the perspective of photoelectric conversion rate, perovskite has gone through a 50 year development path of crystalline silicon in almost 10 years. The technological competition between perovskite and crystalline silicon is essentially a competition between hundreds of thousands of perovskite materials and one crystalline silicon material.
According to the previous analysis of the industry chain, a perovskite battery factory completed the entire process in just 45 minutes, significantly improving production efficiency.
The construction cost of the production line is about 50% of that of crystalline silicon. Photovoltaic enterprises need approximately 5 billion yuan to invest in 1GW of production capacity GaAs (Tum key line); Investing in 1GW of crystalline silicon batteries requires a total investment amount of approximately 75-1 billion yuan; Under mature process conditions, the investment amount of 1 GW of production capacity perovskite batteries can be reduced to about 500 million yuan, which is about 50% of the investment amount of crystalline silicon batteries and 10% of GaAs (Tum key line).
The production energy consumption of perovskite batteries is less than 1/10 of that of crystalline silicon modules. During the process of pulling single crystals, crystalline silicon requires a temperature above 900 ℃ to melt the silicon material, while the processing temperature of each functional layer of perovskite does not exceed 180 ℃, and most processes do not require vacuum conditions. The energy consumption for manufacturing 10000 single crystal modules is approximately 1.52 kWh, while the production energy consumption per watt of perovskite modules is only 0.12 kWh, which is less than 1/10 of the energy consumption of crystalline silicon modules.
2. Factors constraining industrialization
The industrialization advantages of perovskite batteries are obvious, but there are also certain limiting factors. At present, researchers have found some solutions to the constraints, and further exploration is needed in the future.
(1) Congenital defects in material stability
Compared with crystalline silicon batteries, perovskite batteries have significant advantages in cost reduction and efficiency improvement. However, the stability of perovskite and battery components has inherent defects, which can easily lead to the degradation of component lifespan during operation.
Ionic crystal structure, perovskite materials have instability. The instability of perovskite itself can be divided into: 1) physical instability, which means that the material itself has low decomposition energy, ions are prone to diffusion, and differences in temperature or composition can cause component segregation or phase separation in perovskite materials, affecting the photoelectric performance and long-term stability of the perovskite layer; 2) Chemical instability refers to the ion bonding properties of perovskites, which are composed of "soft" ions with low ionic potential and organic ammonium ions that are easily decomposed. This results in a lower formation energy, higher defect density, and higher reactivity of each component in the perovskite system. It is easy to react with water molecules and air in the environment, and phase separation occurs under light, At the same time, the presence of a large number of defects also makes ion migration easy to occur, which is an important reason for the "hysteresis" phenomenon in perovskite solar cells. The accumulation of ion migration can cause the collapse of the perovskite crystal structure, greatly damaging the long-term stability of the device.
The stacking of multiple layers of materials and the interface contact composite reaction affect the battery performance. In addition to the impact of the optoelectronic stability of perovskite materials on device performance, the contact surfaces between the layers of materials in the device also affect device performance
(2) Large area preparation is difficult
The large-scale preparation of high-efficiency perovskite batteries is another major challenge for their industrialization. The efficiency of the laboratory is progressing rapidly, and during the industrialization stage, the battery efficiency will decay with the enlargement of the module area. At present, the efficiency of perovskite battery laboratories is progressing rapidly, but most of them are small area thin films below 1cm. For most photovoltaic technologies, large-area preparation often accompanies a decrease in battery efficiency, mainly due to the linear increase in series resistance with an increase in battery area. For perovskite batteries, the phenomenon of performance degradation with increasing battery area is more pronounced. In addition to the common factors of series resistance, the main factors affecting the large-scale preparation of high-efficiency perovskite batteries are their material properties and preparation methods.
The solution spin coating method is a commonly used method for preparing perovskite solar cells in the laboratory. Although the operation is simple, the film forming speed is fast, and the repeatability is good, it cannot meet the manufacturing requirements of large-scale industrial production of perovskite solar cells, such as large area and low cost. At present, the commonly used production processes for large-area perovskite include solution coating, solution spraying, soft film coating, and vapor deposition. However, there is still a gap in the photoelectric conversion efficiency of large-area perovskite solar cells compared to spin coating.
(3) Environmental issues
The precursor solution in the preparation process of perovskite batteries contains lead. There is a direct relationship between the thickness of perovskite films and the concentration of precursor solutions, and manufacturing efficient perovskite solar cells requires relatively high concentrations of lead containing precursors. Due to the lead content and water-soluble lead iodide in perovskite batteries, if an appropriate recycling method is not adopted, the lead iodide contained in aged perovskite batteries will be leached into the soil and absorbed by plants into the food chain. Compared to lead brought into the environment by other human activities, its mobility is more than 10 times higher.
At present, lead content in perovskite is inevitable. The presence of excessive lead iodide in halide perovskite is the key to the efficiency of perovskite batteries exceeding 20%. At present, lead-free is one of the important directions in the research of perovskite materials, but so far, no other material battery that can match the photoelectric effect with lead-based perovskite batteries has been found. Tin based perovskite can achieve an efficiency of about 16%, but the technology is still not mature. Moreover, lead containing perovskite is more suitable for low-temperature preparation and remains a preferred option for commercialization of perovskite batteries.
Solubility of lead iodide in water at different temperatures (g/L)
Mint planting significantly increases lead content in soil contaminated with lead based perovskite materials
05 Trend outlook
1. The production cost of perovskite components is expected to be significantly reduced in the future
In the future, with the continuous acceleration of the industrialization process of perovskite, perovskite equipment and component enterprises are expected to continue to benefit. For perovskite component enterprises, with the acceleration of industrialization and technological progress, the future production cost of perovskite components is expected to be significantly reduced. At that time, the product competitiveness of perovskite components will be significantly improved, and market share will continue to increase.
2. Layered perovskite is expected to become the ultimate technological form in the photovoltaic field
With its ultra-high photoelectric conversion efficiency, the future perovskite and crystalline silicon stacked battery technology is expected to become the ultimate technological form in the photovoltaic field.
3. Accelerated industrialization process
The rapid progress in research and development efficiency is currently paving the way for the industrialization of perovskite batteries. At the same time, different technology and equipment routes have enterprise layouts, and the industrialization exploration of perovskite is being carried out on a large scale, and industrialization will accelerate its development.
06 Reference research report
1. Dongwu Securities - in-depth report on the perovskite industry: the next generation of photovoltaic cell newcomers, the dawn of industrialization is emerging
2. Galaxy Securities - Mechanical Equipment Industry: Perovskite~Disruptor or Empowerer?
3. Shenwan Hongyuan - Part 2 of the "New Technologies" Series in the Photovoltaic Equipment Industry: Perovskite Battery Technology. The East Wind of Perovskite is Rising, Reducing Costs and Increasing Efficiency. The Future is Promising
4. China Post Securities - Special topic on perovskite in the mechanical equipment industry: Accelerating commercialization process and focusing on equipment investment opportunities
5. Tianfeng Securities - Building Materials Industry: Perovskite batteries, conversion efficiency or ceiling, moving towards commercialization eve
6. Zhongtai Securities - Deep Report on the Industry Chain of Perovskite Battery Industry I: Differentiated Competition, Establishing Wide Prospects for Industrialization
7. Huatai Securities - Special Research on Power Equipment and New Energy Industry: Photovoltaic New Technology Series II, Perovskite
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