Solar cells are the core element of photovoltaic panels: they are where electricity is generated by the photovoltaic effect. Perovskite-based cells are considered the new generation of photovoltaic cells, offering significant advantages in terms of efficiency and manufacturing cost over traditional silicon-based solar cells. In this article, we will explore the unique characteristics of perovskite-based solar panels and explain why they are considered a major breakthrough in solar power generation.
Perovskite is a lead-based material that has attracted considerable interest in the field of solar cells. Perovskite-based solar cells offer high efficiency and lower manufacturing costs than traditional silicon-based photovoltaic cells. Researchers at the École Polytechnique Fédérale de Lausanne (EPFL) in France, together with researchers at the National Renewable Energy Laboratory (NREL) in the USA, have been working on improvements.
What is perovskite?
Perovskite materials are organic-inorganic compounds with the general formula ABX3, where A is an organic cation, B is a metal cation (usually lead or tin) and X is an anion (usually a halide such as iodide, bromide or chloride). They are therefore not metals, but rather a family of organic-inorganic crystalline materials with a specific structure.
They are not extracted directly as minerals, but rather synthesized from their precursors. The constituent elements of perovskites, such as lead andtin, are metals extracted from the earth’s crust. Lead is generally extracted from ores such as galena (PbS), while tin is extracted from cassiterite (SnO2). Lead reserves are mainly found in Australia, China, the USA, Peru and Mexico. The main tin reserves are in China, Indonesia, Peru, Brazil and Bolivia.
Halides are produced from elements such as iodine, bromine and chlorine. Iodine is extracted from sources such as underground potassium iodide deposits and seaweed, while bromine and chlorine are extracted from seawater, salt lakes and underground brines.
Properties of perovskites
The scientific aspects of perovskite-based solar cells are mainly based on their unique crystalline structure and optoelectronic properties.
The crystalline structure of perovskites is responsible for their exceptional optoelectronic properties. Perovskite materials adopt a cubic structure, where A cations are located at the corners of the cube, B cations are in the center and X anions occupy the centers of the edges. This structure allows a tunable bandgap and high light absorption, which is essential for efficient conversion of sunlight into electricity.
Perovskites exhibit remarkable optoelectronic properties, including high light absorption, long charge carrier diffusion lengths and low numbers of crystal defects:
- High light absorption : Perovskites have a high absorption coefficient, which means they can absorb a large part of the solar spectrum. This increases the efficiency of solar cells by capturing more light energy.
- Long charge carrier diffusion length: Charge carriers (electrons and holes) in perovskites have a high diffusion length, enabling them to travel long distances before recombining. This increases the likelihood of charge carriers reaching the electrodes and being collected, thus improving solar cell efficiency.
- Low number of crystalline defects: Perovskite materials have a low number of crystalline defects, which reduces the probability of charge carrier recombination and increases their lifetime. This improves solar cell performance by minimizing energy losses.
These properties enable efficient conversion of sunlight into electricity.
Advantages and disadvantages of perovskite-based photovoltaic panels
Perovskite-based photovoltaic panels offer several advantages and disadvantages over other solar technologies, such as crystalline silicon cells. Here’s an overview of the main advantages and disadvantages of this technology.
- High efficiency: perovskite-based solar cells have achieved efficiencies in excess of 25% in laboratory tests, rivalling those of crystalline silicon cells. Their high absorption coefficient and charge carrier diffusion length enable efficient conversion of sunlight into electricity.
- Low cost: The manufacture of perovskite-based solar cells generally involves low-temperature processes and inexpensive deposition techniques, such as spin-coating, thus reducing production costs.
- Flexible and lightweight: Perovskite-based solar cells can be manufactured on flexible, lightweight substrates, making them suitable for a variety of applications, such as wearable devices, solar textiles and integrated buildings.
- Tandem coupling with other solar cells: Perovskites can be used in tandem with other solar technologies, such as silicon, to improve overall efficiency. Tandem cells exploit different parts of the solar spectrum, enabling more efficient use of sunlight.
- Long-term stability: Perovskite-based solar cells are generally less stable than crystalline silicon cells. Moisture, heat and ultraviolet rays can degrade perovskite materials, affecting their lifespan and performance.
- Lead toxicity: The most commonly used perovskites contain lead, a toxic element. Lead toxicity poses environmental and health problems during the manufacture, use and disposal of solar cells.
- Production scale: Although perovskite-based solar cells have shown considerable potential in the laboratory, challenges remain in moving to large-scale production. Further research is needed to optimize manufacturing techniques and improve cell stability.
- Regulation and certification: Perovskite-based solar cells still have to overcome regulatory hurdles and obtain the necessary certifications to be widely adopted on the market.
How are perovskite solar cells produced?
The production of perovskites for solar cells generally involves the synthesis of precursors and the formation of thin films. Perovskite materials can be synthesized using a variety of deposition methods:
- Solution method: The solution method is a commonly used approach to preparing perovskite thin films. In this process, soluble precursors are dissolved in a suitable solvent to form a solution. This solution is then deposited on a substrate, usually by spin-coating, rotating the substrate at high speed to obtain a uniform film. The film is then dried and heat-treated to form the perovskite crystal structure.
- One-step method: In the one-step method, the perovskite precursors (A, B and X) are dissolved together in a solvent to form a homogeneous solution. This solution is then deposited on a substrate and heat-treated to form the perovskite film. Although this method is simple, it can be difficult to control crystal formation and film quality.
- Two-step method: The two-step method involves the preparation of two separate solutions, one containing precursor B and the other containing precursor X. Film B is first deposited on a substrate, then the solution containing precursor X is deposited on film B. Subsequent heat treatment results in the formation of the perovskite structure. This method offers greater control over crystallization and film quality.
- Evaporation deposition method: The evaporation deposition method involves evaporating solid perovskite precursors under vacuum and depositing them on a heated substrate. This technique enables precise control of film thickness and excellent homogeneity. However, the equipment required for this method is more expensive and complex than that used for solution deposition methods.