Perovskite - The third-generation solar cell technology with a promising future market.

The Development of Perovskite - A New Battery Technology

In terms of technological development, solar cells can be divided into three generations:

The First Generation of Crystalline Silicon Batteries

Represented mainly by polycrystalline silicon and monocrystalline silicon batteries, they currently have relatively high technical maturity, photoelectric conversion efficiency and commercialization degree, and dominate the photovoltaic market. At present, the laboratory conversion efficiency of crystalline silicon batteries is getting closer and closer to its theoretical efficiency limit of 29.4%. The technical maturity and industrial chain have been highly developed, and there is limited room for further improvement.

The Second Generation of Multicomponent Compound Thin-film Batteries

It mainly includes types of solar cells such as gallium arsenide (GaAs). These batteries have the advantages of low raw material consumption, lighter weight and high flexibility of active materials, and can meet a variety of different application requirements. However, due to the toxicity or scarcity of some active materials used in these batteries, they cannot be used as a large-scale mass production technology at present.

The Third Generation of New Batteries

It mainly includes new batteries represented by perovskite solar cells. These batteries have multiple advantages such as non-toxic raw materials, abundant reserves, low cost, simple process and flexible preparation. The theoretical conversion efficiency of single-junction perovskite solar cells reaches 33%. When combined with crystalline silicon batteries to form a tandem cell, the conversion efficiency will be further improved, and the future development prospects are broad. At present, most of the industry is still in the pilot line stage, and some leading enterprises will successively start the construction of GW-level production lines.

Perovskite solar cells belong to the third-generation battery technology.

Data Source: "Research on the Preparation of High-efficiency Perovskite Solar Cells at Low Cost" by Lv Feng, Huachuang Securities

What is a Perovskite Battery? 

It gets its name because its photoelectric conversion layer uses materials with a perovskite structure, referring to a class of materials with the general chemical formula ABX3. In the ABX3 crystal, BX6 forms a regular octahedron, and BX6 is connected by sharing the vertex X to form a three-dimensional framework, and A is embedded in the octahedral gap to stabilize the crystal structure. Among them, A is a monovalent cation with a large radius (such as methylammonium cation MA+, formamidinium cation FA+, cesium ion Cs+, etc.), B is a divalent cation with a small radius (such as lead ion Pb2+, tin ion Sn2+, germanium ion Ge2+, etc.), and X is usually a halogen anion (such as fluoride ion F-, chloride ion Cl-, bromide ion Br-, iodide ion I-, etc.). Common perovskite materials mainly include FAPbI3, MAPbI3, etc.

Figure: The Lattice Structure of Typical Perovskite Materials

Data Source: "Research Progress of Perovskite/Crystalline Silicon Tandem Solar Cells" by Li Chunjing, etc.

Figure: Diversified Application Scenarios

The Development of Perovskite Batteries

Figure: The Conversion Efficiency Rapidly Catches up with That of Crystalline Silicon Batteries

Figure: Important Nodes of the Conversion Efficiency of Perovskite Solar Cells

The Component Structure, Corresponding Production Process and Technology of Perovskite Batteries 

The Development Potential of Perovskite Batteries

The maximum theoretical conversion efficiency of a single-junction perovskite battery is 33%. The bandgap of perovskite materials can be adjusted within a certain range according to different compositions, and the theoretical limit efficiency can reach 33%, which is close to the theoretical conversion efficiency limit of a single-junction battery of 33.7% (corresponding to an ideal bandgap of 1.34 eV), and higher than the theoretical limit of crystalline silicon of 29.4%.

Figure: The Expectation of Cost Reduction and Efficiency Improvement of Perovskite Solar Cells

Tandem cells composed of multi-junction cells can further improve the conversion efficiency. Taking a dual-junction cell as an example, a material with a wide bandgap is usually selected as the top cell, and a material with a narrow bandgap is selected as the bottom cell. Tandem cells have a wider spectral response range and higher conversion efficiency. The theoretical conversion efficiencies of dual-junction and triple-junction cells can reach 45% and 49% respectively.

The Current Challenges of Perovskite Batteries

There are long-term stability problems, and the current lifespan is relatively short.

The stability of perovskite materials is poor, and they are prone to decomposition. Perovskite materials are often used in environments with factors such as humidity, high temperature, and ultraviolet light. In such environments, the materials have poor stability and are prone to decomposition, resulting in changes in the internal structure of the materials, and ultimately causing the photoelectric conversion efficiency of perovskite solar cells to decline continuously.

There is an efficiency loss in the preparation of large-area perovskite batteries, and the manufacturing process requirements are high.

Compared with other types of photovoltaic batteries, as the battery area increases, the conversion efficiency of perovskite batteries decreases more significantly.

Since the crystallization time of perovskite materials is very short, usually the process window is only a few seconds, and the preparation of large-area perovskite batteries requires a longer coating time, and the uniformity of crystallization will be difficult to control. During the crystallization process, if there is a defect, it will affect the conversion efficiency of the entire battery. Therefore, the coating process of the perovskite layer puts forward higher requirements for the stability of production equipment and processes.