A solar cell is a device that directly converts light energy into electrical energy through the photoelectric effect or photochemical effect. Also known as a "solar chip" or "photovoltaic cell," it can instantly output voltage and generate current when a circuit is established, provided it receives sufficient illumination. In physics, this is called solar photovoltaic (PV), or simply photovoltaic.
Solar cells can be classified into two main categories according to their crystallization state: crystalline thin-film and amorphous thin-film (hereinafter referred to as a-). The former is further divided into monocrystalline and polycrystalline forms.
Based on materials, they can be divided into silicon thin film, compound semiconductor thin film, and organic thin film. Compound semiconductor thin film can be further divided into amorphous (a-Si:H, a-Si:H:F, a-SixGel-x:H, etc.), Group IIIV (GaAs, InP, etc.), Group IIVI (Cds system), and zinc phosphide (Zn3p2), etc.
Depending on the materials used, solar cells can be classified as: silicon solar cells, multi-component compound thin-film solar cells, polymer multilayer modified electrode solar cells, nanocrystalline solar cells, organic solar cells, and plastic solar cells. Among them, silicon solar cells are the most mature and dominate in applications.
Performance parameters of solar cells
1. Open circuit voltage
Open-circuit voltage UOC: The output voltage of a solar cell when it is placed under AM1.5 spectral conditions and irradiated by a light source with an intensity of 100 mW/cm2 and its terminals are open.
2. Short-circuit current
Short-circuit current (ISC): This is the current flowing through the two ends of a solar cell when it is placed under AM1.5 spectral conditions and illuminated by a light source with an intensity of 100 mW/cm2 and short-circuited at the output end.
3. Maximum output power
The operating voltage and current of a solar cell vary with the load resistance. Plotting the operating voltage and current values corresponding to different resistance values yields the current-voltage characteristic curve of the solar cell. The maximum output power, denoted by Pm, is achieved when the selected load resistance value maximizes the product of the output voltage and current. The operating voltage and current at this point are called the optimal operating voltage and optimal operating current, denoted by Um and Im, respectively.
4. Fill factor
Another important parameter of solar cells is the fill factor (FF), which is the ratio of the maximum output power to the product of the open-circuit voltage and the short-circuit current.
FF (Frost-Free) is an important indicator of the output characteristics of a solar cell. It represents the maximum power output of a solar cell under optimal load; a higher FF value indicates a higher output power. The value of FF is always less than 1. Series and parallel resistances have a significant impact on the fill factor. The larger the series resistance, the greater the decrease in short-circuit current, and the greater the reduction in fill factor. Conversely, the smaller the parallel resistance, the greater the shunt current, resulting in a greater decrease in open-circuit voltage and a greater reduction in fill factor.
5. Conversion efficiency
The photoelectric conversion efficiency of a solar cell refers to the maximum energy conversion efficiency when the optimal load resistance is connected in the external circuit. It is equal to the ratio of the solar cell's output power to the energy incident on the solar cell surface. The photoelectric conversion efficiency of a solar cell is an important parameter for evaluating its quality and technological level. It is related to the cell's structure, junction characteristics, material properties, operating temperature, radiation damage from radioactive particles, and environmental changes.
