What Is a Padded Cell?

The ratio of the product of the current and voltage when the battery has the maximum output power to the product of the short-circuit current and the open-circuit voltage is called the fill factor. ^[1]

Filling factor refers to the ratio of the maximum power of a solar cell to the product of open circuit voltage and short-circuit current, and is an important parameter for evaluating the output characteristics of a solar cell. The higher its value, the closer the output characteristics of the solar cell to a rectangle, the higher the photoelectric conversion efficiency.

The factors that affect the fill factor are: short-circuit current; open-circuit current; series resistance; parallel resistance; temperature; spectral intensity.

The fill factor mainly depends on the material characteristics of the solar cell itself, and is not highly dependent on the light source used.

Current research has confirmed that among the internal factors that affect the output characteristics of solar cells, the series and parallel resistances have the largest impact on the fill factor: the larger the series resistance, the smaller the parallel resistance, and the smaller the fill factor.

Effect of fill factor sunlight intensity on fill factor

Among the external factors, the most influential factor on solar cell output characteristics is the intensity of sunlight. The change of fill factor with the intensity of sunlight has not yet been clearly stated. In addition, in engineering practice, we have noticed the influence of sunlight intensity on the output characteristics of solar cells: the short-circuit current and the maximum power point current are proportional to the sunlight intensity, and the open circuit voltage and the maximum power point voltage are proportional to the natural logarithm of the sunlight intensity Directly proportional. ^[2]

Effect of fill factor incident light wavelength on load and fill factor

The graph above shows the relationship between the fill factor and the wavelength of the incident light. As the incident light wavelength increases, the fill factor increases first, then decreases, and then increases. Since the incident light at 365 nm is not within the spectral response range of the silicon solar cell, the fill factor is small at the wavelength of the incident light at 365 nm. The blue silicon nitride film on the surface of the solar cell has a strong reflection of blue light at a wavelength of 436 nm, which results in a smaller fill factor of the solar cell when the incident light is at 436 nm.

In general, with the increase of the incident light wavelength, the photon energy utilization rate gradually increases, and the fill factor also gradually increases. ^[3]