**3. Solar cell structure**

When a solar cell is illuminated by sunlight, photon energy of the incident light is converted to direct current electricity through the process of photovoltaic effect of the solar cell. Incident light causes electron–hole pairs to be generated in the semiconductor, and there is an increase in the concentration of minority carriers (electrons in the p-type region and holes in the n-type region) in the depletion region. This increase in the concentration of minority carriers results in the flow of the minority carriers across the depletion region into the quasineutral regions. These photo-generated carriers cause the flow of photo-generated current. When the junction is in the open-circuit condition, no net current can flow inside the p-n junction; thus, the current resulting from the flux of photo-generated and thermally generated carriers is balanced by the opposite recombination current (**Figure 2**).

If a load is connected between the electrodes of the illuminated p-n junction, some fraction of the photo-generated current will flow through the external circuit. The potential difference between the n-type and p-type regions will be lowered by a voltage drop over the load. Also, the electrostatic potential difference over the depletion region will be decreased, which results in an increase in the recombination current [2].

**Figure 2.** Incident light on a typical PN solar cell.

Earth's surface is 343 W/m<sup>2</sup>

2 Solar Panels and Photovoltaic Materials

**3. Solar cell structure**

by the opposite recombination current (**Figure 2**).

in an increase in the recombination current [2].

. It has an integrated power of 1366.1 W/m<sup>2</sup>

**2. History of photovoltaic effect**

AM<sup>0</sup>

1000 W/m<sup>2</sup>

/s. The standard spectrum for space applications is referred to as

(1) the AM1.5 global spectrum is designed for flat plate modules and has an integrated power of

the direct beam from the Sun and the circumsolar component in a disk of 2.5° around the sun.

The photovoltaic effect was discovered in 1839 by the French physicist, Alexandre Edmond Becquerel. While experimenting with metal electrodes and electrolyte, he discovered that conductance increases with illumination. Willoughby Smith discovered the photovoltaic effect in selenium in 1873. Albert Einstein described the phenomenon in 1904. The first silicon monocrystalline solar cell was constructed in 1941. In 1951, the first germanium solar cells were made. Bell's Laboratories published the results of the solar cell operation with 4.5% efficiency. The efficiency was increased to 6% within a few months. In 1957, Hoffman Electronics introduced a solar cell with 8% efficiency. A year later, in 1958, the same company introduced a solar cell with 9% efficiency. The first radiation-proof silicon solar cell was produced for the purposes of space technology in the same year. In 1960, Hoffman Electronics introduced another solar cell with 14% efficiency. In 1977, the world production of photovoltaic modules exceeded 500 kW. In 1984, ARCO Solar introduced the first amorphous modules. In 1985, researchers at the University of New South Wales in Australia constructed a solar cell with more than 20% efficiency. In 1996, BP Solar purchased APS announced a commercial CIS solar cells production. During 2000 and 2001, the production by Japanese manufacturers increased significantly.

When a solar cell is illuminated by sunlight, photon energy of the incident light is converted to direct current electricity through the process of photovoltaic effect of the solar cell. Incident light causes electron–hole pairs to be generated in the semiconductor, and there is an increase in the concentration of minority carriers (electrons in the p-type region and holes in the n-type region) in the depletion region. This increase in the concentration of minority carriers results in the flow of the minority carriers across the depletion region into the quasineutral regions. These photo-generated carriers cause the flow of photo-generated current. When the junction is in the open-circuit condition, no net current can flow inside the p-n junction; thus, the current resulting from the flux of photo-generated and thermally generated carriers is balanced

If a load is connected between the electrodes of the illuminated p-n junction, some fraction of the photo-generated current will flow through the external circuit. The potential difference between the n-type and p-type regions will be lowered by a voltage drop over the load. Also, the electrostatic potential difference over the depletion region will be decreased, which results

The direct and circumsolar spectra have an integrated power density of 900 W/m<sup>2</sup>

and (2) the AM1.5 direct spectrum is defined for solar concentrator work. It includes

. Two standards are defined for terrestrial use:

(**Figure 1**).
