When there is a sufficient amount of sun energy, i.e., when the absorbed photon energy is greater than the bandgap energy of the materials used in the PV cell, the atoms collide and free electrons start to migrate, creating the current of electricity. A p–n junction operated with bias voltage is termed a photodiode. The electrical contacts are designed to block as little of the illumination as possible, without increasing electrical resistance by being too thin. The voltage required to cause these two currents to balance is called the "open-circuit voltage". (Reprinted with permission from (Kempa et al., 2008). Figure 41.1.1. Figure 11.12. Part of the skin could be etched away to give access to the n-type layer beneath. Because the photodiode response varies with wavelength, the manufacturer usually supplies a calibration graph to allow conversion to wavelengths other than that for which it was calibrated. This chapter, considering the above factors, presents a study of solar radiation in Section 3.2, a brief discussion on semiconductor physics in Section 3.3, a review of PV materials in Section 3.4, the electrical characteristics of PV cells in Section 3.5, a note on PV components and standards in Section 3.6, a report on PV systems and technologies in Section 3.7, materials for future PV systems in Section 3.8, and a summary in Section 3.9. Under open circuit conditions, the light-generated carriers forward bias the junction, thus increasing the diffusion current. 11.13 shows another successful example of a solar cell with an efficiency of 3.4%, a FF = 40.7%, an VOC = 0.82 V, and a short-circuit current density (JSC) of 10.2 mA/cm2. The curve labeled “dark” represents conditions in the absence of light; it displays familiar rectification characteristics. 12b represents the part of the irradiated solar cell I–V curve from the fourth quadrant just by its inversion around the voltage axis. In the following years, photovoltaic effects were observed in copper-copper oxide thin film structures as well as in lead sulfide and thallium sulfide. Photoelectric current is directly proportional to intensity of light. Based on these proof-of-concepts and very promising results, the same experiments have been carried on, but now using BNC as a substrate. Figure 17.10 shows the photovoltatic response for various dopants with the same concentration of 1 at% into the base PLZT (3/52/48) under an illumination intensity of 4 mW/cm2 at 366 nm.8 The dashed line in Fig. Further possibilities are photovoltaic devices made out of radial (Figure 13.4(b)) (Christesen et al., 2012; Czaban, Thompson, & LaPierre, 2009; Dong, Tian, Kempa, & Lieber, 2009; Garnett & Yang, 2008; Krogstrup et al., 2013; Mariani et al., 2011; Tang, Huo, Brittman, Gao, & Yang, 2011; Tian et al., 2007; Wang, Pey, Yip, Fitzgerald, & Antoniadis, 2010) or axial (Figure 13.4(c)) (Christesen et al., 2012; Guo et al., 2010; Heurlin et al., 2011; Kempa et al., 2008; Li et al., 2009; Lin et al., 2011; Reimer, 2011; Sivakov et al., 2009) pn junctions within the nanowires. 23.6. For demonstrating the photovoltaic effect let us assume a block of silicon crystal. Solar cells exploit the photovoltaic effect to convert incident light into electricity. Principle operation of a PV cell. The irradiance value of 1000 W/m2 of AM1.5 spectrum has become a standard for measuring the conversion efficiency of solar cells. No single photodiode structure can best meet all system requirements. Promoting policies on PV systems by governments. Since this discovery, technology evolved to allow the production of materials with many types and structures presently used in photovoltaic technology. If the metal and the semiconductor have work functions related in the proper way, this can be a rectifying barrier. Fig. The first silicon solar cell was reported by Chapin, Fuller, and Pearson in 1954 and converted sunlight with an efficiency of 6 percent. The conversion efficiency (η) is determined from these parameters and is calculated as the ratio between the generated maximum power (Pmax) and the incident optical power. Alternatively, some units are supplied with filters to compensate for the wavelength variation of the detector response, so that the response of the entire unit will be wavelength-independent, at least over some interval.