Large-surface-area photo diodes are used in solar cells. Compared to photo diodes, this device has a higher sensitivity to incoming light due to its greater surface area and higher power (larger currents and voltages). When exposed to intense light, a single silicon may be able to generate a 0.5-volt potential that can power up to 0.1 amps. They can be connected in series to recharge nickel cadmium batteries or used to power small devices like solar calculators. In detectors for visible and near-infrared light, solar cells are frequently used as light-sensitive elements (e.g., light meters, light-sensitive triggering mechanism for relays).

Both the more positive and more negative voltage regions in a circuit must be linked to the positive and negative leads of these devices, just like photo diodes. A solar cell’s normal response time is 20 milliseconds. A series or a parallel arrangement of cells can be used to power a device. In bright light, a single solar cell may generate up to 0.1 A at an open-circuit voltage of between 0.45 and 0.5 V. Cells can be added in series to increase the output voltage by summing the voltages of each individual cell. The output current increases as cells are connected in series.

Because the diode drops 0.6 volts, the total voltage is 4.5 volts (0.5 volts for each cell). Diodes in the circuit are used to keep NiCd batteries from discharging through the solar cell when the sun is not shining, which would otherwise damage the battery. For NiCd batteries, it is critical to avoid exceeding the safe charging rate. Add a resistor in line with the batteries to slow the charging rate. The light-activated thyristors are called photothyristors. The light-activated SCR (LASCR) and the light-activated triac are two common photothyristors.

It’s like a switch that flips on and off when it’s exposed to a pulse of light. It is possible to turn the LASCR off even if the light is turned off or the electricity is disconnected. Similar to the LASCR, a light-active triac can handle ac currents. A LASCR’s operation can be better understood with the analogous circuit depicted here. Photons clash with electrons in the pn junction and electrons are expelled across the pn junction into the n side, as in other pn junction optoelectronic devices.

A sufficient base current is generated when a significant number of photons liberate a big number of electrons across the junction, turning the transistors active. After photons are removed, the LASCR will continue to operate until the anode and cathode polarities are switched or the power is shut off. To replicate the transistors, a constant current flows through the anode and cathode leads, simulating their bases continuously.