doubt's

solar cells:  A solar cell or photovoltaic cell is a device that converts solar energy  into electricity by the photovoltaic effect.

Led( Light emitting diode) : is a semiconductor diode that emitsincoherent narrow-spectrum light when electrically biased in the forward direction of the p-n junction, as in the common  LED circuit. This effect is a form of electroluminisence.

Photodiode

A photodiode is a type of photodetector capable of converting light into either current or voltage, depending upon the mode of operation.

Zener diode: A Zener diode is a type of diode that permits current to flow in the forward direction like a normal diode, but also in the reverse direction if the voltage is larger than the breakdown voltage known as "Zener knee voltage" or "Zener voltage". The device was named for Clarence Zener, who discovered this electrical property.