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Basic function of a solar cell

When sunlight strikes on the surface of a cell, it absorbs the lights which generate free electrons and holes. Electrons starts to flow from one doped layer to the other (or we can say from p-junction to n-junction). This way the solar energy can be converted into electricity.

working of a solar cell — Schematic representation of working of Solar Cell

What is single layer solar cell and how it works?

They are generally made of doped Silicons with Boron and Phosphorus to alter the conductivity of semiconductors and metallic contacts are placed on the top and bottom of solar cell. When light hits the surface of p-n junction, the photons create electron-hole pairs. The free electrons in the depletion will come and concentrate to n-type side junction. Similarly, the holes in the depletion will come and concentrate to the p-type side junction. Gradually, concentration will increase in both sides then the p-n junction will behaves like a small battery and which converts solar energy to electricity.

Schematic Representation of Working of a Single Layer Solar Cell

Schematic Representation of Working of a Single Layer Solar Cell

What are multi-junction solar cell and how it works?

They are made of different materials layers and junctions which absorb different wavelengths of sunlight and convert it into electricity.
A clear top layer allows sunlight to fall on an energy conversion layer; different p-n junction made of different semiconductors responds to different wavelength of lights. Using multiple semiconductors allows absorbance of different wavelengths which improves cell efficiency.

Schematic Representation of Working of a Multi-Junction Solar Cell

Comparison between multi-layer and single-layer solar cells

Parameters	Single Layer Solar Cell	Multi-layer Solar Cell
EFFICIENCY	Maximum Efficiency achieved is 25%	Theoretically efficiency could be achieved is 30-40%
MATERIALS	They are typically made using silicon as a semiconductor	They commonly use three separate semiconductors GaInP (Gallium Indium Phosphide) InGaAs (Indium Gallium Arsenide) Ge (Germanium)
COSTS	Less expensive	More expensive
LIFE-SPAN	25+ years	25+ years