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A multijunction solar cell is a highly efficient type of solar cell. It is made up of several layers of semiconducting material, each of which absorbs different wavelengths of light. Trapping light photons according to spectra increases the efficiency from 12% in normal PV cells to almost 40% in these multijunction solar cells. Therefore the greater number of layers, the higher the efficiency.

Since each layer has a different band gap, arrangement is very important. The top layer has the largest bad gap and can therefore absorb photons over a larger wavelength. Subsequent layers are arranged in order of their decreasing bad gaps. Most cells have a maximum of three layers.

These solar cells are created using tandem techniques by use of different materials in design and manufacture. Developers have also adopted this technique to thin film solar cells to achieve greater efficiency.

There are a number of ways that are used to make multijunction solar cells. They include:

- Wiring separate thin film solar cells ‘ this is usually the easier method
- Creating a monolithically integrated cell using mechanical and electrical connection techniques. Care has to be taken in matching photocurrents for the cell to achieve the efficiency levels hoped for.

Developers have to use different semiconducting materials other than silicon to achieve these efficiency levels. Some materials used include:

- Gallium arsenide substrate ‘ This is an alloy that absorbs light in the wavelength range of 1.92eV to 1.87eV. It is mostly used in making dual junction solar cells.
- Germanium substrate ‘ This material has helped create efficiencies of over 35%. It is usually used in triple junction solar cells.
- Indium phosphide substrate ‘ This material is capable of absorbing light in the wavelength range of 1.35eV and 0.74eV.

Multijunction solar cells are usually used where efficiency is as important as saving money. The industry that has applied these cells is the telecommunications industry. They used it in making satellites and in making space vehicles. Developers are working to find ways where the high efficiency levels that a multijunction solar cell provides can be obtained at lower costs and thus allow for easier adoption.