Solar cells convert sunlight into electrical energy using semiconducting materials like silicon. They are made from either monocrystalline or polycrystalline silicon. Monocrystalline solar cells are more efficient because they are made of pure silicon crystals but are more expensive to produce. Polycrsytalline solar cells contain multiple silicon crystals mixed with other materials, making them less efficient but cheaper to manufacture. Solar cells use the photovoltaic effect where light absorption generates voltage across the PN junction of the semiconductor material.