Complex sentence: The rival solar cell technology to crystalline silicon is called thin-film, which is itself an umbrella term that includes several solar cell materials, such as CdTe and CIGS, as well as amorphous silicon (a-Si).
Split into simpler sentences: The rival solar cell technology to crystalline silicon is called thin-film. Thin-film itself is an umbrella term that includes several solar cell materials, such as CdTe and CIGS, as well as amorphous silicon (a-Si).