In the past, there were three main types of solar panels: monocrystalline, polycrystalline, and thin-film solar panels. The names of the first two types of panels refer to the number of photovoltaic (PV) cells the panel has. Monocrystalline solar panels comprise silicon solar cells with a single silicon crystal. Polycrystalline solar panels contain more silicon, which is not cut as intricately as it is in monocrystalline panels. Thin-film panels are made from layers of semiconducting materials, which are placed between transparent conducting layers, with a layer of glass on top. Today, Mono-PERC half cell solar panels, a version of monocrystalline panels that have the solar cell cut in half for maximum efficiency, are the most popular. A new solution, TOPCon panels, is considered more efficient and longer lasting.