New cell types, new materials and new technologies have emerged with the development of photovoltaics. Traditional photovoltaics is divided into generations ( Fig. 1 ).

The first generation are silicon cells: monocrystalline and polycrystalline. The appearance of cells based on amorphous silicon initiated the so-called second generation of cells. This includes thin-film cells made of cadmium telluride (CdTe), a mixture of copper, indium, gallium, selenium (CIGS) or the amorphous silicon, and multi-junction cells. Thin film cells are characterised by a very thin (1-3 micrometre) semiconductor layer.
The third generation includes dye-sensitised and polymer cells. The perovskite cells are also included in the third generation occasionally. However, some sources classify them with hybrid cells in the fourth generation [1]. This classification is therefore chronological. The classification according to the materials used in the manufacture of the cells is shown in Fig. 2 (based on [2]).

Perovskite cells and hybrids are included in a separate category. Perovskites are inorganic materials, but organic materials (e.g., solvents) are used in the manufacture of the cells. Hybrid cells (e.g., silicon-organic) are also made from both organic and inorganic materials.
Each generation has its advantages and disadvantages (e.g., when it comes to performance, silicon photovoltaics is the most efficient). However, each generation is still being developed and has enormous potential.