The use of solar cells is increasing very slowly. One of the reasons is that the most commonly used type, made from silicon, is quite expensive to manufacture. That is why there has been a great deal of research into alternative solar cells over the past few years.
A cheap alternative to silicon solar cells can be found in dye-sensitized solar cells (Dye-sensitized solar cells (DSC) are a relatively new class of low-cost solar cells).
These cells are extremely promising because they are made of low-cost materials and do not need elaborate apparatus to manufacture. In bulk they should be significantly less expensive than older solid-state cell designs.