Photovoltaic energy conversion is the direct production of electrical energy in the form of current and voltage from electromagnetic (i.e., light, including infrared, visible, and ultraviolet) energy. The basic four steps needed for photovoltaic energy conversion are:
1. a light absorption process which causes a transition in a material (the absorber) from a ground state to an excited state,
2. the conversion of the excited state into (at least) a free negative- and a free positive-charge carrier pair, and
3. a discriminating transport mechanism, which causes the resulting free negative-charge carriers to move in one direction (to a contact that we will call the cathode) and the resulting ...