Light absorbing materials are the electron generators in solar cells. The convert photons to electrons via the photovoltaic effect, typically using solar wavelengths of light.

Light absorbing semiconductor materials can be divided into three broad groups depending on the populations of electrons in the band structure in the rest state (dark, no light absorbance).

p-type: a semiconductor that contains impurities (adding atoms, missing atoms, replacing atoms) such that the major charge carriers are positively charged electron holes. Given that the majority carriers are so prevalent relative to the electrons, if you "add" more holes from an outside source, they will be able to diffuse freely through the p-type material with a very low probability of recombining with an electron (i.e. "hole transparent").

i-type: an "intrinsic" semiconductor. This material contains no impurities and the populations of electrons and electron holes are the same. Electron-hole pairs (termed excitons) recombine easily because they are oppositely charged and opposites attract.

n-type: a semiconductor that contains impurities (adding atoms, missing atoms, replacing atoms) such that the major charge carriers are negatively charged electrons. Given that the majority carriers are so prevalent relative to the holes, if you "add" more electrons from an outside source, they will be able to diffuse freely through the n-type material with a very low probability of recombining with a hole (i.e. "electron transparent").