In case of phototransistor made from graphene and PbS hybrid structure it is said that when it is illuminated by laser light then among light induced electron-hole pair, holes are transferred to the graphene.

Now my concern is that about the electron remaining on PbS. After their lifetime how these electron decay? Are all of these electrons decaying through non radiative processes? Or any other things happening there?

Similarly, if electrons are transferred then what about the hole remaining there?