Today's method of flexible solar cell manufaturing, is based on highly purified silicon compounds, which is an expensive procedure. MIT came a step closer to cheaper flexible solar cells, by using organic (carbon-containing) compounds to make lightweight, cheap and flexible cells.
The main problem why carbon did not work so far, was that graphene repels water. Typical procedures for making an electrode on the surface, by depositing the material from a solution do not work. But the MIT team added some impurities onto the surface (doping) and this changed the behavior of graphene, making it possible to bond tightly. Moreover, this doping increased the conductivity of graphene. Read the original article here.