  Thermal annealing is one of most effective way to improve the efficiency of
graphene/n-Si Schottky junction solar cell. Here, its underlying mechanism has
been investigated by comparative studies in terms of the removal of polymethyl
methacrylate (PMMA) residues, using the J-V characteristics, the transient
photocurrent and photovoltage measurements. Experimental results have revealed
that there are trap states which are originated from the PMMA residues and
cause the large photocurrent leakage as the intensity of the incident light
increases. It is also found that the PMMA residues accelerate deterioration and
rapidly invalidate hole doping effects. Such undesirable PMMA residues were
effectively removed by the thermal annealing treatments, serving to reduce the
photocurrent leakage and to increase the stability.
