The S-shaped current-voltage characteristic is a sign of poorly performing organic photocell, since it gives low fill-factor. In this paper, the characteristics of a bulk heterojunction device with PTB7-Th:C-70 composite without thermal annealing, which shows S-shaped current-voltage curve with the power conversion efficiency (PCE) of 1.5% under AM 1.5G 1 sun illumination, under low light illumination are studied. It is found that the current-voltage characteristic of the device under 10(-3) sun illumination does not show the kink and thus the PCE exceeds 5%. A photocell which shows both S-shaped and normal current-voltage characteristics seems to be rarely reported so far.