  In the present work, a light-controlled device cell is established based on
the dye-sensitized solar cell using nanocrystalline TiO2 films. Voltage-current
curves are characterized by three types of transport behaviors: linear
increase, saturated plateau and breakdown-like increase, which are actually of
the typical performances for a photo-gated transistor. Moreover, an asymmetric
behavior is observed in the voltage-current loops, which is believed to arise
from the difference in the effective photo-conducting areas. The photovoltaic
voltage between the shared counter electrode and drain (VCE-D) is investigated
as well, clarifying that the predominant dark process in source and the
predominant photovoltaic process in drain are series connected, modifying the
electric potential levels and thus resulting in the characteristic
phototransistor behaviors.
