Instead of photovoltaic devices which attract much attention

photoconductive devices were objects of our work.Two kinds of PVK/TiO

2

bilayer devices were prepared

including S

1

:ITO/TiO

2

/PVK/Al and S

2

:ITO/PVK/TiO

2

/Al.The properties of charge transportation of organic/inorganic devices were investigated by dark current and photocurrent spectra.The small noises are better properties of PVK/TiO

2

bilayer devices.For these two devices

both of photocurrent response peaks are at 340nm or so

which indicated that the main excited layer is PVK film and photogenerated excitons of PVK influenced on the production of photocurrent.The TiO

2

film functioned as electron transporting and adjuvant excited layer.For dark current of two devices

the dark current of S

1

was much smaller than that of S

2

.Dark current is resulted from: electron injection and transportation in PVK from cathode; hole injection and transportation in TiO

2

from anode; hole transfer from TiO

2

to the value band of PVK.These three points can be used to explain the smaller dark current of S

1

.For photocurrent of the two devices

the peak photocurrent of S

1

at forward bias was 4 times of that of S

1

at reversed bias

which was similar with the peak photocurrent of S

2

at forward and reversed bias.The effective charge transfer at the interface of PVK/TiO

2

proper charge transportation layers and the match of energy level and work function had been considered to be the main factors that influence on the intensity of photocurrent of the devices.The reasons induced different properties of two devices

including: different morphology of PVK/TiO

2

interface caused by different fabricating sequences

the exchanged contacts near PVK film and TiO

2

film and the different absorption because of excited light reaching the different film first which led to photocurrent response spectra of the two devices were different.As a result

the properties of device S

1

is better than that of S

2

.With the increase of applied voltage

the tails of S

1

photocurrent spectra at the short wavelength turned higher

but photocurrent spectra of S

2

nearly had no tails

which may be attributed to the different absorption and trapping energy level.