Ckh. Wong et al., THE MODIFICATION OF ELECTROPHOTOGRAPHIC AND MECHANICAL-PROPERTIES OF ORGANIC - PHOTOCONDUCTORS BY ULTRA-VIOLET IRRADIATION, Journal of electronic materials, 25(9), 1996, pp. 1451-1457
Experiments have shown that UV treatment has a hardening effect on-the
surface of a drum-based organic photoconductor (OPC) and improves the
retentivity. The dark decay and the photoinduced discharge rates were
reduced linearly with the increase of time of UV irradiation. The dar
k decay rate and. photoinduced discharge rates were reduced to 60% and
more than 70% of the initial rate, respectively, while there was an i
ncrease of the activation energy of the charge transport layer. An ini
tial increase in the residual potential was also observed from 20 to a
bout 70 V. After 40 min of UV irradiation, the residual potential was
seen to drop to 50 V again, and at the same time a slight increase of
the hardness of the photoreceptor surface was detected from 13 to 16 i
n Vickers scale (Hv). The phenomena is most likely explained by a phot
ochemical change which reduces the density of charge transport sites,
builds up the number of deep traps and changes the molecular distribut
ion. The decrease in charge transport site density and buildup of deep
traps reduces the conductivity and hence the dark decay and photoindu
ced discharge rates. The fragmentation of charge transport molecules m
ay result in a change of activation energy as well as the increase in
the residue potential. Moreover, the redistribution of molecules leads
to the change in molecular density and hardness.