Absorption spectra of D102 in solution (green solid line), ZnO film from spray pyrolysis (black dotted line), and D102-functionalized ZnO (D102/ZnO) film (red dashed line). The absorption peak of D102 is at ∼500 nm while the excitonic peak of ZnO appears at ∼370 nm. The D102/ZnO, whilst retaining the complete excitonic feature of ZnO, also features a second smaller peak at ∼500 nm which coincides with the absorption of the dye. The inset shows the molecular structure of the dye D102.
Transfer curves of ZnO TFTs (red) and D102-functionalized ZnO TFTs (blue) measured in the dark. The effects of dye-functionalization can be viewed as n-type doping which increases charge carrier density in ZnO, shifting VTH in the negative direction.
Light sensitivity measurement showing transfer characteristics of (a) pristine ZnO TFTs and (b) ZnO TFTs in which the ZnO has been functionalized with the dye D102-functionalized and subjected to different illumination intensities of green light (λmax ∼522 nm) produced by an inorganic light-emitting diode (LED). Changes in the transfer characteristics in the case of ZnO TFTs are most likely attributed to oxygen vacancies while the drastic shifts in the threshold voltage in the case of D102/ZnO TFTs are due to electron transfer from D102 to ZnO as well as the improvement in electron transport in ZnO from trap screening.
Field effect mobility (μFE ) as a function of (a) irradiance and (b) approximated channel charge carrier density. The exponential increase of μFE with carrier density in (b) agrees with the screening of defect energy barriers at grain boundaries according to the GBLT model. The fit (red line) gives a trap density (Qt ) of cm−2.
Plots of (a) responsivity R and (b) photosensitivity P of D102-functionalized ZnO phototransistors. The maximum values of R and P are ∼104 and ∼106, respectively. The sensitivity of the device is also clearly a function of gate bias (VG ), signifying the tunability of the device.
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