Electric-field Assisted Spatioselective Deposition of MIL-101(Cr)PEDOT to Enhance Electrical Conductivity and Humidity Sensing Performance

Poly(3,4-ethylenedioxythiophene)-functionalized (PEDOT) MIL-101(Cr) nanoparticles were deposited via drop-casting onto interdigitated electrodes (IDEs). The application of an alternating potential during drop-casting allowed precise spatioselective deposition of the nanoparticles in the interelectrode gaps, generating percolating nanoparticle chains aligned between the finger electrodes. The resulting conductivities of the aligned and chained samples were up to 4 orders of magnitude higher than that of unaligned samples prepared via regular drop-casting. The performance of the unaligned and aligned samples for resistive humidity sensing was investigated, whereby the aligned samples showed a conductivity gain of 230 times at a relative humidity of 90% versus 10%, whereas the unaligned samples showed a lower gain of 40 times at relative humidity 90% versus 10%. Further, the aligned samples could also be utilized as capacitive humidity sensors, showing a change of sensitivity at different frequencies for the aligned sample, whereas unaligned samples show a resistive behavior unsuitable for capacitive sensing. This work demonstrates that simple drop-casting when carried out in conjunction with an applied alternating potential exerts dielectrophoretic control allowing for precise spatioselective deposition, thus leading to higher sample conductivity and enhanced performances for humidity sensing.