Understanding the Device Physics in Polymer‐Based Ionic–Organic Ratchets

Abstract

High-performance solution-processed ionic-organic ratchets are fabricated using polymer semiconductors. The devices can provide both high short-circuit current and open-circuit voltage at room temperature, and be driven by AC signals with frequencies up to 13.56 MHz. The effects of trap density, mobility, and rectification ratio in the device on short-circuit current are investigated and clarified.

Normal and inverted regimes of charge transfer controlled by density of states at polymer electrodes

“…Likewise conductive polymers can be used as ion pumps to control spatial and temporal ion movement, with applications to drug delivery 5 , 6 . A number of other electrochemical energy-conversion and storage devices have been realized using conductive polymers, including organic electronic ratchets 7 – 9 , redox-flow batteries 10 , 11 , supercapacitors 12 , 13 , electrochromics 14 , 15 , and (photo-)electrochemical cells for catalysis and water purification 16 , 17 .…”

Perovskite Electronic Ratchets for Energy Harvesting

“…This ion redistribution provides the rectifying function of the ratchet, similar to the mechanism proposed for ionic-organic ratchets. [7,10] Thus, the operation of the perovskite electronic ratchet under a time-averaged zero-bias gate signal and zero source-drain bias can be described as such. When the negative voltage bias of the input signal is applied to the gate electrode, holes will accumulate in the channel from the source electrode, although the large V oc (vide supra) suggests that there may also be some injection from the drain electrode.…”

“…In the most popular incarnation of the organic electronic ratchet, an asymmetric potential distribution is developed directly within a chemically doped organic semiconductor by applying a voltage stress. [ 7,10–13 ] While this effect is purported to arise from the electric‐field‐induced redistribution of ions, [ 14 ] direct evidence for ion movement is rarely observed. The exploitation of ion motion in “soft” materials suggests that hybrid organic–inorganic lead‐halide perovskites (LHP), where ion motion is known to be relatively facile, [ 15–21 ] represent potential alternative semiconductor materials for electronic ratchet devices.…”

“…[ 6–8 ] Despite their simplicity, and the demonstration of electronic ratchet behavior at room temperature, the performance of these devices appears to be limited by the low charge‐carrier mobility that governs charge transport within the semiconductor channel material. [ 7,10 ] The asymmetry needed to ratchet charge carriers can be produced directly in the material by (ostensibly) driving ion motion, [ 7,10 ] provided through the choice of electrode work function, [ 11 ] through the use of periodic, asymmetrically patterned gate electrode pairs, [ 6 ] or patterned gate electrodes with individually asymmetric fingers. [ 8 ] The ability for such devices to harvest electromagnetic noise suggests they could potentially provide the energy needed for low‐power, portable applications where electrical grid access and/or charging batteries may be impractical.…”

Doping High‐Mobility Donor–Acceptor Copolymer Semiconductors with an Organic Salt for High‐Performance Thermoelectric Materials

“…Within this background, here we report a systematic study on the thermoelectric properties of a typical high‐mobility D–A copolymer semiconductor poly[4‐(4,4‐dihexadecyl‐4H‐cyclopenta[1,2‐b:5,4‐b′]dithiophen‐2‐yl)‐alt‐[1,2,5]thiadiazolo[3,4‐c]pyridine] (PCDTPT, molecule structure in Figure a) to reveal the potential of D–A copolymers for OTE applications. In conjunction with PCDTPT, an organic salt trityl tetrakis(pentafluorophenyl) borate (TrTPFB, molecule structure in Figure 1b) was employed for doping as it has been reported to p‐dope PCDTPT by a simple solution‐blending method in our previous works 37,38. By varying the doping concentrations, the characteristic parameters of thermoelectric materials such as σ, S and κ were investigated in the temperature range of room temperature (RT ≈ 300 K) to 400 K. It is found that the 5 wt% doped semiconductors have the maximum PF of 7 µW K −2 m −1 with electrical conductivities approaching 4 S cm −1 and Seebeck coefficients of ≈150 µV K −1 .…”