When a polymer is used in solution state, ambulatory chains prefer to remain separate rather than entangling each other. Also, certain polymer chains, such as regioregular polythiophene (rr-P3HT), form nanorod-like structures over distances comparable to their persistence length when dissolved in certain organic solvents such as dichlorobenzene (DCB). This arrangement benefits intra-chain mobility thanks to the lack of bends and twists, which act as impurities and impede π-bond conduction.

Configuring the device

The polymer diodes built by the group have silicon and aluminium electrodes separated by a 40 nm thick SiO2 insulation layer. A solution of P3HT:DCB is prepared and the diode is realized by dipping the electrode structure into the mixture.

In measurements, a current density of 300 mA/cm2 is obtained, which corresponds to at least a six-fold improvement in carrier mobility compared with solid-state polymer counterparts. Solution concentration and hysteresis effects were also investigated.

Future work

The next step is to exploit the various advantages of a liquid interface. Solution-state diodes are relatively easy to integrate with microfluidic devices, which could be highly beneficial for biological applications. Also the microchannel structure can be designed so that the polymer solution can be refreshed or changed as desired, to provide multifunctional devices.