Dynamics of Bulk Polymer Heterostructure/Electrolyte Devices

The application of organic semiconductors and bulk heterojunction (BHJ) devices in photoelectrochemical cells, electrolyte gated field effect transistors, and neuromorphic devices involves the interface of the polymer with an electrolyte. We report the observation of interesting features arising from bulk and interfacial properties of stable polymer/electrolyte devices from photovoltage and differential photocapacitance measurements. A crossover in polarity of the photovoltage signal as a function of BHJ layer thickness and a crossover in the sign of differential photocapacitance as a function of frequency are observed in certain classes of these device structures. The presence of the critical thickness and crossover frequency can be understood in the framework of an electrical transport model and the parameters defining the interfacial capacitance.