Abstract
Poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) is the most widely used conducting polymer in printed and flexible sensors. It is water-processable, can be made compliant, and conducts holes and ions. Most of these properties, and its drift, respond to one variable, the grain morphology of the film, around which this review is organised. The review first describes PEDOT-rich grains in a PSS matrix and the resulting mixed ionic–electronic transport. It then compares secondary doping, post-treatments, ionic additives, and crosslinkers by their effects on conductivity, stretchability, and aqueous stability. Printing routes, inks, application-specific device stacks, and transduction modes follow. Next, failure mechanisms are mapped onto the sensor classes they dominate. Reversible water uptake, ageing, electrochemical de-doping, cracking, delamination, and loss of skin contact produce different drift signatures and need different corrections. Analytical performance is compared across material classes. As a bare chemiresistor, the polymer works in the parts-per-million decade. As the channel of an electrochemical transistor with a functionalised gate, it reaches nanomolar detection limits. Detection limit, linear range, and interference at a stated humidity are rarely reported together. This review documents that gap. Finally, it describes the calibration steps that recover a measurand from a drifting signal and proposes a minimum reporting set.