Fig. 3. Simultaneous biaxial stretching of PSC films.

a AFM topographies of P2 and P4 film under biaxial 100% strain. With suitable molecular ordering and good intrinsic stretchability, the P4 film shows a smooth and uncracked surface even under 400% area expansion. b Averaged FET charge carrier mobilities (for at least 5 devices from 2 batches) and representative transfer curves of PSC films under biaxial strains. The source-to-drain voltage was set as -100V. A dramatic decay of electrical properties is observed for the low molecular weight polymer (i.e., P2), while P4-based FETs exhibit stable and superior electrical performances under strain. c Comparison of charge carrier mobility (averaged from 5–10 devices over 2 batches) of P4 films under uniaxial or biaxial strain. Conditions of even (e.g., 50 × 50%, 100 × 100%, etc.) or uneven (i.e., 25 × 50%, 50 × 75%, and 50 × 100%) biaxial strains are included. Comparable mobility of P4-based FET is observed in the range of 0.1–0.25 cm²V^-1s^-1, suggesting a stable electrical performance will be maintained, even if the film is randomly deformed. d Device configuration and representative electrical characteristics of a fully stretchable FET device based on P4 thin films. The charge carrier mobility of the fully stretchable device is comparable to the devices fabricated on rigid Si substrates. The source-to-drain voltage was set as −60V. e Operational stability of a fully stretchable device under irregular strains by poking with a 15 mL plastic centrifuge tube in a circular motion. Stable current output is observed under a reading gate voltage of −30V.